Full text of "Illinois agronomy handbook, 1999-2000"

See other formats

UNIVWSITVOF

l\CES

NOTICE: Return or renew all Library Materials! The Minimum Fee for
each Lost Book is $50.00.

The person charging this material is responsible for
its return to the library from which it was withdrawn
on or before the Latest Date stamped below.

Theft, mutilation, and underlining of books are reasons for discipli-
nary action and may result in dismissal from the University.
To renew call Telephone Center, 333-8400

UNIVERSITY OF ILLINOIS LIBRARY AT URBANA-CHAMPAIGN

L161— O-1096

ACES LIBRA

JUN 1 ^ 7005

UNtV£RSn^1f Qf mM\

University of Illinois at Urbana-Champaign

College of Agricultural, Consumer and Environmental Sciences

Department of Crop Sciences • University of Illinois Extension • Circular 1360

Agricultural Research and
Demonstration Centers

Northern Illinois
Agronomy Research
Center, DeKalb

Northwestern Illinois
Agricultural Research
and Demonstration
Center, Monmouth

University of Illinois
South Farms

Orr Agricultural
Research and
Demonstration
Center, Perry

Brownstown
Agronomy Research
Center

Dixon Springs
Agricultural Center/
Ilhnois Forest
Resource Center

Research centers administered by the
Department of Crop Sciences at the
University of Illinois. Areas of research
include agronomy, agricultural engin-
eering, agricultural entomology, animal
sciences, forestry, horticulture, and plant
pathology.

UNIVERSITY OF ILLINOIS

EXTENSION

College of AgricullursI, Consumer and Envifonmenlal Sciences

Reference to products in this publication is not intended to be an endorsement lo the exclusion of others that may be similar. Persons using such
products assume responsibility for their use in accordance with the current label directions of the manufacturer.

Urbana, Illinois December 1998

This publication replaces Circular 1344. Managing editor Phyllis
Picklesimer; copyediton Stacey Krejci; designer Joan R. Zagorski;
assistant designer Kathy Fuoss; cover photo: David A. Riecks.

9M— 12-98— Phillips— PYP

Issued in furtherance of Cooperative Extension Work, Acts of
May 8 and June 30, 1914, in cooperation with the U.S. Department
of Agriculture. Dennis Campion, Interim Director, University of
Illinois Extension Service, University of Illinois at Urbana-
Champaign.

The University of Illinois Extension Service provides equal
opportunities in programs and employment.

Copyright © 1998 by University of Illinois Board of Trustees.
Authors and publishers have granted permission for copies of
this work or parts of this work to be reproduced, provided that (1)
copies are distributed at or below the cost of reproduction; (2) the
author, the publication, and the University of Illinois College of
Agricultural, Consumer and Environmental Sciences and the
relevant division within the College are identified; and (3) proper
notice of copyright is affixed to each copy.

ISBN 1-883097-22-3

Michael E. Gray Aaron G. Hager Robert G. Hoeft Steven E. Hollinger

Marshal D. McGlamery James A. Morrison Emerson D. Nafziger Theodore R. Peck Gary E, Pepper

David R. Pike John C. Siemens F. William Simmons Kevin L. Steffey

Contents

1. Agricultural Climatology i

Weather variables 1

Climate variables 1

Crop, insect, and disease environmental
thresholds 8

2. Corn 17

Yield goals 17

Hybrid selection 17

Planting date 20

Planting depth 21

Plant population 21

Row spacing 23

Plant spacing in the row 24

Crop canopy 24

Stand counting 25

Replanting 25

Weather stress in com 26

Estimating yields 26

Specialty types of com 27

3. SOYBEANS 29

Planting date 29

Planting rate 30

Planting depth 32

Crop rotation 32

Row width 32

Double-cropping considerations 33

When to replant 34

Seed source 35

Seed size 35

Varieties 35

4. Small Grains 38

Winter wheat 38

Spring wheat 42

Rye 42

Triticale 42

Spring oats 43

Winter oats 43

Spring barley 43

Winter barley 43

5. GRAIN Sorghum 45

Fertilization 45

Hybrids 45

Planting 45

Row spacing 46

Plant population 46

Weed control 46

Harvesting and storage 46

Marketing 46

Grazing 46

6. Cover Crops and Cropping
Systems 47

Cover crops 47

Cropping systems 49

7. Alternative Crops 51

Sunflower 51

Canola (oilseed rape) 55

Buckwheat 55

Other crops 56

8. Hay, Pasture, and Silage 57

Establishment 57

Fertilizing and liming before or at seeding 58

Fertilization 58

Management 59

Pasture establishment 60

Pasture renovation 60

Selection of pasture seeding mixture 61

Pasture fertilization 61

Pasture management 61

Species and varieties 62

Inoculation 64

Grasses 64

Forage mixtures 65

Additional information 69

9. SEED 70

Seed quality and storage 70

Seed considerations for Illinois crops 71

10. Water Quality 73

Drinking-water standards 73

Illinois water-quality results 73

Drinking-water contaminants 74

Point-source prevention 75

Groundwater vulnerability 75

Surface-water contamination 76

Management practices 76

Chemical properties and selection 76

Precautions for irrigators 77

Well-water testing 77

1 1. Soil Testing and Fertility ...78

Plant analyses 81

Fertilizer management related to tillage systems .... 81

Calcium-magnesium balance in Illinois soils 87

Nitrogen 87

Phosphorus and potassium 101

Phosphorus 105

Potassium 107

Secondary nutrients Ill

Micronutrients 113

Method of fertilizer application 114

Nontraditional products 116

12. SOIL Management and
Tillage Systems 117

Conservation compliance 117

Conservation tillage systems 117

No-till 118

Ridge-till 118

Mulch-till 118

Other tillage systems 118

Systems named by major implement 118

Minimum tillage 118

Reduced tillage 119

Rotary-till 119

Effects of tillage on soil erosion 119

Residue cover 119

Crop production with conservation tillage 120

Soil temperature 120

Allelopathy 121

Moisture 121

Organic matter and aggregation 122

Soil density 122

Stand establishment 122

Fertilizer placement 123

Weed control 123

No-till weed control 123

Insect management 123

Disease control 124

Crop yields 124

Production costs 125

Machinery and labor costs 125

13. No Tillage 129

No-till planters 129

Strip till 130

No-till drills 131

Weed control 133

Fertilizer management 133

Soil density 134

Soil organic matter and aggregation 134

Soil drainage 134

Alleviating soil compaction 134

Crop rotation 135

Adaptability of no-till to specific locations 135

14. Water Management 136

The benefits of drainage 136

Drainage methods 137

Benefits of irrigation 140

Deciding to irrigate 141

Subsurface irrigation 142

Irrigation for double-cropping 142

Fertigation 143

Cost and return 143

Irrigation scheduling 143

Management requirements 145

15. 1999 Weed Control for
Corn, Soybeans, and Sorghum 147

Precautions 147

Cultural and mechanical control 150

Herbicide incorporation 150

Chemical weed control 153

Conservation tillage and weed control 158

Herbicides for com 161

Herbicides for sorghum 176

Herbicides for soybeans 176

Problem perennial weeds 190

Contact herbicides to suppress perennial weeds ... 193

16. 1999 WEED Control for
Small Grains, Pastures, and
Forages 195

Small grains 195

Grass pastures 200

Forage legumes 201

Preplant-incorporated herbicides 203

Postemergence herbicides 208

17. Management of Field Crop
Insect Pests 210

Key field crop insect pests 213

18. Disease Management for
Field Crops 228

Fungicides 228

Disease management of specific crops 229

Integrated pest management 229

19. On-Farm Research 240

Setting goals for on-farm research 240

Types of on-farm trials 241

Risk considerations 243

Getting started with on-farm research 243

A word about statistics 244

Digitized by the Internet Archive

in 2011 with funding from

University of Illinois Urbana-Champaign

http://www.archive.org/details/illinoisagronomy1360univ

Chapter l.

Agricultural Climatology

Year-to-year and day-to-day variation of weather
complicates the scheduling of agricultural practices.
However, the use of continuous weather observations,
weather forecasts, and climate data may assist in sched-
uling crop management practices for optimum benefit.

Accurate recording of weather conditions each year
helps to indicate the current status of crop and pest
development. The future development of crops and
pests can be estimated using observed weather data
related to current time, combined with past climate
data and weather forecasts. Forecasts are available up
to 90 days into the future, with forecast skill decreas-
ing as the length of the forecast period increases (with
a 90-day forecast the least reliable). Short-term forecasts
(defined as those between 12 hours and 5 days) include
information on anticipated temperature, rainfall, rela-
tive humidity, and winds. Longer-term forecasts (6- to
10-day, 30-day, and 90-day) are limited to indications of
future temperature and precipitation.

Weather Variables

Variables including air and soil temperatures, precipi-
tation, humidity, solar radiation, soil moisture, and
wind are measured frequently throughout the day,
week, and month. Information gathered from these
measurements is used to calculate other variables that
are important to agriculture, such as evapotranspira-
tion, growing degree days, heat and cold stress days,
and days suitable for field work.

Although often viewed as the same products,
weather and climate data are different. Weather data
describe the state of the atmosphere at a specified
time, whereas climate data summarize weather condi-
tions over many years. Climate data reflect the mean
and variation of weather conditions during given
time periods. Climate data can be used to estimate the
timing of biological events, such as crop growth and
crop, insect, and disease stages. These estimates can
then be used to plan the timing of production practices.

The number of days available for completing
spring and fall field work is determined by the
weather and plays a major role in limiting the number
of acres a producer can farm. A region's climate thus
helps determine the size and number of tractors, com-
bines, and tillage implements needed to complete
field work in a timely manner.

This chapter discusses the importance of under-
standing the climate of Illinois as it relates to factors
that influence the management of agricultural crops.

Climate Variables

Temperature

The growing season is generally defined as the period
between the last spring frost and the first fall frost.
Most annual crops are planted after the major risk of
frost or freeze has passed. However, late frosts — par-
ticularly very late frosts — can damage both annual
and perennial crops during the spring. Mean dates of
last spring frosts occur as early as April 9 in southern
Illinois and as late as May 4 in northern Illinois (Fig-
ure 1.01). In 1 out of every 10 years, the last spring
frost can occur as early as March 27 and as late as
April 24 in southern Illinois, and as early as April 21
and as late as May 14 in northern Illinois.

The average dates of first fall frosts range from Oc-
tober 6 in northern Illinois to October 21 in southern
Illinois. In 1 out of 10 years, the first fall frost occurs
by September 26 in northern Illinois and October 6 in
southern Illinois (Figure 1.02). In 9 out of 10 years, the
first frost occurs before or on October 21 in northern
Illinois and November 5 in southern Illinois.

Mean minimum temperatures (°F) for Illinois range
from the mid-teens to mid-twenties in winter to the
low to mid-sixties in the summer (Figure 1.03). Mean
minimum temperatures during the spring and au-
tumn range from the upper thirties to mid -forties.
Mean maximum temperatures range from the low
thirties to mid-forties during the winter. Summer

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

1 Year In 10

Apr 19 Apr 19

NH-i^l /lApr9

5 Years in 10

9 Years in 10

Apr 29

Apr 9

Apr 19

May 19

Apr 19

.May 9

May 9

Apr 29

Figure 1.01. Probable dates of last spring frost (32°F minimum temperature).

1 Year in 10

5 Years in 10

Sep 26

Oct 6

9 Years in 10

Oct 26 Oct 16 Oct 26

>Nov S

Nov 5 ,

Oct 26

Nov 5

Figure 1.02. Probable dates of first fall frost (32°F minimum temperature).

mean maximum temperatures range from the low
eighties in the northern regions of Illinois to the high
eighties in the southern regions. Spring and autumn
mean maximum temperatures range from the high fif-
ties to low sixties in the north and in the mid- to high
sixties in the south. In the north, mean maximum tem-
peratures tend to be cooler in the spring than in the
autumn.

Soil temperature. Soil temperatures in the autumn
determine when ammonium nitrogen fertilizer may
be applied without excessive nitrification occurring
during the autumn and winter. At soil temperatures
below 50°F the rate of nitrification is reduced, but the
process does not stop until temperatures are below
32°F. Soil temperatures throughout the state are below

SO^F by mid-November 9 years out of 10 (Figure 1.04).
Maps showing the dates when soil temperatures fall
below 60°F are included as a guide for estimating
when anhydrous ammonia application with a nitrifi-
cation inhibitor can begin. As a guideline, 50°F soil
temperatures occur 25 to 30 days after 60°F soil
temperatures.

Precipitation

The type, timing, and amount of precipitation re-
ceived during the year play a critical role in crop
productivity. Mean annual rainfall ranges from 36
inches in the north to 45 inches in the south (Figure
1.05). Annual rainfall of less than 28 inches in the
north and less than 34 inches in the south can be

I • AGRICULTURAL CLIMATOLOGY

Minimum Temperature l\/laximum Temperature

Spring

Summer

Autumn

Winter

V-jqju'

40 40

^Zd

60 60

641

Figure 1.03. Mean maximum and minimum temperatures (°F) for spring, summer, autumn, and winter.

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

1 Year in 10

Sep 2 Sep 2

60T

Sep 17^

Sep 17

Sep 22

SOT

5 Years In 10

Sep 17 Sep 17 Sep 17

9 Years in 10

Oct 2

Sep 27^

Oct 12

'Oct 17

Oct 22

Oct 7

Oct 22

Nov 6

Nov6

Nov 11 /

Nov 16

^ Nov 11

Nov 16

Figure 1.04. Probable first dates in the fall when 4-inch soil temperatures drop below 60°F and 50°F.

1 Year in 10

5 Years in 10

9 Years in 10

26 28 28

Figure 1.05. Probable annual rainfall amounts (inches).

expected 1 year out of 10. Annual rainfall can be ex-
pected to be greater than 46 inches in the north and
greater than 52 inches in the south 1 year out of 10.

Winter is the driest season, with approximately

5 inches of precipitation in the north and 10 inches in

the south (Figure 1.06). Spring is the wettest season

1 • AGRICULTURAL CLIMATOLOGY

Spring

Summer

Autumn

Winter

1 Year in 10

'xxn

5 Years in 10

9 Years in 10

13 13

'sazr

^J^^^

yi3

^14

7 8

Figure 1.06. Probable seasonal rainfall (inches).

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 1.01. Average Growing-Season Days with
Rain and Average Amounts Per Storm

n.w. wifh Average rain per storm (in.)

Month rain

(> 0.10 in.)

North

Central

South

April

0.53

0.54

0.64

May

0.54

0.59

0.70

June

0.68

0.65

July

0.65

0.68

0.72

August

0.80

0.68

0.64

September

0.76

0.72

0.64

October

0.52

0.56

0.60

in the south, with more than 13 inches of rain,
whereas summer is the wettest season in the north,
with 12 inches of rain.

Rain greater than 0.10 inch often delays field
work, especially in the spring and early summer,
when the soils are the wettest. On average, there are
7 days each month with rainfall greater than 0.10
inch during April and May (Table 1.01), 6 days each
in June and July, and 5 days each in August, Septem-
ber, and October. The average rain amount in each
storm is larger during the summer than during the
spring (Table 1.01). Generally, the average number of
days with 0.10 inch of rain in dry and wet years does

not change more than 1 day from normal years; the
major difference is in the amount of rain received in
each storm.

POTENTIAL EVAPOTRANSPIRATION

Evapotranspiration is the removal of water from soil
by a combination of evaporation from the soil surface
and transpiration (loss of water vapor) from plant
leaves. Surface evaporation is limited to the upper
2 to 4 inches of soil, while transpiration results in re-
moval of water from the soil to a depth equal to the
deepest roots.

"Potential" evapotranspiration is the amount of
water that would evaporate from the soil surface and
from plants when the soil is at field capacity. Field ca-
pacity defines the amount of water soil holds after it
has been saturated and then drained, until drainage
virtually ceases. Soil drier than field capacity will ex-
perience actual evapotranspiration less than the po-
tential evapotranspiration, as will plant canopies that
do not totally cover the soil.

Potential evapotranspiration is greatest in dry
years with low humidity and predominantly clear
skies and least in wet years with high humidity and
cloudier-than-normal skies. Total potential evapo-
transpiration from April though September ranges
from about 33 inches in dry years to about 27 inches
in wet years. Actual evapotranspiration during wet

I I Pcpn-Wef H Pcpn-Average ^ Pcpn-Dry
I I PET-Wet H PET-Average | PET-Dry

April May June July August September

Month

Figure 1.07. Total monthly precipitation (Pcpn) and potential evapotranspiration (PET) during wet, average, and dry years.

1 • AGRICULTURAL CLIMATOLOGY

years will equal the potential maximum but will be
less than the potential maximum in dry years. During
the growing season, the normal total monthly evapo-
transpiration is least in September and greatest in
June and July (Figure 1.07). Drought conditions occur
when the potential evapotranspiration exceeds rain-
fall by more than the normal difference for several
months in a row.

Soil Moisture

The amount of water held in soil is determined by
soil texture, soil drainage, precipitation, and evapo-
transpiration. During the summer months, evapo-
transpiration generally exceeds the rainwater ab-
sorbed by the soil, and the soil profile dries out. From
October through April, evapotranspiration is less than
precipitation, and the soil profile is recharged. In Illi-
nois, soUs generally become saturated at some time in
the spring.

Wet spring soils play an important role in deter-
mining how many days are suitable for spring field
work. When soil moisture is normal or wetter than
normal, even small rains will result in field work de-
lays on all but the sandiest soils in Illinois. Excessive
soil moisture in late spring and early summer may re-
sult in loss of nitrogen through denitrification and
leaching and may lead to the development of seed,
root, and crown diseases. Conversely, dry soil during
planting may result in poor stand establishment and
may cause plant stress when dryness occurs during
the periods of flowering and seed set.

The typical arable soil in Illinois is a silt loam or
silty clay loam and will, on average, hold approxi-
mately 7.5 inches of plant-available water in the top
40 inches of soil. Plant-available water is defined as
the amount of water in the soil between field capacity
and wilting point. In the uppermost 40 inches of Illi-
nois soils, the average amount of water held at field
capacity is approximately 14 inches. The wilting point

is defined as the amount of water still in the soil when
plants are unable to recover at night from wilting dur-
ing the day. Illinois soils hold about 6.5 inches of wa-
ter in the upper 40 inches of soil at the wilting point.
Water in the top 40 inches of soil at saturation is ap-
proximately 17.5 inches. Individual soils will vary sig-
nificantly from the average. Coarse-textured soils,
such as sands, will hold less water at the wilting point
and field capacity than fine-textured soils or soils
with high clay content.

During the spring planting season, the amount of
water in the top 6 inches of soil controls field work
activities. When the top 6 inches of soil is wet, plant-
ing is delayed, and nitrogen can be lost to either
denitrification or leaching. Traffic on or tillage of
fields when soil is near field capacity (80 percent of
saturation) causes maximum compaction. During av-
erage springs, soil moisture conditions in April are
wet enough that rains greater than 0.3 inch will bring
the soil water to field capacity (Table 1.02). In the wet-
test years, rains greater than 0.3 inch will result in sig-
nificant periods of near-saturated soils in the upper
6 inches. The rainfall amounts shown in Table 1.02 are
the minimum amounts of rain needed to trigger deni-
trification and provide optimum compaction condi-
tions. When the subsurface soil levels are dry, more
rain than the amounts shown is needed to have this
effect. Only in the driest years will soils seldom reach
field capacity.

Whenever plant-available water in the to 40 inches
of soil is less than 3.8 inches in June, July, or August,
plants will show significant moisture stress during
the day. Soil moisture is generally below this limit
only during the driest months of July and August
(Table 1.03). Even in these months, soils should expe-
rience some periods above this stress threshold, espe-
cially following rains. In the wettest years, plant-
available water exceeds plant needs, and periods of
saturation may occur during the summer months.

Table 1.02. Water Content in the Top 6-Inch Soil Layer of a Typical Illinois Silt Loam or Silty Clay Loam
During April, May, and June, and the Minimum Rain Needed to Bring Soil Moisture to
Field Capacity

Dry

Average

Wet

Month

Water

content

(in.)

Rain needed

for field capacity

(in.)

Water

content

(in.)

Rain needed

for field capacity

(in.)

Water

content

(in.)

Rain needed

for field capacity

(in.)

April

May

June

1.5

1.18

0.94

0.72
1.11
1.35

1.9

1.57

1.50

0.32
0.72
0.79

2.36
2.17
1.97

0.00
0.12
0.32

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 1.03. Plant- Available Water in the Top 40-
Inch Soil Layer of a Typical Illinois
Silt Loam or Silty Clay Loam During
June, July, and August

Plant-available water (in.)

Month

Dry

Average Wet

June
July
August

4.37
2.79
2.01

5.16 7.52
5.16 9.04
4.37 6.74

Effects of El Nino and La Nina on
Illinois Crops and Weather

Recent extreme weather events in the United States
and around the world have been blamed on extremes
of sea surface temperatures in the equatorial Pacific
Ocean. When sea surface temperatures in the equato-
rial Pacific are above normal, an El Nifio event is oc-

curring. Conversely, when the sea surface tempera-
tures are below normal, a La Nifia event is occurring.
During years when equatorial Pacific sea surface tem-
peratures are cooling in the spring and summer, com
and soybean yields are below the general yield trends
in Illinois. When sea surface temperatures are increas-
ing or not changing, com and soybean yields are
above the yield trends or near normal (Figure 1.08).
Yield deviations tend to be above the trend when
spring rainfall is below normal and summer rainfall
is above normal.

Crop, Insect, and Disease
Environmental Thresholds

Crop Environmental Thresholds

Crops are generally grown in regions where tempera-
ture and rainfall conditions favor their growth. Where
temperature is favorable but natural rainfall is insuffi-
cient, crops are irrigated if sufficient water is avail-
able. Temperature is a major factor in determining
where a specific crop is grown if rainfall or irrigation

IL-

■D

E
p

c
.9

Corn I j Spring temp.

Soybean ^^M Summer temp.

Spring rainfall
Summer rainfall

-10

El-El

El-N

N-EI N-N N-La

Spring-summer El Nino conditions

La-La

La-N

Figure 1.08. Corn and soybean yield response to El Nifio, normal, and La Nina conditions. EI-El = El Nifio spring fol-
lowed by an El Nino summer; El-N = El Nino spring followed by a normal summer; N-El = Normal spring followed by
an El Nifio summer; N-N = Normal spring and summer; N-La = Normal spring followed by La Nifia summer; La-La = La
Nina spring and summer; La-N = La Nifia spring followed by a normal summer. A normal summer is one in which the
equatorial Pacific sea surface temperatures are near normal. Corn and soybean yield deviations are in bu/ac, temperature
deviations are °F, and rainfall deviations are in inches.

1 • AGRICULTURAL CLIMATOLOGY

water is sufficient. Minimum, optimum, and maxi-
mum temperatures — called the "cardinal" tempera-
tures— for growth of the major crops in Illinois are
presented in Table 1.04. The corresponding tempera-
tures for photosynthesis are in most cases lower than
those for growth. A combination of moisture and tem-
perature stress may result in some type of crop dam-
age. For example, temperatures above 95°F during
pollination of com will result in a reduction of pollen
viability and, therefore, a possible reduction in the
number of kernels set. Moisture stress during this
same period may result in delayed silk emergence
and a further reduction in the number of kernels set.

There is little a producer can do to control tempera-
tures across large areas. However, knowledge of how
crops respond to temperature can be used to estimate
possible yield losses due to temperature stresses.
These estimates can be used in planning marketing
strategies or pest control procedures.

Growing-degree-day accumulation. Because tem-
perature is a major determinant of the rate of crop de-
velopment, growing degree days (GDD) have been
used for many years to track the development rate of
crops and to estimate the time of harvest. (See Chap-
ter 2 for a complete description of growing degree
days.) GDD, also called growing degree units (GDU),
are calculated by subtracting the lower temperature
threshold for crop development (base temperature)
from the daily mean temperature, then summing over
days. Below the base temperature, or above the maxi-
mum temperature, the rate of development is negli-
gible. For example, the base temperature for com is
SCPF. If the temperature is below 50°F, com develop-
ment is very slow. The development rates of com and
soybeans are also slowed when the maximum tem-
perature exceeds 86°F.

Modem com hybrids are rated by the number of
GDU after planting necessary to reach maturity. GDU
accumulations can be used to help select alternate
com hybrids in years when com planting is delayed.
In years when com can be planted in late April, there
is a greater than 95 percent chance (Figure 1.09) that
more GDU are accumulated before the normal first
frost date than are needed for maturing a 2,800-GDU
com hybrid in all of the state except the northern
third. If planting is delayed until late May, a 2,800-
GDU com hybrid has only a 5 to 10 percent chance of
maturing before frost in northern Illinois, a 50 percent
chance in central Illinois, and a 95 percent chance in
extreme southern Illinois. A 2,400-GDU com hybrid
planted in late May has a 95 percent chance of matur-
ing in the southem half of the state, but only a 50 per-
cent chance in the extreme northern part of Illinois.

Temperature stress. Crops begin to experience
stress whenever the maximum or minimum tempera-
ture falls outside the range of optimum temperatures
(Table 1.04). Heat stress days represent the frequency
of daily maximum temperatures exceeding an opti-
mum growing temperature. Cold stress days account
for the frequency of daily minimum temperatures be-
low some base temperature.

Most crops in Illinois will experience some degree
of heat stress when maximum temperatures exceed
90°F. As maximum temperatures approach 100°F,
crops experience significant heat stress, and yields are
affected, especially if there is a moisture stress and the
extreme temperatures occur for an extended period.
Heat stress degree days (sum of the degrees by which
the daily maximum temperature exceeds 90°F) pro-
vide a measure of the degree of high-temperature
stress experienced by summer crops. Heat stress can
begin to occur as early as May 17, and the chance of
heat stress days continues until September 20 in the
north and October 4 in the south (Figure 1.10).
Chances of having heat stress days are highest during
the week of July 12 to 18.

Minimum temperatures below 50°F cause summer
crops to experience cold stress. For soybeans, mini-
mum temperatures below 50°F reduce the rate of
photosynthesis the following day. Maximum photo-
synthesis will not resume until a daily minimum tem-
perature over 63"F occurs. Estimates of the effect of
temperature below 50°F on summer crops are pro-
vided by the cold stress days. A cold stress degree day
occurs when the minimum temperature is less than
50°F but greater than 32°F. Cold stress days can occur
as late as June 21 in southem Illinois and as late as
July 5 in the north (Figure 1.10). Cold stress days be-
gin to occur again by August 2 in the north and Au-
gust 30 in the south.

Insect Environmental Thresholds

The development rates of insects and their ability to
survive are closely connected to temperature. Devel-
opment generally occurs only after the temperature is
greater than the threshold temperature for a specific
insect. An insect heat unit (IHU) is the difference be-
tween the mean air temperature and a threshold
(base) temperature. IHUs are based on the same con-
cept as GDUs but use different base temperatures.
Many insect growth stages have been correlated to
IHUs. Therefore, IHUs can be used to estimate the
start of field scouting of insects that overwinter in Illi-
nois and begin development shortly after January 1.
Survival temperatures, base development tempera-
tures, and IHU accumulations for several important
agronomic insects follow.

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 1.04. Environmental- Variable Thresholds of Different Growth Stages of Important Illinois
Agronomic Crops

Minimum

Water-use

Solar radiation for

Crop

Growth stage

Temperature,
soil or air (°F)^

soil moisture
bars

efficiency
(lb Hp/lb-dm")

maximum growth
(% full sun)

Alfalfa

Planting to
emergence

Dormancy

Minimum 34
Optimum 86
Maximum 100

Minimum -4

-12 to -15

Growing
season

Minimum 32-50
Optimum 50-86
Maximum 86-104

993

Com

Planting to
emergence

Minimum 46-50
Optimum 90-95
Maximum 104-110

-10 to -12

Growing
season

Minimum 50-59
Optimum 86-90
Maximum 104-122

388

Small grains

Planting to
emergence

Minimum 37-41
Optimum 59-81
Maximum 86-104

-15 to -20

Growing
season

Minimum 32-50
Optimum 50^6
Maximum 86-104

613

Sorghum

Planting to
emergence

Minimum 46-50
Optimum 90-95
Maximum 104-110

-8 to -15

Growing
season

Minimum 50-59
Optimum 86-104
Maximum 104-122

402

Soybean

Planting to
emergence

Minimum 48
Optimum 80-90
Maximum 108

-7

Growing
season

Minimum 50-59
Optimum 80-90
Maximum 104-122

704

Grass pasture Dormancy

Growing
season

Minimum 32-50
Optimum 50-86
Maximum 86-104

*Soil temperatures from planting to emergence, air temperatures during growing season.
^Water-use efficiency, pound of water used per pound of dry matter produced.

1 • AGRICULTURAL CLIMATOLOGY

April 30

May 15

May 30

June 10

2,400 GDU

75 75 75

2510 5 5 5 10

2,600 GDU

10 5

2,800 GDU

25 25 25

10 5

Figure 1.09. Probability of accumulating enough growing degree units (GDU) to mature com hybrids with different
maturity ratings.

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

" 10

Marl Mar 22 Apr 12 May 3 May 24 Jun 14 Jul 5 Jul 26 Aug 16

Week beginning

Sep 6 Sep 27 Oct 18

North
Central
•South

^~. "* —

30 --■ -^ — — -mrT--!.'— .

May 3 May 17 May 31 Jun 14 Jun 28 Jul 12 Jul 26 Aug 9 Aug 23 Sep 6 Sep 20 Oct 4 Oct 18 Nov 1

Week beginning

Figure 1.10. Mean heat stress and cold stress days experienced by summer crops in Illinois.

Alfalfa weevil. The alfalfa weevil {Hypera postica)
begins growth and development at 48°F. Eggs begin to
hatch when approximately 200 base 48 IHUs have ac-
cumulated from January 1 (Table 1.05). Normally,
temperatures cold enough to kill the early weevil lar-
vae (Table 1.06) do not exist in Illinois after the accu-
mulation of 200 to 300 base 48 IHUs. Larval survival
rate is high at 54°F.

Nine years in 10, the alfalfa weevil egg hatch will
begin by March 31 (Figure 1.11) in southern Illinois,
and as early as March 1 for 1 year in 10. In northern
Illinois, alfalfa weevil egg hatch normally begins by
April 20, but it will start as early as April 10 for 1 year
in 10 and by April 30 for 9 years in 10.

Cereal leaf beetle. The cereal leaf beetle {Oulema
melanopus) overwinters in diapause, which is nor-
mally completed by mid-December. Therefore, IHU

accumulations begin on January 1. Table 1.06 shows
the minimum, maximum, and optimum tempera-
tures at which eggs will hatch, the survival tempera-
ture thresholds for different stages of the cereal leaf
beetle. Table 1.05 shows the base 48°F growing-
degree-day accumulations necessary to reach certain
growth stages.

Egg-laying by the cereal leaf beetle begins 1 year in
10 as early as March 31 in southern Illinois and April
20 in northern Illinois (Figure 1.11). Nine years in 10,
egg-laying has started by April 20 in the south and by
May 10 in the north.

Stalk borer. The stalk borer {Papaipema nebris) over-
winters as an egg in Illinois, and 50 percent egg hatch
should be completed when approximately 278 base
48°F growing degree days have accumulated after
January 1. First-generation adults emerge when

1 • AGRICULTURAL CLIMATOLOGY

Table 1.05. Insect Heat Units (IHU) Required to Reach Various Stages for Important Agronomic Insects
in Illinois

Base

temperature

First

Second

Third

Fourth

Insect

(°F)

flight

Egg

instar

Pupae

Adult

Alfalfa weevil

200

270

340

407

497

587

810

Cereal leaf beetle

450

607

668

722

785

853

1,274

Black cutworm

146

200

280

330

610

960

Com earworm

360

756

European com borer

423

736

844

969

1,139

1,287

1,520

1,748

Table 1.06. Minimum, Maximum, and Optimum Temperatures ("F) for Insects That Attack Agronomic Crops
in Illinois

First

Second

Third

Fourth

Fifth

Insect

Temperature

Egg

instar

Pupae

Adult

Alfalfa weevil

Minimum

-11

-2

Optimum

Maximum

Cereal leaf beetle

Minimum
Optimum
Maximum

54-90

46
93

57-86

Black cutworm

Minimum

-A

European com borer

Minimum
Maximum

-8

about 3,670 base 41.5°F IHUs have been accumulated.

Egg-hatching of the stalk borer begins in northern
Illinois approximately the same time as egg-laying by
the cereal leaf beetle. However, the stalk borer egg
hatch is 1 to 2 days behind the start of alfalfa weevil
egg-hatching (Figure 1.11).

Bean leaf beetle. The development of the bean leaf
beetle {Cerotoma trifurcata) can be estimated by accu-
mulating IHUs above a base temperature of 45.5°F
starting January 1. Bean leaf beetles overwinter as
adults and begin emerging from winter habitats after
300 IHUs have accumulated. Bean leaf beetles can be
found throughout Illinois. Excessively wet and dry
soils result in reduced egg hatching.

Black cutworm. Black cutworm moths {Agrotis
ipislon) migrate into Illinois in the spring and lay eggs
on winter armual weeds in com fields. Eggs are gener-
ally laid before com planting. Survival temperatures

for black cutworm eggs, larvae, and adults are shown
in Table 1.06. The development of black cutworm in
Illinois can be estimated using a base 50°F IHU, with
accumulation beginning after the first intense black
cutworm flight in the spring (Table 1.05). An intense
flight is defined as 9 or more moths captured per trap
over 1 or 2 days. Plant-cutting begins when 300 base
50°F IHUs have accumulated after an intense flight.
The projected dates for beginning black cutworm cut-
ting are published in the Pest Management & Crop De-
velopment Bulletin.

Com earworm. The com earworm (Helicoverpa zea)
is also a migrant into Illinois. Therefore, growing-
degree-day accumulations must begin only after ar-
rival of adult moths. The base temperature for IHU
accumulation is 54°F, and egg hatch generally occurs
after 77 base 54°F IHUs have accumulated (Table 1.05)
after egg-laying.

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

1 Year in 10

Apr 10

Mar 31

Alfalfa
Weevil

Mar 21

Cereal

Leaf

Beetle

Apr 20

Apr 10

Mar 31

5 Years in 10

9 Years in 10

Apr 10

Apr 20

Apr 10

Apr 30

Apr 20

Apr 10

May 10

Apr 30

Figure 1.11. Probable dates when scouting for alfalfa weevil and cereal leaf beetle should begin.

European com borer. Adult moths from the over-
wintering European com borer larvae (Ostrinia
nubilalis) begin to emerge after approximately 420
base 50°F IHUs have accumulated since January 1.
(Table 1.05). Egg hatch begins approximately
100 IHUs after the eggs are laid, or approximately
736 IHUs from January 1. Egg survival is reduced
when maximum temperatures exceed 97°F (Table
1.06). The first instar larvae have a difficult time sur-
viving when maximum temperatures exceed 90°F.

Moths from the overwintering European com borer
begin to appear (1 year in 10) as early as April 10 in
southern Illinois and by May 5 in northern Illinois
(Figure 1.12). Adults from the overwintering genera-
tion have begun to emerge by April 30 in the south
and by May 20 in the north (9 years in 10). These
dates mark the start of the appearance of the first
flight of adults. Adults will continue to emerge for 1
to 2 weeks after the earliest appearance.

Corn flea beetle. The overwintering adult com flea
beetle {Chaetocnema pulicaria) becomes active after
270 base 61°F IHUs have accumulated from January 1.

Large populations of the com flea beetle may be ex-
pected when the December, January, and February av-
erage temperature is greater than 33°F. Small popula-
tions may be expected if the December, January, and
February mean temperature is less than 27°F.

The com flea beetle reaches the adult stage as early
as April 20 in the south and May 10 in the north (1
year in 10; Figure 1.13). Nine years in 10, the com flea
beetle reaches the adult stage by May 20 in the south
and June 9 in the north. Normally, the adult stage of
the com flea beetle is reached by April 30 in the south.
May 15 in central Illinois, and May 25 in the north.

Disease Environmental Thresholds

Disease infestations are influenced by both tempera-
ture and humidity. Some diseases occur under warm,
humid conditions, others under hot, dry conditions.
Thresholds that define hot, warm, cool, and cold
growing-season temperatures and high, moderate,
and low humidity conditions are presented in Table
1.07. These data can be used in conjunction with cli-

1 • AGRICULTURAL CLIMATOLOGY

1 Year in 10

5 Years in 10

9 Years in 10

May 10

Apr 20

May 20

Apr 30

Apr 10

May 30

May 10

Apr 20

Apr 30

Figure 1.12. Probable dates of the first appearance of the adult European corn borer.

May 10

Apr 30

Apr 20

9 Years in 10

Jun 9 Jun 9

May 30

May 20

May 10

May3(

Apr 30

Jun 9

May 30

May 20

Figure 1.13. Probable dates of the first appearance of the adult com flea beetle.

mate maps and the Field Crop Scouting Manual to
evaluate the risks of disease in a given area. When
coupled with weather conditions during the current
year and climate probabilities, disease risk for a given
year may be estimated along with the probable time
of disease expression.

Mean daily relative humidities exceeding 85 per-
cent favor the development of many diseases. Nor-

mally there are 2 or 3 days each month when the mean
daily relative humidity exceeds 85 percent (Table 1.08).
In August and September, an east-west relative humid-
ity gradient exists, and more days with mean daily rela-
tive humidity exceeding 85 percent occur in the western
part of the state. July is a transition month, with the
most days with mean daily relative humidity greater
than 85 percent occurring in the west-central region.

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 1.07. Temperature and Humidity
Classifications for Disease
Infestation Conditions During
the Illinois Growing Season

Temperature Temperature
conditions (°F)

Hot
Warm
Cool
Cold

>82
72-82
59-71

<59

Humidity Relative
conditions^ humidity (%)

High

Moderate

Low

>85

50-85

<50

^All humidity conditions can be experienced in the different
temperature conditions.

Table 1.08. Number of Days with Relative
Humidity Exceeding 85 Percent
During the Illinois Growing Season

Days with daily mean

relative

humidity > 85

percent

1 year

in 5 years

9 years in

Month

April

May

June

July

August

September

Author

Steven E. Hollinger

Department of Natural Resources
and Environmental Sciences
and Illinois State Water Survey

Chapter 2.

CORN

Yield Goals

Management decisions are made more easily if the
com producer has set realistic yield goals based on
the soil, climate, and available equipment. It is not re-
alistic, for example, to set yield goals of 180 bushels
per acre for a soil rated to produce only 130 bushels
per acre and from which the highest yield ever pro-
duced was 150 bushels per acre. Instead, managing to
achieve a realistic yield goal should result in yields
greater than the goal in years when conditions are
better than average and reduced losses when the
weather is unfavorable.

The first step in establishing a yield goal is a thor-
ough examination of the soil type. Information for
each soil type, such as the productivity ratings given
in Soils of Illinois (Bulletin 778), can be a useful guide-
line. This information, however, should be supple-
mented by 3- to 5-year yield records, county average
yields, and the yields on neighboring farms. An at-
tempt should be made to ignore short-term weather
and to set a goal based on actual yields.

Perhaps the simplest way to set a yield goal is to
ignore the highest yield and lowest yield for the past
5 or 6 years that com was produced in a field and
average the remaining yields. It may be appropriate
to add 5 to 10 bu/acre to this average to account for
better hybrids and management.

HYBRID SELECTION

When tested under uniform conditions, the range in
yields among available hybrids is often 50 or more
bushels per acre. Thus it pays to spend some time
choosing the best hybrids. Maturity, yield for that ma-
turity, standability, and disease resistance are the most
im.portant factors to consider when making this
choice.

Concern exists with what many consider to be a
lack of genetic diversity among commercially avail-

able hybrids. Although it is true that a limited number
of genetic pools, or populations, were used to pro-
duce today's hybrids, it is important to realize that
these pools contain a tremendous amount of genetic
diversity. Even after many years of breeding, there is
no evidence that this diversity has been fully ex-
ploited. In fact, a number of studies have shown that
breeding progress for most traits is not slowed even
after a large number of cycles of selection. Continued
improvements in most desirable traits are evidence
that this is true. Many of today's hybrids are substan-
tially better than those only a few years old. For this
reason, some producers feel that a hybrid "plays out"
within a few years. Actually, the performance of a
given hybrid should remain constant over the years;
but comparison with newer and better hybrids may
make it appear to have declined in yielding ability.

Despite considerable genetic diversity, it is still
possible to buy the same hybrid from several different
companies. This happens when different companies
buy the same inbreds from a foundation seed com-
pany that has a successful breeding program, or when
hybrid seed is purchased on the wholesale market,
then resold under a company label. In either case, hy-
brids are being sold on a nonexclusive basis, and
many companies simply put their own names and
numbers on the bags of seed.

Many producers, however, would like to avoid
planting all their acres to the same hybrid. One way to
do this is to buy from only one company, though this
may not be the best strategy if it discourages looking
at the whole range of available hybrids. Another way
of ensuring genetic diversity is to use hybrids with
several different maturities. Finally, many dealers
have at least some idea of what hybrids are very simi-
lar or identical and can provide such information if
asked.

It is also important to remember that genetics are
only part of the performance potential of any hybrid.
The way hybrid seed is produced — the care in

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

detasseling, harvesting, drying, grading, testing,
and handling — can and does have a substantial
effect on its performance. Be certain that the seed
being bought was produced in a professional manner.

Maturity is one of the important characteristics
used in choosing a hybrid. Hybrids that use most of
the growing season to mature generally produce
higher yields than those that mature more quickly.
The latest-maturing hybrid should reach maturity at
least 2 weeks before the average date of the first kill-
ing freeze (32°F), which occurs about October 8 in
northern Illinois, October 18 in central Illinois, and
October 25 in southern Illinois. Physiological maturity
is reached when kernel moisture is 30 to 35 percent; it
is easily identified by the appearance of a black layer
on the base of the kernel where it attaches to the cob.
The approach to maturity also can be monitored by
checking the "milk line," which moves from the
crown to the base of the kernel as starch is deposited.
The kernel is mature about the time this milk line dis-
appears at the base of the kernel.

Although full-season hybrids generally produce
the highest yields, most producers choose hybrids
of several different maturities. This practice allows
harvest to start earlier and also reduces the risk of
stress damage by lengthening the pollination period.

Most farmers and seed companies describe the ma-
turity of a particular hybrid in terms of "days." This
designation does not predict how many days the hy-
brid will take to produce a crop. Rather, it refers to a
"relative maturity" rating based on comparison with
hybrids of known maturity. This rating is useful,
therefore, only as a comparative measurement — it
tells us whether a hybrid will mature earlier or later
than another hybrid.

A more precise method of describing the maturity
of a com hybrid is to define the accumulated tem-
perature needed for that hybrid to reach maturity.
Research has shown that the development of the com
plant follows very closely the accumulation of aver-
age daily temperatures during the plant's life. This
accumulation is calculated as "growing degree days"
(GDD). The GDD concept has been very useful in
knowing how the crop will respond to temperatures
and in helping to fit hybrids into situations where ex-
pected GDD accumulations are known from weather
records.

The following formula can be used to calculate
GDD accumulated on any given day:

GDD = ^t^ - 50°F

with H being the high temperature for the day (but no
higher than 86°F) and L the low temperature (but no

lower than 50°F). For example (see the following
table), if the daily high temperature were 95°F, substi-
tute 86°F, the cutoff point for high temperatures. If the
daily low temperature were 40°F, substitute 50°F, the
cutoff point for low temperatures. These high and low
cutoff temperatures are used because growth rates do
not increase above 86°F or decrease below 50°F.

The following figures are examples of daily high
and low temperatures and the resulting GDD, calcu-
lated using the GDD formula:

Daily temperature

High

Low

GDD

It is useful to keep a running total of daily GDD
from the time of planting. For a full-season hybrid
grown in central Illinois, the following table gives the
approximate GDD required to reach certain growth
stages:

Stage

GDD

Emergence
Two-leaf

120
200

Six-leaf (tassel initiation)
Ten-leaf

475
740

Fourteen-leaf

1,000

Tassel emergence
Silking
Dough stage
Dented

1,150
1,400
1,925
2,450

Physiological maturity (black layer)

2,700

Com hybrids grown in Illinois have GDD require-
ments ranging from 2,300 to 2,400 for early hybrids
grown in the northern part of the state, to 2,800 to
2,900 for late hybrids grown in the southernmost part
of the state. The proportion of total required GDD
needed to reach each stage from the previous stage is
relatively similar for different maturities, but later-
maturing hybrids tend to use a larger proportion of
their required GDD to reach silking than do early-ma-
turing hybrids; the number of GDD required from
pollination to "natural" physiological maturity is rela-
tively constant among hybrids.

2 • CORN

2700 2500 2600

2600

2700
2800

3100

3200

Figure 2.01. Average number of growing degree days
(base 50°F from May 1 througti September 30) based on
temperature data provided by Midwestern Climate
Center, 1961-1990. See Chapter 1 for more information on
GDD accumulations in Illinois.

A full-season hybrid for a particular area generally
matures in several hundred fewer GDD than the
number given in Figure 2.01. Thus, a full-season hy-
brid for northern Illinois would be one that matures
in about 2,500 GDD, while for southern Illinois a hy-
brid that matures in about 2,900 GDD would be con-
sidered full season. This GDD "cushion" reduces the
risk of frost damage and also allows some flexibility
in planting time; it may not be necessary to replace a
full-season hybrid with one maturing in fewer GDD
unless planting is delayed until late May or early
June.

In some recent work in Indiana and Ohio, research-
ers found that the GDD requirement for com hybrids
decreased when planting was later than May 1. For
each day that planting was delayed after May 1, the
reduction in GDD requirement was about 6.5 GDD;

thus, a 2,700 GDD com hybrid planted on May 20 re-
quires only 2,700 - (20 x 6.5) = 2,570 GDD. While the
actual decrease in GDD varied somewhat among
years, the fact that there is an expected decrease indi-
cates that changing to a shorter-season hybrid should
be delayed even more. This decrease in GDD require-
ment, however, usually comes at the cost of decreased
yield; planting on time is still an important goal.

After yield and maturity, resistance to lodging is
probably the next most important factor in choosing a
hybrid. Because large ears tend to draw nutrients
from the stalk, some of the highest-yielding hybrids
also have a tendency to lodge. Such hybrids may be
profitable due to their high yields, but they should be
watched closely as they reach maturity. If lodging be-
gins, or if stalks become soft and weak (as determined
by pinching or pushing on stalks), then harvesting
these fields should begin early.

Resistance to diseases and resistance to insects are
important characteristics in a com hybrid. Leaf diseases
are easiest to spot, but stalks also should be checked
for diseases. Resistance to insects such as the Euro-
pean com borer also is being incorporated into mod-
em hybrids. Another useful trait is the ability of the
hybrid to emerge under cool soil conditions, which is
especially important in reduced- or no-till planting.

Seed companies have recently begun to release hy-
brids containing a number of different "genetically
engineered" traits. All of these are single-gene traits,
and the gene was inserted into the com plant from an-
other organism; for example, the Bt gene came from a
bacterium. This technology holds a great deal of po-
tential, since it means that genes found anywhere in
the world, or even genes produced in the laboratory,
can be put into com. Most of the genes released in this
way so far have been for resistance to insects or herbi-
cides, and they have been incorporated into connmer-
cial hybrids using backcrossing. Backcrossing takes
time, and except for the inserted gene, the product is
no better than the parent that the gene was crossed
into, so this technique slows the pace of overall ge-
netic improvement. Another drawback to genetic en-
gineering is that complex traits such as yield or
growth rate are usually controlled by many genes that
interact with one another. Such groups of interacting
genes will likely be difficult to isolate and transfer, so
progress for traits such as yield will continue to de-
pend on traditional methods of breeding.

With the many hybrids being sold, choosing the
best one is difficult. An important source of informa-
tion on hybrid performance is the annual report Per-
formance of Commercial Corn Hybrids in Illinois, pub-
lished as a newspaper insert in the fall in Illinois
Agri-News, as a separate report available in Extension

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 2,01. Days and Percentages of Calendar Days
Available for Field Operations in
Illinois^

Northern

Central

Southern

Illinois

Period

Days

Days %

April 1-20"

5.8

4.2

2.6 13

April 21-30^

3.5

3.1

2.6 26

May 1-10^

5.8

4.3

3.5 35

May 11-20^

5.5

5.0

4.4 44

May 21-30^

7.4

5.8

5.4 54

May 31-June 9^

6.0

5.4

5.6 56

June 10-19<^

6.0

5.4

5.8 58

"Summary prepared by R.A. Hinton, Department of
Agricultural and Consumer Economics of the University of
Illinois. Data are from the Cooperative Crop Reporting
Service's estimates of favorable work days, 1955-1975. The
summary is the mean of favorable days omitting Sundays,
less one standard error, representing the days available 5
years out of 6.
"20 days,
no days.

offices, and on the Web at <http://w3.aces.uiuc.edu/
CropSci/research/vt/index.html>. This report sum-
marizes hybrid tests run each year in nine Illinois lo-
cations and includes yield information from the previ-
ous 2 years. The report gives data on yields, kernel
moisture, and lodging of hybrids. Other sources of in-
formation include your own tests and tests conducted
by seed companies, neighboring producers, and Ex-
tension staff.

Producers should see the results of as many tests as
possible before choosing a hybrid. Good performance
for more than one year is an important criterion. Hy-
brid choice should not be based on the results of only
one "strip test." Such a test uses just one strip of each
hybrid; the difference between two hybrids may
therefore be due to location in the field rather than an
actual genetic difference.

Planting Date

Long-term studies show that the best time to plant
com in Illinois is the last week of April, with little or
no yield loss when planting is within a week on either
side of this period. Weather and soil conditions per-
mitting, planting should begin sometime before this
date to allow for days when fieldwork is impossible
(Table 2.01). Com that is planted 10 days or 2 weeks
before the optimal date may not yield quite as much

as that planted on or near the optimal period, but it
will often yield more than that planted 2 weeks or
more after the optimal period.

In general, yields decline slowly as planting is de-
layed up to May 10. From May 10 to May 20, the yield
declines about one-half bushel for each day that
planting is delayed. This loss increases to 1 to 1V2
bushels per day from May 20 to June 1, with greater
reductions in northern than in southern Illinois. After
June 1, yields decline very sharply with delays in
planting. The latest practical date to plant com ranges
from about June 15 in northern Illinois to July 1 in
southern Illinois. If you plant this late, expect only 50
percent of the normal yield.

Early planting results in drier com in the fall, al-
lows for more control over the planting date, and al-
lows for a greater choice of maturity in hybrids. In ad-
dition, if the first crop is damaged, the decision to
replant often can be made early enough to allow use
of the first-choice hybrid. Of course, early planting
has some disadvantages: (1) cold, wet soil may pro-
duce a poor stand; (2) weed control may be more dif-
ficult; and (3) plants may suffer from frost. Improved
seed vigor, seed treatments, and herbicides have
greatly reduced the first two hazards, and the fact that
the growing point of the com plant remains below the
soil surface for 2 to 3 weeks after emergence mini-
mizes the third hazard. Because this part of the plant
is below the surface, it is seldom damaged by cold
weather unless the soil freezes. Even when com is
frosted, therefore, the probability of regrowth is excel-
lent. For these reasons, the advantages of early plant-
ing outweigh the disadvantages.

The lowest temperature at which com germinates
is about 50*'F. You can take your own soil temperature
or use reported measurements that are taken beneath
bare soil. Soil temperature, however, is not the only
consideration in deciding when to start planting. A
more important consideration may be the condition of
the soil: It generally is a mistake to till and plant when
soils are wet, and the advantages of early planting
may well be lost to soil compaction and other prob-
lems associated with "mudding in" com, whether us-
ing conventional tillage or no-till techniques. If the
weather conditions have been warm and dry enough
to result in workable soils by early April, then plant-
ing can probably begin by April 10 or 15 with little
danger of loss. The weather may change after plant-
ing, however, and a return to average temperatures
means slow growth for com planted this early. It may
be desirable to increase seeding rates by 1,000 to 2,000
seeds per acre for April planting, mainly to allow for
greater losses and to take advantage of the more fa-
vorable growing conditions that the crop is likely to

2 • CORN

210

Planting date
O Mid-April
• Late April
A Early May
A Late May

15 20 25 30

Plant population at harvest (thousands/acre)

Figure 2.02. Response of com planted at different times to
plant population. Data are averages of two hybrids planted
at two locations (Monmouth and DeKalb) for 4 years.

encounter. Recent research shows little change in opti-
mal plant population when planting time ranges from
mid-April through early May (Figure 2.02).

With typical spring weather, preparation for com
planting can begin sometime in the first half of April.
Delays due to low soil temperature (below 50°F)
should be considered only if the weather outlook is
for continued cold air temperatures. After April 20,
soil temperature should be ignored as a factor, and
com should be planted as soon as soil conditions al-
low. Low-lying areas (such as river bottoms) may be
planted last because they warm up more slowly and
are more prone to late freezes.

When planting begins in April, it is generally best
to plant very-full-season hybrids first, but planting
the midseason and early hybrids in sequence tends to
"stack" the times of pollination and harvest of the dif-
ferent nnaturities. It is probably better to alternate be-
tween early and midseason hybrids after the full-sea-
son hybrids are planted. This practice helps to spread
both pollination risks and the time of harvest.

Planting Depth

Ideal planting depth varies with soil and weather con-
ditions. Emergence is more rapid from relatively shal-
low-planted com, so early planting should not be as
deep as later planting. For normal conditions, an ideal
depth is IV2 to 2 inches. Early-planted com should be
in the shallower end of this range. Later in the season,
when temperatures are higher and evaporation is
greater, planting as much as 2y2 inches deep to reach
moist soil may be advantageous.

Depth-of-planting studies show not only that
fewer plants emerge when planted deep but also that
those emerging often take longer to reach the polli-
nating stage and may have higher moisture in the fall.

PLANT POPULATION

The goal at planting time is to establish the highest
population per acre that can be supported with nor-
mal rainfall without excessive lodging, barren plants,
or pollination problems. One way to know when the
plant population in a field is near the optimum is to
estimate the average ear weight. Check at maturity, or
estimate by counting kernels (number of rows multi-
plied by number of kernels per row) once the kernel
number is set. Most studies in Illinois suggest that the
optimal plant population produces ears weighing
about one-half pound and having about 640 kernels.
A half-pound ear should shell out about 0.4 pound of
grain at 15 percent moisture.

The data shown in Figure 2.02 were used to gener-
ate Table 2.02 which gives expected yield at different
plant populations planted on different dates. One im-
portant finding in this study was that the plant popu-
lation producing the highest yield did not change
with the planting date; there is no reason to increase
or decrease plant population when planting early or
late, except that a higher percentage of seeds may es-
tablish plants with later planting, and the number of
seeds dropped thus may decrease a bit when planting
is late.

The data in Table 2.02 can be used to make replant-
ing decisions (see the text section on replanting). The
latest planting in this study was late May, however, so
effects of replanting in June cannot be accurately de-
termined from this work. Note that the highest yields
were from populations around 30,000 per acre, which
produced ears with less than 0.4 pound of grain on
average. Though the eight trials combined here were
not always high-yielding (the study included the
drought year of 1988), there is little reason to decrease
plant populations below the upper 20,000s under pro-
ductive conditions, at least in the northern half of the
state.

More recent studies have confirmed the need for
relatively high plant populations to maximize yields.
Figure 2.03 contains the results of studies conducted
at four locations, with data averaged over 4 years
(1991-1994) and six hybrids. The plant populations
were established by thinning after emergence and
thus are very close to harvest populations. These re-
sults show rather clearly that plant populations need
to be in the range of 25,000 to 30,000 for best yields
under most conditions.

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 2.02. Percent of Maximum Yield Expected from Planting on Different Dates and at Different Plant
Populations Using Data Generated from the Results in Figure 2.02

Plant population

per acre

Planting date

10,000

12,500

15,000

17,500

20,000

22,500

25,000

27,500

30,000

32,500

35,000

% of maximum yield expected -

April 10

April 15

April 20

April 25

100

April 30

100

May 4

May 9

May 14

May 19

May 24

May 29

The same data, but plotted with individual years
and locations separately in Figure 2.04, show this
more directly. Optimal yields and plant populations
were calculated as the point at which the last addition
of seed just paid for itself in extra yield. We can con-
clude from these data that, when weather conditions
are favorable for high yields, we need high plant
populations to reach those yield potentials. Optimal
plant populations were above 25,000 for all but one of

220

200

180

3
0)

160

140

120

the 16 trials conducted.

The development of variable-rate planter drives
means that we are now able to change planting rates
as we drive across a field. Unforttmately, we don't
have good guidelines to tell us that different parts of
a field should have different plant populations. The
data in Figure 2.04 at least hint that higher-yielding
areas may need more plants. But using a yield moni-
tor in a field to identify low-yielding areas and then
reducing plant population there is counterproductive
if low yields result from low plant populations, as is
often the case. Limited research to date has indicated
that most productive fields in Illinois will probably

260

240

ra 220

5
0)
■>.

200

180

160

I 140
° 120

T Brownstown
• DeKalb
■ Monmouth
A Urbane

100

10 15 20 25 30 35

Plant population (hundreds/acre)

Figure 2.03. Yield response of com to plant population at
four Illinois locations. Data are averages over 4 years
(1991-1994) and six hybrids.

100

25 26 27 28 29 30 31 32
Optimum plant population (hundreds/acre)

Figure 2.04. Optimal economic yields and plant popu-
lations, calculated from the individual year-location data
shown in Figure 2.03. Data are averages over six hybrids.

2 • CORN

show little return from varying populations. Fields
with both heavy and light soils may benefit, espe-
cially if experience shows that plants in the lighter
soils are often barren or that yields are usually low.
In more uniform fields, it is more important to have
populations high enough for best yields, and popula-
tions should probably not be changed more than 10
percent or so from the normal population when the
planting rate is varied. It is very easy to test the effects
of variable-rate population: simply vary the popula-
tion while driving in one direction and leave it uni-
form when driving the other direction, thus stripping
the field with VRT and uniform populations. Check
yields of these contrasting strips with a yield monitor
to see if VRT plant population increases yield.

Two very important controllable factors influenc-
ing the efficiency of water use are soil fertility and
weeds. Keep the fertility of the soil at optimum levels
and the weed population low.

Other factors that are important include these:

1. Hybrid selection. Though hybrids differ in
tolerance to the stress of high populations, such
differences can be difficult to predict. Most modem
hybrids can, however, tolerate populations of
23,000 to 25,000 per acre on most Illinois soils.
Most need higher populations — up to 30,000

per acre — to produce the best yields, especially on
more productive soils.

2. Planting date. Early planting enables the plant to
produce more of its vegetative growth during the
long days of summer and to finish pollinating be-
fore the hot, dry weather that is normal for late July
and early August. Early planting usually produces
larger root systems as well. In the study reported in
Figure 2.02 and Table 2.02, however, planting date
had little effect on optimal plant population.

3. Row spacing. The more uniform distribution of
plants grown in narrow rows may improve the effi-
ciency of water use. Earlier canopy development
with narrow rows may, however, also dry soils
more quickly.

4. Insect and disease control. The harvest population
is always less than the number of seeds planted. In-
sects, diseases, adverse soil conditions, and other
hazards take their toll. Expect from 10 to 20 percent
fewer plants at harvest than seeds planted (Table 2.03).

Row Spacing

Because a clear yield advantage comes from using a
row spacing of less than 40 inches, most producers
have reduced row spacing. More than 80 percent of

Table 2.03. Planting Rate That Allows for a 10 or a

15 Percent Loss from Planting to Harvest

Seeds

per acre

T~k1 ■

at planting time

Plants per acre

at harvest

10% loss

15% loss

20,000

22,200

23,500

22,000

24,400

25,900

24,000

26,700

28,200

26,000

28,900

30,600

28,000

31,100

32,900

30,000

33,300

35,300

32,000

35,600

37,600

34,000

37,800

40,000

the com acres in Illinois are planted in 30-inch rows,
with most of the rest in 36-inch rows, and with in-
creasing acreage in rows less than 30 inches apart.
Very recently, there has been a great increase in inter-
est in rows narrower than 30 inches apart. This inter-
est has grown for a number of reasons: Reports from
the northern part of the Com Belt (Minnesota and
Michigan) have been very positive; newer hybrids
can, unlike those used in 20-inch-row experiments in
the 1960s, stand and yield well at the higher popula-
tions that normally accompany narrow rows; and
the required equipment is more widely available.

Although some of our work in Illinois in the 1980s
had shown yield increases of 5 to 8 percent when row
spacing was reduced from 30 to 20 inches, more re-
cent results have not shown as much yield increase.
Figure 2.05 shows the response to row spacing and
plant population in a series of studies conducted from
1992 to 1994 at Monmouth and DeKalb, Illinois. Data
are averaged over the 3 years and two locations as
well as over two hybrids, which differed little in their
response. At low populations, narrow rows produced
higher yields than wide rows. As plant populations
rose above 25,000, however, the yield advantage of
20-inch rows over 30-inch rows disappeared. It may
be that the hybrids used in this study were simply
able to form a full canopy at high populations, even
in 30- inch rows.

Despite some questions about the yield response
expected from narrowing the rows to less than 30
inches, some farmers are investing in the equipment
needed to make this change. Other benefits may in-
clude slightly more yield stability over a range of
weather conditions, better suppression of early-
emerging weeds, and the fact that narrower rows

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

200

180

^ 160
o

3
X2

140

120

100

5 10 15 20 25 30 35

Plant population (hundreds/acre)

Figure 2.05. Com response to row spacing and plant
population. Data are averaged over 3 years (1992-1994)
and two hybrids.

Table 2.04. Effect of Planter Speed on Plant Spacing
Variability (Standard Deviation), Plant
Population, and Yield

^ Planter
speed
(mph)

Standard
deviation
(in.)

Plant

population
(per acre)

Yield
(bu/ac)

• 20-inch
■ 30-inch
A 40-inch

5
7

2.87
2.99
3.22

27,230
27,370
27,000

153
152
153

Data are averages of 11 trials conducted by fanners in East
Central Illinois, 1994^96.

the effect of plant distribution in the row may be
summed up as follow^s: within reason, plant spacing
uniformity within the row has little effect on yield if plant
population is adequate for high yields.

usually mean a decision to use somewhat higher
plant populations, which (as Figure 2.03 shows) may
produce higher yields — even if these higher yields are
a "by-product" of the equipment change.

PLANT Spacing in the Row

In recent years a number of researchers have re-
ported that uneven distribution of plants down the
row can decrease yield. The evenness of distribution
of plants in the row can be measured using a statistic
called the standard deviation, which is calculated from
measurements of individual plant-plant distances,
and which ranges from zero with perfect spacing to 6
inches or more where stands are very unevenly dis-
tributed. Standard deviation tends to increase with
lower plant populations, because missing plants in
such cases leave a large gap in the row. Doubles —
two plants in the space usually occupied by one plant
— also increase standard deviation.

Table 2.04 gives the results of a series of planter
speed studies that were conducted by farmers in east
central Illinois. These results showed that, even
though planting faster tended to increase the standard
deviation of plant spacing, it had little effect on plant
population or yield. In only 1 of the 11 trials that were
averaged to produce the data in Table 2.04 did faster
planting decrease yield, and in that trial faster plant-
ing also decreased the plant population. If a planter
can drop the intended number of seeds when run at a
faster speed, there appears to be little reason to slow it
down, tmless faster planting causes a lot of variation
in the depth of planting. Our general conclusion on

Crop Canopy

Figure 2.06 illustrates the importance of canopy cover
during grainfill. These data were taken in 1992-1994
from the plant population trial at Urbana. They help
explain some of the variability in response to both
row spacing and plant population. Though there may
be exceptions, such as when pollination fails or pests
are severe, it is clear that forming and maintaining a
canopy that intercepts at least 95 percent of the sun-
light after pollination is essential for high com yields.
In a real sense, managing row spacing and plant

■D

■>«

/•ri

70 75 80 85 90 95

Canopy light interception (%)

100

Figure 2.06. Relationship between light interception
during grainfill and com yield. Data are from a plant
population trial conducted at Urbana, Illinois, and are
averaged over 3 years (1992-1994).

2 • CORN

population for a particular com hybrid should be
seen as managing to produce and maintain this
canopy.

The success of an attempt to "manage for canopy"
can best be measured by looking down the rows at
about noon on a clear day in early August. Although
you probably can't tell whether light interception is
95 percent or slightly less than that, streaks of sun-
light or many large patches of sunlight on the soil be-
neath the canopy indicate that you probably have not
optimized the management of that particular hybrid
for that field and weather.

Stand Counting

Though the most common method of taking plant
populations has been to count the number of plants in
Vi.ooo of an acre, that length of row is small enough
that it's easy to bias the count by consciously or un-
consciously selecting better places to count. The
method described here generally provides more accu-
rate counts. The method uses a measuring wheel,
which is available for $60 to $100. Here's how it
works:

1. Walk out into the field, set the measuring wheel to
zero, and push it down a row while counting
plants. It's much faster to count plants in groups
of three.

2. When you've counted up to 150 plants, stop and
note how many feet of travel the measuring wheel
has recorded.

3. Divide the number of feet traveled into the follow-
ing factor to determine plant population:

Row spacing (in.)

Factor

3,920,400

3,564,000

3,267,000

3,015,700

2,800,300

2,613,600

2,450,250

2,306,100

2,178,000

2,063,350

For example, if you walked 124 feet while counting
150 plants in 30-inch rows, the population is
2,613,600/124 = 21,077. Write down the factor for your

row spacing, and enter it into calculator memory to
use while you're taking counts.

Because a longer row length is counted and it is
more difficult to bias the count, this method requires
fewer counts per acre than the older method. If stands
are reasonably uniform, you can probably get a good
estimate of plant population by taking one count for
each 5 to 10 acres in the field. If the first two or three
counts are very different from one another, then more
counts may be needed.

Replanting

Although it is normal that 10 to 15 percent of planted
seeds fail to establish healthy plants, additional stand
losses due to insects, frost, hail, flooding, or poor
seedbed conditions may call for a decision on whether
or not to replant a field. The first rule in such a case is
not to make a hasty decision. Com plants often out-
grow leaf damage, especially when the growing point,
or tip of the stem, is protected beneath the soil surface
or up to about the six-leaf stage. If new leaf growth
appears within a few days after the injury, the plant is
likely to survive and produce near-normal yields.

When deciding whether or not to replant a field,
assemble the following information: (1) original plant-
ing date; (2) possible replanting date and expected
plant stand; and (3) cost of seed and pest control for
replanting.

When the necessary information on stands and
planting and replanting dates has been assembled,
use Table 2.02 to determine both the loss in yield to be
expected from the stand reduction and the yield ex-
pected if the field is replanted.

To use Table 2.02, locate the expected yield of the
reduced plant stand by reading across from the origi-
nal planting date to the plant stand after injury. Then
locate the expected replant yield by reading across
from the expected replanting date to the stand that
would be replanted. The difference between these
numbers is the percent yield increase (or decrease) to
be expected from replanting. For example, com that
was planted on April 25 but has a plant stand reduced
to 15,000 by cutworm injury would be expected to
yield 82 percent of a normal stand. If such a field were
replanted on May 19 to establish 30,000 plants per
acre, the expected yield would be 91 percent of nor-
mal. Whether it would pay to replant such a field de-
pends on whether the yield increase of 7 percentage
points would repay the replanting costs. In this ex-
ample, if replanting is delayed until near the end of
May, the yield increase to be gained from replanting
disappears.

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

WEATHER Stress in Corn

Com frequently encounters some weather-related
problems during the growing season. The effect of
such problems differs with the severity and duration
of the stress and the stage of crop development at the
time of the stress. Some possible stress conditions and
their effects on com growth and yield follow:

A. Flooding. The major stress caused by flooding is
simply a lack of oxygen needed for the proper
function of the root system. When plants are very
small, generally they are killed after about 5 or 6
days of being submerged. Death occurs more
quickly if the weather is hot, because high tem-
peratures speed up the biochemical processes that
use oxygen, and warm water has less dissolved
oxygen. Cool weather, by contrast, may allow
plants to live for more than a week under flooded
conditions. When plants reach the six- to eight-leaf
stage, they can tolerate a week or more of standing
water, though total submergence may increase dis-
ease incidence, and plants suffer from reduced root
growth and function for some days after the water
recedes. Tolerance to flooding generally increases
with age, but reduced root function from lack of
oxygen is probably more detrimental to yield be-
fore and during pollination than during rapid veg-
etative growth or during grainfill.

B. Hail. The most common damage from hail is loss
of leaf area, though stalk breakage and bruising of
the stalk and ear can be severe. Loss charts based
on leaf removal studies generally confirm that de-
foliation at the time of tasseling causes the greatest
yield loss, while loss of leaf area during the first
month after planting or when the crop is near ma-
turity generally causes little yield loss. Loss of leaf
area in small plants usually delays their develop-
ment, however, and plants that experience hail
may not always grow normally afterward.

C. Cold injury. Com is of tropical origin and is not es-
pecially tolerant of cold weather. Although the
death of leaves from frost is the most obvious type
of cold injury, leaves are damaged by temperatures
below the low 40s, and photosynthesis can be re-
duced even if the only symptom is a slight loss of
leaf color. The loss of leaves from frost is generally
not serious when it happens to small plants,
though such loss delays plant development and
could delay pollination to a less favorable (or, infre-
quently, a more favorable) time. Frost injury symp-
toms may appear on leaves even when nighttime
temperatures do not fall below the mid-30s; radia-
tive heat loss can lower leaf temperatures to several

degrees below air temperatures on a clear, calm
night. If frost kills leaves before physiological ma-
turity (black layer) in the fall, sugars usually can
continue to move from the stalk into the ear for
some time, although yields generally are lowered,
and harvest moisture may be high due to high grain
moisture at the time of frost and slow drying rates
that usually follow premature death.

D. Drought. Through the late vegetative stage (the
end of June in normal years), com is fairly tolerant
of dry soils, and mild drought during June may
even be beneficial because roots generally grow
downward more strongly as surface soils dry, and
the crop benefits from the greater amount of sun-
light that accompanies dry weather. During the 2
weeks before and 2 weeks following pollination,
com is very sensitive to drought, however, and dry
soils during this period can cause serious yield
losses. Most of these losses are due to failure of pol-
lination, and the most common cause is the failure
of silks to emerge from the end of the ear. When
this happens, the silks do not receive pollen; thus
the kernels are not fertilized and do not develop.
Drought later in grainfill has a less serious offect on
yield, though root function may decrease and ker-
nels may not fill completely.

E. Heat. Because drought and heat usually occur to-
gether, many people assume that high tempera-
tures are a serious problem for com. In fact, com is
a crop of warm regions, and temperatures lower
than 100°F usually do not cause much injury if soil
moisture is adequate. Extended periods of hot, dry
winds can cause some tassel "blasting" and loss of
pollen, but pollen shed usually takes place in the
cooler hours of the morning, and conditions severe
enough to cause this problem are unusual in Illi-
nois. There is evidence that hybrids vary in their
sensitivity to both heat and drought, though ge-
netic drought tolerance usually means some loss in
yield potential. As a result,such hybrids may not be
good choices for average conditions.

Estimating Yields

Making plans for storing and marketing the crop of-
ten calls for estimating yields before the com is har-
vested. Such estimates are easier to make for com than
for most other crops because the number of plants or
ears per acre can be counted fairly accurately.

Estimating com yields is done by counting the
number of ears per acre and the number of kernels
per ear, then multiplying these two numbers to get an
estimate of the number of kernels per acre. Next, simply

2 • CORN

Table 2.05. Row Length Required to Equal
1/1,000 Acre

Row width

Row length

20"

28"
30"
32"
36"
38"
40"

26'1"
18'8"
17'5"
16'4"
14'6"
13'9"
13'1"

divide by an average number of kernels in a normal
bushel to get the yield in bushels per acre.

Com yields can be estimated after the kernel num-
ber is fixed — about 2 weeks after the end of pollina-
tion. The following steps are suggested:

1. Walk out in the field a predetermined number of
rows and paces. For example, go 25 rows from the
edge of the field and 85 paces from the end of the
field. If this pattern is not determined beforehand,
there is a tendency to stop where the crop looks
better than average. Stop exactly where planned.

2. Measure Vi.ooo of an acre (Table 2.05), and count the
number of ears (not stalks) in that distance. Do not
count ears with only a few scattered kernels.

3. Take three ears from the row that was counted. To
avoid taking only good ears, take the third, sixth,
and tenth ears in the length of row. Do not take
ears with so few kernels that they were not in-
cluded in the ear count.

4. Count the number of rows of kernels and the num-
ber of kernels per row on each ear. Multiply these
two numbers together for each ear, then average
this kernel count for the three ears.

5. Calculate yield using the following formula:

number of ears per Vi,ooo acre x
bu/acre = average number of kernels per ear

6. To get a reliable average, repeat this process at least
once for every 5 acres in a field.

The formula uses the number 90 on the assumption
that a bushel of normal-sized seed contains about
90,000 kernels. The zeros are dropped because the
plant population is given in thousands per acre.

Specialty Types of Corn

Erratic and generally low world corn prices have re-
sulted in considerable interest among producers in
growing various specialty types of com, either for ex-
port or for domestic use. This may mean higher prof-
its if the supply of such types is quite small. Because
the total demand might also be quite limited, how-
ever, the price advantage may disappear as more pro-
ducers start growing a particular specialty type. It is
therefore important to have other uses for the crop
(for example, as livestock feed) and to grow types that
do not yield substantially less than normal com, in
the event that the com cannot be sold for its intended
special use.

Many specialty types are grown under contract.
The contract buyers often specify what hybrids may
or may not be used, and they may specify other pro-
duction practices to be used. Some contracts also may
include pricing information and quality specifications.

Risks associated with growing specialty types of
com vary considerably. Milling companies may buy
com with "food-grade endosperm," requiring only
that the grower choose hybrids from a relatively long
list of popularly grown hybrids; the risk in this case is
small. By contrast, tnbreds used to produce some hy-
brids are not very vigorous, and seed com production
with such inbreds might be very risky. Production
contracts in such cases may shift some of the risk to
the buyer. In any case, every grower of specialty types
of com should be aware of risks associated with each

type-
Fortunately, most of the specialty types of com that
are available require production practices much like
those of normal, yellow dent com. In most cases, pol-
lination with normal com results in "intermediate"
kernel types, which usually lower the value of the
com as a specialty type. Isolation from normal com,
or harvesting the outside rows of the specialty type
(where most of the normal pollen would land) and
using them for feed or other nonspecialty use, will
usually improve the quality of the specialty type.

White com and yellow, food-grade com are both
used for human consumption. Many normal hybrids
produce good quality for use as food. White hybrids
have not been bred quite as extensively as yellow hy-
brids, and most of the white hybrids tend to be later
in maturity than hybrids commonly grown in north-
em Illinois. Buyers of food-grade com may require
that grain be dried to a certain moisture content in the
field, and that drying temperatures be kept low. Waxy
com contains 100 percent amylopectin starch, com-
pared to 75 percent in normal com. Amylopectin
starch has certain characteristics that are useful in

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

food and industrial products. In contrast, high-amy-
lose com has lower amylopectin, and more than 50
percent amylose, which has different properties than
amylopectin, and so has use in a different group of
food and industrial products.

In the past few years, high-oil com hybrids have
been developed using topcross technology, in which
male-sterile hybrids are pollinated by 7 to 10 percent
of the plants in the field whose pollen carries the
high-oil characteristic. Because oil content of grain
from these hybrids is 6.5 to 7.5 percent — about double
the normal oil content — this grain has higher caloric
value for livestock feed. At present, premiums are
paid for this grain based on oil content. Because the
caloric content of the grain is higher, such hybrids

may yield slightly less on average than do their nor-
mal-oil counterparts.

Popcorn has very hard endosperm that expands
rapidly when water in the endosperm is turned to
steam by rapid heating. Most popcorn is produced
under contract to a processor. Popping volume is an
important characteristic of popcorn hybrids, and pre-
miums may be paid for hybrids that have high pop-
ping volume but less yield. There are yellow- and
white-hulled popcorn hybrids, as well as types with
purple or black seedcoat colors. Most popcorn hy-
brids are less vigorous than normal com hybrids, and
so are less tolerant of adverse weather. Increasing
amounts of popcorn are grown under irrigation.

AUTHOR

Emerson D. Nafziger

Department of Crop Sciences

Chapter 3.
SOYBEANS

Planting Date

Soybeans generally yield best when planted in May,
with full-season varieties tending to yield best when
planted in early May. Earlier varieties, however, often
yield more when planted in late May than in early
May. When the planting of full-season varieties is de-
layed until late May, the loss in yield is minor com-
pared with the penalty for planting com late. There-
fore, planting soybeans after com has been planted is
accepted and wise.

The loss in yield of soybeans becomes more severe
when planting is delayed past early June. The pen-
alty, however, for late-planted com is proportionally
greater, and the danger of wet or soft com becomes
such a threat that soybeans are, under most condi-
tions, a better crop for late planting than com.

Planting date affects the length of time required for
soybeans to mature, with delays resulting in fewer
days needed for the plant to complete its life cycle. It
is primarily vegetative development before onset of
flowering that is shortened by planting delays. Plant-
ing until the beginning of flowering is typically 45 to
60 days for full-season varieties planted at the normal
time. This interval is shortened as planting is delayed;
it may be only about 25 days when such varieties are
planted in late June or early July. A rule of thumb is
that for each 2- to 3-day delay in planting, maturation
of the plant is delayed by one day. The lengths of the
flowering period and of pod-filling also are short-
ened, but the effect of planting delays on these phases
of development is minor.

Soybeans are photoperiod sensitive, meaning that
the lengths of day and of night strongly influence
when the plant initiates flowering. When planting is
delayed, the day length to which soybean seedlings
are exposed differs from that experienced with timely
seeding in May. The response to photoperiod is the
primary factor to which the crop responds, with the
plant ultimately devoting fewer days to vegetative
development before flowering begins. Warm tem-

peratures at night also accelerate the onset of flower-
ing. Figure 3.01 presents data collected over many
years and many locations in Illinois, illustrating that
delayed planting shortens the days required for soy-
beans to mature.

As stated previously, soybeans yield best when
planted in May. Some growers have questioned
whether planting before May would benefit the crop.
Experience at research fields in Illinois and other
midwestem states suggests that planting before May
frequently puts the crop at risk due to soil conditions
that are too cold and wet, as well as possibly exposing
early emerged soybeans to a frost or freeze. Low tem-
peratures inhibit germination, while cold and wet
conditions favor disease on the seed or seedling.
While planting in April occasionally works, it will nei-
ther work every year nor consistently yield the most

15 20 25

Planting date in May

Dates are average planting and maturity dates compiled

from USDA Uniform Soybean Tests Northern States, 1980-1993.

Figure 3.01. Planting date effect on maturity of soybeans
with Group II, III, and IV maturities.

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

productive crop. Figure 3.02 summarizes the results of
various planting dates for soybean at DeKalb and
Monmouth and Indicates no advantage in planting
before late April or early May.

When spring conditions do not allow timely plant-
ing of soybean in May, the planting date may extend
well into June, or in some cases early July. Such delays
in planting have serious consequences to yield poten-
tial. The 1995 and 1996 weather patterns created prob-
lems with timely planting of soybean in Illinois. De-
lays into June tend to result in a shorter soybean plant
with considerably fewer leaves, thus reducing the
yield potential per plant. It is possible to offset some-
what the disadvantageous changes in plant morphol-
ogy that lengthy delays cause by planting late-seeded
soybeans in narrow rows and at a density higher than
is used for timely May seeding.

Research in recent years on the best management
for late-planted soybeans is limited; however, pio-
neering research at Dixon Springs on double-crop
soybean management indicated an advantage to nar-
rowing rows and increasing plant density in such
late-planted fields. Tables 3.01 and 3.02 illustrate these
benefits to soybean yield.

Delays in planting into mid-June may not require
increased plant densities equivalent to those used in
double-cropped fields, but an increase in planting rate
of 20 to 30 percent should be advantageous. Soybeans
planted during the end of June can also be expected to
benefit from increased plant density similar to the
double-crop results reported in Table 3.01. Combined
with narrowed row spacing, increased plant density
will benefit soybean yield when the crop is planted
well past the most desirable planting date.

DeKalb

•a

10 20 30 40 50

Planting date - days after April 1

Figure 3.02. Seeding date effect on soybean yield,
Monmouth and DeKalb.

Table 3.01. Double-Cropped Soybean Response to
Increased Plant Densities

Plant density (thousands/A)

Yield (bu/A)

87
135
200
244
289

38
43
47
52
56

I
I

Table 3.02. Double-Cropped Soybean Response to
Narrowed-Row Spacing

30" spacing

20" spacing

Experiment 1
Experiment 2

Average

35.9

44.5

32.7

41.6

34.3

43.0

PLANTING RATE

Maximum yield from May-planted soybeans gener-
ally results from planting sufficient seed to establish
6 to 9 plants per foot of row in 30-inch rows, 5 to 6
plants per foot of row in 20-inch rows, and 3 to 4
plants per foot of row in 10-inch rows. Higher plant
densities may be able to stand up with lodging-resis-
tant varieties, but populations greater than 150,000
plants per acre are unlikely to consistently enhance
yield. Excess plant densities require more seed to
plant, which adds to production cost, and if weather
happens to favor rank vegetative growth, varieties
considered resistant to lodging can fall over.

An insufficient plant population will limit yield, as
plants fail to form the complete canopy of leaves
needed to fully use the available sunlight. It is par-
ticularly important to soybean yield that a complete
canopy be in place by the time pods begin to form.
Thin stands also allow more weed competition to de-
velop in the crop and also encourage plants to branch
and pod closer to the soil line, possibly adding to har-
vest losses.

Studies have demonstrated that the productive ca-
pacity of soybean is surprisingly good at rather low
plant densities. At extremely low densities, a consid-
erable amount of the production may not be effi-
ciently harvested with a combine due to low podding
and excessive branching low on the main stem of the
plant. Precipitation and planting date actually deter-
mine what the "ideal" plant density may be in a given

3 • SOYBEANS

year. In a dry year, when vegetative development of
plants is restricted, higher densities of soybean are
desirable so that a full canopy can develop. In con-
trast, a year with abundant rainfall following timely
planting can result in excessive vegetative growth,
possibly leading to lodging. At planting we cannot
predict weather during vegetative growth, so a com-
promise in seeding rate offers the most yield potential.

Seeding-rate trials conducted in 30-inch row spac-
ings suggest that a wide range of seeding rates will
produce good yields. Seeding rates that result in ap-
proximately 150,000 plants per acre tend to produce
best yields (Figure 3.03). Soybeans in narrow-row
planting (drilled or otherwise) are often planted at a
seeding rate resulting in densities greater than
150,000 plants per acre. If lodging-resistant varieties
are planted, plant density can likely be increased to
the range of 180,000 to 200,000 plants per acre with-
out risk of lodging. Benefits to yield are often ques-
tionable, however, when plant densities exceed
150,000 plants per acre in a timely planted stand with
uniform plant distribution.

The more rapid full canopy, which develops in
fields planted to narrow rows at higher plant densi-
ties, has often been reported to aid in weed manage-
ment through the shading imposed on weedy species.
Shade pressure on weeds will help reduce weed
growth but should not be relied upon solely as a
means to suppress weedy competitors in narrow-row
soybeans.

For seed of average size, planting 40 to 60 pounds
per acre can achieve a stand of 110,000 to 150,000
plants per acre. Planting at rates toward the higher

100

end of this range helps ensure a full stand; planting
toward the low end might fail to produce adequate
stands in an unfavorable environment, which limits
emergence. It is generally wise to plant at a rate that
achieves a stand toward the upper limit in plant den-
sity which the soybean variety will tolerate without
lodging. Research on planting rates and yield poten-
tial indicates that virtually all varieties respond simi-
larly to changes in seeding rate until the plant density
reaches a level that results in lodging.

As previously mentioned, soybeans that are not
timely planted in spring, and especially those planted
after harvest of winter wheat, will have reduced veg-
etative development (fewer leaves per plant and a
shorter stem) and will tend to be more resistant to
lodging. Soybeans planted late or double-cropped
need to be established at higher densities per acre and
in narrow rows to allow the crop to fully intercept
sunlight by the time pod development begins. Rec-
ommendations on planting rate therefore change as
seeding is delayed from May to June or early July.

As row spacing narrows, fewer plants per foot of
row are needed to achieve a given population of
plants per acre (Table 3.03). The actual amount of
seed needed per acre will be determined by the popu-
lation density desired, seed size, and seed quality, as
well as by field conditions and equipment consider-
ations which relate to emergence of a viable seed. The
extent to which seeds are dropped in excess of the de-
sired plant density per acre depends on how probable
it is for a viable seed to emerge. Seed drop rate per
acre can be determined by the following calculation:

desired stand /acre
% germination x % survival of viable seed

p 60
a>

^ 40

0 50 100 150 200

Plant density (thousands/acre)

Figure 3.03. Effect of plant density on soybean yields.

250

Table 3.03. Soybean Plants Per Foot of Row for

Different Populations in Various Row
Spacings

Row

Soybean population

spacmg
(in.)

125,000

150,000

175,000

200,000

225,000

Average

number

of plants/foot of row required

36"

8.6

10.3

12.0

13.8

15.5

30"

7.2

8.6

10.0

11.5

12.9

15"

3.6

4.3

5.0

5.7

6.5

10"

2.4

2.9

3.3

3.8

4.3

1.9

2.3

2.7

3.1

3.4

1.7

2.0

2.3

2.7

3.0

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

The germination for a seedlot can be taken from the
seed tag, but the survival of viable seed is highly de-
pendent on the environment and on placement by the
planting equipment. Seedbed temperature and mois-
ture level will determine how well germination can
proceed. Planting equipment varies in the ability to
maintain an appropriate depth of seed placement and
uniformity of soil covering. The tillage system used
will determine the crop residue remaining on the soil
surface at planting, which in turn will influence seed-
bed moisture and temperature conditions at planting.
The experience of the individual producer is needed to
formulate a value for the survival of viable seed when
planted in given fields. Once the seed drop rate per acre
needed is known, the quantity of seed needed for plant-
ing can be determined (Table 3.04).

PLANTING DEPTH

Emergence will be more rapid and stands will be
more uniform if soybeans are planted only V/z to 2
inches deep. Deeper planting often results in lower
emergence and poor stands.

Varieties differ in their ability to emerge when
planted more than 2 inches deep. The description of a
variety may mention an "emergence score," which re-
flects the ability of the seedling hypocotyl to elongate
sufficiently when planting is deeper than recom-
mended. Scores for emergence are usually given on a
l-to-5 scale, with a score of 1 indicating that the likeli-
hood of emergence is very good and a score of 5 indi-
cating that such probability is very weak. Special at-
tention should be given to the planting depth of
varieties that are known to have weaker emergence
potentials. Because a variety has a tendency to emerge

Table 3.04. Soybean Seeding Requirements for
Different Seed Sizes and Seed Drop
Rates

Lb of seed required
for desired seed drop/acre

150,000 175,000 200,000 225,000

Seed
per lb

1,800
2,000
2,200
2,400
2,600
2,800
3,000
3,200

83
75
68
63
58
54
50
46

111

125

88
80

100
91
83

113

102

Location

DeKalb

Dixon

Urbana

Brownstown

slowly or weakly from excessively deep planting does
not mean it lacks the ability to produce a good crop
when planted at a reasonable depth. It simply means
that extra attention to depth of planting is needed to
ensure a good stand.

Crop Rotation

The crop preceding soybeans has an influence on
yield potential. If soybeans are planted after soybeans,
diseases and other pest problems may be intensified
in the second and later years of production. Difficult-
to-control weed problems will become worse. Re-
search evidence also suggests that growth-inhibiting
substances (allelopathic chemicals) are released from
soybean residue as it decomposes in the soil. These
substances have a negative effect on the growth and
production of soybeans. To avoid this problem, suffi-
cient time must elapse between one soybean crop and
the next to allow decomposition of the soybean crop
residue. Planting soybeans after soybeans will not
provide a sufficient interval.

Several studies on the rotation benefits for soybean
yield have been done. Table 3.05 summarizes these re-
sults, which indicate that higher yields tend to result
from soybeans grown in rotation, compared to those
from soybeans after soybeans.

ROW WIDTH

If weeds are controlled, soybeans often will yield
more in narrow rows than in traditional row spacings
of at least 30 inches. The yield advantage for narrow
rows is usually greatest for earlier-maturing varieties,
with full-season varieties showing smaller gains in
yield as row spacing is reduced to less than 30 inches.
Numerous studies have evaluated yield benefits asso-
ciated with narrow rows in spring-planted soybeans,
and their results are variable. Enhanced yield can be
as much as 15 or 20 percent in some situations, while
in others no enhanced yield is obtained. The advan-

Table 3.05. Effect of Crop Rotation on Soybean
Yields

Soybeans after

Soybeans

Com

Bushels per acre
39 44

30 35

44 50

30 35

3 • SOYBEANS

tage to yield realized in rows less than 30 inches will
be determined by how well spacings of 30 inches or
more can intercept light by the time reproductive
growth on the plant begins. To predict whether nar-
rowed rows will benefit yield, follow this rule of
thumb: If a full canopy of leaves is not developed over
the soil by the time pod development begins, then nar-
rower row spacings can likely be advantageous to yield.

The relative maturity of the variety produced,
growing conditions during the vegetative period of
plant development, and planting date all influence
the extent of canopy development by the time pod-
ding begins. Varieties that mature relatively early gen-
erally have the smallest canopies when podding be-
gins and consequently can benefit most from
narrow-row spacings. Dry or otherwise undesirable
weather early in the season will reduce the amount of
canopy developed before the onset of podding. When
such weather patterns occur, rows that are narrower
help develop a full canopy by the time podding be-
gins. Delays in planting reduce the amount of canopy
that develops before seed formation activity begins;
thus when planting is delayed considerably, soybeans
respond to narrower rows with yield increases.
Double-crop soybeans planted after the small-grain
harvest should be planted with a grain drill.

Interest in planting soybeans with a grain drill or
other narrow-row equipment has grown considerably
in recent years. A 1996 survey reported that average
soybean row space was down to only 16 inches in Illi-
nois. Advances in postemergence herbicides as well as
available planting equipment have allowed growers to
reduce row spacings in soybeans.

With spring planting in Illinois, it appears that row
spacings in the range of 15 to 20 inches are generally
adequate to facilitate full-canopy development by the
time pod development begins on the crop, allowing
narrow-row benefits to yield to be fully realized. Re-
search has generally failed to demonstrate an advan-
tage for drilled spacings compared to 15 to 20 inches
when timely spring planting. This indicates that using
rows spaced at 7 to 10 inches (drilled planting) is not
required to gain the full benefits to yield associated
with narrowed rows in Illinois. Several narrow-row
planters have become available in recent years, indi-
cating that the equipment industry is responding to
the research-documented benefits of rows spaced 15
to 20 inches.

Double-Cropping Considerations

Double-cropped soybeans (planted following harvest
of winter wheat in late June or early July) can be suc-
cessfully produced most years in central and southern

parts of Illinois. In some years the practice works in
northern portions of the state as well, but in others
the onset of cold weather will take a major toll on
yield and quality of the crop produced.

Vegetative development on the double-cropped
soybean plant is profoundly influenced by the late
June or early July planting date. The environment
into which double-crop soybeans emerge can be too
dry for good emergence, and higher temperatures
speed along the onset of flowering. An exceptionally
early frost in the fall can damage the crop, which
needs all of the average growing season to reach ma-
turity. Yield potential of soybeans double-cropped is
typically 50 or 60 percent of that obtained with timely
planting in the first half of May.

The typical double-cropped soybean plant has a
much shorter stem and fewer leaves than one timely
planted in the first half of May. Shorter stems pro-
vide fewer potential places for pod formation.
Higher populations of plants per acre are needed to
allow the plant to intercept sunlight and maximize its
yield potential. The smaller leaf area per plant cre-
ates a plant that responds favorably to narrow-row
spacings. While the number of plants per acre estab-
lished in double-crop tends to be much higher than
with May planting, the short stature of the plant re-
duces greatly the chance of lodging problems.

Research on double-crop management across the
Midwest suggests that planting with a grain drill is
essential to obtain the full yield potential of double-
crop soybeans. Small-statured plants are more re-
sponsive to narrow-row planting than plants result-
ing from May seeding. Increasing plant densities by
50 to 100 percent over that used with timely spring
seeding has been found to benefit yield. Greater
numbers of smaller-statured plants are required to
capture sunlight effectively. Because July and August
often are hot with limited rainfall, planting double-
crop soybeans with a no-till drill is a practical means
of conserving soil moisture, which is often in short
supply following planting.

The double-crop soybean will germinate in a much
warmer environment than do May-planted soybeans,
which will allow for rapid emergence if moisture is
available. Higher temperatures, though, especially at
night, will limit vegetative development before flow-
ering begins. The time devoted to vegetative devel-
opment is abbreviated much more than is the interval
devoted to podding and seed fill.

Varieties that tend to produce best double-crop
yields are those which are classified as mid-season to
full-season for the area. If a variety that is early for a
location is planted, vegetative development prior to
flowering is extremely limited. Those varieties with

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

determinate growth habit should not he planted for
double-crop production. The stem terminates growth
when flowering begins in determinate varieties, and
because flowering occurs shortly after emergence on
double-cropped soybeans, a determinate variety
would produce an extremely short plant with low
yield.

Based on research experiences across the Midwest,
a recipe for successful double-crop soybeans needs to
include narrow-row spacings, high plant densities per
acre, varieties classified as mid-season to full-season
for the area, management that helps conserve soil
moisture, and a first fall frost that is no earlier than
average.

When to Replant

Uniform full stands have been compared to those
with irregular deficiencies of varying magnitudes to
evaluate yield potentials of stands that are less than
perfect (Tables 3.06 and 3.07). Studies strongly suggest
that the soybean stand has a tremendous ability to
compensate for missing plants. Because existing
plants will develop more branches and pod more
heavily, the effect of missing plants in the stand is of-
ten not detected in yields. The yield reduction associ-
ated with very poor stands may still be more profit-
able to the grower than a replanted field, which has
additional costs associated with replanting and a re-
duced yield potential because of a delayed seeding
date.

Data in Table 3.06 illustrate the soybean's ability to
compensate for missing plants when randomly placed
gaps occur in the stand. The influence of plant density
in the remaining row sections is also apparent. For
soybeans to exhibit their full capacity to compensate
for missing plants, it is necessary to control weed
growth in the areas without soybean plants. In a field
situation where poor stands are realized, management
to control weeds is essential to prevent further yield
losses due to the poor stand. Maintaining the neces-
sary weed control must be considered a cost of keep-
ing a less-than-perfect stand.

Growers who replant do so at a later planting date
than is best. A penalty to yield due to delayed plant-
ing of 2 to 3 weeks is reflected in values presented in
Table 3.07. The plant density per foot of row achieved
with replanting, along with possible gaps in that
stand, will also influence yield potential. It is wise to
remember that replanted soybeans are not guaranteed
to grow: A perfect stand is not always achieved when
a poor stand is destroyed and the field is replanted.

At a given level of stand reduction, the impact on
yield is minimized if the gaps are small rather than

Table 3.06. Percent of Full-Yield Potential for
Timely Planted Soybeans, as
Influenced by Plant Density Established
and Stand Reduction

Stand reduction^

Plants per foot of row''
8 6

0 (full stand)
10 percent
20 percent
30 percent
40 percent
50 percent
60 percent

Percent of full-yield potential

100 97 95

98 96 93

96 93 91

93 90 88

89 86 83

84 81 78

78 75 73

^Reduction in stand achieved by random placement gaps

12 inches long.

Tlants per foot of row in row sections with no gaps or

skips.

Table 3.07. Percent of Full Yield Expected from

Replanting Soybeans, as Influenced by
Plants Per Foot of Row and Stand
Deficiency

Plants per foot of row''

Stand-deficiency level^

6 4

Percent

of full-yield potential

0 (full stand)

86 83

10 percent

85 83

20 percent

84 81

30 percent

81 79

40 percent

78 75

50 percent

74 71

60 percent

69 66

■"Reduction in stand achieved by random placement gaps

12 inches long.

''Plants per foot of row in row sections with no gaps or

skips.

large. A gap of 16 inches has been found to have no
influence on yield of soybeans grown in 30-inch row
spacing, provided adjacent rows have a full stand.
Compensation for gaps in the row occurs not only in
the row where the gap is located but also in the rows
bordering the gap. The degree of compensation exhib-
ited by soybeans should be enhanced as rows are
spaced closer together. Under such planting arrange-
ments, the plants are initially more uniformly spaced

3 • SOYBEANS

Table 3.08. Quality Differences in Soybeans from
Different Sources

Seed

Germi-

Pure

Inert

Seed

germi-
nation

nation

seed

matter

cleaned

tested

Source

(%)

1985 survey

Certified seed

88.2

99.5

0.42

100

Bin-run seed

85.9

98.1

1.19

1986 survey

Certified seed

89.0

99.4

0.29

100

Bin-run seed

87.7

98.6

1.59

in the field, making it more likely they can fully com-
pensate for a stand deficiency of a given level. Exten-
sion Circular 1317, Managing Deficient Soybean Stands,
can be useful to growers making a replanting decision.

Seed Source

To ensure a good crop, you must select high-quality
seed. When evaluating seed quality, consider the per-
cent germination, percent pure seed, percent inert
matter, percent weed seed, and the presence of dis-
eased and damaged seed.

Samples of soybean seed taken from the planter
box as farmers were planting showed that home-
grown seed was inferior to seed from other sources
(Table 3.08). The number of seeds that germinate and
the pure seed content of homegrown seeds were
lower. Weed seed content, percent inert material
(hulls, straw, dirt, and stones), and presence of other
crop seeds (particularly com) were higher in home-
grown seed.

This evidence indicates that the Illinois farmer can
improve soybean production potential by using
higher quality seed. Homegrown seed is the basic
problem. Few producers are equipped to carefully
harvest, dry, store, and clean seeds and to perform
laboratory tests that adequately assure high quality. A
grower who is not a professional seed producer and
processor may be well advised to market the home-
grown soybeans and obtain high-quality seed from a
reputable professional dealer.

A state tag is attached to each legal sale from a seed
dealer. Read the analysis and evaluate if the seed be-
ing purchased has the desired germination, purity,
and freedom from weeds, inert material, and other
crop seeds. The certification tag verifies that an unbi-

ased nonprofit organization (in our state, the Illinois
Crop Improvement Association) has inspected the
production field and the processing plant. These in-
spections certify that the seeds are of a particular vari-
ety as named and have met certain minimum quality
standards. Because some seed dealers may have
higher quality seed than others, it always pays to read
the tag.

Seed Size

The issue of how the size of seed planted affects soy-
bean growth and the final yield often arises following
a year with stress during the seed-fill period, which
reduces final seed size. Research suggests little detri-
mental effect from planting seed smaller than normal.

Across a broad range of seed sizes, insignificant ef-
fects on emergence have been reported. Seeds of ex-
tremely small size, which normally do not make their
way into the market, may be reduced in emergence
when planted at a normal depth of 1 to 2 inches.

Final differences in plant size, which might result
from planting seeds of different sizes, do not suggest
any problems with using small seed. Any differences
reported on final plant size are so small (less than 4
inches) that they would likely not have a significant
effect on yield.

The size of seed produced by soybeans is deter-
mined by a combination of genetic factors for the vari-
ety and the environment in which the seeds develop.
Whether soybeans are large or small, seed for a given
variety has the same genetic potential. The size of the
seed produced on a plant established by planting a
small seed is thus expected to be the same as the size
of the seed from a plant grown from large seed.

Effects of seed size on final yield, which is the ulti-
mate concern of growers, appears to be minimal.
When you shop for soybean seed, seed quality should
be a more important consideration than size. If
smaller-than-normal seed will be used to establish
soybeans, check your planter calibration to meter the
seed at the proper rate. Excessive seeding rates, re-
sulting from misadjusted planting equipment meter-
ing small seed, can result in excessively thick stands
that will be more prone to lodging.

Varieties

Soybean varieties are divided into groups according
to their relative times of maturity (see Table 3.09). Va-
rieties of Maturity Group I are nearly full season in
northernmost Illinois but are too early for good
growth and yield farther south. In extreme southern
Illinois, varieties in Maturity Groups IV and V are
best adapted.

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 3.09. Characteristics of Public Soybean Varieties

Relative

maturity

(days)

Lodging

score^
(1-5 scale)

Soybean cyst
resistance'' (races)

Phytophthora

resistance''

Races Races Races

1, 2 4, 5 3, 6-9

Seed

protein*^

(%)

Seed
oiP

Variety

(%)

Group I

IA1006

-11

2.2

34.1

19.2

Group II

Burlison

-3

1.9

38.3

17.5

Dwight*

1.5

35.8

18.4

IA2036*

-3

2.8

36.0

17.3

Jack

2.9

35.5

18.4

Savoy

-3

1.3

37.3

18.2

Group III

Edison

-2

1.8

36.2

18.8

IA3005

-1

2.1

—

34.7

19.3

Iroquois

-3

2.0

35.2

19.3

Linford

2.1

—

36.5

18.9

Macon

1.9

34.8

19.2

Maverick

2.8

—

34.8

18.8

Pana*

2.8

33.3

19.5

Probst

-1

2.1

35.5

19.2

Resnik

9/21

1.5

35.4

18.7

Saline

2.5

—

34.1

20.2

Thomed

1.9

35.7

19.4

Yale

2.0

—

35.4

19.8

Group IV
Bronson

2.7

36.4

18.7

Flyer

1.8

36.3

18.8

Ina**

3.0

33.9

18.7

Omaha

1.7

36.2

19.8

Rend**

2.6

36.5

18.3

NOTE: Height and lodging score comparisons should be made within maturity groups.

*Available to farmers in 1999.

**Available to farmers in 2000.

■"l = all plants standing, 5 = all plants flat.

''R = resistant, MR = moderately resistant, S = susceptible.

''Protein and oil values based on 13% moisture content, 1995-96 average.

•^Variety is resistant to brown stem rot.

3 • SOYBEANS

Traditionally, soybeans grown in the Midwest have
had indeterminate growth habits; that is, vegetative
growth continues beyond the time when flowering
begins, continuing generally until seed fllling begins.
In the late 1970s and early 1980s a few short-statured
determinate varieties having maturities appropriate to
Illinois were released. The primary advantage of such
varieties was excellent resistance to lodging in a high-
yield environment. The determinate growth-habit
trait terminates vegetative development on the main
stem when flowering begins. While reduced main
stem length reduces lodging potential, determinate
varieties require above-average growing conditions
prior to flower in order to consistently offer a yield
advantage. Stress early in the season or delayed plant-
ing date can severely limit yield of determinate variet-
ies in the Midwest because inadequate vegetative de-
velopment prior to flower results. There are currently
a very limited number of soybean acres planted to de-
terminate varieties in Illinois.

Literally hundreds of soybeans are available for the
producer's consideration, with most varieties offered
by private seed companies. Varieties from private
companies now occupy most soybean fields in Illi-
nois, with the remainder of acres planted to public va-
rieties (released by universities or USDA). Soybeans

from public sources are elaborated in Table 3.09,
which summarizes many agronomic characters, dis-
ease reactions, and other traits of the major and newer
public soybeans being used currently in Illinois.

Most soybean acres in Illinois are planted from Ma-
turity Group II, III, or IV. A few Group I and Group V
varieties are grown in the northern and southern ex-
tremes of the state, respectively. For specific perfor-
mance data on both public and private varieties, con-
sult the latest issue of Performance of Commercial
Soybeans in Illinois from the Soybean Variety Testing
Project.

Regardless of the soybean variety a producer
chooses to plant, considering the overall advantages
of the options available is important. When choosing
a variety, first consider a suitable maturity coupled
w^ith a good yield-to-performance record. Further re-
fine the selection process by considering the variety's
genetic resistance to prevalent pest problems. If you
are producing for niche-market contracts, your
choices will be relatively limited and may not include
the best-yielding or most pest-resistant varieties. If
current trends in variety development continue, one
can anticipate that consideration of herbicide toler-
ance or resistance may be included in the variety se-
lection process.

AUTHOR

Gary E. Pepper

Department of Crop Sciences

Chapter 4.
Small Grains

Winter Wheat

Although both soft red and hard red winter wheat can
be grown in Illinois, improved soft wheat varieties are
widely adapted in the state; nearly all of Illinois wheat
is the soft type. The primary reasons for this are the bet-
ter yields of soft wheat and the sometimes poor
bread-making quality of hard wheat produced in our
warm and humid climate. Because it may be difficult
to find a market for hard wheat in many parts of the
state, it is advisable to line up a market before plant-
ing the crop.

Wheat in the Cropping System

In recent years, wheat acreage in Illinois has averaged
about 1.4 million acres planted, with an average of
about 1.2 million acres harvested. Most of the wheat
acreage is in the southern half of the state, and a ma-
jority of the acreage south of 1-70 is double-cropped
with soybeans each year. Much of the crop in the
northern part of the state is planted by livestock pro-
ducers, who often value the straw as much as the
grain, and who often spread manure on the fields af-
ter wheat harvest. For those considering producing
wheat, these points may help in making the decision:

1. State average yields have ranged from 32 to 59
bushels per acre over the past 15 years, with county
average yields often correlated with average com
yields. Under very favorable spring weather condi-
tions (i.e., dry weather in May and June), yields on
some farms have exceeded 100 bushels per acre. As
a rule of thumb, wheat yields average about one-
third those of com, but they are about one-half
those of com when weather is favorable for both
crops. Having different weather requirements from
com and soybeans, wheat helps spread weather
risks.

2. Wheat costs less to produce than com, but gross
and net incomes from wheat are likely to be less

than for com or soybeans. Added income from
double-crop soybeans or from straw, however, im-
proves the economic return from wheat. Wheat
also provides income in midsummer, several
months before com and soybean income.

3. Wheat is one of the best annual crops in Illinois for
erosion control, because it is in the field for some
8V2 to 9 months of the year and is well established
during heavy spring rainfall. Wheat can also serve
to break crop rotations that would otherwise lead
to buildups in diseases or insects.

4. Wheat crop abandonment is higher than for other
crops, but wheat acres not harvested can be
planted to spring-seeded crops, usually at their
optimum planting times.

Dates of Seeding

The Hessian fly-free dates for each county in Illinois
are given in Table 4.01. Wheat planted on or after the
fly-free date is much less likely to be damaged by the
insect than wheat planted earlier. It also will be less
severely damaged in the fall by diseases such as
Septoria leaf spot, which is favored by the excessive
fall growth usually associated with early planting. Be-
cause the aphids that carry the barley yellow dwarf
(BYD) virus and the mites that carry the wheat streak
mosaic virus are killed by freezing temperatures, the
effects of these viruses will be less severe if wheat is
planted shortly before the first killing freeze. Finally,
wheat planted on or after the fly-free date will prob-
ably suffer less from soil-borne mosaic; most varieties
of soft red winter wheat carry resistance to this dis-
ease, but some show symptoms if severely infested.
The decreases in yield as planting is delayed past
the fly-free date vary considerably, depending on the
year and the location within Illinois. In general, stud-
ies have shown that yields decline little with planting
delays for the first 10 days after the fly-free date.
From 10 to 20 days late, yields decline at the rate of a

4 • SMALL GRAINS

Table 4,01. Hessian Fly-Free Dates for Seeding Wheat

Average date

of seeding

wheat for

County

highest yield

County

highest yield

County

highest yield

County

highest yield

Adams

Sept. 30-Oct. 3

Ford

Sept. 23-29

Livingston

Sept. 23-25

Randolph

Oct. 9-11

Alexander

Oct. 12

Franklin

Oct. 10-12

Logan

Sept. 29-Oct. 3

Richland

Oct. 8-10

Bond

Oct. 7-9

Fulton

Sept. 27-30

Macon

Oct. 1-3

Rock Island

Sept. 20-22

Boone

Sept. 17-19

Gallatin

Oct. 11-12

Macoupin

Oct. 4-7

St. Clair

Oct. 9-11

Brown

Sept. 30-Oct. 2

Greene

Oct. 4-7

Madison

Oct. 7-9

Saline

Oct. 11-12

Bureau

Sept. 21-24

Grundy

Sept. 22-24

Marion

Oct. 8-10

Sangamon

Oct. 1-5

Calhoun

Oct. 4-8

Hamilton

Oct. 10-11

Marshall-

Schuyler

Sept. 29-Oct. 1

Carroll

Sept. 19-21

Hancock

Sept. 27-30

Putnam

Sept. 23-26

Scott

Oct. 2-A

Cass

Sept. 30-Oct. 2

Hardin

Oct. 11-12

Mason

Sept. 29-Oct. 1

Shelby

Oct. 3-5

Champaign

Sept. 29-Oct. 2

Henderson

Sept. 23-28

Massac

Oct. 11-12

Stark

Sept. 2S-25

Christian

Oct. 2-A

Henry

Sept. 21-23

McDonough

Sept. 29-Oct. 1

Stephenson

Sept. 17-20

Clark

Oct. 4-6

Iroquois

Sept. 24-29

McHenry

Sept. 17-20

Tazewell

Sept. 27-Oct. 1

Clay

Oct. 7-10

Jackson

Oct. 11-12

McLean

Sept. 27-Oct. 1

Union

Oct. 11-12

Clinton

Oct. 8-10

Jasper

Oct. 6-8

Menard

Sept. 30-Oct. 2

Vermilion

Sept. 28-Oct. 2

Coles

Oct. 3-5

Jefferson

Oct. 9-11

Mercer

Sept. 22-25

Wabash

Oct. 9-11

Cook

Sept. 19-22

Jersey

Oct. 6^

Monroe

Oct. 9-11

Warren

Sept. 23-27

Crawford

Oct. 6-8

Jo Daviess

Sept. 17-20

Montgomery

Oct. 4-7

Washington

Oct. 9-11

Cumberland

Oct. 4-5

Johnson

Oct. 10-12

Morgan

Oct. 2-A

Wayne

Oct. 9-11

DeKalb

Sept. 19-21

Kane

Sept. 19-21

Moultrie

Oct. 2-A

White

Oct. 9-11

DeWitt

Sept. 29-Oct. 1

Kankakee

Sept. 22-25

Ogle

Sept. 19-21

Whiteside

Sept. 20-22

Douglas

Oct. 2-3

Kendall

Sept. 20-22

Peoria

Sept. 23-28

Will

Sept. 21-24

DuPage

Sept. 19-21

Knox

Sept. 23-27

Perry

Oct. 10-11

Williamson

Oct. 11-12

Edgar

Oct. 2-4

Lake

Sept. 17-20

Piatt

Sept. 29-Oct. 2

Winnebago

Sept. 17-20

Edwards

Oct. 9-10

LaSalle

Sept. 19-24

Pike

Oct. 2-A

Woodford

Sept. 26-28

Effingham

Oct. 5-8

Lawrence

Oct. 8-10

Pope

Oct. 11-12

Fayette

Oct. 4-8

Lee

Sept. 19-21

Pulaski

Oct. 11-12

bushel or so per day. This yield loss accelerates to as
much as 2 bushels per day from 20 to 30 days late,
with sharper declines in the northern part of the state.
By one month after the fly-free date, yield potential is
probably only 60 to 70 percent of normal, making this
about the latest practical date to plant wheat. Wheat
may survive even if planted so late that it fails to
emerge in the fall, but reduced tillering and marginal
winterhardiness often results in large yield decreases.
The planting date has a major effect on the winter
survivability of the wheat plant. It is best if the plant
can grow to about the 3-leaf stage, usually forming a
tiller or two. By the tin\e the plant reaches this
growth stage, it has stored some sugars in the crown
(lower stem) of the plant. These sugars act as anti-
freeze, allowing the crown and new buds to survive
soil temperatures down to 15°F or so. Late-planted
wheat does not have time to produce and store such
sugars before soils freeze, while early planting tends

to result in rapid plant growth with less storage of
sugars. Freeze-thaw cycles during the winter tend to
use up stored sugars, thereby decreasing winter-
hardiness. Varieties also differ in their ability to sur-
vive low temperatures, but many of the higher-yield-
ing varieties begin growth early in the spring, and this
trait tends to be associated with less winterhardiness.

Rates of Seeding

While seeding rate recommendations for wheat have
usually been expressed as pounds of seed per acre,
differences in seed size can mean that the number
of seeds per acre or per square foot may not be very
precisely specified. Research in Illinois has measured
yields in response to varying the number of seeds
from 24 to 48 per square foot. Results given in
Table 4.02 indicate that seed rates within this range
affect yields very little, though in northern Illinois,
where there was some cold injury in the spring, the

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 4.02. Effect of Seed Rates on Wheat Yield

Wheat

yield (bu/A)

Seeds per
square foot

Southern
Illinois^

Northern
Illinois''

24
36

77.2
77.6
77.8

71.8
74.0
75.9

^Average of four trials conducted at Belleville and

Brownstown.

''Average of four trials conducted at Urbana and DeKalb.

Table 4.03. Conversion Chart for Number of Wheat
Seeds or Plants Per Square Foot, Per
Acre, and Per Linear Foot of Drilled
Row

Seeds or Seeds or

plants per plants

square per acre

foot (millions)

Seeds or plants per foot of row^
at row spacing of:

6 in.

7 in. 8 in. 10 in.

20
24

28
32
36
40

0.87
1.05
1.22
1.39
1.57
1.74

10
12
14
16
18
20

12
14
16
19
21
23

13
16
19
21
24
27

17
20
23
27
30
33

Table 4.04. Conversion Chart for Pounds of Wheat
Seeds of Different Sizes Needed Per
Square Foot and Per Acre

Seeds Seeds

per per

square acre

foot (millions)

Lb of seed needed per acre when
seed size (in seeds per pound) is:

11,000 13,000 15,000 17,000

24
28
32
36
40

1.05
1.22
1.39
1.57
1.74

95
111

127
143
158

107

121

134

105

116

61
72
82
92
102

extra plants gave a slight yield advantage. On aver-
age, though, it appears that a seeding rate of about 30
to 35 seeds per square foot is adequate for top yields
when planting is done on time.

Seed size in wheat varies by variety and by
weather during seed production but usually ranges
from 11,000 to 17,000 seeds per pound. Table 4.03 con-
verts seed rates per square foot to those per acre and
per linear foot. These numbers are useful for calibrat-
ing a drill. Some seed bags list the number of seeds
per pound. If not, a simple estimate may be needed.
Large seed has 11,000 to 13,000 per pound; medium
14,000 to 16,000 per pound; and small 17,000 to 18,000
per pound. Table 4.04 gives the pounds of seed per
acre needed for various seed sizes. A stand of 25 to 30
plants per square foot is generally considered the op-
timum, and a minimum of 15 to 20 plants per square
foot is needed to justify keeping a field in the spring.

If planting is delayed much past the fly-free date,
then fall growth and spring tillering are likely to be
reduced. To compensate, the seeding rate should be
increased by 10 percent for each week of delay in
planting after the fly-free date.

Seed Treatment

Treating wheat seeds with the proper fungicide or
mixture of fungicides is an inexpensive way to help
ensure improved stands and better seed quality. Un-
der conditions that favor the development of seedling
diseases, the yield from treated seed may be 3 to 5
bushels higher than that from untreated seed. See
Chapter 18, "Disease Management for Field Crops,"
for more information.

Seedbed Preparation

Wheat requires good seed-soil contact and moderate
soil moisture for germination and emergence. Gener-
ally, one or two trips with a disk harrow or field culti-
vator will produce an adequate seedbed if the soil is
not too wet. It is better to wait until the soil dries suf-
ficiently before preparing it for wheat, even if plant-
ing is delayed.

No-Tilling

While some producers prefer to do some tillage to im-
prove seed-soil contact for wheat, others have had
good success drilling wheat without tillage. This ap-
proach requires adequate weight and covering
mechanisms on the drill. Other considerations for no-
tilling wheat include these:

1. Residue from the previous crop must be spread
uniformly to prevent seed placement problems.

2. Without tillage to destroy emerging weeds, herbi-
cides may need to be considered in the fall.

3. Seed rates should be equal to or slightly higher
than those used for tilled fields.

4 • SMALL GRAINS

4. Com residue should be allowed to dry in the

morning before drilling to prevent its being pushed
down into the seed furrow.

There has also been concern about residue from the
previous crop providing a place for diseases (such as
head scab) to build up. While this may well be a fac-
tor, fields that are tilled also have suffered heavy
damage when conditions are favorable for disease de-
velopment; tillage is not the deciding factor in most
cases. Wet soils and compaction from harvest equip-
ment have also been found to reduce no-till stands
more than when soils are tilled.

Depth of Seeding

Wheat should not be planted deeper than 1 to IV2
inches. Deeper planting may result in poor emer-
gence. Drilling is the best way to ensure proper depth
of placement.

Though a drill is best for placing seed at the right
depth, a number of growers use fertilizer spreaders to
seed wheat. This practice is somewhat risky but often
works well, especially if rain falls after planting. An
air-flow fertilizer spreader usually gives a better dis-
tribution than a spinner type. If seed is broadcast, the
seeding rate should be increased by 20 to 30 percent
to compensate for uneven placement. After broadcast
seeding, the field may be rolled with a cultipacker or
cultimulcher (with the tines set shallow), or it may be
tilled very lightly with a disk or tine harrow to im-
prove seed-soil contact.

Row Spacing

Research on row spacing generally shows little ad-
vantage for planting wheat in rows that are less than
7 or 8 inches apart. Yield is usually reduced by wider
rows, with a reduction of about 1 to 2 bushels in 10-
inch rows. Wisconsin data show greater yield reduc-
tions in 10-inch rows, probably due to slower early
growth than is common in Illinois.

Varieties

The genetic improvement of wheat has continued
with the involvement of both the private sector and
public institutions. As a result, there are now some 50
varieties sold in Illinois, with more than half provided
by private companies.

Both public and private varieties are tested at six
locations in Illinois each year, and the results are as-
sembled in a report titled Wheat Performance in Illinois
Trials. The report also describes varieties, including
both agronomic characteristics and resistance to dis-
eases. Copies of this report are available in Extension

offices by mid-August to allow use of the information
before planting.

Intensive Management

Close examination of the methods used to produce
very high wheat yields in Europe has increased inter-
est in application of similar "intensive" management
practices in the United States. Such practices generally
include narrow row spacing (4 to 5 inches); high seed-
ing rates (3 to 4 bushels per acre); high nitrogen rates,
split into three or more applications; and heavy use of
foliar fungicides for disease control and plant growth
regulators to reduce height and lodging.

From research conducted in Illinois, it has become
apparent that responses to these inputs are much less
predictable in Illinois than in Europe, primarily be-
cause of the very different climatic conditions. Fol-
lowing is a summary of research findings to date:

1. Research in Indiana and other states shows that the
response to rows narrower than 7 or 8 inches is
quite erratic, with little evidence to suggest that the
narrow rows will pay added equipment costs.

2. Seeding rates of 30 to 35 seeds per square foot gen-
erally produce maximum yields.

3. Increasing nitrogen beyond the recommended rates
of 50 to 110 pounds per acre has not increased
yields. Splitting spring nitrogen into two or more
applications has not increased yields in most cases,
but it may do so if very wet weather after nitrogen
application results in loss of nitrogen.

4. Although foliar fungicides are useful if diseases are
found, routine use has resulted in yield increases of
only 3 to 5 bushels per acre (Table 4.05) and is
probably not economically justified, unless disease
levels are high.

Table 4.05. Response of Caldwell Wheat to Tilt
Fungicide

Yield (bu/A)

Treatment

Southern Northern
Illinois^ Illinois''

-Tilt
-hTilt

55.2 64.3
57.7 69.5

^Average of four trials at Brownstown and Belleville.
''Average of four trials at Urbana and DeKalb.

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Wheat Management for Best Yields

Despite our best efforts at managing wheat, harsh
winter weather or wet weather in May and June can
spell disaster for the crop, and there may be little that
can be done to maintain good yields. To help ensure
good yields when the weather is favorable, follow
these steps:

1. Choose several top varieties.

2. Apply some nitrogen and necessary phosphorus
fertilizer before planting: 18-46-0 provides both
nutrients.

3. Drill the seed on or near the fly-free date, using 30
to 35 seeds per square foot of good-quality seed.

4. Topdress additional nitrogen at the appropriate rate
in late winter or early spring, at about the time that
the crop breaks dormancy and begins to green up.
Application to frozen soil is acceptable, but some
nitrogen may run off if rain falls on sloping soil be-
fore it thaws.

5. Scout for weeds, insects, and diseases beginning in
early April and treat for control only if necessary.

6. Hope for dry weather during and after heading.

Spring Wheat

Spring wheat is not well adapted to Illinois. Because
it matures more than 2 weeks later than winter wheat,
it is in the process of filling kernels during the hot
weather typical of late June and the first half of July.
Consequently, yields average only about 50 to 60 per-
cent of those of winter wheat.

With the exception of planting time, production
practices for spring wheat are similar to those for win-
ter wheat. Because of the lower yield potential, nitro-
gen rates should be 20 to 30 pounds less than those for
winter wheat. Spring wheat should be planted in early
spring, as soon as a seedbed can be prepared. If plant-
ing is delayed beyond April 10, yields are likely to be
very low, and another crop should be considered.

Very little spring wheat is grown in Illinois, and
there has been little testing of spring wheat varieties.
Most spring wheat varieties that may grow reason-
ably well in Illinois were bred in Minnesota or other
northern states, and so there is a risk when they are
grown here. Some of the varieties that have been
tested in the past include Wheaton, Sharp, Grandin,
Marshall, and Guard, all of which produced similar
yields (around 40 bushels per acre) in Illinois trials.
There are no clearly superior varieties for either yield
or quality.

RYE

Both winter and spring varieties of rye are available,
but only the winter type is suitable for use in Illinois.
Winter rye is often used as a cover crop to prevent
wind erosion of sandy soils. The crop is very winter-
hardy, grows late into the fall, and is quite tolerant of
drought. Rye generally matures 1 or 2 weeks before
wheat. The major drawbacks to raising rye are the
low yield potential and the very limited market for
the crop. It is less desirable than other small grains as
a feed grain.

The cultural practices for rye are similar to those
for wheat. Planting can be somewhat earlier, and the
nitrogen rate should be 20 to 30 pounds less than that
for wheat because of lower yield potential. Watch for
shattering as grain nears maturity. Watch also for the
ergot fungus, which replaces grains in the head and is
poisonous to livestock. Ergot may develop when
weather is wet at heading.

There has been very little development of varieties
specifically for the Com Belt, and little yield testing
has been done recently in Illinois. Much of the rye
seed available in Illinois is simply called common rye;
some of this probably descended from Balbo, a vari-
ety released in 1933 and widely grown many years
ago in Illinois. More recently developed varieties that
may do reasonably well in Illinois include Hancock,
released by Wisconsin in 1979, and Rymin, released
by Minnesota in 1973. Spooner is another Wisconsin
variety that may be suitable.

Triticale

Triticale is a crop that resulted from the crossing of
wheat and rye in the 1800s. The varieties currently
available are not well adapted to Illinois and are usu-
ally deficient in some characteristic such as
winterhardiness, seed set, or seed quality. In addition,
they are of feed quality only. They do not possess the
milling and baking qualities needed for use in human
food.

Cultural practices for triticale are much the same as
those for wheat and rye. The crop should be planted
on time to help winter survival. As with rye, the nitro-
gen rate should be reduced to reflect the lower yield
potential. With essentially no commercial market for
triticale, growers should make certain they have a use
for the crop before growing it. Generally when triti-
cale is fed to livestock, it must be blended with other
feed grains. Triticale is also used as a forage crop. The
crop should be cut in the milk stage when it is har-
vested for forage.

A limited testing program at Urbana indicates that
the crop is generally lower yielding than winter

4 • SMALL GRAINS

wheat and spring oats. Both spring and winter types
of triticale are available, but only the winter type is
suitable for Illinois. Caution must be used in selecting
a variety because most winter varieties available are
adapted to the South and may not be winterhardy in
Illinois. Yields of breeding lines tested at Urbana have
generally ranged from 30 to 70 bushels per acre.

Spring Oats

To obtain high yields of spring oats, plant the crop as
soon as you can prepare a seedbed. Yield reductions
become quite severe if planting is delayed beyond
April 1 in central Illinois and beyond April 15 in
northern Illinois. After May 1, another crop should be
considered unless the oats are being used as a com-
panion crop for forage crop establishment and yield
of the oats is not important.

When planting oats after com, it will probably be
desirable to disk the stalks; plowing may produce
higher yields but is usually impractical. When plant-
ing oats after soybeans, disking is usually the only
preparation needed, and it may be unnecessary if the
soybean residue is evenly distributed. Make certain
that the labels of the herbicides used on the previous
crop allow oats to be planted; oats are quite sensitive
to a number of common herbicides.

Before planting, treat the seed with a fungicide or
a combination of fungicides. Seed treatment protects
the seed during the germination process from seed-
and soil-borne fungi. See Chapter 18, "Disease Man-
agement for Field Crops."

Oats may be broadcast and disked in but will yield
7 to 10 bushels more per acre if drilled. When drilling,
plant at a rate of 2 to 3 bushels per acre. If the oats are
broadcast and disked in, increase the rate by Vi to 1
bushel per acre.

For suggestions on fertilizing oats, see Chapter 11,
"Soil Testing and Fertility."

Varieties

Illinois has for years been a leading state in the devel-
opment of oat varieties. Excellent progress has been
made in selecting varieties with high yield, good
standability, and resistance to barley yellow dwarf
mosaic virus (also called redleaf disease), which is the
most serious disease of oats in Illinois.

Some of the newer spring oat varieties include
Blaze, Brawn, Chaps, Don, Hazel, Ogle, and Rodeo,
all developed in Illinois; Newdak from North Dakota,
Prairie from Wisconsin, and Classic from Indiana.
Yield and test weight data and descriptions of these
varieties are published by the Illinois Crop Improve-
ment Association in their annual Oat Decision Maker.

Winter Oats

Winter oats are not as winterhardy as wheat and are
adapted to only the southern third or quarter of the
state; U.S. Highway 50 is about the northern limit
for winter oats. Because winter oats are somewhat
winter-tender and are not attacked by Hessian fly,
planting in early September is highly desirable. Ex-
perience has shown that oats planted before Sep-
tember 15 are more likely to survive the winter than
those planted after September 15. Barley yellow
dwarf virus n^ay infect early-planted winter oats,
however.

The same type of seedbed is needed for winter oats
as for winter wheat. The fertility program should be
similar to that for spring oats. Seeding rate is 2 to 3
bushels per acre when drilled.

Development of winter oat varieties has virtually
stopped in the Midwest because of the frequent win-
ter kill. Of the older varieties, Norline, Compact, and
Walken are sufficiently winterhardy to survive some
winters in the southern third of the state. All of these
varieties were released more than 20 years ago.
Walken has the best lodging resistance of the three.

Spring Barley

Spring barley is damaged by hot, dry weather and
therefore is adapted only to the northern part of Illi-
nois. Good yields are possible, especially if the crop is
planted in March or early April, but yields tend to be
erratic. Markets for malting barley are not established
in Illinois, and malting quality may be a problem. Bar-
ley can, however, be fed to livestock.

Plant spring barley early — about the same time as
spring oats. Drill 1 to 2 bushels of seed per acre. To
avoid excessive lodging, harvest the crop as soon as it
is ripe. Fertility requirements for spring barley are es-
sentially the same as for spring oats.

The situation with spring barley varieties is similar
to that for spring wheat: most varieties originate in
Minnesota or North Dakota and have not been widely
tested or grown for seed in Illinois. Some of these va-
rieties are Azure, Hazen, Manker, Morex, Norbert, Ro-
bust, and Excel. Seed for any of these will likely need
to be brought in from Minnesota or the Dakotas.

WINTER Barley

Winter barley is not as winterhardy as the commonly
grown varieties of winter wheat and should be
planted 1 to 2 weeks earlier than winter wheat. Sow
with a drill and plant 2 bushels of seed per acre.

The fertility requirements for winter barley are
similar to those for winter wheat except that less

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

nitrogen is required. Most winter barley varieties are
less resistant to lodging than are winter wheat variet-
ies. Winter barley cannot stand "wet feet"; it should
not be planted on land that tends to stay wet. The bar-
ley yellow dwarf virus is a serious threat to winter
barley production.

Varieties

The acreage of winter barley is very small in Illinois,
and variety testing has not been extensive. Based on
limited testing, the varieties described here appear to
have the best chance of producing a good crop under
Illinois conditions. There has been little or no certified

seed of these varieties produced in Illinois, but the
higher yields may make it worthwhile to find seed in
another state.

Pennco, released in 1985 by Pennsylvania, is a
high-yielding variety with good disease resistance
and standability. It is a few days earlier and slightly
more winterhardy than Wysor and is considerably
more winterhardy (though later in maturity) than
Barsoy, an old variety that was once common in Illinois.

Wysor, released in 1985 by Virginia, is a high-
yielding variety with good disease resistance and
winterhardiness.

AUTHOR

Emerson D. Nafziger

Department of Crop Sciences

Chapter 5.
Grain Sorghum

Although grain sorghum can be grown throughout
Illinois, its greatest potential, in comparison with
other crops, is in the southern third of the state. It is
adapted to almost all soils, from sand to heavy clay.
Its greatest advantage over com is tolerance of mois-
ture extremes. Grain sorghum usually yields more
than com when moisture is in short supply, but it of-
ten yields less than com under better growing condi-
tions. Grain sorghum is also less affected by late
planting and high temperatures during the growing
season, but the crop is very sensitive to cool weather
and will be killed by even light frost.

Although few side-by-side comparisons of com
and grain sorghum in southern Illinois are available,
some indication of relative yields is available from the
hybrid trials that are conducted annually. Averaged
across 14 trials in southern Illinois, com yielded about
15 bushels per acre more than grain sorghum (Table
5.01). In general, grain sorghum yields more than com
when com yields less than 100 bushels per acre, and
less than com when com yields more than 100 bush-
els per acre. This illustrates the advantage that grain
sorghum may have under unfavorable weather condi-
tions and indicates that grain sorghum may provide

Table 5.01. Average Com and Grain Sorghum
Yields from Hybrid Comparison
Trials in Southern Illinois, 1991-1995

Location

Com

Grain sorghum

Brownstown^
Carbondale''
Dixon Springs'^

Average

128

168

130

114
114
116

115

'1992 data are not included due to failure of grain sorghum

trial.

''Trials were at Ina in 1991-92.

Trials are located in productive bottomland.

more yield stability than com if com often yields less
than 100 bushels per acre.

Fertilization

The phosphorus and potassium requirements of grain
sorghum are similar to those of com. The response to
nitrogen is somewhat erratic, due largely to the exten-
sive root system's efficiency in taking up soil nutri-
ents. For this reason, and because of the lower yield
potential, the maximum rate of nitrogen suggested is
about 125 pounds per acre. For sorghum following a
legume such as soybeans or clover, this rate may be
reduced by 20 to 40 pounds.

Hybrids

The criteria for selecting grain sorghum hybrids are
very similar to those for selecting com hybrids. Yield,
maturity, standability, and disease resistance are all
important. Consideration should also be given to the
market class (endosperm color) and bird resistance,
which may be associated with palatability to livestock.
Performance tests of commercial grain sorghum hy-
brids are conducted at three locations in southern Illi-
nois, and results are available (in the same report as the
commercial com hybrid yields) in Extension offices in
December. Because of the limited acreage of grain sor-
ghum in the eastern United States, most hybrids are
developed for the Great Plains and may not have
been extensively tested under Midwest conditions.

PLANTING

Sorghum should not be planted until soil temperature
is at least 65°F. In the southern half of the state, mid-
May is considered the starting date; late May to June
15 is the planting date in the northern half of the state.
Such late planting — along with a shorter, cooler grow-
ing season — means that hybrids used in northern
Illinois must be early-maturing.

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Sorghum emerges more slowly than com and re-
quires relatively good seed-soil contact. Planting
depth should not exceed IV2 inches, and about 1 inch
is considered best. Because sorghum seedlings are
slow to emerge, growers should use caution when us-
ing reduced- or no-till planting methods. Surface resi-
due usually keeps the soil cooler and may harbor in-
sects that can attack the crop, causing serious stand
losses, especially when the crop is planted early in the
season.

Row Spacing

Row-spacing experin\ents have shown that narrow
rows produce more than wide rows (Table 5.02). Drill-
ing in 7- to 10-inch rows works well if weeds can be
controlled without cultivation, but if weed problems
are expected, wider rows that will allow cultivation
may be a better choice than drilled grain sorghum.

Plant Population

Because grain sorghum seed is sn\all and some plant-
ers do not handle it well, there is a tendency to plant
based on pounds of seed per acre rather than by
number of seeds. This usually results in overly dense
plant populations that can cause lodging and yield
loss. Aim for a plant stand of 50,000 to 100,000 plants
per acre, with a lower population on droughtier
soils. Four to 6 plants per foot of row in 30-inch rows
at harvest and 2 to 4 plants per foot in 20-inch rows
are adequate. Plant 30 to 50 percent more seeds than
the intended stand. Sorghum may also be drilled us-
ing 6 to 8 pounds of seed per acre. When drilling, be
sure not to use excessive seed rates; plant stands
when drilled should not be much higher than those
in rows.

WEED Control

Because emergence of sorghum is slow, controlling
weeds presents special problems. Suggestions for
chemical control of weeds are given in the back of this

Table 5.02. Yield of Grain Sorghum as Affected by
Row Spacing in a Missouri Trial

Row spacing

(in.)

Yield (bu/acre)

121

118

103

NOTE: Data are 3-year averages.

handbook. As with com, a rotary hoe is useful before
weeds become permanently established.

HARVESTING AND STORAGE

Timely harvest is important. Rainy weather after sor-
ghum grain reaches physiological maturity may cause
sprouting in the head, weathering (soft and mealy
grain), or both. Harvest may begin when grain mois-
ture is 20 percent or greater, if drying facilities are
available. Sorghum dries very slowly in the field. Be-
cause sorghum does not die until frost, the use of a
desiccant (sodium chlorate) can reduce the amount of
green plant material going through the combine, mak-
ing harvest easier.

Marketing

Before planting, check on local markets. Because the
acreage in Illinois is limited, many elevators do not
purchase grain sorghum.

Grazing

After harvest, sorghum stubble may be used for pas-
ture. Livestock should not be allowed to graze for one
week after frost because the danger of prussic acid or
hydrocyanic acid (HCN) poisoning is especially high.
Newly frosted plants sometimes develop tillers high
in prussic acid.

Author

Emerson D. Nafziger

Department of Crop Sciences

Chapter 6.

Cover Crops and Cropping Systems

While two crops, com and soybeans, are grown in 2-
year rotations in most cultivated fields in Illinois, re-
cent "freedom to farm" legislation, along with con-
cerns about the existing cropping patterns, has some
farmers thinking about trying some different crop-
ping systems. Although there is little evidence to sug-
gest that the 2-year rotation common in Illinois is less
stable than cropping systems common elsewhere,
farmers are trying alternatives in an attempt to spread
risks and to learn about other possible uses of the
land they farm.

Cover Crops

Rye, wheat, ryegrass, hairy vetch, and other grasses
and legumes are sometimes used as winter cover
crops in the Midwest. The primary purpose for using
cover crops is to provide plant cover for soil to help
reduce erosion during the winter and spring. Winter
cover crops have been shown to reduce total water
runoff and soil loss by 50 percent or more, although
the actual effect on any one field will depend on soil
type and slope, the amount of cover, the planting and
tillage methods, and intensity of rainfall. A cover crop
can protect soil only while it or its residue is present,
and a field planted after a cover crop has been plowed
under may lose a great deal of soil if there is intense
rainfall after planting. The use of winter cover crops
in combination with no-till com may reduce soil loss
by more than 90 percent. Cover crops can also help to
improve soil tilth, and they often contribute nitrogen
to the following crop.

The advantages of grasses such as rye as cover
crops include low seed costs, rapid establishment of
ground cover in the fall, vigorous growth, recovery of
residual nitrogen from the soil, and good winter sur-
vival. Most research has shown, however, that com
planted into a grass cover crop often yields less than
when grown without a cover crop. There are several
reasons for this. Residue from grass crops, including

com, has a high carbon-to-nitrogen ratio, so nitrogen
from the soil is often tied up by microbes as they
break down the residue. Second, a vigorously grow-
ing grass crop such as rye can dry out the surface soil
rapidly, causing problems with stand establishment
under dry planting conditions. When the weather at
planting is wet, heavy surface vegetation from a cover
crop can also cause soils to stay wet and cool, reduc-
ing emergence. Finally, chemical substances released
during the breakdown of some grass crops have been
shown to inhibit the growth of a following grass crop
or of grass weeds. This phenomenon is known as
allelopathy.

There are several benefits associated with the use
of legumes as cover crops. Legumes are capable of ni-
trogen fixation; so, providing that they have enough
time to develop this capability, they may provide
some "free" nitrogen — fixed from the nitrogen in the
air — to the following crop. Most leguminous plants
have a lower carbon-to-nitrogen ratio than grasses,
and soil nitrogen will not be tied up as much when
legume plant material breaks down. On the negative
side, early growth by legumes may be somewhat
slower than that of grass cover crops, and many of the
legumes are not as winter-hardy as grasses such as
rye. Legumes seeded after the harvest of a com or
soybean crop thus often grow little before winter, re-
sulting in low winter survivability, limited nitrogen
fixation before spring, and ground cover that is inad-
equate to protect the soil.

Hairy vetch, at least in the southern Midwest, has
usually worked well as a winter cover crop. It offers
the advantages of fairly good establishn\ent, good fall
growth, and vigorous spring growth, especially if it is
planted early (during the late summer). When al-
lowed to make considerable spring growth, hairy
vetch has provided as much as 80 to 90 pounds of
nitrogen per acre to the com crop that follows. One
disadvantage to hairy vetch is its lack of sufficient
winterhardiness; severe cold without snow cover

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

will often kill this crop in the northern half of Illinois,
especially if it has not made at least 4 to 6 inches of
growth in the fall. The seed rate of 20 to 40 pounds
per acre, with seed costs ranging up to $1 per pound,
can make use of this crop quite expensive; some farm-
ers in the Midwest are growing their own seed to re-
duce the expense. Hairy vetch can also produce a con-
siderable amount of hard seed, which may not
germinate for 2 or 3 years, at which time it may be a
serious weed, especially in a crop such as winter
wheat. Other legume species that may be used as
winter cover crops include mammoth and medium
red clovers, alfalfa, and ladino clover.

To get the maximum benefit from a legume cover
crop, such crops must be planted early enough to
grow considerably before the onset of cold weather in
the late fall. The last half of August is probably the
best time for planting these cover crops. They can be
aerially seeded into a standing crop of com or soy-
beans, although dry weather after seeding may result
in poor stands of the legume. Some attempts have
been made to seed legumes such as hairy vetch into
com at the time of the last cultivation. This practice
may work occasionally, but a very good com crop will
shade the soil surface enough to prevent growth of a
crop underneath its canopy, and cover crops seeded in
this way will often be injured by periods of dry
weather during the summer. All things considered,
the chances for successfully establishing legume cover
crops are best when they are seeded into small grains
during the spring or after small grain harvest, or
when they are planted on set-aside or other idle fields.

There is some debate as to the best management of
cover crops before planting field crops in the spring.
There is usually a trade-off of benefits: Spring plant-
ing delays will allow the cover crop to make more
growth (and to fix more nitrogen in the case of le-
gumes), but this extra growth may be more difficult to
kill, and it sometimes depletes soil moisture. Most in-
dications are that killing a grass cover crop several
weeks before planting is preferable to killing it with
herbicide at the time of planting. Legumes can also
create some of the same problems as grass cover
crops, especially if they are allowed to grow past the
middle of May.

Research at Dixon Springs in southern Illinois has
illustrated both the potential benefits and possible
problems associated with the use of hairy vetch. In
these studies, hairy vetch accumulated almost 100
pounds of dry matter and about 2.6 pounds of nitro-
gen per acre per day from late April to mid-May
(Table 6.01). The best time to kill the cover crop with
chemicals and to plant com, however, varied consid-
erably among the 3 years of the study. On average.

Table 6.01.

Dry Matter and Nitrogen Contents of
Hairy Vetch Killed by Herbicide at
Dixon Springs, 1989-1991

Kill date

Dry matter Nitrogen
(lb/acre) (lb/acre)

Late April
Early May
Mid-May

1,300 55
2,509 85
3,501 115

com planted following vetch yielded slightly more
when the vetch was killed 1 or 2 weeks before plant-
ing (Table 6.02). Also, com planted in mid-May
yielded more than com planted in early May, prima-
rily due to a very wet spring in 1 of the 3 years, in
which vetch helped to dry out the soil. Vetch also
dried out the soil in the other 2 years, but this proved
to be a disadvantage because moisture was short at
planting. The conclusions from this study were that
vetch should normally be killed at least a week before
planting and that planting should not be delayed
much past early May because yield decreases due to
late planting can quickly overcome benefits of addi-
tional vetch growth.

Table 6.02. Effect of Vetch Kill Date and Com

Planting Time on Com Yield at Dixon
Springs, 1989-1991

Vetch kill date

Com
planting time

1 to 2 weeks
before com planting

At com
planting

Early May
Mid-May
Late May

116

129

114

125

N/A

Although the amount of nitrogen contained in the
cover crop may be more than 100 pounds per acre
(Table 6.01), the rate applied to a com crop following
the cover crop cannot be reduced one pound for each
pound of nitrogen contained in the cover crop. A
study in Illinois {journal of Production Agriculture, Vol.
7, No. 1, 1994) demonstrated that the economically
optimum nitrogen rate dropped by only about 20
pounds per acre when a hairy vetch cover crop was
used, even though the hairy vetch contained more
than 70 pounds of nitrogen per acre. This was due to
the fact that yields were shghtly higher (about 3 bush-

6 • COVER CROPS AND CROPPING SYSTEMS

els per acre) following cover crops — even at high rates
of nitrogen (Figure 6.01) — showing that not all of the
cover crop benefit was its contribution of nitrogen.
Even including the higher yield and lower nitrogen
requirement, however, these researchers concluded
that the use of hairy vetch was not economically justi-
fied. In the same study, rye caused a substantial yield
loss (Figure 6.01), and it would be difficult to justify
the use of rye based on these results.

Whether to incorporate cover-crop residue is de-
batable, with some research showing no advantages
to incorporation and other results showing some ben-
efit. Incorporation may enhance the recovery of nutri-
ents such as nitrogen under some weather conditions,
it may offer more weed control options, and it will
help in stand establishment, both by reducing compe-
tition from the cover crop and by providing a better
seedbed. On the other hand, incorporating cover-crop
residue removes most or all of the soil-retaining ben-
efit of the cover crop during the time between plant-
ing and crop canopy development, a period of high
risk for soil erosion caused by rainfall. Tilling to incor-
porate residue can also stimulate the emergence of
weed seedlings. One alternative to tillage for residue
management is to have livestock graze off most of the
top growth before planting.

Cropping Systems

The term cropping system refers to the crops and crop
sequences and the management techniques used on a
particular field over a period of years. This term is not

Hairy vetch

No cover crop
Rye

0 20 40 60 80 100 120 140 160 180 200 220 240
Nitrogen fertilizer (lb N/acre)

Figure 6.01. The effect of nitrogen fertilizer on grain yield
of a summer grain crop (com or grain sorghum) following
either a hairy vetch or rye cover crop or fallow. Data are
from five separate trials in Illinois, 1990-1991.

a new one, but it has been used more often in recent
years in discussions about sustainability of our agri-
cultural production systems. Several other terms
have also been used during these discussions:

• Allelopathy is the release of a chemical substance
by one plant species that inhibits the growth of an-
other species.

• Double-cropping (also known as sequential crop-
ping) is the practice of planting a second crop im-
mediately following the harvest of a first crop,
thus harvesting two crops from the same field in

1 year. This is a case of multiple cropping.

• Intercropping is the presence of two or more crops
in the same field at the same time, planted in an
arrangement that results in the crops competing
with one another.

• Monocropping refers to the presence of a single
crop in a field. This term is often used incorrectly
to refer to growing the same crop year after year in
the same field.

• Relay intercropping is a technique in which dif-
ferent crops are planted at different times in the
same fields. An example would be dropping
cover-crop seed into a standing soybean crop.

• Strip cropping is the presence of two or more
crops in the same field, planted in strips such that
most plant competition is within each crop, rather
than between crops. This practice has elements of
both intercropping and monocropping, with the
width of the strips determining the degree of each.

Crop rotations, as a primary aspect of cropping
systems, have received great attention in recent
years, with many people contending that most cur-
rent rotations are unstable and (at least indirectly)
harmful to the environment and are therefore not
sustainable. During the past 50 years, the number
and complexity of crop rotations used in Illinois have
decreased as the number of farms producing forages
and small grains has declined. The corn-soybean
rotation (with only one year of each crop) is now by
far the most common one in the state. Although some
contend that this crop sequence barely qualifies as a
rotation, it offers several advantages to growing ei-
ther crop continuously. These benefits include more
weed control options and, often, fewer difficult weed
problems, fewer insect and disease buildups, and less
nitrogen fertilizer use than with continuous com. Pri-
marily because of these reasons (and others, some
poorly understood), both com and soybeans grown
in rotation yield about 10 percent more than if they
were grown continuously. Growing these two crops

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

in rotation also allows for more flexibility in market-
ing, and it offers some protection against weather-
and pest-related problems in either crop.

The specific effects of a corn-soybean rotation on
nitrogen requirements are discussed in Chapter 11 of
this handbook. Figure 11.06 provides data on the ef-
fect of the previous crop on com yields and on the ni-
trogen requirements of the com crop. These data
show that, except in the case of alfalfa, most of the ef-
fect of the previous crop on com yields could be over-
come with the use of additional nitrogen. Other studies
also have shown that the yield differential due to crop
rotation can be overcome partially by additional nitro-
gen, but the differential usually cannot be eliminated.

One frequent question is whether input costs can
be reduced by using longer-term, more diverse crop

rotations. Studies into this question have compared
continuous com and soybean and the corn-soybean
rotation with rotations lasting 4 or 5 years that contain
small grains and legumes, either as cover crops or as
forage feed sources. Like the corn-soybean rotation,
certain longer rotations can reduce pest-control costs,
while including an established forage legume can pro-
vide considerable nitrogen to a succeeding com crop
(Figure 11.06). At the same time, most of the longer-
term rotations include forage crops or other crops
with smaller, and perhaps more volatile, markets than
com and soybeans. Lengthening rotations to include
forages will be difficult unless the demand for live-
stock products increases. Such considerations will
continue to favor production of crops such as com
and soybeans.

AUTHOR

Emerson D. Nafziger

Department of Crop Sciences

Chapter 7.
Alternative Crops

Many alternative crops could be grown in Illinois, but
they have not been produced commercially. A few
have been produced on a limited scale and are sold in
limited quantities to local markets. Many alternative
crops are associated with high market prices or high
income potential per acre and thus are eye-catching
to farmers who might learn about them. Upon inves-
tigation, such crops often have requirements which
cannot be met under Illinois conditions, have high
costs of production, or have no established or very
limited markets.

Before undertaking production of an alternative
crop, study market availability, demand, and growth
potential. Crops with limited demand can easily be-
come surplus in supply, driving down previously
high prices. Unless alternative crops are desired by
large populations, potential market expansion is lim-
ited. Delivery to a local market is most desirable, but
many alternative crops must be transported great dis-
tances to markets — reducing profitability. Market fac-
tors must be considered first with alternative crops!

Some alternative crops can be used on-farm, per-
haps substituting for purchased livestock feed. If pro-
duction cost is sufficiently low, it may be possible to
increase overall farm profitability with an alternative
crop. The feeding value of the alternative crop should
be included in such a consideration: While some
crops can substitute for protein supplements, they
may not result in equal animal gain or performance.

It is possible to produce a number of alternative
crops in Illinois, but their optimum yields may be ob-
tained under different climatic regimes. Various types
of beans can be grown in Illinois, but because of tem-
perature and rainfall patterns, yield may be impaired,
or disease may take a toll on yield or quality.

Specialized equipment and facilities — or a large
supply of inexpensive labor — may be needed to pro-
duce an alternative crop. Unless equipment or special
facilities are used across many acres of a crop, the
cost will be prohibitive. Some alternative crops require

large labor supplies not available in the Com Belt.
Success of many crops in foreign countries is due to
abundant low-cost labor.

Profitability of producing alternative crops is the
fundamental consideration for farmers. Unless eco-
nomically viable on-farm consumption is possible,
market demand and delivery points will determine
income potential from each unit of any crop har-
vested. Highest yield from any crop will occur in a
specific environment, but Illinois cannot provide the
environments needed by many crops. Equipment and
special facilities can be costly, and labor for some
crops may not be affordable. Many factors can take
profitability out of what may initially appear to be an
exceptional farming opportunity.

Table 7.01 lists alternative crops which might be
produced on Illinois farms. Information is provided
on the botany, use, environmental needs, and poten-
tial problems for each crop. In all cases, the crops do
not have large or established markets in Illinois. A
few may have limited local markets, perhaps requir-
ing the producer to market the crop directly to the
consumer. More information on the crops listed can
be obtained from Alternative Field Crops Manual
(available from the Center for Alternative Plant and
Animal Products, 340 Alderman Hall, University of
Minnesota, St. Paul, MN 55108).

Sunflower, canola, and buckwheat crops have been
produced on Illinois farms in recent years. Brief over-
views of these crops and their production require-
ments are provided in subsequent sections.

Sunflower

Sunflower is an alternative crop which some Illinois
farmers have produced profitably. Interest seems to
be stimulated following drought years which sup-
press com and soybean yields. Two kinds of sunflow-
ers can be produced in Illinois: the oil type and the

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 7.01. Alternative Crop Characteristics, Uses, and Considerations

Crop

Botany

Uses

Environmental needs Potential problems

Adzuki bean Legume; indeterminate Food — confectionery Similar to soybean and
growth habit; 110 to items, fillings for drybeans.

120 days to maturity. bread.

Amaranth Relative of red root Grain, forage, and Widely adapted to Mid-

pigweed; 5 to 7 ft tall, green leafy vegetable, west and western U.S.

areas.

Limited varieties; dis-
ease; limited markets.

Uniform varieties not
available; no herbicides
labeled for crop; har-
vest losses; limited
markets.

Broomcom

Annual type of sor-
ghum; 6 to 15 ft tall.

Long panicle branches
used to make brooms.

Warm summer, soil moist Harvest and curing of
and fertile — widely fiber is very labor in-

adapted, tensive; disease prob-

lems; limited markets.

Buckwheat Indeterminate growth; Nutritious grain used

will not die until killed for human food and

by frost; harvest in 10 livestock; smother

to 12 weeks. crop or green manure.

Cool and moist climate;
tolerates low fertility bet-
ter than other grains.

Limited varieties avail-
able; seed shatter eas-
ily; limited markets.

Canola Edible type of rape;

spring and winter
growth habits avail-
able.

Chickpea Annual legume up to

40 in. tall; produces
protein-rich seed; fairly
drought resistant.

Cowpea Annual legume,

known as blackeye
pea; produces protein-
rich seed.

Nutritious oil in grain; Well-drained, fertile soil;
meal fed to livestock; cool temperature range;
forage use. cannot tolerate water-

saturated soil.

Soups and salads; can
be fed to livestock.

Grain, fresh vegetable,
or forage for livestock.

Temperature of 70° to
80°F optimum; fertile soil
with good drainage.

Adapted to humid trop-
ics and temperate zones;
tolerant of heat and
drought, but not frost;
needs well-drained soil.

May not survive winter
in Illinois; timely plant-
ing in a corn-soybean
rotation; seed shatter
easily; limited delivery
points in the Midwest.

Excess water induces
disease and lodging;
limited markets.

Disease, nematodes,
and virus problems can
occur; specialized har-
vest equipment required
for fresh harvesting;
limited markets in the
Midwest.

Crambe Annual herb up to 40

in. tall; produces seed
with inedible oil used
by industry.

Manufacture of plas-
tic, nylon, adhesives,
and synthetic rubber.

Cool season; well-
drained, fertile soil;
cannot tolerate water-
saturated soil.

No developed market;
seed meal has little
value; limited varieties
available; no herbicide
or insecticide labeled
for crop.

7 • ALTERNATIVE CROPS

Table 7.01. Alternative Crop Characteristics, Uses, and Considerations (cont.)

Crop

Botany

Uses

Environmental needs Potential problems

Fababean

Ginseng

Kenaf

Lentil

Lupine

Millet

Annual legume; takes
80 to 120 days to ma-
ture; seedlings frost-
tolerant; seed size var-
ies greatly by variety.

Human food; livestock
feed; forage or silage.

Cool, moist conditions;
hot weather is injurious;
well-drained soil; does
not tolerate waterlogged
soil conditions.

Negligible demand in
the U.S., thus limited
markets; no insecticide
or herbicide labeled
for the crop.

Perennial herb prized In East Asia in soft Moist climate; 70 to 90% Disease and insect

in East Asian cultures
for its medicinal prop-
erties.

drinks, toothpaste, tea, shade; soil high in or-

and candy; sold as ganic matter, with pH

extracts, crystals, and near 5.5.
powder capsules.

Annual fiber crop na- Fiber for paper, card-
tive to Africa; 8 to 14 ft board, rope, twine,
tall. rugs, and bagging;

forage.

Cool season legume
grain crop; 12 to 20 in.
tall; seed varied in
color; stems tend to
lodge.

Annual legume crop
with good protein con-
tent; older types had
bitter alkaloids.

Soups, stews, and
salads.

Flour and pasta; feed
for dairy cows, lambs,
and poultry, but not
swine.

Annual grass up to
4 ft tall; several types,
with proso, foxtail,
and some barnyard
types grown in the
Midwest.

Bird food and live-
stock feed; hay and
silage.

problems; shade struc-
tures, labor, and time
make production ex-
pensive; harvest is at
least 3 years after
planting.

Widely adapted, but long Limited varieties, with

none developed for
the Midwest; special-
ized equipment
needed for harvest;
markets lacking.

Plants are weak com-
petitors, thus weed
control is essential;
lodging of stems
slows harvest; volatile
price; limited market
opportimities.

Poor competitor with
weeds; very few herbi-
cides cleared for use;
diseases likely with
excess moisture; seed
costs are high (3x soy-
bean); limited markets.

Warm temperatures (frost Limited herbicides la-
sensitive); well-drained, beled; limited markets
loamy soil; will not toler- available through bird
ate waterlogged soil or food suppliers,
extreme drought.

growing seasons with
high temperatures and
abundant rainfall yield
best.

Cool temperatures with
10 to 12 in. precipitation
annually (seedlings frost-
tolerant); soil with good
drainage required.

Cool season; relatively
tolerant of spring frost;
well-drained soil with
pH below 7.

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 7.01. Alternative Crop Characteristics, Uses, and Considerations (cont.)

Crop

Botany

Uses

Environmental needs Potential problems

Mung bean

Safflower

Spelt

Sunflower

Annual legume; 1 to 5 Bean sprouts or

ft tall; upright or viney canned for human

types; seed color var- food; livestock feed,
ies with variety.

Annual oilseed; pro-
duces a high-quality
edible oil low in satu-
rated fatty acids.

Primarily oil, but also
protein meal and bird-
seed.

Wheat relative with Feed grain, pasta, and

protein content similar high-fiber cereals; can

to oats; growth habit replace soft red winter

like winter wheat. wheat in baked goods.

Annual; produces
high-quality edible oil;
world's third-largest
oilseed crop.

Vegetable oil, snack
food, birdseed, protein
meal, soaps, deter-
gent, plastics, adhe-
sives, and paints.

Warm season like soy-
bean; fertile, well-
drained soil with good
internal drainage and pH
less than 7.2.

Warm, sunny, less than
15 in. rain/year; dry
weather during flower
and seed fill; deep, fer-
tile, well-drained soil.

Typical Midwest cli-
mates; is reported more
winter-hardy than most
soft red winter wheat;
grows on sandy and
poorly drained soils.

Semiarid regions; toler-
ates high and low tem-
peratures; can survive
drought but is inefficient
water user; grows on
wide range of soil types.

Many broadleaf herbi-
cides damage the crop;
pod maturity not uni-
form; seed costs higher
than soybean; limited
market opporttmities.

Broadleaf weeds are
difficult to control; wet
weather can induce
disease; no established
market.

Feed value could be
lower than oats, as test
weight is sometimes
lower; no established
market.

Bird, disease, and in-
sect problems can limit
yield; modified com-
bine needed for effi-
cient harvest; limited
local markets in the
Midwest.

Triticale Created from the cross

of wheat and rye;
spring and winter
types grow like wheat
and rye.

Livestock feedgrain,
forage, baked goods;
inferior to wheat.

Needs of winter types
similar to fall-planted
wheat and rye; spring
types need conditions
similar to spring oats,
barley, and wheat.

Ergot disease may
occur with spring
plantings; other dis-
eases may occur; mar-
kets limited.

confectionery, or non-oil, type. Production practices
tend to be the same, but end uses of the grain differ.

Oilseed sunflower produces a relatively small seed
with an oil content of up to 50 percent. The hull on the
grain is thin and dark colored and adheres tightly to
the kernel. Oil from this type of sunflower is highly
regarded for use as a salad and frying oil. Meal from
the kernel is used as a protein supplement in livestock
rations. Sunflower meal is deficient in lysine, and thus
except for ruminant animals, it cannot be used as the
only source of protein.

The confectionery (non-oil) type of sunflower
is used for human and bird food. The seed is larger

than the oil type, with a considerably lower oil
content. The hull is lighter in color and usually
striped, and the hull separates easily from the
kernel.

Sunflower planting coincides with that of com in
Illinois. Many hybrids offered for sale will reach
physiologic maturity in only 90 to 100 days and thus
can be planted following harvest of small grain crops.
Use of sunflower as a double-crop may be a good
choice if soybean cyst nematode is a pest, because
sunflower is not attacked by cyst nematode.

Populations of 20,000 to 25,000 plants per acre are
suitable for oilseed sunflower types produced on soils

7 • ALTERNATIVE CROPS

with good water-holding capacity. Stands of 16,000 to
20,000 per acre are appropriate for coarser textured
soils with low water-holding capacity. The confection-
ery-type sunflower should be planted at lower popu-
lations to help ensure production of large seed. Plant-
ing of seed should be at V/2- to 2-inch depth, similar
to placement for com. Performance will tend to be
best in rows spaced at 20 to 30 inches.
1 A seed moisture of 18 to 20 percent is needed to
! permit sunflower harvest. Once physiologic maturity
I of seed occurs (at about 40 percent moisture), a desic-
I cant can be used to speed drying of green plant parts.
I Maturity of kernels occurs when the backs of heads
I are yellow, but the fleshy head and other plant parts
take considerable time to dry to a level that permits
combine harvest. A conventional combine head can be
used for harvest, with losses reduced considerably if
special panlike attachments extending from the cutter
bar are used. Long-term storage of sunflower is fea-
sible, but levels of less than 10 percent moisture need
to be maintained.

Locating a market for sunflower is important be-
fore producing the crop. A limited number of market-
ing sites exist for oil-type sunflower, but most con-
fectionery sunflowers are produced under contract
for local feed distributors or health food stores. Be-
cause the head containing seed is exposed at the top
of the plant, insects, disease, and birds can be pest
problems. The location of sunflower fields relative to
wooded areas will have an impact on the extent of
bird damage.

Canola (Oilseed Rape)

Canola is a member of the mustard family with
unique chemical properties allowing consumption of
edible oil and protein-rich meal from the seed. Rape,
from which canola was selected, is a crop which has
been used as an oilseed in many countries for centu-
ries. Unlike rape, canola has a low erucic acid con-
tent in the oil and low levels of glucosinolates in the
meal produced from the seed. Only since 1985 has
canola been approved for consumption in the United
States.

Varieties of canola with spring and winter growth
habits are available, but the winter type is more likely
to succeed in Illinois because hot weather occurs dur-
ing seed production when spring types are grown.
Winterhardiness under Illinois conditions has proven
to be a problem for the winter types, which are
planted in the fall shortly before wheat is typically
seeded.

Site selection is critical to successful production of
canola, because waterlogged soil cannot be tolerated.

Only fields with good drainage should be used; ex-
cess moisture (ponding) will kill the crop.

Planting 2 or 3 weeks in advance of normal wheat
planting time is adequate for plant establishment,
provided that fall temperatures do not arrive unusu-
ally early. The very small seeds need to be planted
shallowly with a grain drill at a rate of only 5 to 6
pounds per acre. Canola needs adequate time to be-
come established before fall temperatures decline, but
it does not need to develop excessively. Plants with 8
to 10 leaves are considered adequate for winter sur-
vival. A tap root 5 to 6 inches deep generally develops
with desired levels of topgrowth in the fall.

Soil-fertility needs of canola are similar to winter
wheat, with a small amount of nitrogen applied in the
fall to stimulate establishment and a larger topdress
nitrogen application in the early spring to promote
growth. Too much nitrogen available in the fall can
delay the onset of dormancy of canola, putting it at
greater risk for winter injury. Excess fertility can ac-
centuate lodging tendencies.

Growth of canola resumes early in the spring, with
harvest maturity being reached about the same time
as winter wheat. Harvest needs to be done in a timely
manner, for seeds tend to shatter easily from pods.
Only the top portion of the plant containing the seed
pods is harvested. Combining works well when seeds
reach 10 percent moisture, but further drying of seeds
(to 9 percent moisture or less) and occasional aeration
are needed for storage. As seeds are very small, tight
wagons, trucks, and bins are needed for transporta-
tion and storage.

Locating a nearby delivery site for canola is pres-
ently a problem.

Buckwheat

Nutritionally, buckwheat is a very good grain, with
an amino acid composition superior to all cereals, in-
cluding oats. Producing the crop as a livestock feed is
possible, but markets for human consumption tend to
be small. An export market exists in Japan, where
noodles are made from the grain.

Buckwheat has an indeterminate growth habit;
consequently, it grows until frost terminates growth
that is most favored by cool and moist conditions. In
a short period (75 to 90 days), it can produce grain
ready for harvest. High temperatures and dry
weather during flowering can seriously limit grain
formation. Little breeding work has been done to en-
hance yield potential; it is naturally cross-pollinated
and cannot be inbred because of self-incompatibility.
A limited number of varieties are available.

ILLINOIS AGRONOMY HANDBOOK, 1999*1000

Because it produces grain in a short time, buck-
wheat can be planted as late as July 10 to 15 in
northern Illinois and during late July in southern
parts of the state. Rapid vegetative growth of the
plant provides good competition to weeds. Fertility
demands are not high, so buckwheat may produce a
better crop than other grains on infertile, poorly
drained soils.

With the exception of those that can use the crop
for livestock feed, producers should determine mar-
ket opportunities before planting buckwheat. A few
grain companies in the Midwest handle the crop for
export to Japan.

OTHER Crops

There is plenty of opportunity for individuals or small
groups to explore production and marketing of the al-
ternative crops described here. However, it is difficult
to imagine a substantial shift away from com, soy-
beans, or wheat in favor of any of these crops. People
and livestock require very large amounts of carbohy-
drates, protein, and edible oil to meet dietary needs.
A good balance of these is provided by the crops now
grown in Illinois.

Author

Gary E. Pepper

Department of Crop Sciences

Chapter 8.

Hay, Pasture, and Silage

Thick, vigorous stands of grasses and legumes are
needed for high yields. A thick stand of grass will
cover nearly all the ground. A thick stand of alfalfa is
about 30 plants per square foot at the end of the seed-
ing year, 10 to 15 plants per square foot the second
year, and 5 to 7 plants per square foot in succeeding
years.

Research has shown that stem density is a better
indicator of potential yield than plants per square
foot. A stem count can be taken when the plants are 4
to 6 inches tall and is done by counting any stem the
mower would cut. Fifty-five stems per square foot is
optimum, and if there are fewer than 39 stems per
square foot, consider tearing up the stand. If evaluat-
ing a stand in the early spring, you may have to base
decisions on the number of plants per square foot,
since a stem count may not be possible.

Fall is the best time to make stand evaluations. A
health assessment of the crown and root needs to be a
part of the evaluation.

Vigorous stands are created and maintained by
choosing disease- and insect-resistant varieties that
grow and recover quickly after harvest, by following

tgood seeding practices, by fertilizing adequately, by
harvesting at the optimum time, and by protecting the
stand from insects. Soil drainage characteristics, along
with winter hardiness and drought tolerance of the
species, also affect the vigor of the stand.

Establishment

spring seeding date for hay and pasture species in
Illinois is late March or early April, as soon as a seed-
bed can be prepared. Exceptions are seedings that are
made in a fall-seeded, winter annual companion crop;
for such seedings, seed hay and pasture species about
the time of the last snow.

Sowing hay and pasture species into spring oats in
the spring should be done when the oats are seeded,
as early as a seedbed can be prepared.

Spring seedings are more successful in the north-
em half of Illinois than in the southern half. The fre-
quency of success in the southern one-quarter to one-
third of the state indicates that late-summer seedings
may be more desirable than spring seedings.

Late-summer seeding date is August 10 in the
northern quarter of Illinois, August 30 in central Illi-
nois, and September 15 in the southern quarter of Illi-
nois. Seedings should be made close to these dates, and
no more than 5 days later, to ensure that the plants be-
come well established before winter. Late-summer
seedings that are made extremely early may suffer from
drought following germinahon or invasion of summer
annual weeds when plentiful moisture is present.

Frost seeding (or overseeding) is the surface broad-
cast placement of seed into existing vegetation in late
winter or very early spring. Success of this seeding
method is dependent on soil freeze-thaw cycles, a late
snowfall, spring rain, and the management given to
the existing vegetation prior to and after seeding.
Red clover and ladino clover, plus ryegrass and
orchardgrass, are two legumes and grasses, respec-
tively, that are well adapted to frost seeding.

Seeding rates for hay and pasture mixtures are
shown in Table 8.01. These rates are for seedings
made under average conditions, either with a com-
panion crop in the spring or without a companion
crop in late summer. Higher rates may be used to ob-
tain high yields from alfalfa seeded without a com-
panion crop in the spring. Seeding rates higher than
described in Table 8.01 have proven economical in
northern and central Illinois when alfalfa was seeded
as a pure stand in early spring and two or three har-
vests were taken in the seeding year. In northern and
central Illinois, but not in south-central Illinois, seed-
ing alfalfa at 18 pounds per acre has produced yields
0.2 to 0.4 ton higher than seeding at 12 pounds per
acre. Selecting varieties with high yield potential, high
seedling vigor, and rapid seeding growth rate helps ob-
tain extra yield potential from the higher seeding rate.

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Packer
wheel

rrs Fertilizer Ij" to 2"

Figure 8.01. Placement of seed and high-phosphate
fertilizer with grain drill.

The two basic methods of seeding are band seed-
ing and broadcast seeding. With band seeding, a band
of phosphate fertilizer (0-45-0) is placed about 2
inches deep in the soil with a grain drill; then the for-
age seed is placed on the soil surface directly above
the fertilizer band (Figure 8.01). Before the forage
seeds are dropped, the fertilizer should be covered
with soil, which occurs naturally when soils are in
good working condition. A presswheel should roll
over the forage seed to firm the seed into the soil sur-
face. Many seeds will be placed Vs to y4 inch deep with
this seeding method, an excellent depth for most for-
age legume and grass species.

With broadcast seeding, the seed is spread uni-
formly over a firm, prepared seedbed; then the seed is
pressed into the seedbed surface with a corrugated
roller. The fertilizer is applied at the early stages of
seedbed preparation. The seedbed is usually disked
and smoothed with a harrow. Most soil conditions are
too loose after these tillage operations and should be
firmed with a corrugated roller before seeding. The
best seeding tool for broadcast seeding is the double
corrugated roller seeder.

Which is the better seeding method? Illinois stud-
ies have shown that band seeding often results in
higher alfalfa yields than broadcast seedings for Au-
gust and spring seedings. Seedings on soils that are
low in phosphorus yield more from band seeding
than from broadcast seeding. Early seeding on cold,
wet soils is favored by banded phosphorus fertiliza-
tion. The greater yield from band seeding may be a
response to abundant, readily available phosphorus
from the banded fertilizer. Broadcast seedings may
yield as high as band seedings when the soils are me-
dium to high in phosphorus-supplying capacity and
are well drained, so that they warm up quickly in the
spring. Forage crop seeds are small and should be
seeded no deeper than Vs to Va inch. They should be in
close contact with soil particles. The double corru-

gated roller seeder and the band seeder with press-
wheels roll the seed into contact with the soil and are
the best-known methods of seeding forages.

Fertilizing and Liming
Before or at Seeding

Lime. Apply lime at rates suggested in Figure
11.05. If rate requirements exceed 5 tons, apply half
before the primary tillage (in most cases, plowing)
and half before the secondary tillage (harrowing or
disking). For rates of less than 5 tons, make a single
application, preferably after plowing, although apply-
ing either before or after plowing is acceptable.

Nitrogen (N). Nitrogen should not be applied for
legume seedings on soils with an organic-matter con-
tent more than 2.5 percent. Applying as much as 20
pounds of nitrogen per acre may help ensure rapid
seedling growth of legume-grass mixtures on soils
with less than 2.5 percent organic matter. For seeding
a pure grass stand, 50 to 100 pounds of nitrogen per
acre in the seedbed are suggested. For band seeding,
apply nitrogen with phosphorus through the grain
drill. For broadcast seeding, apply broadcast with phos-
phorus and potassium during seedbed preparation.

Phosphorus (P). Apply all phosphorus at seeding
time (Tables 11.22 and 11.25), or broadcast part of it
with potassium. For band seeding, reserve at least 30
poimds of phosphate (P2O5) per acre to be applied at
seeding time. For broadcast seeding, broadcast all the
phosphorus with the potassium, preferably after pri-
mary tillage and before final seedbed preparation.

Potassium (K). Fertilize before or at seeding.
Broadcast application of potassium is preferred
(Tables 11.24 and 11.26). For band seeding, you can
safely apply a maximum of 30 to 40 pounds of potash
(K^O) per acre in the band with phosphorus. The re-
sponse to band fertilizer will be mainly from phos-
phorus unless the potassium soil test is very low (per-
haps 100 pounds per acre or less). For broadcast
seeding, apply all the potassium after the primary till-
age. You can apply up to 600 pounds of K^O per acre
in the seedbed without damaging seedlings if the fer-
tilizer is broadcast and incorporated.

Fertilization

Nitrogen. In Chapter 11, "Soil Testing and Fertil-
ity," see the subsection about nitrogen and Table 11.11.

Phosphorus. This nutrient may be applied in large
amounts, which is adequate for 2 to 4 years. The an-
nual needs of a hay or pasture crop are determined
from yield and nutrient content of the forage har-
vested (Table 11.25). Grasses, legumes, and grass-

8 • HAY, PASTURE, AND SILAGE

legume mixtures contain about 12 pounds of P^O^
(4.8 pounds of phosphorus) per ton of dry matter.
Total annual fertilization needs include the mainte-
nance rate (Table 11.25) and any needed build-up
rate (Table 11.22).

Potassium. Because potassium helps the plant con-
vert nitrogen to protein, grasses need large amounts
of potassium to balance high rates of nitrogen fertili-
zation. As nitrogen rates increase, the percentage of
nitrogen in the plant tissue also increases. If potas-
sium is deficient, however, some nitrogen may remain
in the plant as nonprotein nitrogen.

Legumes feed heavily on potassium. Potassium, a
key element in maintaining legumes in grass-legume
stands, is credited with improving winter survival.

Annual potassium needs are determined from
yield, nutrient content in the forage that is harvested,
and nutrient build-up requirements of a particular soil
(Tables 11.24 and 11.26). Grasses, legumes, and grass-
legume mixtures contain about 50 pounds of K^O
(41.5 pounds of potassium) per ton of dry matter.

Boron (B). Symptoms of boron deficiency appear
on second and third cuttings of alfalfa during
droughty periods in some areas of Illinois. But yield
increases from boron fertilization have been infre-
quent. Application of boron on soils with less than 2
percent organic matter is recommended for high-
yielding alfalfa production in Illinois. If you suspect a
boron deficiency, topdress a test strip in your alfalfa
fields with 30 pounds per acre of household borax (3.3
pounds of boron). For general application, have boron
added to the phosphorus-potassium fertilizer to apply
3 to 4 pounds of boron per acre. Apply boron each
year of forage production except the last year if com
follows in the rotation.

Management

Seeding year. Hay and pasture crops seeded into a
companion crop in the spring will benefit by early re-
moval of the companion crop. Oats, wheat, or barley
should be removed when the grain is in the milk
stage. If these small grains are harvested for grain, it
is important to remove the straw and stubble as soon
as possible. As small-grain yields increase, the under-
seeded legumes and grasses face greater competition,
and fewer satisfactory stands are established by the
companion-crop method. Forage seedings established
with a companion crop may have one harvest taken
by late August in northern Illinois and occasionally
twc harvests by September 10 in central Illinois and
by September 25 in southern Illinois.

Spring-seeded hay crops and pastures without a
companion crop should be ready for harvest 65 to

70 days after an early April seeding. Weeds very
likely must be controlled about 30 days after seeding,
unless a preemergence herbicide was used. Postemer-
gence herbicides 2,4-DB, Buctril, and Pursuit are effec-
tive against most broadleaf weeds. Grassy weeds are
effectively controlled by Poast Plus. Pursuit controls a
few grassy weeds. Follow label directions. Leafhop-
pers often become a problem between 30 to 45 days
after an early April seeding and must be controlled to
obtain a vigorous, high-yielding stand.

Second and third harvests may follow the first har-
vest at 35- to 40-day intervals. The last harvest of the
season should be in late August for the northern quar-
ter of Illinois, by September 10 for the central section,
and by September 20 for the southern quarter.

Established stands. Maximum dry-matter yield
from alfalfa and most forages is obtained by harvest-
ing or grazing the first cutting at nearly full bloom
and harvesting every 40 to 42 days thereafter until
September. This management produces a forage that
is relatively low in digestibility. Such forage is suitable
for livestock on maintenance rations, produces slow
weight gain, and can be used in low-performance
feeding programs. In contrast, high-performance
feeding programs require a highly digestible forage.
The optimal compromise between high digestibility
and dry-matter yield of alfalfa is to harvest or graze
the first cutting at the late-bud to first-flower stage
and to make subsequent cuttings or grazings at 32- to
35-day intervals. Producers desiring high-quality al-
falfa hay at first cutting are encouraged to use the
scissor clip technique or the predictive equations for
alfalfa quality (PEAQ) as a guide in selecting the har-
vest date. Both methods provide an in-field estimate
of preharvest quality of standing alfalfa. They are not
designed for ration balancing.

The scissor clip procedure involves taking clippings
by hand at mower height in several places within a
field early in the morning. Clippings should be taken
twice a week, and each sample should be no more
than 1 pound fresh weight. Deliver the sample to a
forage quality-testing laboratory for analysis via NIRS.
As a general guide, the first harvest should be taken
when the relative feed value (RFV) based on the scis-
sor clip analysis is 15 percent above what is desired;
for example, harvest at RFV 170 to obtain RFV 150.

The PEAQ method predicts RFV and fiber by using
a five-point maturity index to stage the most mature
stem in a 2-square-foot area, plus the height of the
tallest stem in the area. With the use of either an equa-
tion or a table, estimates of RFV and fiber are ob-
tained. Samples are not submitted to a laboratory.
PEAQ is an estimate of quality of the standing alfalfa,
and harvest and storage losses are not accounted for.

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Rotational grazing is essential to maintaining le-
gumes in pastures. A rotational grazing program of 5
to 6 pastures should provide for 5 to 7 days of grazing
and 30 to 35 days of rest. More intensive grazing, us-
ing 8 to 11 pastures, 3 to 4 days of grazing, and 30 to
33 days of rest, increases meat or milk production per
acre but may not increase individual animal perfor-
mance. Managing pastures intensively is a method
many livestock producers in Illinois are adopting.

Because high levels of root reserves (sugars and
starches) are needed for winter survival and vigorous
spring growth, the timing of the fall harvest is critical.
Following a harvest, root jeserves decline as new
growth begins. About 3 weeks after harvesting, root
reserves are depleted to a low level, and the top
growth is adequate for photosynthesis to support the
plant's needs for sugars. Then root reserves are re-
plenished gradually until harvest or until the plant
becomes dormant in early winter. Harvests in Sep-
tember and October affect late-fall root reserves of al-
falfa more than summer harvests do. After the Sep-
tember harvest, alfalfa needs a recovery period until
late October to restore root reserves. On well-drained
soils in central and southern Illinois, a "late" harvest
may be taken after plants have become dormant in
late October or early November. Fall dormancy is
triggered or influenced by the variety and air and soil
temperature.

PASTURE ESTABUISHMENT

Many pastures can be established through a hay-crop
program. Seedings are made on a well-prepared, pro-
perly fertilized seedbed. If it is intended that the hay
crop becomes a pasture, the desired legume and grass
mixture should be seeded. When grasses and legumes
are seeded together, 2,4-DB or Buctril can be used for
broadleaf weed control. Apply 2,4-DB or Buctril about
30 days after seeding when the legumes are 2 to 4
inches tall and the weeds less than 4 inches tall.

PASTURE RENOVATION

Pasture renovation usually means changing the plant
species in a pasture to increase the pasture's quality
and productivity. Improving the fertility of the soil is
basic to this effort. A soil test helps identify the need
for lime, phosphorus, and potassium — the major nu-
trients important to establishing new forage plants.

Before seeding new legumes or grasses into a pas-
ture, reduce the competition from existing pasture
plants. Tilling, overgrazing, and herbicides — used
singly or in combination — have proven useful in sub-
duing existing pasture plants.

For many years, tilling (plowing or heavy disking)
has been used to renovate pastures, but success has
been variable. Major criticisms have been that tilling
can cause soil erosion, that the pasture supply for the
year of seeding is usually limited, and that a seeding
failure would leave no available permanent vegeta-
tion for pasturing or soil protection.

No-till seeding of new pasture plants into existing
pastures began when herbicides and suitable seeders
were developed. The practice of using a herbicide to
subdue existing pasture plants and then seeding with
a no-till seeder has proven very successful in many
research trials and farm seedings. Following are eight
basic steps to no-till pasture renovation:

1. Graze the pasture intensively for 20 to 30 days be-
fore the seeding date to reduce the vigor of existing
pasture plants.

2. Lime and fertilize, using a soil test as a guide. Soil
pH should be between 6.5 and 7.0. Desirable test
levels of phosphorus and potassium vary with soil
type; phosphorus should be in the range of 40 to 50
pounds per acre, and potassium in the range of 260
to 300 pounds per acre. For more information, see
Chapter 11.

3. One or 2 days before seeding, apply a herbicide to
subdue the vegetation. Gramoxone Super (para-
quat) and Roundup (glyphosate) are approved for
this purpose.

4. Seed the desired species, using high-yielding vari-
eties. Alfalfa and red clover are legumes with high-
yield potential and are often the species seeded into a
pasture that has a desirable grass species and in
which Gramoxone Super is to be used in preference
to Roundup. To change the grass species in the pas-
ture, use Roundup at label rates. To seed, use a no-
till drill that places the seed in contact with the soil.

5. Seedings may be made in early spring throughout
the northern two-thirds of Illinois and in late August
throughout the southern three-fourths of Illinois.

6. Apply insecticides as needed. Insects that eat ger-
minating seedlings are more prevalent in southern
Illinois than in northern Illinois, and an insecticide
may be needed. Leafhoppers will usually appear
throughout Illinois in early summer and remain
during most of the growing season. They must be
controlled where alfalfa is seeded, especially in
spring-seeded pastures, because leafhopper feed-
ing devastates new alfalfa seedlings. Several insec-
ticides are approved; for more information, see the
current Illinois Agricultural Pest Management Hand-
book chapter on "Insect Pest Management for Field

8 • HAY, PASTURE, AND SILAGE

and Forage Crops." Well-established alfalfa plants
are injured but not killed by leafhoppers; red clover
and grass plants are not attacked by leafhoppers.
White clover (ladino) and other nonpubescent clo-
vers may be attacked by leafhoppers, causing stunt-
ing of plants, reddening, and bronzing of leaflets.

7. Initiate grazing 60 to 70 days after spring seedings
and not until the next spring for late- August
seedings. Spring-seeded alfalfa and red clover
should be approaching 50 percent bloom at the first
grazing. Alfalfa and red clover seeded in late Au-
gust should be in the late-bud to first-flower stage
of growth when grazing begins. Use rotational or
intensive grazing management. Rotational grazing
requires a maximum of 5 to 7 grazing days, 28 to
30 resting days, and 5 to 6 pastures per paddock.
For higher-quality feed, higher yield and greater
animal product per acre, and increased persistence
of interseeded legumes, use intensive grazing man-
agement. To use this method, graze 1 to 3 days and
rest 28 to 30 days. It requires 11 to 30 or more pad-
docks. Use one or two strands of electric fencing
for interior barriers to separate paddocks. Movable
fencing is very practical for interior fencing in in-
tensive grazing management paddocks.

8. Fertilize pastures annually on the basis of esti-

1 mated crop removal. Each ton of dry matter from a
pasture contains about 12 pounds of phosphate
(PPj) and 50 to 60 pounds of potash (Kp). Do not
use nitrogen on established pastures where the
sward is at least 30 percent alfalfa, red clover, or
both. Because 20 to 80 percent of the nutrients
grazed may be returned to the pasture in the form
of urine and manure, fertilization rates for pastures
will be less than for hay production. Rotational and
intensive grazing management improves unifor-
mity of distribution and utilization of manure and
urine on pastures. The efficiency of nutrient recy-
cling is increased, which reduces the need for
supplemental fertilization. Soil-test pastures thor-
oughly every 4 years, and adjust the fertilization
program according to the results. Usually less
phosphate and potash are needed on pastures than
hay fields.

Selection of

Pasture Seeding Mixture

Alfalfa is the best species for increasing yield and im-
proving the quality of pastures throughout Illinois.
Consider using a "grazing type" of alfalfa, which has
been specifically selected to tolerate grazing. Many
seed companies have varieties available. Red clover.

adapted throughout Illinois, has been an excellent le-
gume for pastures in the southern region of the state.
Red clover produces very well in the first 2 years after
seeding but contributes very little after that. Birdsfoot
trefoil establishes slowly and increases to 40 to 50 per-
cent of the yield potential of alfalfa. Birdsfoot trefoil is
best suited to the northern half of Illinois. It tolerates
soils that are somewhat poorly drained, have a pH of
6.0 or higher, and have moderate phosphorus and po-
tassium levels. Mixtures of alfalfa at 8 pounds and red
clover at 4 pounds per acre or of birdsfoot trefoil at 4
pounds and red clover at 4 pounds per acre have de-
monstrated high yield. Red clover diminishes from
the stand about the third year; and the more persis-
tent species, alfalfa or birdsfoot trefoil, increases to
maintain a high yield level for the third and subse-
quent years.

Pasture Fertilization

The yield and quality of many pastures can be im-
proved by fertilization. The soil pH is basic to any fer-
tilization program. Pasture grasses tolerate a lower
soil pH than do hay and pasture legumes. For pas-
tures that are primarily grass, the lowest pH should
be 6.0. A pH of 6.2 to 6.5 is more desirable because nu-
trients are more efficiently used in this pH range than
at lower pH values. Lime should be applied to correct
the soil acidity to one-half plow depth. This liming is
effective half as long as when a full rate is applied and
plowed into the plow layer. Consequently, liming is
required more often (but at lower rates) in pastures
than in cultivated fields.

The need for nitrogen is based on the percentage of
legumes in the pasture, as discussed in Chapter 11.
Phosphorus and potassium needs are assessed by a
soil test. Without a soil test, the best guess is to apply
what the crop removes. Pasture crops remove about
12 pounds of phosphate (PjO^) and 50 pounds of pot-
ash (K^O) per ton of dry matter removed. Very pro-
ductive pastures yield 5 to 6 tons of dry matter per
acre; moderately productive pastures yield 3 to 5 tons;
and less productive pastures, 1 to 3 tons. Recycling of
nutrients from urine and manure reduces the total nu-
trients removed from a pasture by 20 to 80 percent,
varying with the intensity of pasture management.
Soil-test every 4 years to monitor changes in the fertil-
ity status of pastures.

Pasture Management

Rotational grazing of grass pastures results in greater
production (animal product yield per acre) than does
continuous grazing, except for Kentucky bluegrass
pastures. Pastures that include legumes need rotational

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

grazing to maintain the legumes. A rotational-grazing
plan that works well is 5 to 7 days of grazing with 28
to 30 days of rest, requiring 5 or 6 fields. This plan
provides the high-quality pasture needed by growing
animals and dairy cows. A more intense grazing sys-
tem for high-performance livestock and for high ani-
mal product per acre is a rotational grazing system of
8 to 11 fields, 3 to 4 days of grazing, and 30 to 33 days
of rest per pasture field. A less-intensive and less-pro-
ductive grazing plan for beef cow herds, dry cows,
and stocker animals is 10 days of grazing with 30
days of rest, requiring 4 pastures.

When adopting a rotational or management-inten-
sive pasture grazing system, consider the forage qual-
ity requirement of the livestock, estimate forage pro-
duction and stocking density, determine the number
of paddocks needed, remember to fence tonnage and
not acres, and remain flexible. The amount of forage
growth that can be removed per grazing period and
the needed rest period will vary with the species and
grazing season.

Weed control is usually needed in pastures. Clip-
ping pastures after each grazing cycle helps in weed
control, but herbicides may be needed for problem ar-
eas. Banvel and 2,4-D are effective on most broadleaf
weeds. Banvel is more effective than 2,4-D for most
conditions but has more restrictions. Thistles can usu-
ally be controlled by 2,4-D or Banvel, although re-
peated applications of the herbicide may be necessary.
Multiflora rose may be controlled with Banvel applied
in early spring, when the plant is actively growing,
but before flower bud formation. Grazing and haying
restrictions vary with most pesticides for different
classes of livestock, for rates of pesticide application,
and use of the animal product. Consult the label on
the pesticide and /or reliable references supplied by
the manufacturer and others, such as the current Illi-
nois Agricultural Pest Management Handbook.

Species and Varieties

The University of Illinois has conducted a testing pro-
gram of public and private forages for many years.
The 1998 test field locations were Freeport
(Stephenson County), Shabbona (DeKalb County),
Urbana (Champaign County), Perry (Pike County),
and Carlyle (Clinton County). The Freeport site is lo-
cated on a dairy farm; the Carlyle site is hosted by a
hay merchandiser; and the other locations are on Uni-
versity of Illinois Agronomy Research Centers.

The Department of Crop Sciences publishes yearly
a report entitled Forage Crop Variety Trials in Illinois.
This publication summarizes performance data by
seeding year of forage species and varieties grown at

the test field locations. The publication is available at
Extension offices.

When selecting a variety you should consider yield
potential, persistence, winterhardiness, disease and
insect resistance, and forage quality.

Alfalfa is the highest-yielding perennial forage
crop suited to Illinois, and its nutritional qualities are
nearly unsurpassed. Alfalfa is an excellent hay-crop
species and with proper management may be used in
pastures, as already mentioned.

Bloat in ruminant animals often is associated with
alfalfa pastures. Balancing soil fertility, including
grasses in mixtures with alfalfa, maintaining animals
at good nutritional levels, and using bloat-inhibiting
feed amendments are methods to reduce or essen-
tially eliminate the bloat hazard.

Many varieties of alfalfa are available. Many were
developed privately; some were developed at public
institutions. Private varieties usually are marketed
through a few specific dealers. Not all varieties are
available in Illinois.

Bacterial wilt is one of the major diseases of alfalfa
in Illinois. Stands of susceptible varieties usually de-
cline severely in the third year of production and may
die out in the second year under intensive harvesting
schedules. Moderate resistance to bacterial wilt en-
ables alfalfa to persist as long as 4 or 5 years. Varieties
listed as resistant usually persist beyond that.

Phytophthora root rot is a major disease of alfalfa
grown on poorly drained soils, primarily in the north-
em half of Illinois. This disease attacks both seedlings
and mature plants. The root develops a black lesion,
which progresses and rots the entire root. In mature
stands, shortened taproots are a symptom of this dis-
ease. Many alfalfa varieties with high-yield perfor-
mance have resistance or moderate resistance to
Phytophthora root rot.

Anthracnose is an important disease in the south-
em half of Illinois and may be important in northern
Illinois during warm, humid weather. The disease
causes the stem and leaves to brown, with the tip of
the stem turning over like a hook. The fungus causes
a stem lesion, usually diamond-shaped in the early
stages, that enlarges to completely encircle the stem.
Many alfalfa varieties with high-yield performance
have resistance or moderate resistance to anthracnose.

Verticillium wilt is a root-rot disease similar to bac-
terial wilt. Verticillium wilt develops slowly, requiring
about 3 years before plant loss becomes noticeable.
Associated with cool climates and moist soils, this
fungus is gradually spreading southward in Illinois.
Producers in the northern quarter of Illinois should
seek resistant varieties and producers in the rest of the
northem half of the state should observe their fields

8 • HAY, PASTURE, AND SILAGE

and consider using resistant varieties when seeding
alfalfa. Many alfalfa varieties with high-yield perfor-
mance have resistance or moderate resistance to verti-
cillium wilt.

Other diseases and insects are problems for alfalfa,
and some varieties of alfalfa have particular resistance
to these problems. You should question your seed
supplier about these attributes of the varieties being
offered to you.

Alfalfa produces a water-soluble toxin that reduces
the germination and growth of new alfalfa seedings.
This is called autotoxicity. At least one-half of the toxin
is found in the above-ground plant parts. When a
stand is more than 1 year of age, enough of the toxin
may be present to cause damage to new seedings re-
established into that field. In this situation, ideally a
grass crop (com is best) should be grown for 1 year
before reestablishing to alfalfa. This allows the toxin
time to degrade and leach away from the root zone.

Alfalfa stands less than one year of age have not
produced enough of the toxin, so if necessary, alfalfa
could be reestablished.

Red clover (medium red clover) is the second most
important hay and pasture legume in Illinois. Al-
though it does not have the yield potential of alfalfa
under good production conditions, red clover can per-
sist in wetter and more acidic soils and under more
shade competition than can alfalfa. And, although red
clover is physiologically a perennial, root and crown
diseases limit the life of red clover to 2 to 3 years.
Many new varieties have an increased resistance to
root and crown diseases and are expected to be pro-
ductive for at least 3 years.

Red clover does not have as much seedling vigor
or as rapid a seedling growth rate as alfalfa. Red clo-
ver thus does not fit into a spring seeding program
without a companion crop as well as alfalfa does.

Red clover has more shade tolerance at the seed-
ling stage; therefore, red clover is recommended in-
stead of alfalfa for most pasture renovation mixtures
where shading by existing grasses occurs. The shade
tolerance of red clover enables it to establish well in
companion crops such as spring oats and winter
wheat.

There are fewer varieties of red clover than of al-
falfa. Private breeders are active in developing more.

Fewer acres are dedicated to mammoth red clover
because its yields have been lower than most of the
improved varieties of medium red clover.

Ladino clover is an important legume in pastures,
but it is a short-lived species. The very leafy nature of
ladino makes it an excellent legume for swine pas-
tures. It is also a very high quality forage for ruminant
animals, but problems of bloat are frequent.

Ladino lacks drought tolerance because its root sys-
tem is shallower than that of red clover or alfalfa.

Kura clover is a perennial clover with rhizomatous
rooting. Kura clover seedlings develop slowly, and
general growth is less vigorous than red clover. The
rhizomatous rooting may enable this species to be a
useful pasture legume. This clover requires a special
Rhizobium inoculum to enable it to fix nitrogen. Kura
clover, a nonpubescent, is attacked by the potato leaf-
hopper, whereas most pubescent clovers are not.
Evaluations of the species are in progress.

Birdsfoot trefoil has been popular in permanent
pastures in northern Illinois. It has a long life but be-
comes established very slowly. Seedling growth rate
is much slower than that of alfalfa or red clover.

A root rot has made birdsfoot trefoil a short-lived
crop throughout southern Illinois. The variety Dawn
may have adequate resistance to persist throughout
the state.

Rooting depth of birdsfoot trefoil is shallower than
that of alfalfa, thus birdsfoot trefoil is not as produc-
tive during drought.

Crownvetch is well known for protecting very erod-
ible soil areas. As a forage crop, crownvetch is much
slower than alfalfa or red clover in seedling emer-
gence, seedling growth rate, early-season growth, and
recovery growth. Growth rate is similar to that of
birdsfoot trefoil. The potential of crownvetch as a hay
or pasture plant seems restricted to very rough sites
and soils of low productivity. Crownvetch does not
tolerate defoliation (grazing or hay harvesting) as
well as alfalfa, red clover, or birdsfoot trefoil.

Cicer milkvetch is a perennial legume adapted to
the western United States. The varieties of the species
that have been evaluated in Illinois have been winter-
hardy and moderate in seedling vigor and seedling
growth rate, similar to birdsfoot trefoil. Its productiv-
ity appears to be less than birdsfoot trefoil's and simi-
lar or slightly greater than kura clover's. Cicer milk-
vetch may have a place in some pastures of Illinois as
a drought-resistant and winter-hardy legume. A spe-
cial Rhizobium inoculum is needed for symbiotic ni-
trogen fixation.

Sainfoin is a legume that was introduced into the
western United States from Russia. In Illinois tests,
this species has failed to become established well
enough to allow valid comparisons with alfalfa, red
clover, and others. Observations indicate that sainfoin
has a slow growth and recovery growth rate and is
not well suited to the humid conditions in Illinois.

Hairy vetch is a winter annual legume that has
limited value as a hay or pasture species. Low pro-
duction and its vinelike nature have discouraged
much use. Hairy vetch may reseed itself and become a

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

weedy species in small-grain fields. Hairy vetch
seeded with winter wheat at 22 to 25 pounds per acre
has increased the protein yield of wheat-vetch silage.
Hairy vetch is a popular cover crop, providing ap-
proximately 60 pounds of available nitrogen to a fol-
lowing crop. Hairy vetch should be seeded in Septem-
ber and not killed until mid-May to obtain high
nitrogen contributions.

Lespedeza is a popular annual legume in the
southern third of Illinois. It flourishes in midsummer
when most other forage plants are at low levels of
productivity. It survives on soils of low productivity
and is low yielding. Even in midsummer, it does not
produce as well as a good stand of alfalfa, nor will it
encroach on a good alfalfa stand. As alfalfa or other
vigorous pasture plants fade out of a pasture, lespe-
deza may enter.

INOCULATION

Legumes — such as alfalfa, red clover, kura clover,
crownvetch, cicer milkvetch, hairy vetch, ladino, and
birdsfoot trefoil — can meet their nitrogen needs from
the soil atmosphere if the roots of the legume have the
correct Rhizobium species and favorable conditions of
soil pH, drainage, and temperature. Rhizobium bacte-
ria are numerous in most soils; however, the species
needed by a particular legume species may be lacking.

There are seven general groups and some other
specific strains of Rhizobium, with each group specifi-
cally infecting roots of plants within its corresponding
legume group and some specific strains infecting only
a single legume species. The legume groups are (1) al-
falfa and sweet clover; (2) true clovers (such as red,
ladino, white, and alsike); (3) peas and vetch (such as
field pea, garden pea, and hairy vetch); (4) beans
(such as garden and pinto); (5) cowpeas and lespe-
deza; (6) soybeans; and (7) lupines. Some of the indi-
vidual Rhizobium strains are specific to (1) birdsfoot
trefoil, (2) crownvetch, (3) cicer milkvetch, (4) kura
clover, or (5) sainfoin.

Grasses

Cool-Season Perennials

Timothy is a popular hay and pasture grass in Illi-
nois, although it is not as high yielding and has less
midsummer production than smooth bromegrass or
orchardgrass. A cool-season species, it is best suited to
the northern half of Illinois. Variety choice is limited.
There are few active timothy breeding programs in
the United States.

Smooth bromegrass is probably the most widely
adapted high-yielding grass species for northern and
central Illinois. Smooth bromegrass combines well

with alfalfa or red clover. It is productive but has lim-
ited summer production when moisture is lacking and
temperatures are high. It produces well in spring and
fall and can use high-fertility programs. There are sev-
eral improved varieties, and breeding work continues.

Orchardgrass is one of the most valuable grasses
used for hay and pasture in Illinois. It is adapted
throughout the state, being marginally winter-hardy
for the northern quarter of the state. Orchardgrass
heads out relatively early in the spring and thus
should be combined with alfalfa varieties that flower
early. One of the more productive grasses in midsum-
mer, it is a high-yielding species and several varieties
are available.

Reed canarygrass is not widely used, but it has
growth attributes that deserve consideration. Reed
canarygrass is the most productive of the tall, cool-
season perennial grasses that are well suited to Illi-
nois hay and pasture lands. Tolerant of wet soils, it
also is one of the most drought-resistant grasses and
can use high fertility. It is coarser than orchardgrass
and smooth bromegrass and can be as coarse as tall
fescue when mature. Grazing studies indicate that,
under proper management, reed canarygrass can
produce good weight gains on cattle equal to those
produced by smooth bromegrass, orchardgrass, or
tall fescue. Reed canarygrass should be considered
for grazing during spring, summer, and early fall.
Cool temperatures and frost retard growth and
induce dormancy earlier than in tall fescue, smooth
bromegrass, or orchardgrass. New low-alkaloid
varieties have improved animal performance.

Tall fescue is a high-yielding grass. It is out-
standing in performance when used properly and is
a popular grass for beef cattle in southern Illinois.
Because it grows well in cool weather, tall fescue is
especially useful for winter pasture, and it is also
most palatable during the cool seasons of spring and
late fall. A fungus living within the plant tissue (en-
dophyte) has a major influence on the lower palat-
ability and digestibility of this grass during the
warm summer months. Varieties are available that
are fungus-free or low in fungus. Tall fescue is mar-
ginally winter-hardy when used in pastures or hay
crops in the northern quarter of the state.

Rescuegrass, variety Matua, has been introduced
to Illinois markets in recent years from New Zealand.
Matua establishes well but is only moderately winter-
hardy, suffering injury during severe winters.

Warm-Season annuals

Sudangrass, sudangrass hybrids, and sorghum-
sudangrass hybrids are annual grasses that are very
productive during the summer. These grasses must be

8 • HAY, PASTURE, AND SILAGE

seeded each year on a prepared seedbed. Although
the total-season production from these grasses may be
less than that from perennial grasses with equal fertil-
ity and management, these annual grasses fill a need
for quick, supplemental pastures or green feed. These
tall, juicy grasses are difficult to make into high-
quality hay. Sudangrass and sudangrass hybrids have
finer stems than the sorghum-sudan hybrids and thus
will dry more rapidly; they should be chosen for hay
over the sorghum-sudan hybrids. Crushing the stems
with a hay conditioner will help speed drying. These
crops may be used for silage, green chop, or pasture
more effectively than for hay.

Sudangrass, sudangrass hybrids, and sorghum-
sudangrass hybrids produce prussic acid, a com-
pound that is toxic to livestock. Prussic acid is the
common name for hydrogen cyanide (HCN). The
compound in sorghum plants that produces HCN is
dhurrin. Two enzymes are required to hydrolyze
dhurrin to HCN. The microflora in the rumen of ru-
minant animals are capable of enzymatic breakdown
of dhurrin, producing HCN. The concentration of
dhurrin is highest in young tissue, with more found
in leaves than in stems. There is more dhurrin in the
forage of grain or forage sorghums than in sorghum-
sudangrass hybrids, and more in sorghum-sudangrass
hybrids than in sudangrass hybrids or sudangrass.

Sudangrass and sudangrass hybrids are considered
safe for grazing when they are 18 inches tail. Sorghum-
sudangrass hybrids should be 24 inches tall before
grazing is permitted. Very hungry cattle or sheep
should be fed other feeds that are low in prussic-acid
potential before turning them onto a lush sudangrass
or sorghum-sudangrass pasture. This prefeeding will
prevent rapid grazing and a sudden influx of forage
that contains prussic acid. These animals can tolerate
low levels of prussic acid because they can metabolize
and excrete the HCN.

Frost on the crops of the sorghum family breaks
cell walls and permits the plant enzymes to come into
contact with dhurrin and HCN to be released rapidly.
For this reason, it is advisable to remove grazing
ruminant livestock from freshly frosted sudangrasses
and sorghums. When the frosted plant material is
thoroughly dry, usually after 3 to 5 days, grazing can
resume. Grazing after this time should be observed
closely for new tiller growth, which is high in dhurrin;
and livestock should be removed when there is new
tiller growth that is being grazed.

The sorghums can be ensiled. The fermentation of
ensiling reduces the prussic acid potential substan-
tially. This method is the safest for using feed that has
a questionably high prussic acid potential.

Harvesting these crops as hay is also a safe way of
using a crop with questionably high levels of prussic-
acid potential.

Toxic levels of prussic acid (HCN) vary. Some
workers report toxicity at 200 ppm HCN of tissue dry
weight, while others report moderate toxicity at 500 to
750 ppm HCN of tissue dry weight. Laboratory diag-
nostic procedures can determine relative HCN poten-
tial. An alkaline picrate solution is commonly used to
detect HCN in plant tissue.

Millets are warm-season annual grasses that are
drought tolerant. Four commonly known millets are
pearlmillet {Pennisetum typhoides [Burm.] Stapf & C.E.
Hubb.), browntop millet {Panicum ramosum L.), foxtail
or Italian millet {Setaria italica [L.] Beav.), and Japanese
millet {Echinochloa crusgalli var. frumentacea [Roxb.]
W.F. Wight). Pearlmillet has been evaluated in grazing
trials and is a suitable alternative for summer annual
pastures.

Pearlmillet requires a warmer soil for rapid estab-
lishment than does sudangrass. Seedings should be
delayed until the seedbed averages 70°F.

Pearlmillet does not have a prussic-acid potential
as does sudangrass, nor is pearlmillet as susceptible
to leaf diseases. Pearlmillet is more drought tolerant
than is sudangrass, thus producing more pasture dur-
ing the hot, dry periods of late summer.

Forage Mixtures

Mixtures (Table 8.01) of legumes and grasses usually
are desirable. Yields tend to be greater than with ei-
ther alone. Grasses are desirable additions to legume
seedings to fill in where the legume ceases to grow, to
reduce soil erosion, to increase the drying rate, to re-
duce legume bloat, and perhaps to improve animal
acceptance. Mixtures of two or three well-chosen spe-
cies usually yield more than mixtures that contain five
or six species, some of which are not particularly well
suited to the soil, climate, or use.

Warm-Season Perennials

Warm-season perennial grasses also are known as na-
tive prairie grasses. These prairie grasses normally
provide ample quantities of fair- to good-quality pas-
ture during midsummer when cool-season perennials
are low yielding and often of low quality. Switch-
grass, big bluestem, and indiangrass have been the
more popular prairie grasses for use in Illinois.

Switchgrass {Panicum virgatum L.) is a tall, coarse-
stemmed grass with long, broad leaves that grows 3
to 5 feet tall, with short rhizomes. It is not as palatable
as smooth bromegrass. It is native to the Great Plains.

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

In Illinois, switchgrass starts growing in May but makes
most of its growth in June to August. Switchgrass is one
of the earliest maturing prairie grasses. Grazing or
harvesting should leave a minimum of a 4- to 6-inch
stubble. Close grazing or harvesting quickly dimin-
ishes the stand.

Switchgrass needs abundant moisture and fertility
for maximum growth. Because switchgrass is tolerant
of moist soils, it is often used in grass waterways.

Varieties. Blackwell, Caddo, Kanlow, Nebraska 28,
Pathfinder, and Trailblazer were selected in the south-
em and central Great Plains. Trailblazer, released in
1985, is more digestible than the other varieties. Cave-
rn-Rock was selected from southern Illinois in 1958
and released by the Soil Conservation Service,
Elsberry, Missouri, in 1972. Cave-in-Rock has yielded
well in Illinois trials.

Switchgrass should be seeded in mid-April to early
May. A continuous supply of soil moisture is needed
for germination and early seedling development. Pre-
cipitation during the first 10 days following seeding
has been more important for the establishment of
switchgrass than the seeding date.

A seeding rate of 6 pounds of pure live seed (PLS)
per acre of switchgrass is adequate if weeds are con-
trolled and precipitation is favorable. Increasing the
seeding rate increases the number of seedlings estab-
lished but has little effect on forage yield or forage
quality of established stands.

Frequent grazing or hay harvesting — more often
than every 6 weeks — reduces the yield and vigor of
switchgrass. A harvest may be taken after frost with-
out reducing yield and vigor the following year.

Crude protein and digestible dry matter of switch-
grass decline with maturity. Animal gains on switch-
grass may be less than on big bluestem or indian-
grass.

Switchgrass, indiangrass, and big bluestem yield
well as pasture plants. A major portion of the growth
occurs after July 1, and nearly all growth from these
grasses is completed by August 1 in southern Illinois.
The dry-matter yield of switchgrass is greater than
that of indiangrass and big bluestem.

The crude protein content of switchgrass is higher
than indiangrass or big bluestem at comparable matu-
rities during the pasture season. The crude protein
values range from 3.4 to 6.4 percent for the major
yield of the season. These values are very low if these
forages are the only protein source for cattle, sheep, or
horses. Big bluestem tends to have a higher crude
protein content than indiangrass.

The digestible dry matter of warm-season peren-
nial grasses tends to be below 50 percent. This level is
below the maintenance level for pregnant beef cows.

which may need supplemental feed when pasturing
on switchgrass. Indiangrass and big bluestem tend to
be a little higher in digestibility than switchgrass, but
they are marginal for maintenance of pregnant beef
cows. Dry-matter digestibility may be underestimated
by in vitro analysis methods.

Warm-season perennial grasses may yield 5.5 to 7.5
tons of hay dry matter per acre throughout Illinois.

Big bluestem {Andropogon gerardii Vitman) grows
4 to 7 feet tall and is a sod-forming, warm-season pe-
rennial grass. It was a major contributor to the devel-
opment of the deep, dark, prairie soils of Illinois. This
perennial has short rhizomes, but it makes a very
tough sod. Big bluestem thrives on moist, well-
drained loam soils of relatively high fertility. It is one
of the dominant grasses of the eastern Great Plains
and is found in association with little bluestem,
switchgrass, and indiangrass. Big bluestem estab-
lishes slowly from seed.

Big bluestem begins growth in May and makes a
large part of its growth in late July through August.
Grazing should leave a 6-inch stubble to prevent loss
of stand.

This grass is palatable and nutritious in its early
stages of growth. It withstands close grazing late in
the season if it is protected from close grazing early in
the season. Good hay may be made if harvested be-
fore seed heads emerge. Seed matures in late Septem-
ber and October.

Roundtree big bluestem was released by the Soil
Conservation Service and the Missouri Agricultural
Experiment Station in 1983. Other varieties of big
bluestem are Champ, Kaw, and Pawnee. Other blue-
stem varieties include Plains (Yellow Bluestem), re-
leased by the Oklahoma Agricultural Experiment Sta-
tion in 1970, and King Ranch.

Seedings should be made from mid-May to mid-
June at 10 pounds of PLS per acre. Seed at H inch
deep, on a prepared seedbed that has been firmed
with a corrugated roller. Use no nitrogen during the
seeding year. See Table 8.02 for yield information.

Indiangrass {Sorghastrum nutans [L.] Nash) is a
sod-forming grass with a deep, extensive root system
with short rhizomes. It is adapted to deep, well-
drained soils.

Indiangrass produces fair- to good-quality forage
during the summer months. Grazing months are July
through mid-September. Harvest indiangrass for hay
at the early boot stage. Begin grazing after the plant
reaches 18 inches. Graze to a minimum of a 10-inch
stubble.

Varieties are Holt, from the Nebraska Agricultural
Experiment Station; Osage, from the Kansas Agricul-
tural Experiment Station; Oto, from the Nebraska

8 • HAY, PASTURE, AND SILAGE

Table 8.01. Forage Seed Mixture Recommendations in Pounds Per Acre

FOR HAY CROPS

Northern, Central Illinois Southern Illinois

FOR ROTATION AND PERMANENT PASTURES

Northern, Central Illinois Southern Illinois

Moderately to well-drained soils

Modera

tely to well-drained soils

Alfalfa

Orchardgrass

Smooth bromegrass

Orchardgrass

Smooth bromegrass

Alfalfa

Timothy

Alfalfa

Tall fescue

Alfalfa

Tall fescue

Alfalfa

Smooth bromegrass

8
4

Orchardgrass^

Ladino clover

Timothy

Alfalfa

Tall fescue

Alfalfa

Orchardgrass^

Alfalfa

Timothy

Smooth bromegrass

Poorly drained soils

Red clover
Ladino clover

Timothy

Ladino clover

Red clover

Orchardgrass^

Timothy

Smooth bromegrass

Red clover

Ladino clover

Ladino clover
Orchardgrass

Red clover
Ladino clover

Vi
4

Smooth bromegrass
Alsike clover

Alsike clover
Reed canarygrass

2
8

Tall fescue
Ladino clover

6-8

Timothy

Red clover

Orchardgrass^

Alsike clover

■ — iv^vAXJ. IV/ V.l.\-/ V v.. X

Alsike clover

Tall fescue

Birdsfoot trefoil

Tall fescue

6-8

Reed canarygrass

Red clover

Timothy

Orchardgrass

Birdsfoot trefoil

Alsike clover
Redtop

4
4

Ladino clover

Tall fescue

Timothy

Smooth bromegrass

Orchardgrass^

Droughty soils

Tall fescue""

Alfalfa

Poorly drained soils

Smooth bromegrass

Orchardgrass

Alsike clover

Alfalfa

Ladino clover

Tall fescue^

Tall fescue

Timothy

Tall fescue

Alfalfa

Birdsfoot trefoil

Alsike clover

Smooth bromegrass

Timothy

Ladino clover
Reed canarygrass

Vz
8

For PASTURE RENOVATION

Alsike clover

Ladino clover

Northern, Central Illinois

Southern Illinois

Reed canarygrass

Moderately to well-drained soils

Alsike clover

Alfalfa

Ladino clover

Red clover

Tall fescue

Poorly drained soils

Droughty soils

Birdsfoot trefoil

Red clover

Northern, Central 111

inois

Southern Illinois

Red clover

Ladino clover

Alsike clover

Alfalfa

/'^ 1 J

Smooth bromegrass

Orchardgrass

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 8.01. Forage Seed Mixture Recommendations in Pounds Per Acre (cont.)

FOR ROTATION AND PERMANENT PASTURES (CONT.)

Droughty soils (cont.)
Northern, Central Illinois Southern Illinois

Alfalfa
Orchardgrass^

Alfalfa
Tall fescue

Red clover
Orchardgrass''

Red clover
Tall fescue

Alfalfa
Tall fescue

Alfalfa
Red clover
Orchardgrass^

Alfalfa
Red clover
Tall fescue

Single species

Switchgrass 6

Eastern gamagrass 12

Big bluestem 10

Caucasian bluestem 3

Indiangrass 10

Mixtures

Big bluestem
Indiangrass

Switchgrass
Big bluestem
Indiangrass

8
6

3
4

6-8

FOR WARM-SEASON PERENNIAL GRASSES

Moderately to well-drained and droughty soils,^
anywhere in Illinois

FOR HORSE PASTURES

Northern, Central Illinois Southern Illinois

Moderately to well-drained soils

Alfalfa 8

Smooth bromegrass 6

Kentucky bluegrass 2

Alfalfa 8

Orchardgrass^ 3

Kentucky bluegrass 5

Alfalfa 5

Red clover 4

Orchardgrass^ 3

Kentucky bluegrass 5

Alfalfa

Orchardgrass
Kentucky bluegrass

Alfalfa

Smooth bromegrass

Kentucky bluegrass

Alfalfa
Red clover
Orchardgrass
Kentucky bluegrass

Poorly drained to somewhat poorly drained soils

Red clover 8

Smooth bromegrass 6

Kentucky bluegrass 2

Timothy 2

Alfalfa 5

Red clover 4

Smooth bromegrass 6

Kentucky bluegrass 2

Red clover
Orchardgrass
Kentucky bluegrass

Ladino clover
Orchardgrass
Kentucky bluegrass

FOR HOG PASTURES

All soil types, anywhere in Illinois

Alfalfa
Ladino clover

1/2

^Central Illinois only.

''Not recommended for poorly drained soils.

Agricultural Experiment Station; and Rumsey, from a
native stand in south-central Illinois.

Seedings should be made from mid-May to mid-
June at 10 pounds of PLS per acre. Seed at V^ inch
deep, on a prepared seedbed that has been firmed
with a corrugated roller. Use no nitrogen during the
seeding year. See Table 8.02 for yield information.

Eastern gamagrass (Tripsacum dactyloides [L.] L.) is
related to com. The seed heads have the female flow-
ers on the lower portion and the male flowers above.
It grows in large clumps in low areas, is quite palat-
able, and often is destroyed by close grazing. Eastern
gamagrass produces a large tonnage of forage and
can be used for hay or silage.

Seedings should be made from mid-May to mid-
June at 12 pounds of PLS per acre. Seed at Vi inch
deep, on a prepared seedbed that has been firmed
with a corrugated roller. Use no nitrogen during the
seeding year. See Table 8.02 for yield information.

Caucasian bluestem or old world bluestems
(Bothriochloa caucasica C.E. Hubb.), a perennial bunch-
grass, is an introduction from Russia that shows
promise as a pasture and hay grass in Illinois. It is
easily established from seed and makes good growth
even if moisture supplies are low. It bears an abun-
dance of small, viable seed that shatter readily.

Seedings should be made from mid-May to mid-
June at 3 pounds of PLS per acre. Seed at Va inch deep.

8 • HAY, PASTURE, AND SILAGE

Table 8.02. Species and Varieties of Warm-Season
Perennial Grasses at Dixon Springs

Species/variety^

2-year average
dry matter, tons per acre

Switchgrass/Cave-in-Rock
Eastern gamagrass/Pete
Big bluestem/Roundtree
Caucasian bluestem
Indiangrass / Rumsey

5.47
7.20
4.84
3.58
6.03

*Each variety is harvested twice a year.

on a prepared seedbed that has been firmed with a
corrugated roller. Use no nitrogen during the seeding
year. See Table 8.02 for yield information.

Establishment of

Warm-Season Perennial Grasses

Establishment of warm-season perennial grasses is
slow. Seedings need to be made early in the season,
from April through June, to allow adequate time for
the seedlings to establish well. Atrazine (at 2 pounds
of active ingredients per acre) may be applied to the
surface after seeding big bluestem. Switchgrass and
indiangrass seedlings are damaged by atrazine.

Suggested seeding rates are 6 pounds of PLS per
acre of switchgrass and 10 pounds of PLS per acre of
big bluestem and indiangrass. Do not graze until
plants are well established, at least 1 year old. Weeds
may be reduced during the seeding year by clipping.
The first clipping should occur about 60 days after
seeding, at a height of 3 inches. Later clippings should
be at no less than 6-inch stubble height. Do not clip
after August 1.

Seedings should be made on prepared seedbeds
that are very firm. The drill or seeder must be able to

handle the seed, because seeds of indiangrass and big
bluestem are light and feathery. Debearding will help
to get the seed through the seeders.

Seedings may be made into existing grass sods, but
the grass must be destroyed. Roundup will remove
most grasses, when applied according to label instruc-
tions. Atrazine also may be used for seeding big blue-
stem into a grass sod. A no-till drill is needed to place
seeds into soil surface for good soil-seed contact.

Fertilization

Warm-season perennial grasses prefer fertile soils but
grow well in moderate fertility conditions. Warm-sea-
son perennials do not respond to nitrogen fertilization
as much as cool-season perennials. Warm-season pe-
rennial grasses use minerals and moisture more effi-
ciently than cool-season perennial grasses.

For establishment, fertilize with 30 to 40 pounds of
nitrogen, 24 to 30 pounds of phosphate, and 40 to 60
pounds of potash per acre.

For pasture or hay production of established
stands, fertilize with 100 to 120 pounds of nitrogen, 50
to 60 pounds of phosphate, and 100 to 120 pounds of
potash per acre.

Corn Silage

Com silage is an important crop on many Illinois
livestock farms. Several of the cultural practices are
the same as com grown for grain and thus are dis-
cussed in Chapters 2 and 11.

In selecting hybrids for com silage, consider grain
yield, whole plant silage yield, relative maturity,
standability, pest resistance, and silage quality.

Additional Information

Additional information can be found in the North
Central Regional (NCR) Extension publication NCR
547, Alfalfa Management Guide, which is available at
Extension offices.

Author

James A. Morrison

Extension Educator, Crop Systems
Rockford Extension Center

Chapter 9.
Seed

Seed production is not only the basis of a large indus-
try in Illinois; it is also a vital part of all crop produc-
tion in the state. It has appropriately been said that
all successful crop production begins with good seed.
Seed represents both the product of grain crop pro-
duction and the beginning of the next life cycle of the
crop. A seed contains, in a fairly small package, a tiny
plant with embryonic roots, stem, and leaves; a food
supply that provides energy, fats, and proteins
needed to support the growth of the seedling during
germination; and a seed coat to help protect the con-
tents from insects and diseases.

SEED Quality and Storage

Genetic purity and good seed quality are the major
goals of most seed producers. Genetic purity begins
with careful selection for plant uniformity by breeders
and removal of off-type plants during early seed gen-
erations, and is then maintained by careful sanitation
— cleaning of equipment and storage structures — as
succeeding generations of seed are produced. Seed
quality is defined by germinability — the percentage of
seeds that will germinate to produce a new seedling,
and by vigor, the ability of the seed to produce a
healthy seedling quickly, even under conditions that
are not ideal. Germinability and vigor are somewhat
related, but it is possible for seed to germinate well
but still not be very vigorous.

Seed quality is generally measured using one or
more germination tests. The standard warm germina-
tion test consists of placing seeds on germination pa-
per for a specified period of time at a specified
(warm) temperature, and then counting the percent-
age of seeds that produce seedlings. The standard
warm germination percentage is required to be put on
seed tags for retail sale. Under ideal field conditions,
emergence percentage in the field may be almost as
high as the standard warm germination percentage.

The cold test consists of keeping the seed at a tem-
perature— usually 50°F — at which germination is very

slow, in the presence of unsterilized soil, and then
placing the seeds and soil in warm temperatures for
several days before reading emergence percentage.
This test is designed to duplicate difficult (cold, wet)
field conditions, and to see how seed will germinate
and emerge under such conditions. It is used rou-
tinely by companies before seed is delivered for sale.
The cold test is not standardized due to the difficulty
in having uniform soil and soil microbes among dif-
ferent labs; different labs may produce different cold
test results. Another type of "stress test" is the acceler-
ated aging test, which measures germination after
keeping the seed at high temperatures and high hu-
midity for several days. While this does not duplicate
field conditions, it accelerates the rate of deterioration
of seed vigor, and hence it identifies seed that might
be declining rapidly in quality, even though its initial
germination percentage may still be high.

Relative changes in germinability and vigor of seed
during storage are illustrated in Figure 9.01. How
soon the decline in vigor and germinability begins

High

Low

\ Germinability

Vigor \

Time

Figure 9.01. Relative changes in seed germinability and
vigor during storage.

9 • SEED 71

will vary with storage conditions; longer storage is
possible with drier seed and lower storage tempera-
tures. In general, seeds such as soybean that contain
higher oil percentages are more difficult to store,
partly due to biochemical reasons and also to the fact
that such seeds may be more easily damaged by me-
chanical handling. Soybean seed can be stored for at
least a year under normal conditions, but longer stor-
age requires more attention to temperature and seed
moisture. Seed of crops such as com and wheat store
much better than oilseeds. It is often possible to store
such seeds for 3 years or more without much loss in
vigor, though some refrigeration may be used in the
summer.

Seed Considerations
FOR Illinois Crops

There are different considerations pertaining to seed
of different crops grown in Illinois:

1. Corn seed production is a major industry in Illi-
nois. Com seed is nearly all hybrid seed, produced
by one inbred parent that was pollinated in the
field by a second inbred. Com is very well suited
to this type of seed production, since it has sepa-
rate male and female flowers — the tassel and ear —
and it naturally cross-pollinates to a large extent.
To force two plants or rows of plants to cross-polli-
nate, all one need do is remove the tassels of one of
the parents (usually called the female or seed par-
ent), and then let the other plant or row (the male or
pollinator parent) serve as the source of pollen. Tas-
sel removal is usually done mechanically or by
hand, though there is some genetic male sterility
that prevents the shedding of pollen. Genetic pu-
rity is assessed by visual inspection to see how well
pollen shed has been controlled, and by growing
seed in the field (in warm climates) during the win-
ter (called growouts) to see if plants that grow from
it are uniform. A com hybrid is genetically uni-
form only in the first generation, and succeeding
generations segregate, or produce a great deal of ge-
netic variability. Thus seed produced from hybrid
seed cannot be used as seed for another generation
without a large loss in yield potential.

Com seed is usually harvested early to prevent it
from being injured by frost. It is usually harvested
as ears, which are then carefully dried and shelled
in a way that minimizes mechanical damage. Com
seed is usually sold for retail in bags that contain
80,000 kernels (called a unit), with weight varying
with seed size. There is also some movement to-
ward selling in bulk containers to save costs of bag-
ging and handling. Com seed is usually sized me-

chanically (graded) in order to make it feed more
uniformly through planting mechanisms. Grades
are usually designated by both size and shape (e.g.,
"small rounds" or "medium flats"), but in practical
terms grades are of importance only in how they
affect uniformity of metering by planting mecha-
nisms. Research has generally shown little or no
effect of seed grade on field emergence or yielding
ability.

2. Soybean seed is, as indicated above, somewhat
more difficult to produce and maintain quality in
than is com seed. Genetic purity is maintained by
field inspections, either by producing companies or
by official seed certifying agencies (the Illinois
Crop Improvement Association in Illinois), and by
using growouts or other genetic tests. Seed compa-
nies often use special handling equipment to re-
duce mechanical injury to soybean seed.

Like other self-pollinated crops, soybean "breeds
true," meaning that, once genetic purity is attained
by selection for uniformity, each generation is ge-
netically identical to the previous generation. Thus
the use of "bin-run" seed, which is seed produced
and kept by farmers for their own use, is an issue
in soybean. The Plant Variety Protection Act of
1970 restricted the commercial production and sale
of protected varieties to the companies that owned
or licensed such varieties, but it allowed limited
sales to neighboring farmers by farmers who were
not in the seed business. A modification of this law
several years ago further restricted the sale of pro-
tected seed, effectively prohibiting sale of such
seed to one's neighbors. Finally, recent genetic de-
velopments, such as Roundup Ready, require
agreements that farmers will not keep seed even
for their own use.

Even without legal restrictions on keeping one's
own seed or buying it from neighbors, the use of
bin-run seed may not always be the best manage-
ment choice for farmers. For example, the market
price of the seed needs to be considered as part of
the cost; the use of bin-run seed may slow the rate
of use of newer, better varieties; lack of specialized
handling and cleaning equipment may reduce seed
quality; and lack of controlled germination tests
may result in the use of substandard seed. Many
producers prefer to buy their seed in bags or bulk
from professional seed producers rather than take
chances with seed that they produced themselves.
Any seed kept for one's own use should be cleaned
by a special seed cleaner to remove weed seeds and
broken or misshapen seeds, and germination
should be tested by a professional lab.

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

3. Wheat and oats seed, though they store consider-
ably better than soybean seed and are less subject
to mechanical injury, are handled, cleaned, and
tested much like seed of other self-pollinated crops
such as soybean. Winter wheat seed is planted
only a few months after it is harvested, and so usu-
ally is of good quality if harvested on time and
properly cleaned. There can be some dormancy
(biochemical inability to germinate) in newly har-
vested winter wheat seed, but a few months of
storage usually restores it to full germinability.
Both wheat and oats seed are usually treated with
a fungicide to reduce the incidence of seedling
diseases.

4. Forage legume seed is produced to a very limited
extent in Illinois, though some red clover, sweet
clover, and hairy vetch (for cover crop) seed is pro-
duced. Such legumes usually require bees or other
insects for successful pollination, though the lack
of availability of beehives or other means to man-
age insect pollinators means that forage legume
seed producers often "take what they can get" in
terms of seed yield. Most often, red clover seed is
produced from the second growth of the crop after
the first growth is harvested for forage. Insect pol-
linators are also more active in mid- to late sum-
mer, thus raising yields of seed produced later in
the season.

AUTHOR

Emerson D. Nafziger

Department of Crop Sciences

Chapter 10.
Water Quality

The protection of water quality is an important part of
any crop production system. Illinois farmers have a
great stake in protecting drinking water quality be-
cause they often consume the water that lies directly
under their farming operation. Their domestic water
wells are often near agricultural operations or fields
and thus must be safeguarded against contamination.
The majority of crop protection chemicals never reach
groundwater. In Illinois, favorable soil and geologic
conditions help degrade or retard movement of pesti-
cides. However, vulnerable site conditions are found
in some parts of Illinois. In these areas (described in
detail later) appropriate chemical selection and man-
agement decisions need to be made to ensure good
water quality.

Drinking-water Standards

New federal drinking-water standards for 18 pesti-
cides and pesticide breakdown products went into
effect on July 30, 1992. This regulation requires that
public water supplies be monitored for these com-
pounds at least four times annually. The most com-
monly used herbicides on the list are atrazine and
alachlor. Many other commonly used herbicides are
currently unregulated but will be monitored in the
drinking-water samples. Currently, only surface-wa-
ter supplies (lakes, reservoirs) are monitored, and
groundwater sources will be phased in over the next 3
years.

Compliance with the federal standards is based on
the average of the samples taken consecutively over a
1-year period. For example, atrazine has a standard of
3 parts per billion (ppb), so if the sum of four quar-
terly samples is equal to 12 ppb or more, the water is
out of compliance. A single detection of over 12 ppb
would therefore immediately put a water supply out
of compliance.

If standards are exceeded, water customers are no-
tified by local media and subsequently on their water

bill. If a water source is in violation, water blending
with an uncontaminated supply or extensive decon-
tamination treatment is required. The additional wa-
ter-treatment expense can be prohibitive to small
communities; this underlines the importance of agri-
culture-management practices that reduce the entry of
herbicides into the aquatic system.

Illinois Water-Quality Results

The Illinois Environmental Protection Agency ana-
lyzed finished drinking water at 129 surface-water
supplies in 1991 and 1992. The study provides a look
at the potential for noncompliant water supplies in
the coming years (Table 10.01). About 13 percent of
the surface water samples exceeded the 3-ppb drink-
ing-water standard for atrazine. Detections of atrazine
exceeded 50 percent for both years of the study. The
drop in detections in 1992 may be related to a drier
spring that resulted in less cropland runoff directly
following herbicide application. Trifluralin is a herbi-
cide that is tightly held to soil particles. Trifluralin's

Table 10.01. Herbicide Detections in Selected

Community Water Supplies in Illinois

Percent

Mini-

Percent

supply

Maxi-

mum

exceeding

detections

mum
concen-

concen-
tration

maximum

contaminant

Pesticide

1991

1992

tration

detected

level (MCL)

ugll

Atrazine

13.0

.03

Alachlor

2.0

.02

Metolachlor

30.0

.02

Trifluralin

0.36

.02

Cyanazine

16.0

.06

SOURCE: Illinois EPA.

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

presence in 23 percent of the samples in 1991 suggests
that erosion of soil with attached herbicide may be re-
sponsible for some of the detections.

A statewide study of rural private water supplies
involving 337 wells was conducted cooperatively by
the Illinois Department of Agriculture, the U of I Co-
operative Extension Service, and the state Geological
Survey. The study was completed in 1992 (Table
10.02). Results of the study offer the first statistically
valid estimate of the condition of well water in Illi-
nois. About 12 percent of the 360,000 rural private
wells in the state contained detectable concentrations
of at least one herbicide, and 10.5 percent of the wells
had nitrate nitrogen above the drinking-water stan-
dard of 10 ppm. Preliminary interpretation of the data
suggests that shallow wells and dug wells were more
likely to be contaminated than deep-drilled wells.
Wells drawing water from aquifers within 20 feet of
land surface were more likely to contain high levels of
nitrate. The 2.1 percent of wells containing pesticide
concentrations above the drinking-water standards
were fully accounted for by three compounds:
alachlor (Lasso), dieldrin (a pesticide whose registra-
tion has been canceled), and heptachlor epoxide (a
degradation product of a discontinued insecticide).

No interpretation of contamination source is pos-
sible with this study, so it is impossible to determine
whether the compounds originated from a point
source (spill) or a nonpoint source (leached into water
from regular farm practices). Pesticides detected in
greater than 1 percent of the wells include acifluorfen
(1.4 percent. Blazer), atrazine (2.1 percent, AAtrex);
bentazon (1.4 percent, Basagran); dieldrin (1.6 per-
cent); dinoseb (3.7 percent, Dyanap); and prometon
(1.2 percent, Pramitol). The following pesticides were
detected in 0.1 to 1.0 percent of the wells: alachlor (0.7

Table 10.02. Statewide Estimates for Percent and
Number of Rural, Private Wells
Containing Pesticides and Nitrate

Estimated
Estimated number of

percentage Confidence wells in
of wells interval Illinois

12.1

7.5 to 16.7 43,600

Pesticides
Pesticides

(MCL/HAL) 2.1 0.6 to 3.6 7,560

Nitrate nitrogen

(>10ppm) 10.5 6.7 to 14.3 37,800

NOTE: MCL = maximum contaminant level; HAL = health
advisory level; ppm = parts per million.

percent. Lasso); aldrin (0.3 percent); bromacil (0.3 per-
cent, Hyvar-X); chloramben (0.2 percent, Amiben);
2,4-D (0.1 percent); endrin (0.8 percent); metolachlor
(0.3 percent. Dual); metribuzin (0.1 percent, Lexone,
Sencor); simazine (0.2 percent, Princep); and trifluralin
(1.0 percent, Treflan). Atrazine was not found in any
well at concentrations above the drinking-water stan-
dard of 3 ppb. Additionally, 19 of the pesticides (or
their breakdown products) were not detected in any
of the wells. These include butylate (Sutan+);
cyanazine (Bladex); 2,4-DB; dicamba (Banvel); and
EPTC (Eptam).

Results from surface- and well-water samples sug-
gest that atrazine is the most likely herbicide to ap-
pear in surface water but does not appear to be widely
found in well water at levels above drinking-water
standards. Alachlor and several discontinued insecti-
cides are the predominant organic pesticide contami-
nants in rural well water. Nitrate nitrogen contamina-
tion is often associated with shallow wells and surface
water and may be an indication of movement of fertil-
izers, manures, and other wastes into these water sup-
plies. The greatest challenge facing Illinois producers
may be to keep herbicides out of the surface-water
supplies. Management practices that reduce runoff
may help in this regard.

In other studies, the highest levels of detection are
often from wells near chemical handling sites, or wells
known to have been contaminated directly by an acci-
dental point-source introduction of the chemical, such
as back-siphoning.

Protection of groundwater drinking sources is a
critical and achievable task that can be accomplished
by (1) preventing point source contamination of the
well; (2) evaluating the groundwater contamination
susceptibility as determined by soil and geologic con-
ditions and the water-management system; (3) select-
ing appropriate chemicals and chemical application
strategies; and (4) practicing sound agronomy that
uses integrated pest management principles and ap-
propriate yield goals.

Drinking-water Contaminants

Many substances in the environment, whether related
to industry or agriculture or of natural derivation,
have been associated with health problems in humans
and livestock. The scope of this chapter does not war-
rant a full discussion of all pollutants but rather fo-
cuses on the contaminants that are associated with ag-
riculture and the rural farmer. The most frequent
contaminant of rural wells is coliform bacteria, which
are associated with livestock or human waste. These
bacteria enter wells laterally through a septic tank

10 • WATER QUALITY

leach field or over land into a wellhead as runoff from
livestock impoundments. Nitrate-nitrogen is the sec-
ond most common substance that occurs in levels ex-
ceeding health advisories. Although the presence of
nitrates (NO^) in drinking water is frequently blamed
on agriculture, nitrates come from many sources, in-
cluding septic tanks, livestock waste, and decaying
organic matter. Bacteria and nitrates are often the
"first to arrive" in a well with high potential for con-
tamination. Together their presence suggests a pos-
sible pathway to the well from an established con-
taminating source.

A variety of herbicides were detected in trace
amounts in potable water supplies. A recently com-
pleted nationwide survey found detectable levels of
herbicides in 13 percent of the wells surveyed. Atra-
zine, detected in 12 percent of the wells surveyed,
constituted more than 90 percent of the total detec-
tions. Although the herbicides were detected in a sig-
nificant percentage of the wells, only 0.11 percent of
the wells had herbicide concentrations above the
health-advisory levels.

Point-Source Prevention

Control of point-source contamination is a farmer's
most important action in protecting a groundwater
drinking source. A point source is a well-defined and
traceable source of contamination such as a leaking
pesticide container, a pesticide spill, or back-siphon-
ing from spray tanks directly into a well. Because
point sources involve high concentrations or direct
movement of contaminants to the water source, the
purifying ability of the soil is bypassed. The following
handling practices, based largely on common sense,
minimize the potential for groundwater contamination:

• Never mix chemicals near (within 200 feet of)
wells, ditches, streams, or other water sources.

• Prevent back-siphoning of mixed pesticides from
the spray tank to the well by always keeping the fill
hose above the overflow of the spray tank.

• Store pesticides downslope from well-water
sources and a safe distance from both wells and sur-
face waters.

• Triple-rinse pesticide containers, and put rinsate
back into the spray tank to make up the final spray
mixture.

• Avoid introducing pesticides or fertilizers into
sinkholes or abandoned wells. Lateral movement of
contaminants in the groundwater to a drinking-water
well may be more rapid than vertical movement
through the soil.

• Seal abandoned wells to prevent connection be-
tween agricultural practices and the groundwater.

Groundwater Vulnerability

Site characteristics, including the soil and geologic
properties, water table depth, and depth of the well,
will determine the potential of nonpoint contamina-
tion of the groundwater. Nonpoint sources of con-
tamination are difficult to pinpoint, originate from a
variety of sources, and are affected by many pro-
cesses. Contaminants moving into groundwater from
routine agricultural use are an example of a nonpoint
source. Producers applying pesticides in vulnerable
areas should pay strict attention to chemical selection
and management practices.

Soil Characteristics

Water-holding capacity, permeability, and organic-
matter content are important soil properties that de-
termine a soil's ability to detain surface-applied pesti-
cides in the crop root zone. Fine-textured, dark prairie
soils have large water-holding capacities, low per-
meabilities, and large organic-matter contents, all at-
tributes that reduce pesticide leaching due to reduced
water flow or increased binding of pesticides. The for-
est soils that dominate the landscape in western and
southern Illinois are slightly lower in organic matter
and thus may be less effective at binding pesticides.

The most vulnerable soils for groundwater con-
tamination are the sandy soils that lie along the major
river valleys of Illinois. Sandy soils are highly perme-
able, have low organic-matter contents, and often are
irrigated. All of these factors represent increased risks
to groundwater quality. Extra precautions in chemical
selection and application method should be taken in
these vulnerable soils. Irrigators in particular should
pay attention to groundwater advisory warnings that
restrict the use of some herbicides on sandy soils.

Geology

The geologic strata beneath a farming operation may
be important in determining the risk of nonpoint con-
tamination. In Illinois the most hazardous geology for
groundwater pollution is the karst or limestone re-
gion that occurs along the margins of the Mississippi
River and in the northwestern part of the state. Sink-
holes and fractures that occur in the bedrock in these
areas may extend to the soil surface, providing access
for runoff directly to the groundwater. Water moving
into these access points bypasses the natural treat-
ment provided by percolation through soil. Karst ar-
eas should be farmed carefully with due attention to
buffer zones around sinkholes to prevent runoff entry

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

to the groundwater. Agronomic practices that mini-
mize runoff are effective ways to reduce the potential
for pesticide movement to the groundwater.

Groundwater and Well Depths

Deep aquifers that lie under impermeable geologic
formations are the most protected from contamination
by surface activities. Shallow water-table aquifers are
more vulnerable to contamination because of their
proximity to the surface. Shallow dug wells in water-
table or shallow aquifers are also more vulnerable due
to typically inadequate wellhead protection.

Surface-water Contamination

Although groundwater protection receives the major-
ity of media attention, surface water quality is gener-
ally at greater risk. Surface waters have a greater ca-
pacity for breaking down pesticides because biological
breakdown processes operate at a faster rate than in
groundwater. A recent survey of surface waters in
Illinois by the U.S. Geological Survey found detect-
able herbicide levels in 90 percent of the samples
taken in May and June of 1989. Control of surface-
water contamination is best achieved by controlling
runoff n\ovement of water and sediment. Soil-conser-
vation practices and prudent use of buffer strips near
stream banks generally reduce the probability of sur-
face-water contamination.

Management Practices

Many effective management practices outlined in
other sections of this handbook have been recom-
mended with due consideration to water quality.
Management is most critical in areas that are the most
vulnerable to contamination.

Nutrient Management

Soil testing is a basic foundation for fertilizer recom-
mendations. Testing manures for nutrient content al-
lows accurate crediting for fertilizer replacement. A
sound nitrogen-management program for grain crops
that emphasizes appropriate yield goals and credit for
prior legumes will optimize the amount of fertilizer
nitrogen introduced to the field. Splitting nitrogen ap-
plications on sandy irrigated soils is wise because it
reduces the chances for excessive leaching that might
occur if a single nitrogen application is used.

Use of a nitrification inhibitor on fine-textured soils
where nitrogen is fall applied may reduce leaching of
nitrate-nitrogen. Adding nitrapyrin (N-Serve) to fall-
applied nitrogen reduced nitrate leaching an average
of 10 to 15 percent in a study in Minnesota. Even less
nitrate leaching occurred when N was spring applied.

Integrated Pest Management

It is generally assumed that reduced pesticide use re-
sults in a reduced probability of groundwater con-
tamination. Integrated pest management reduces un-
necessary use of pesticides. Two examples are the
recommended practice of crop rotation that reduces
the need for com rootworm insecticides in continuous
com and the use of crop rotation and tolerant variet-
ies to control plant diseases.

Conservation Tillage

Reducing tillage and retaining crop residues on the
soil surface limits the runoff and overland flow that
carries pesticides and nutrients out of the field. The
effect of conservation tillage and no-till on ground-
water quality is controversial and the subject of much
research. Reduction of runoff and erosion is accom-
plished by increasing infiltration of water. Increased
infiltration, particularly through earthworm-formed
macropores, offers a transport system to the subsoil
that soil-applied pesticides can follow. Conversely, the
macropores are not the primary routes of water flow
unless heavy rainfall or flooding occurs and allows
rapid movement of "clean" rainwater past the soil
layers that contain pesticides. Conservation tillage
methods are most in^portant in controlling soil ero-
sion on sloping land. Adopting more severe tillage
to protect groundwater quality is not warranted
based on our current knowledge.

Cover Crops

A cover crop such as a small grain or legume may
provide water-quality benefits from several stand-
points. The effectiveness of cover crops in controlling
erosion is well documented, and controlling erosion
is an important component of surface-water-quality
protection. Small-grain cover crops have shown
some efficiency at retrieving residual nitrogen from
the soil following fertilized com or vegetable crops.
This feature may be important on sandy irrigated
soils where winter rainfall leaches much of the re-
sidual nitrogen.

Legumes may provide a source of nitrogen to sub-
sequent crops. Refer to the chapter on cover crops in
this handbook for further information.

Chemical Properties
AND Selection

The selection of agricultural chemicals is most critical
for producers on vulnerable soils and geologic sites.
Herbicide selection is a complex task that must take
into account the crop, the tillage system, target spe-
cies, and a host of other variables. Chemical proper-

I
I

10 • WATER QUALITY

Table 10.03. Herbicide and Herbicide Premixes with
Groundwater Advisories

Trade name

Common (generic) name

AAtrex, atrazine
Basis Gold

Bleep II, Bleep Lite II

Bladex/Cy-Pro

Broadstrlke + Dual

Broadstrlke + Treflan

Bronco

Buctrll + atrazine

Bullet/Lariat

Canopy

Contour

Detail

DoublePlay

Dual II

Extrazine Il/Cy-Pro AT

Frontier

Guardsman

Harness

Harness Xtra

Hornet
Laddok S-12
Lasso/Micro-Tech
Marksman
Prlncep, Slmazine
Scorpion III

Sencor/Lexone
Shotgun
Stinger

Surpass/TopNotch
Surpass 100

Turbo

atrazine
rimsulfuron +

nicosulfuron + atrazine
metolachlor + atrazine +

safener
cyanazine

flumetsulam + metolachlor
flumetsulam + trifluralin
alachlor + glyphosate
bromoxynll + atrazine
alachlor + atrazine
metribuzin + chlorimuron
imazethapyr + atrazine
imazaquin + dimethenamid
acetochlor + EPTC + safener
metolachlor + safener
cyanazine + atrazine
dimethenamid
dimethenamid + atrazine
acetochlor + safener
acetochlor + atrazine +

safener
flumetsulam + clopyralid
bentazon + atrazine
alachlor

dicamba + atrazine
simazine
flumetsulam + clopyralid

+ 2,4-D
metribuzin
atrazine + 2,4-D
clopyralid
acetochlor + safener
acetochlor + atrazine +

safener
metribuzin + metolachlor

ties of the herbicide are important to consider when
evaluating their potential to leach to the groundwa-
ter. The three most important characteristics of a pes-
ticide that influence leaching potential are solubility

in water, ability to bind with the soil (adsorption),
and the rate at which it breaks down in the soil.
High solubility (dissolves readily), low binding abil-
ity, and slow breakdown all increase a pesticide's
ability to move to the groundwater. Among the fre-
quently used herbicides that have a greater potential
to leach and are labeled with groundwater advisories
are those that contain alachlor, atrazine, clopyralid,
cyanazine, metribuzin, metolachlor, or simazine
(Table 10.03).

Precautions for Irrigators

Chemigation refers to the application of fertilizers and
pesticides through an irrigation system and is a man-
agement tool that has benefits and potential draw-
backs for groundwater protection. The greatest ben-
efit of chemigation is for fertigation, which is the
application of fertilizers, particularly nitrogen,
through the irrigation system. Nitrogen application
can be more carefully spread out in the vegetative
growth period of grain crops, thereby minimizing the
susceptibility of leaching.

Chemigation systems should be equipped with
back-flow-prevention devices. These greatly reduce
the threat of back-siphoning undiluted chemicals into
the irrigation well. Back-flow-prevention devices are
mandatory on irrigation systems that inject fertilizers
and pesticides. Reputable irrigation dealers do not
sell irrigation systems without this important feature.

Well-Water Testing

The most important step in well-water testing is to
contact the local health department and determine the
procedure for sampling and submitting water for ni-
trate and bacteria determinations. In most counties
the service is provided at no cost or for a nominal fee.
The presence of coliform bacteria with or without el-
evated nitrates is a sign that a well is contaminated by
runoff or a septic system. Faulty well construction
and improper wellhead protection are major causes of
contamination. Pesticide testing is expensive and re-
quires sensitive analytical equipment. Several private
water-testing laboratories, certified by the Illinois
Environmental Protection Agency, will perform water
analyses for citizens. Contact a local Extension adviser
for information on nearby laboratories.

Author

F. William Simmons

Department of Crop Sciences

Chapter 1 1.

Soil Testing and

Fertility

Soil testing is the single most important guide to the
profitable application of fertilizer and lime. When soil
test results are combined with information from the
soil profile about the nutrients that are available to the
various crops (Figures 11.13 and 11.14), the farmer has
a reliable basis for planning the fertility program on
each field.

Traditionally, soil testing has been used to decide
how much lime and fertilizer to apply. With increased
emphasis on economics and the environment, soil
tests are also a logical tool to determine areas where
adequate or excessive fertilization has taken place. In
addition, soil tests are used to monitor the impact of
past fertility practices on changes in a field's nutrient
status. To accomplish this, one must (1) collect
samples to the proper depth; (2) collect enough
samples per unit of land area; (3) collect samples from
precisely the same areas of the field that were
sampled in the past; and (4) collect samples at the
proper time.

Depth of sampling. The proper sampling depth for
pH, phosphorus, and potassium is 7 inches. For fields
in which reduced-tillage systems have been used,
proper sampling depth is especially important, as
these systems result in less thorough mixing of lime
and fertilizer than a tillage system that includes a
moldboard plow. This stratification of nutrients has
not adversely affected crop yield, but misleading soil
test results may be obtained if samples are not taken
to the proper depth.

Under reduced-tillage systems, it is important to
monitor surface soil pH by collecting samples to a
depth of 2 inches from at least three areas in a 40-acre
field. These areas should represent the low, intermedi-
ate, and high ground of the field. If surface soil pH is
too high or too low, the efficacy of some herbicides
and other chemical reactions may be affected.

Number of samples per unit of land area. The num-
ber of soil samples taken from a field is a compromise
between what should be done (information) and what

can be done (cost). Sampling at the rate of one com-
posite from each 2y2-acre area is suggested. (See Fig-
ure 11.01 for sampling directions.)

Field sampling studies show large differences of
soil test levels in short distances in some fields. If you
can use computerized spreading techniques and sus-
pect large variations in test values over a short dis-
tance, collecting one sample from each 1.1 -acre area
(Figure 11.01, bottom diagram) will provide a better
representation of the actual field variability. The in-
creased sampling intensity will increase cost of the
base information but allows for more complete use of
technology in mapping soil fertility patterns and thus
more appropriate fertilizer application rates. The most
common mistake is taking too few samples to repre-
sent a field adequately. Taking shortcuts in sampling
may produce unreliable results and lead to higher fer-
tilizer costs, lower returns, or both.

Precise sample locations. Since test results may
vary markedly in short distances, it is important to
collect soil samples from precisely the same points
each time the field is tested. This practice reduces the
variation often observed between sampling times.
Sample locations may be identified using global posi-
tioning system (GPS) equipment or by accurately
measuring the sample points with a device such as a
measuring wheel. Once locations have been identi-
fied, collect and composite five soil core samples
1 inch in diameter to a 7-inch depth from within a
10-foot radius around each point.

How to sample. A soil tube is the best implement
for taking soil samples, but an auger or a spade also
can be used (Figure 11.02). Five soil cores taken with a
tube will give a satisfactory composite sample of
about 1 to 2 cups.

When to sample. Sampling every 4 years is strongly
suggested. To improve the consistency of results,
samples should be collected at the same time of year.
Sampling done within a few months of lime or fertil-
izer treatment will be more variable than after a year.

11 • SOIL TESTING AND FERTILITY

165 ft I

f 165 ft

I 330 ft T

-_ 330 ft --
sll ' HS

330

ft I

330 ft t 330 ft 1

,..t». 1

330 ft

S S

330

ijs

330

■ f

■ t
" t

nl —^ [Is

330 ft

330 ft
330 ft

330 ft

One sample per 2.5 acres

HOftf
S

10ft

220 ft

sQ sQ sQ] sQ sEP

220 ft I

I s

220 ft I

I s

220 ft I

s|3 s|3 8^3

220 ft I

I s|

220 ft I

I s

220 ft ||220ft I

l^sl

220 ft

220 ft I

] sQ]

220 ft I

220 ft I
220 ft I

220 ft I

s|^ S^ S^

220 ft jf

220 ft I

220 ft
One sample per 1.1 acres

220 ft I

3 sE

220 ft I

■ sj

220 ft I
220 ft I
220 ft I

] ^E

220 ft

Figure 11.01. How to collect soil samples from a 40-acre
field. Each sample should consist of five soil cores, 1 inch
in diameter, collected to a 7-inch depth from within a
10-foot radius around each point. Higher frequency samp-
ling (lower diagram) is suggested for those who can use
computerized spreading techniques on fields suspected of
having large variations in test values over short distances.

Late summer and fall are the best seasons for col-
lecting soil samples because potassium test results are
most reliable during these times. The potassium soil

Soil slice
1/2" thick

Soil Probe

Auger

Spade

Figure 11.02. How to take soil samples with an auger, a
soil probe, and a spade.

test tends to be cyclic, with low^ test levels in late sum-
mer and early fall and high test levels in late January
and early February.

Where to have soil tested. Illinois has about 40
commercial soil-testing services. An Extension office
or a fertilizer dealer can provide information about
soil-testing services available in your area.

Information to accompany soil samples. The best
fertilizer recommendations are based on both soil test
results and a knowledge of field conditions that will
affect nutrient availability. Because the person making
the recommendation does not know the conditions in
each field, it is important that you provide adequate
information with each sample.

This information includes cropping intentions for
the next 4 years; name of the soil type or, if not
known, the nature of the soil (clay, silty, or sandy;
light or dark color; level or hilly; eroded; well drained
or wet; tiled or not; deep or shallow); fertilizer used
(amount and grade); lime applied in the past 2 years;
and proven yields or yield goals for all proposed
crops.

What tests to have made. Soil fertility problems in
Illinois are largely associated with acidity, phospho-
rus, potassium, and nitrogen. Recommended soil tests
for making decisions about lime and fertilizer use are
the water pH test, which shows soil reaction as pH
tmits; the Bray P^ test for plant-available soil phos-
phorus, which is commonly reported as pounds of
phosphorus per acre (elemental basis); and the potas-
sium (K) test, which is commonly reported as pounds
of potassium per acre (elemental basis). Guidelines
for interpreting these tests are included in this section.
An organic-matter test made by some laboratories is
particularly useful in selecting proper rates of herbi-
cide and agricultural limestone.

Because nitrogen can change forms or be lost from
soil, testing to determine nitrogen fertilizer needs for
Illinois field crops is not recommended in the same
sense as testing for the need for lime, phosphorus, or
potassium fertilizer. Testing soil to predict the need

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

for nitrogen fertilizer is complicated by the fact that
nitrogen availability — both the release from soil or-
ganic matter and the loss by leaching and denitrifica-
tion — is regulated by unpredictable climatic condi-
tions. Under excessively wet conditions, both soil and
fertilizer nitrogen may be lost by denitrification or
leaching. Under dry conditions, the amount of nitro-
gen released from organic matter is low, but under
ideal moisture conditions, it is high. Use of the or-
ganic-matter test as a nitrogen soil test, however, may
be misleading and result in underfertilization.

Scientists in Vermont and Wisconsin have identi-
fied nitrogen soil tests that work well under their con-
ditions. Specifics of the tests, along with an evaluation
of their potential and limitations for Illinois, are dis-
cussed in the nitrogen section of this chapter. Guide-
lines for planning nitrogen fertilizer use are also
provided.

Tests are available for most secondary nutrients
and micronutrients, but interpretation of these tests is
less reliable than of tests for lime, phosphorus, and
potassium. Complete field history and soil informa-
tion are especially important in interpreting results.
Even though these tests are less reliable, they may be
useful in two ways:

1. Troubleshooting (diagnosing symptoms of abnormal
growth). Paired samples representing areas of good
and poor growth are needed for analyses.

2, "Hidden-hunger checkup" (identifying deficiencies
before symptoms appear). Soil tests are of little
value in indicating marginal levels of secondary
nutrients and micronutrients when crop growth is
apparently normal. For this purpose, plant analysis
may yield more information.

Soil test ratings (given in Table 11.01) have been de-
veloped to put into perspective the reliability, useful-
ness, and cost-effectiveness of soil tests as a basis for
planning a soil fertility and liming program for Illi-
nois field crops. Additional research will undoubtedly
improve some test ratings.

Interpretation of soil tests and formulation of soil
treatment program. See page 83 for suggested pH
goals and pages 105 and 107 for phosphorus and po-
tassium information. Formulate a soil treatment pro-
gram by preparing field soil test maps to observe ar-
eas of similar test levels that will benefit from similar
treatment. Areas with differences in soil test pH of 0.2
unit, phosphorus test of 10, and potassium test of 30
are reasonable to designate for separate treatment.

When the soil test is variable. When there is large
variation among tests on a field, the reason and, more
important, what to do about it may not be obvious.
First look at the pattern of the tests over the field. If

there is a definite pattern of high tests in one part and
low in another, check to see whether there is a differ-
ence in soil type. Second, try to recall whether the area
was farmed as separate fields in the recent past. Third,
check records for this field from previous tests or, if
there are no records, try to remember whether por-
tions were ever limed or fertilized differently during
the past 5 to 10 years. Whether or not the explanation
for large differences in tests is found, split the field
and apply basic treatments of lime and fertilizer ac-
cording to need.

If there is no consistent pattern of high and low tests,
select the median test, which is the test that falls in the
middle of a ranking of tests from the area from low to
high. If no explanation for large differences in tests is
found, consider taking a new set of samples.

Cation-exchange capacity. Chemical elements exist
in solution as cations (positively charged ions) or an-
ions (negatively charged ions). In the soil solution, the
plant nutrients hydrogen (H), calcium (Ca), magne-
sium (Mg), potassium (K), ammonium (NH^), iron
(Fe), manganese (Mn), zinc (Zn), and copper (Cu) ex-
ist as cations. The same is true for nonplant nutrients

Table 11.01. Ratings of Soil Tests

Test

Rating^

Water pH
Salt pH
Buffer pH
Exchangeable H

100
30
30
10

Phosphorus
Potassium

85
70

Boron (alfalfa)

Boron (com and soybeans)

60
10

Iron (pH > 7.5)
Iron (pH < 7.5)

30
10

Organic matter
Calcium

75
40

Magnesium
Cation-exchange capacity

40
60

Sulfur

Zinc

Manganese (pH >
Manganese (pH <

7.5)
7.5)

40
10

Copper (organic soils)
Copper (mineral soils)

*On a scale of 0 to 100; 100 indicates a very reliable, useful,
and cost-effective test, and 0 indicates a test of little value.

n • SOIL TESTING AND FERTILITY

such as sodium (Na), barium (Ba), and metals of envi-
ronmental concern, including mercury (Hg), cadmium
(Cd), chromium (Cr), and others. Cation-exchange
capacity is a measure of the amount of attraction for
the soil with these chemical elements.

In soil, a high cation-exchange capacity is desirable,
but not necessary, for high crop yields, as it is not a di-
rect determining factor for yield. Cation-exchange ca-
pacity in soil arises from negatively charged electro-
static charges in minerals and organic matter.

Depending on the amount of clay and humus, soil
types have a characteristic amount of cation exchange.
Sandy soils have up to 4 milliequivalent (meq) per 100
grams of soil; light-colored silt loam soils have 8 to 12
meq; dark-colored silt loam soils have 15 to 22 meq;
and clay soils have 18 to 30 meq.

Cation-exchange capacity facilitates retention of
positively charged chemical elements from leaching,
yet it gives nutrients to a growing plant root by an ex-
change of hydrogen (H). Farming practices that re-
duce soil erosion and maintain soil humus favor the
maintenance of cation-exchange capacity. The cation-
exchange capacity of organic residues is low but in-
creases as the residues convert to humus, which re-
quires from 5 years to centuries.

Plant Analyses

Plant analyses can be useful in diagnosing problems,
in identifying hidden hunger, and in determining
whether current fertility programs are adequate. For
example, they often provide more reliable measures
of micronutrient and secondary nutrient problems
than do soil tests.

How to sample. When making a plant analysis to
diagnose a problem, select paired samples of compa-
rable plant parts representing the abnormal and nor-

mal plants. Abnormal plants selected should repre-
sent the first stages of a problem.

When using the technique to diagnose hidden hun-
ger in com, sample several of the leaves opposite and
below the ear at early tassel time. For soybeans,
sample the most recent fully developed leaves and
petioles at early podding. Samples taken later will not
indicate the nutritional status of the plant. After collect-
ing the samples, deliver them immediately to the labo-
ratory. They should be air-dried if they cannot be de-
livered immediately or if they are going to be
shipped.

Environmental factors may complicate the inter-
pretation of plant analysis data. The more information
provided concerning a particular field, the more reli-
able the interpretation will be. Suggested critical nu-
trient levels are provided in Table 11.02. Lower levels
may indicate a nutrient deficiency.

Fertilizer Management related
TO Tillage Systems

Fertilizer management will be affected by tillage sys-
tems because relatively immobile materials such as
limestone, phosphorus, and potassium move slowly
in most soils unless they are physically mixed by till-
age operations. Such "stratification" of nutrients, with
higher concentrations developing near the surface,
has been well documented in a number of studies but
has not been shown to reduce yields of com or soy-
beans in Illinois. Limited research indicates that
plants develop more roots near the soil surface in
conservation-tillage systems, due apparently to both
the improved moisture conditions caused by the sur-
face mulch of crop residues and the higher levels of
available nutrients. With continued reduced tillage
practices, soil fertility levels at deeper depths may be

Table 11,02. Suggested Critical Plant Nutrient Levels for Com and Soybeans

Crop Plant part

N P K Ca Mg S

Zn Fe Mn Cu B

percent

Com Leaf opposite
and below the
ear at tasseling 2.9 0.25 1.90 0.40 0.15 0.15

Soy- Fully developed
beans leaf and petiole
at early podding

0.25 2.00 0.40 0.25 0.15

ppm

15 25 15 5 10

15 30 20 5 25

N = nitrogen, P = phosphorus, K = potassium, Ca = calcium, Mg = magnesium, S = sulfur, Zn - zinc, Fe = iron, Mn
manganese, Cu = copper, B = boron.

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

depleted such that future soil fertility practices may
need adaptation.

Soil tests are important for phosphorus, potassium,
and limestone management under any tillage system.
Consult the earlier section on "How to sample," and
make sure the samples are taken from the full 7-inch
depth. If either limestone (which raises pH) or nitro-
gen fertilizer (which lowers pH) is applied to the sur-
face and not incorporated with tillage, pH tests of the
upper 2 inches of soil are needed to aid in the man-
agement of some herbicides.

See guidelines for adjusting limestone application
rates under different tillage systems. For any system,
the rate of application information in the later section
on "Phosphorus and Potassium" is valid.

Nitrogen fertilizer management may be affected to
a limited extent by changing tillage systems. The in-
formation in the section on "Nitrogen" will be valid in
all tillage systems, with only the following exceptions:

• Where crop residue is present, a coulter may be
needed in front of an applicator knife to properly
inject anhydrous ammonia or liquid nitrogen
fertilizers.

• In no-till systems, where the surface soil may be
firm, special care is needed to make sure that the
slit left by an ammonia applicator knife is com-
pletely closed to prevent nitrogen loss through the
escape of gaseous ammonia.

• Because crop residue in reduced-tillage systems
may inhibit urea or urea-containing fertilizers from
making direct contact with the soil and thus in-
crease the possibility of nitrogen loss through vola-
tilization, these materials should be mechanically
incorporated. Urease inhibitors will aid in prevent-
ing this loss.

• The higher moisture conditions under a residue
mulch may also cause a higher rate of nitrogen loss
through denitrification. Judicious management —

including timing of application and the use of nitri-
fication inhibitors — may help avoid significant
denitrification losses.

• A risk of occasional anhydrous ammonia damage
to com seed and seedlings exists in fields with any
tillage system, especially when the soil is dry, the
ammonia is placed shallow, or com is planted im-
mediately after ammonia application. Com in no-
till fields seems to be particularly vulnerable to
such damage in spring preplant ammonia applica-
tions whenever the seed is placed directly over the
ammonia band. Keeping the anhydrous ammonia
and the com separated in either distance or time
will reduce the potential for this problem.

Starter fertilizer. Starter fertilizer is more effective
than broadcast applications under cool, moist condi-
tions when phosphorus soil test levels are low, irre-
spective of tillage system. At high soil test levels,
starter fertilizer often results in early growth response
on conventional tillage systems but seldom results in
increased yield at harvest.

Early season growth of no-till com is frequently
less vigorous than conventional tillage. This slower
growth is likely the result of cooler soil temperatures
and higher soil moisture conditions associated with
the high residue mulch. Both of these conditions tend
to slow root growth and thus the ability of the plant to
absorb nutrients.

In a 3-year study at four locations, starter fertilizer
placed 2 inches below and 2 inches to the side of the
seed increased grain yield at 10 of the 11 site years
(Table 11.03). Study results revealed several important
considerations when deciding whether to use starter
fertilizer for no-till com.

1. Nitrogen provided the majority of the response at
Ashton, Pana, and Oblong. The summary table
does not show this for Oblong, but the individual-
year data show that nitrogen was the most impor-
tant element in 2 of the 3 years.

Table 11.03. Effect of Starter Fertilizer on Grain Yield of No-Till Com

Starte

'r fertilizer (lb /A)

PA K,o

Location/previous

1 crop

Ashton/com

Gridley /soybean

Pana /soybean

Oblong/soybean

- yield (bu/A) -

131

120

128

146

141

123

136

150

147

129

139

155

146

137

133

160

N = nitrogen, P^Oj = phosphorus, KjO = potassium.

n • SOIL TESTING AND FERTILITY

2. Addition of phosphorus with the nitrogen increased
yield more than enough to pay for the phosphorus.
This was true even at Ashton, which had a soil test
level in excess of 90 pounds of phosphorus per acre.

3. Including potassium in the starter did not signifi-
cantly affect yield at either Ashton or Pana. At the
other two locations, potassium had a significant
impact in 1 of the 3 years of the study. At Gridley,
the increase from potassium occurred in a year
with a wet spring, which resulted in delayed
planting, followed by very dry conditions during
early plant growth. Since this was a long-term
no-till field, the inherent potassium was primarily
in the upper inch of the soil profile, where root
activity was limited during the dry period. There
was adequate moisture at the 4-inch depth for
good root activity and potassium uptake from
the fertilizer band. At Oblong, the soil test potas-
sium was low. In the year in which potassium had
not been broadcast prior to planting, there was
good response to potassium in the starter However,
in the other 2 years, when potassium was broadcast,
there was no response to starter potassium.

Attempts to attain the starter response with other
application techniques met with mixed success. While
placement of up to 10 pounds of nitrogen per acre
directly with the seed increased yield, the increase
was not as consistent as with 2x2 starter And in a
dry spring, placement of as little as 10 pounds of
nitrogen per acre significantly reduced stand in some
experiments. Placement of a band of nitrogen (25-0-0)
or nitrogen plus phosphorus (25-30-0) on the soil sur-
face near the seed row resulted in higher average
yields than with no starter, but yield increases were not
as high or as consistent as for the banded treatments.

Lime

Soil acidity is one of the most serious limitations to
crop production. Acidity is created by a removal of
bases by harvested crops, leaching, and an acid re-
sidual that is left in the soil from nitrogen fertilizers.
IXiring the last several years, limestone use has
tended to decrease in Illinois while crop yields and
nitrogen fertilizer use have increased (Figure 11.03).

At the present rate of limestone use, no lime is
being added to correct the acidity created by the
removal of bases or the acidity created in prior years
that has not been corrected. A soil test every 4 years is
the best way to check on soil acidity levels.

The effect of soil acidity on plant growth. Soil
acidity affects plant growth in several ways. When-
ever soil pH is low (and acidity is high), several situa-
tions may exist:

1.1
1.0
0.9
0.8
0.7

0.6 ^

0.5
0.4
0.3

CD
O)

3
C
<D
O)
O

Nitrogen

0.2 -

0.1

Years

\ '
1997

Figure 11.03. Use of agricultural limestone and commercial
nitrogen fertilizer, 1930-97.

A. The concentration of soluble metals may be toxic.
Damage from excess solubility of aluminum and
manganese due to soil acidity has been shown in
field research.

B. Populations and the activity of the organisms re-
sponsible for transformations involving nitrogen,
sulfur, and phosphorus may be altered.

C. Calcium may be deficient. This usually occurs only
when the cation-exchange capacity of the soil is ex-
tremely low.

D. Symbiotic nitrogen fixation in legume crops is im-
paired greatly. The symbiotic relationship requires
a narrower range of soil reaction than does the
growth of plants not relying on nitrogen fixation.

E. Acidic soils are poorly aggregated and have poor
tilth. This is particularly true for soils that are low
in organic matter

F. The availability of mineral elements to plants may
be affected. Figure 11.04 shows the relationship be-
tween soil pH and nutrient availability. The wider
the dark bar, the greater the nutrient availability.
For example, the availability of phosphorus is
greatest in the pH range between 5.5 and 7.5, drop-
ping off below 5.5. Because the availability of mo-
lybdenum is increased greatly as soil acidity is de-
creased, molybdenum deficiencies usually can be
corrected by liming.

Suggested pH goals. For cash-grain systems (no
alfalfa or clover), maintaining a pH of at least 6.0 is a
realistic goal. If the soil test shows that the pH is 6.0 or

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

less, apply limestone. After the initial investment, it
costs little more to maintain a pH at 6.5 than at 6.0.
The profit over 10 years will be little affected because
the increased yield will approximately offset the cost
of the extra limestone plus interest.

Nitrogen

Phosphorus

Potassium

Calcium

Magnesium

Manganese

Copper and Zinc

Molybdenum

4.0

5.0

6.0 7.0

8.0

9.0

Research indicates that a profitable yield response
from raising the pH above 6.5 in cash-grain systems is
unlikely.

For cropping systems with alfalfa and clover, aim
for a pH of 6.5 or higher unless the soils have a pH of
6.2 or higher without ever being limed. In those soils,
neutral soil is just below plow depth; it will probably
not be necessary to apply limestone.

Liming treatments based on soil tests. The limestone
requirements in Figure 11.05 assume the following:

A. A 9-inch plowing depth. If plowing is less than 9
inches, reduce the amount of limestone; if more
than 9 inches, increase the lime rate proportion-
ately. In no-till systems, use a 3-inch depth for calcula-
tions (one-third the amount suggested for soil mold-
board-plowed 9 inches deep).

B. Typical fineness of limestone. Ten percent of the
particles are greater than 8-mesh; 30 percent pass
an 8-mesh and are held on 30-mesh; 30 percent
pass a 30-mesh and are held on 60-mesh; and 30
percent pass a 60-mesh.

C. A calcium carbonate equivalent (total neutralizing
power) of 90 percent. The rate of application may
be adjusted according to the deviation from 90.

Instructions for using Figure 11.05 are as follows:

1. Use Chart I for grain systems and Chart II for al-
falfa, clover, and lespedeza.

Figure 11.04. Available nutrients in relation to pH.

Chart!

Grain farming

systems

Chart II

Cropping systems

with alfalfa, clover,

or lespedeza

None needed

if naturally

pH6.2

or above

Slightly
acid

Moderately '
acid

'Ohgly
acid

Slightly
acid

Moderately
acid

Neutral
Figure 11.05. Suggested limestone rates based on soil type, pH, cropping systems, and 9-inch depth of tillage.

Strongly
acid

11 • SOIL TESTING AND FERTILITY

2. Decide which classification fits the soil:

a. Dark-colored silty clays and silty clay loams
(CEC > 24)

b. Light- and medium-colored silty clays and silty
clay loams; dark-colored silt and clay loams
(CEC 15-24)

c. Light- and medium-colored silt and clay loams;
dark- and medium-colored loams; dark-colored
sandy loams (CEC 8-15)

d. Light-colored loams; light- and medium-colored
sandy loams; sands (CEC < 8)

e. Muck and peat

Soil color is related to organic matter. Light-colored
soils usually have less than 2.5 percent organic matter;
medium-colored soils have 2.5 to 4.5 percent organic
matter; dark-colored soils have more than 4.5 percent
organic matter; sands are excluded.

Limestone quality. Limestone quality is measured
by the neutralizing value and the fineness of grind.

The neutralizing value of limestone is measured by its
calcium carbonate equivalent: the higher this value,
the greater the limestone's ability to neutralize soil
acidity. Rate of reaction is affected by particle size; the
finer that limestone is ground, the faster it will neu-
tralize soil acidity. Relative efficiency factors have
been determined for various particle sizes
(Table 11.04).

If you are liming an acid soil just before seeding al-
falfa, it is important to have highly reactive particles;
the figures for 1 year are the best guide. If you apply
lime before com, the 4-year values are adequate.

The quality of limestone is defined as its effective
neutralizing value (ENV). This value can be calcu-
lated for any liming material by using the efficiency
factors in Table 11.04 and the calcium carbonate
equivalent for the limestone in question. The "typi-
cal" limestone on which Figure 11.05 is based has an
ENV of 46.35 for 1 year and 67.5 for 4 years.

The Illinois Department of Agriculture, in coopera-
tion with the Illinois Department of Transportation,
collects and analyzes limestone samples from quarries
that wish to participate in the Illinois Voluntary

Worksheet

Evaluation for 1 year after application of lime

Efficiency factor

% of particles greater
than 8-mesh

% of particles that
pass 8-mesh and are
held on 30-mesh

% of particles that
pass 30-mesh and are
held on 60-mesh

% of particles that
pass 60-mesh

X 5

100

X 20

X 50

X 100

Total fineness efficiency

ENV = total fineness efficiency

% calcium carbonate equivalent
^ 100

Correction = ENV of typical limestone (46.35)
factor ENV of sampled limestone ( )

Correction factor x limestone requirement (from Figure
11.05) = tons of sampled limestone needed per acre

Evaluation for 4 years after application of lime

Efficiency factor

% of particles greater
than 8-mesh

% of particles that
pass 8-mesh and are
held on 30-mesh

% of particles that
pass 30-mesh and are
held on 60-mesh =

% of particles that
pass 60-mesh

X 15

100

X 45

X 100

Total fineness efficiency

ENV = total fineness efficiency

% calcium carbonate equivalent
^ 100

Correction = ENV of typical limestone (67.5)
factor ENV of sampled limestone ( )

Correction factor x limestone requirement (from Figure
11.05) = tons of sampled limestone needed per acre

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Example from the worksheet

year

13.1%

X 5 =

0.65

100

40.4%

X 20 =

8.08

100

14.9%

X 50 =

7.45

100

31.6%

X 100 =

31.60

100

Total fineness

efficiency:

47.78

ENV

= 47.78

X 86.88 =
100

= 41.51

46.35

X 3 =

3.35 tons

per acre

41.51

years

13.1%

X 15 =

1.96

100

40.4%

X 45 =

18.18

100

14.9%

X 100 =

14.90

100

31.6%

X 100 =

31.60

100

Total fineness

efficiency:

66.64

ENV

= 66.64

X 86.88
100

= 57.9

67.5

X 3 = 3.5 tons per acre

57.9

Table 11.04. Efficiency Factors for Various
Limestone Particle Sizes

Limestone Program. These analyses, along with the
calculated correction factors, are available from the Il-
linois Department of Agriculture, Division of Plant In-
dustries and Consumer Services, P.O. Box 19281,
Springfield, IL 62794-9281, in the annual publication
Illinois Voluntary Limestone Program Producer Infor-

Efficiency

factor

Particle sizes

1 year after
application

4 years after
application

Greater than 8-mesh
8- to 30-mesh
30- to 60-mesh
Passing 60-mesh

100

mation. To calculate the ENV for materials not re-
ported in that publication, obtain the analysis of the
material in question from the supplier and use the
worksheet provided here for making calculations.

As an example, consider a limestone that has a cal-
cium carbonate equivalent of 86.88 percent and a
sample that has 13.1 percent of the particles greater
than 8-mesh, 40.4 percent that pass 8-mesh and are
held on 30-mesh, 14.9 percent that pass 30-mesh and
are held on 60-mesh, and 31.6 percent that pass 60-
mesh. Assume that 3 tons of typical limestone are
needed per acre (according to Figure 11.05). The
amounts of limestone with these characteristics that
would be needed to meet the 3-ton recommendation
would be 3.35 tons and 3.5 tons on a 1- and 4-year ba-
sis, respectively. (See the calculations to the left.)

At rates up to 6 tons per acre, if high initial cost is
not a deterrent, the entire amount may be applied at
one time. If cost is a factor and the amount of lime-
stone needed is 6 tons or more per acre, apply it in
split applications of about two-thirds the first time
and the remainder 3 or 4 years later.

Fluid lime suspensions (liquid lime). These prod-
ucts are obtained by suspending very finely ground
limestone in water. Several industrial by-products
with liming properties also are being land-applied as
suspensions, either because they are too fine to be
spread dry or they are already in suspension. These by-
products include residue from water treatment plants,
cement plant stack dusts, paper mill sludge, and other
waste products. These materials may contain as much
as 50 percent water.

The chemistry of liquid liming materials is the
same as that of dry materials. Research results have
confirmed that the rate of reaction and the neutraliz-
ing power for liquid lime are the same as for dry ma-
terials when particle sizes are the same.

Results from one study indicate that application
of liquid lime at the rate of material calculated by
the following equation is adequate to maintain soil

n • SOIL TESTING AND FERTILITY

pH for at least 4 years at the same level as typical
lime.

ENV of typical limestone [use 46.35]

100 (fineness % calcium carbonate, % dry

efficiency x equivalent, dry x matter
factor) matter basis 100

100

X tons of limestone needed per acre =

tons of liquid lime needed per acre

During the first few months after application, the
liquid material will provide a more rapid increase in
pH than will typical lime, but after that the two mate-
rials will provide equivalent pH levels in the soil.

As an example, assume a lime need of 3 tons per
acre (based on Figure 11.05) and liquid lime that is 50
percent dry matter and has a calcium carbonate
equivalent of 97 percent on a dry-matter basis. The
rate of liquid lime needed would be calculated as
follows:

46.35

100 X 97
100

X 50

X 3 = 2.87 tons of liquid lime per acre

100

Lime incorporation. Lime does not react with
acidic soil very far from the particle, but special tillage
operations to mix lime with soil usually are not neces-
sary in systems that use a moldboard plow. Systems
of tillage that use a chisel plow, disk, or field cultiva-
tor rather than a moldboard plow, however, may not
mix limestone deeper than 4 to 5 inches.

Calcium-Magnesium Balance
IN Illinois Soils

Soils in northern Illinois usually contain more magne-
sium than those in central and southern Illinois be-
cause of the high magnesium content in the rock from
which the soils developed and because northern soils
are geologically younger. This relatively high level of
magnesium has caused speculation as to whether the
level is too high. Although there have been reported
suggestions that either gypsum or low-magnesium
limestone should be applied, no research data have
been put forth to justify concern over a too-narrow ra-
tio of calcium to magnesium.

On the other hand, concern is justified over a soil
magnesium level that is low — because of its relation-
ship with hypomagnesaemia, a prime factor in grass

tetany or milk fever in cattle. This concern is more rel-
evant to forage production than to grain production.
Very high potassium levels (more than 500 pounds
per acre) combined with low soil magnesium levels
contribute to low-magnesium grass forages. Research
data to establish critical magnesium levels are very
limited. However, levels of soil magnesium less than
60 pounds per acre on sands and 150 pounds per acre
on silt loams are regarded as low.

Calcium and magnesium levels of agricultural
limestone vary among quarries in the state. Dolomitic
limestone (material with an appreciable magnesium
content, as high as 21.7 percent MgO or 46.5 percent
MgCOj) occurs predominantly in the northern three
tiers of Illinois counties, in Kankakee County, and in
Calhoun County. Limestone occurring in the remain-
der of the state is predominantly calcific (high cal-
cium), although it is not uncommon for it to contain
1 to 3 percent MgCOg.

There are no agronomic reasons to recommend
either that grain farmers in northern Illinois bypass
local limestone sources, which are medium to high in
magnesium, and pay a premium for low -magnesium
limestone from southern Illinois or that grain farmers
in southern Illinois order limestone from northern Illi-
nois quarries because of magnesium content.

For farmers with a livestock program or who pro-
duce forages in the claypan and fragipan regions of
the south, where soil magnesium levels may be mar-
ginal, it is appropriate to use a soil test to verify con-
ditions and to use dolomitic limestone or magnesium
fertilization or to add magnesium to the feed.

Nitrogen

About 40 percent of the original nitrogen and organic-
matter content has been lost from typical Illinois soils
since farming began, the result of erosion and in-
creased oxidation of organic matter. Erosion reduces
the nitrogen content of soils because the surface soil is
richest in nitrogen and this erodes first. Farming
practices that improve aeration of the soil, including
improved drainage and tillage, have increased the
rate of organic matter degradation. Further nitrogen
losses result from denitrification and leaching.

Because harvested crops remove more nitrogen
than any other nutrient from Illinois soils, the use of
nitrogen fertilizer is necessary if Illinois agriculture is
to be competitive in the world market. Economics,
along with concern for the environment, make it
imperative that all nitrogen fertilizers be used as
efficiently as possible. Factors that influence efficiency
are discussed in the following sections.

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Nitrogen Recommendation Systems

Nitrogen recommendations in the humid regions of
the Com Belt have been based primarily on expected
yield, with an adjustment for previous crop and man-
agement programs. Although this system has worked
well, there are documented reports of near-optimal
com yields with little or no supplemental nitrogen.
Such results have encouraged researchers to develop
a reliable and practical soil nitrogen test that would
let farmers and advisers identify conditions where the
nitrogen application rate could be modified to en-
hance crop profits without harming the environment.

Total soil nitrogen. Because 5 percent of soil or-
ganic matter is nitrogen, some have theorized that
organic-matter content of a soil could be used as an
estimate of the amount of supplemental nitrogen that
would be needed for a crop. As a rough guideline,
many assume that 2 percent of the organic nitrogen
will be released each year. This would amount to a
release of 100 pounds of nitrogen per acre on fields
with 5 percent organic matter. Attempts to use this
procedure have been unsuccessful because mineral-
ization of organic matter varies significantly over time
due to variation in available soil moisture. Addition-
ally, soils high in organic matter usually have a higher
yield potential due to their ability to provide a better
environment for crop growth.

Early-spring nitrate nitrogen. This procedure has
been used for several years in the more arid parts of
the Com Belt (west of the Missouri River) with rea-
sonable success. It involves collecting soil samples in
1-foot increments to a 2- to 3-foot depth in early
spring for analysis of nitrate nitrogen. Although the
use of the information varies somewhat from state to
state, the consensus is to reduce the normal nitrogen
recommendation by the amount found in the soil pro-
file sampled. Results obtained by scientists in both
Wisconsin and Michigan have found this procedure to
work well, but research in Iowa indicated that the
procedure did not accurately predict nitrogen needs.

Since samples are collected in early spring, this
procedure measures potential for nitrogen carryover
from the previous crop. It thus will have the greatest
potential for success on continuous com, especially in
fields where adverse growing conditions have limited
yields the previous year. Additional work is needed to
ascertain the sampling procedure that will best char-
acterize the field conditions, especially when nitrogen
has been injected in prior years. When excessive pre-
cipitation is received in late spring or early summer,
this procedure will not likely be successful because
most of the nitrogen that is detected early may be
leached or denitrified before the plant has an oppor-
tunity to absorb it from the soil.

Late-spring nitrate nitrogen. Success with this
procedure was first observed with work in Vermont.
Follow-up work in some of the Com Belt states also
indicates that the procedure accurately characterizes
nitrogen needs. Soil samples are collected to a 1-foot
depth when com plants are 6 to 12 inches tall and
analyzed for nitrate nitrogen. University agronomists
suggest that no additional nitrogen be applied when
soil test levels exceed 22 to 25 parts per million and
that full rate be applied if nitrate nitrogen levels are
less than 10 parts per million. They suggest propor-
tional adjustments in nitrogen rates when test levels
are between 10 and 26 parts per million. To minimize
the potential for decreased yield that might be
caused by delayed nitrogen application, agronomists
at Iowa State University suggest that 50 to 70 percent
of the normal nitrogen application be applied pre-
plant. If the fertilizer was broadcast, they suggest col-
lecting 16 to 24 core samples within an area not ex-
ceeding 10 acres. If the fields have been fertilized
with anhydrous ammonia, they suggest a modified
soil test. The modified test can be used under the fol-
lowing conditions: (a) the rate of ammonia applica-
tion did not exceed 125 pounds of nitrogen per acre;
(b) the soil sample is derived from at least 24 cores
collected without regard to location of ammonia in-
jection bands; and (c) fertilizer nitrogen recommen-
dations are adjusted to reflect that one-third of the
nitrogen applied was not revealed by the soil test.

By sampling later in the season, this test provides a
measure of the mineralization of organic nitrogen that
has occurred and the amount of residual carryover
that is still present in the soil. Obvious limitations of
this procedure include these: (a) its use only on fields
that receive sidedress application of nitrogen; (b) the
short time available between sampling and the need
to apply fertilizer, which could be especially critical in
wet years and could result in com plants becoming
too large to use conventional application equipment;
and (c) no existing correlation for use of the proce-
dure on fields that have received a banded nitrogen
application.

Because none of the nitrogen soil test procedures
have given adequate crop nitrogen requirement pre-
dictions, their use is not encouraged under Illinois
conditions. It is suggested that nitrogen rates be deter-
mined using the following materials as a guide.

Yield potential. Research trials conducted by the
University of Illinois Crop Sciences Department have
demonstrated that use of the following system for de-
termining nitrogen rate will optimize yield. There
are years when this system will recommend more ni-
trogen than needed, but very few years in which the
recommendation will be so low as to markedly re-

11 • SOIL TESTING AND FERTILITY

duce yield. It appears that use of this system will
help reduce the amount of nitrogen being lost to the
environment.

The worksheet on page 90 is designed to help you
determine your fertilizer nitrogen need. You can also
use this equation to calculate nitrogen need for com:

Fertilizer nitrogen needed = (Target yield in
bushels X 1.2 lb N/bushel) - legume N - manure
N - incidental N

Target yield is one of the major considerations in
determining the optimum rate of nitrogen application
for com. The target yield should be established for
each field, taking into account the soil type and man-
agement level under which the crop will be grown. If
yield records are available, use the 5-year average
yield as the basis. When figuring the average, elimi-
nate years of abnormally low yields that resulted
from drought or other weather-related conditions.
Increase the average yield by 5 percent because of im-
proved varieties and cultural practices.

If yield records are not available for a particular
field, suggested productivity-index values are given
in Illinois Agricultural Experiment Station Bulletin
778, Soils of Illinois. Yield goals are presented for both
basic and high levels of management. Annual varia-
tions in yield of 20 percent above or below the pro-
ductivity-index values are common because of varia-
tions in weather conditions. However, applying
nitrogen fertilizer for yields possible in the most fa-
vorable year will not result in nnaximum net return
when averaged over all years.

The 1.2 lb N/bushel coefficient was derived assum-
ing a com-to-nitrogen price ratio (price of com per
bushel divided by the price of N per pound) between
10:1 and 20:1. If the price ratio goes above 20:1, then
the optimum rate would increase to 1.3 lb N/bushel.

Take credit for "home-grown" nitrogen, including
com following a legume crop such as soybean, al-
falfa, or clover and for manure applied to the field.
(See the subsection about rate adjustments on page
93.) Incidental nitrogen is that nitrogen applied with
phosphates, applied as a part of the starter fertilizer,
and/or applied as a carrier for herbicides.

Evaluation of nitrogen recommendation systems
for corn. Experiments were conducted at 77 locations
around Illinois to evaluate the potential for using the
nitrate nitrogen soil test systems to improve nitrogen
recommendations. Use of the systems was compared
to use of yield potential, multiplied by a factor, minus
adjustments for previous crops and legumes. Consid-
ering only those locations exhibiting a significant re-
sponse to applied fertilizer nitrogen, all three systems
— those based on yield potential with adjustments for
home-grown and incidental nitrogen, and those based
on yield potential with an adjustment for the amount
of nitrate nitrogen observed in the soil at early spring
or at pre-sidedress time — gave recommendations
within 8 pounds of the amount needed for the fields
on the average (Table 11.05). Adjustments based on
the early spring nitrate nitrogen test resulted in rec-
ommendations about 25 pounds less than needed to
obtain the most return per acre.

None of the three systems provided accurate rec-
ommendations for fields where adverse weather con-
ditions limited yield potential far below expectation
and limited yield response to applied nitrogen (Table
11.06). At locations where manure had been applied
prior to planting, all three recommendation systems
predicted a need for little supplemental fertilization.

Based on results so far, none of the nitrogen soil
test procedures now available offers enough improved
accuracy or reliability over the yield potential system
described earlier to justify its use on Illinois fields. An
exception appears to be on fields that have received a

Table 11.05. Relationship Between Experimentally Derived, Economically Optimum Nitrogen Rates and
Nitrogen Recommendations from Three Recommendation Systems

Yield goal
(bu/A)

Optimum
yield (bu/A)

Optimum
N rate (bu/A)

Recommendation system

Locations

FY- PPNT" PSNT^
(lb N/acre) (lb N/acre) (lb N/acre)

Responding sites: 44
Nonresponding sites: 33

139

143

161
145

138
0

137 107 130
111 76 113

* Proven yield. University of Illinois Department of Crop Sciences recommendations using proven yield.

''Preplant nitrogen test. U of I Department of Crop Sciences recommendations, minus nitrate content in top 2 feet of surface

soil in early spring.

•^ Pre-sidedress nitrogen test. Iowa State University Department of Agronomy nitrogen recommendations.

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Nitrogen Rate Worksheet for Com

1. Determine your average yield for the last 5-year period:

Yield last 5 years (bu/acre)

Sum across
years

Divided by
number of
years

Average

Yearl

Year 2

Years

Year 4

Years

2. Multiply average yield by 1.05 to obtain target yield; the increase of 0.05 accounts for increased yield
potential due to improved variety and cultural practices.

xl.05

Bu/acre

Average yield

Target yield

3. Multiply target yield by 1.20 lb N/bu to obtain N needed per acre:

xl.20

Lb N/acre

Target yield

N needed

Reduce N needed by subtracting all N credits (adjust for all of the following that apply):

a) Previous crop of soybeans (40 lb N/acre).

b) Previous crop of alfalfa/clover (> 5 plants/ft = 100 lb N;

2-4 plants/ft = 50 lb N).

c) Application of ammoniated phosphate (multiply lb material by

percent N). Ex.: 200 lb 18-46-0 = 200 x 0.18 = 36 lb N/acre.

d) Manure application (total lb N in manure divided by 2).

e) Weed and feed N (multiply gallon per acre times 3 for 28% N

or times 3.5 for 32% N solutions).

f) Starter (multiply rate by percent N).

g) N in irrigation water (inches irrigation water X ppm NO3-N X 0.23).

Total N credits (a + b + c + d + e + f-f-g)

5. Amount N to apply:

(N needed) - (N credit)

11 • SOIL TESTING AND FERTILITY

Table 11.06. Relationship Between Experimentally Derived, Economically Optimum Nitrogen Rates and
Nitrogen Recommendations from Three Recommendation Systems as Influenced by Manure
Application, Environmental Factors, and Previous Crop

Recommendation system

Locations

Yield goal
(bu/A)

Optimum
yield (bu/A)

Optimum
N rate (bu/A)

pya

(IbN/acre)

PPNT"
(lb N/acre)

PSNTP
(lb N/acre)

Manured sites: 9
Drought-affected sites: 8
Forage legume sites: 4

144
153
148

185

164

24
163
102

10
118

128

'Proven yield. University of Illinois Department of Crop Sciences recommendations using proven yield.

•"Preplant nitrogen test. U of I Department of Crop Sciences recommendations, minus nitrate content in top 2 feet of surface soil

in early spring.

■^Pre-sidedress nitrogen test. Iowa State University Department of Agronomy nitrogen recommendations.

broadcast application of manure or other materials
containing organic nitrogen. In those cases, if the ni-
trate nitrogen test exceeds 25 parts per million at the
time the com is 6 to 12 inches tall, there is no need for
additional nitrogen fertilizer.

Soybeans. Based on average Illinois com and soy-
bean yields from 1995 and 1996 and average nitrogen
content of the grain for these two crops, the total ni-
trogen removed per acre by soybeans (151 pounds)
was greater than that removed by com (91 pounds).
Research results from the University of Illinois, how-
ever, indicate that when properly nodulated soybeans
were grown at the proper soil pH, the symbiotic fixa-
tion was equivalent to 63 percent of the nitrogen re-
moved in harvested grain. Thus, the net nitrogen re-
moval by soybeans (56 pounds) was less than that of
com (91 pounds).

This net removal of nitrogen by soybeans in 1995-
96 was equivalent to 29 percent of the amount of fer-
tilizer nitrogen used in Illinois. On the other hand,
symbiotic fixation of nitrogen by soybeans in Illinois
(465,169 tons of nitrogen) was equivalent to 50 per-
cent of the fertilizer nitrogen used in Illinois.

Even though there is a rather large net nitrogen removal
from soil by soybeans (56 pounds of nitrogen per acre), re-
search at the University of Illinois has generally indicated
no soybean yield increase caused by either residual nitro-
gen in the soil or nitrogen fertilizer applied for the soybean
crop.

1. Residual from nitrogen applied to corn (Table 11.07).
Soybean yields at four locations were not increased
by residual nitrogen in the soil, even when nitro-
gen rates as high as 320 pounds per acre had been
applied to com the previous year.

2. Nitrogen on continuous soybeans (Table 11.08). After
18 years of continuous soybeans at Hartsburg,

yields were unaffected by applications of nitrogen
fertilizer.

3. High rates of added nitrogen (Table 11.09). Moderate
rates of nitrogen were applied to soybeans in the
first year of a study at Urbana. Rates were in-
creased in the second year so that the higher rates
would furnish more than the total nitrogen needs
of soybeans. Yields were not affected by nitrogen
in the first year, but with 400 pounds per acre of ni-
trogen, a tendency toward a yield increase occurred

Table 11.07. Soybean Yields at Four Locations as

Affected by Nitrogen Applied to Com
the Preceding Year (4- Year Average)

N applied

Soybean yield (bu/A)

to com

(lb/A)

Aledo

Dixon

Elwood

Kewanee

Average

160

240

320

Table 11.08. Yields of Continuous Soybeans with
Rates of Added Nitrogen at Hartsburg

Soybean yield (bu/A)

Nitrogen (lb/A)

1968-71

1954-71

120

43
42
43

37
36
37

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 11.09. Soybean Yields at Urbana as Affected
by High Rates of Nitrogen

Nitrogen (lb/A)

Soybean yield (bu/A)

1st

2nd 3rd

1st

2nd

3rd

year

year year

year

0 0

200 200

400 400

120

800 800

160

1,600 1,600

in the second and third years. However, the yield
increase would not pay for the added nitrogen at
current prices.

Kansas researchers have reported soybean yield in-
creases associated with the application of up to 40
pounds nitrogen per acre at the R4 stage of growth.
Generally, these responses have occurred on irrigated,
high-yielding (check yields of 58 bushel per acre)
fields. In 1995 yield increases ranging from 9 to 12
bushels per acre were observed at 3 of 4 locations.
The control yield at the nonresponding location was
43 bushel per acre.

Wheat, oats, and barley. The rate of nitrogen to
apply on wheat, oats, and barley depends on soil
type, crop and variety to be grown, and future crop-
ping intentions (Table 11.10). Light-colored soils (low
in organic matter) require the highest rate of nitrogen
application because they have a low capacity to sup-
ply nitrogen. Deep, dark-colored soils require lower
rates of nitrogen application for maximum yields.

Estimates of organic-matter content for soils of Illinois
may be obtained from Agronomy Fact Sheet SP-36,
Average Organic Matter Content in Illinois Soil Types, or
by using University of Illinois publication AG-1941,
Color Chart for Estimating Organic Matter in Mineral
Soils.

Nearly all modem varieties of wheat have been
selected for improved standability, so concern about
nitrogen-induced lodging has decreased considerably.
Varieties of oats, though substantially improved with
regard to standability, will still lodge occasionally; ni-
trogen should be used carefully. Barley varieties, espe-
cially spring barley, are prone to lodging, so rates of
nitrogen application shown in Table 11.10 should not
be exceeded.

Some wheat and oats in Illinois serve as compan-
ion crops for legume or legume-grass seedings. On
those fields, it is best to apply nitrogen fertilizer at
well below the optin\um rate because unusually
heavy vegetative growth of wheat or oats competes
unfavorably with the young forage seedlings (Table
11.10). Seeding rates for small grains should also be
somewhat lower if used as companion seedings.

The introduction of nitrification inhibitors and
improved application equipment now provide two
options for applying nitrogen to wheat. Research has
shown that when the entire amount of nitrogen need-
ed is applied in the fall with a nitrification inhibitor,
the resulting yield is equivalent to that obtained when
a small portion of the total need was fall-applied and
the remainder was applied in early spring. Producers
who are frequently delayed in applying nitrogen in
the spring because of muddy fields may wish to con-
sider fall application with a nitrification inhibitor. For
fields that are not usually wet in the spring, either
system of application will provide equivalent yields.

Table 11.10. Recommended Nitrogen Application Rates for Wheat, Oats, and Barley

Soil situation

Fields with alfalfa
or clover seeding

Fields with no alfalfa
or clover seeding

Organic
matter Wheat Oats and barley Wheat Oats and barley

Low in capacity to supply nitrogen: inherently
low in organic matter (forested soils)

<2% 70-90

- nitrogen (lb/A)

60-80 90-110

70-90

Medium in capacity to supply nitrogen: mod-
erately dark-colored soils

2-3% 50-70

40-60

70-90

50-70

High in capacity to supply nitrogen: deep,
dark-colored soils

>3% 30-50

20-40

50-70

30-50

11 • SOIL TESTING AND FERTILITY

Table 11.11. Nitrogen Fertilization of Hay and
Pasture Grasses

Time of application

Species

After After
Early first second Early
spring harvest harvest September

nitrogen (lb/A)

Kentucky

bluegrass 60-80 (see text)

Orchardgrass 75-125 75-125
Smooth

' bromegrass 75-125 75-125 50^

Reed canary

grass 75-125 75-125 50^

Tall fescue for

winter use 100-125 100-125 50^

'Optional if extra fall growth is needed.

The amount of nitrogen needed for good fall
growth is not large because the total uptake in roots
and tops before cold weather is not likely to exceed 30
to 40 pounds per acre.

Hay and pasture grasses. The species grown, pe-
riod of use, and yield goal determine optimum nitro-
gen fertilization (Table 11.11). The lower rate of appli-
cation is recommended on fields where inadequate
stands or moisture limits production.

Kentucky bluegrass is shallow-rooted and suscep-
tible to drought. Consequently, the most efficient use
of nitrogen by bluegrass is from an early spring appli-
cation, with September application a second choice.
September fertilization stimulates both fall and early
spring growth.

Orchardgrass, smooth bromegrass, tall fescue, and
reed canarygrass are more drought-tolerant than blue-
grass and can use higher rates of nitrogen more effec-
tively. Because more uniform pasture production is
obtained by splitting high rates of nitrogen, two or
more applications are suggested.

If extra spring growth can be utilized, make the
first nitrogen application in March in southern Illinois,
early April in central Illinois, and mid- April in north-
em Illinois. If spring growth is adequate without extra
nitrogen, the first application may be delayed until
after the first harvest or grazing cycle to distribute
production more uniformly throughout the summer.
Total production hkely will be less, however, if nitro-
gen is applied after first harvest rather than in early
spring. Usually the second application of nitrogen is
made after the first harvest or first grazing cycle; to

Table 11.12. Adjustments in Nitrogen
Recommendations

Factors resulting in reduced nitrogen requirement

1st year after 2nd year after
alfalfa or clover alfalfa or clover

Crop After pigj^^g/ f^ Plants/sq ft

to be soy- . i__

grown beans 5 2-A <2 5

< 5 Manure

- nitrogen reduction (lb/A) - -

Corn

100

50 0 30 0

Wheat

10 0 0 0

^Nitrogen contribution in pounds per ton of manure. See
Table 11.13 for adjustments for liquid manure.

stimulate fall growth, however, this application may
be deferred until August or early September.

Legume-grass mixtures should not receive nitrogen
if legumes make up at least 30 percent of the mixture.
Because the main objective is to maintain the
legume, the emphasis should be on applying phos-
phorus and potassium rather than nitrogen.

After the legume has declined to less than 30 per-
cent of the mixture, the objective of fertilizing is to
increase the yield of grass. The suggested rate of
nitrogen is about 50 pounds per acre when legumes
make up 20 to 30 percent of the mixture.

Rate Adjustments

In addition to determining nitrogen rates, producers
should consider other agronomic factors that influ-
ence available nitrogen. These factors include past
cropping history and the use of manure (Table 11.12),
as well as the date of planting.

Previous crop. Com following another crop con-
sistently yields better than continuous com. This is
especially true for com following a legume such as
soybeans or alfalfa (Figure 11.06). This is due in part
to residual nitrogen from the legumes as the differ-
ences in yield between rotations become smaller with
increasing nitrogen rates. When no nitrogen was
applied, the data indicate that soybeans and alfalfa
contributed the equivalent of 65 and 108 pounds of
nitrogen per acre, respectively. At the optimum pro-
duction level, soybeans contributed the equivalent
of about 40 pounds of nitrogen per acre. The contri-
bution of legumes, either soybeans or alfalfa, to
wheat will be less than the contribution to com be-
cause the oxidation of the organic nitrogen from
these legumes will not be as rapid in early spring,
when nitrogen needs of small grain are greatest, as it

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 11.13. Average Composition of Manure

Nutrients (Ib/t

on)

Nitrogen

Phospho-

Potassium

Manure type

(N)

rus (PP3)

(Kp)

Dairy cattle

Beef cattle

Hogs

Chicken

Dairy cattle (liquid)

5(26)^

2(11)

4(23)

Beef cattle (liquid)

4(21)

1(7)

3(18)

Hogs (liquid)

10(56)

5(30)

4(22)

Chicken (liquid)

13(74)

12(68)

5(27)

^Parenthetical numbers are pounds of nutrients per 1,000
gallons.

is in the summer, when nitrogen needs of com are
greatest.

Com following oats had a higher yield than con-
tinuous com (Figure 11.06). Although oats are not a
legume, a part of this yield differential may be be-
cause nitrogen was released from the soil after the oat
crop had completed its nitrogen uptake, and thus it
was carried over to the next year's com crop.

Idled acres. Depending on the crop grown, the ni-
trogen credit from idled acres may be positive or
negative. Plowing under a good stand of a legume
that had good growth will result in a contribution of
60 to 80 pounds of nitrogen per acre. If either stand or
growth of the legume was poor or if com was no-
tilled into a good legume stand that had good growth.

180

40
20

o Corn
• Soybean
A Oats
A Alfalfa
□ Fallow

80 160

Nitrogen (pounds/acre)

240

Figure 11.06. Effect of crop rotation and applied nitrogen
on com yield, DeKalb.

the legume nitrogen contribution could be reduced to
40 to 60 pounds per acre. Because most of the net ni-
trogen gained from first-year legumes is in the herb-
age, fall grazing reduces the nitrogen contribution to
30 to 50 pounds per acre.

Manure. Nutrient content of manure varies with
source and method of handling (Table 11.13). The
availability of the total nitrogen content also varies by
method of application. When manure is incorporated
during or immediately after application, about 50 per-
cent of the total nitrogen in dry manure and 50 to 60
percent of the total nitrogen in liquid manure will be
available for the crop that is grown during the year
following manure application.

Time of planting. Research at the Northern Illinois
Research Center for several years showed that as
planting was delayed, less nitrogen fertilizer was re-
quired for most profitable yield. Based upon that re-
search, Illinois agronomists suggest that for each
week of delay in planting after the optimum date for
the area, the nitrogen rate can be reduced 20 pounds
per acre down to 80 to 90 pounds per acre as the mini-
mum for very late planting in a corn-soybean crop-
ping system. Suggested reference dates are April 10 to
15 in southern Illinois, April 20 to May 1 in central
Illinois, and May 1 to 10 in northern Illinois. This ad-
justment is of course possible only if the nitrogen is
sidedressed.

Because of the importance of planting date, farmers
are encouraged not to delay planting just to apply ni-
trogen fertilizer: plant, then sidedress.

Reactions in the Soil

Efficient use of nitrogen fertilizer requires under-
standing how nitrogen behaves in the soil. Key points
to consider are the change from ammonium (NHp to
nitrate (NO3) and the movements and transforma-
tions of nitrate.

A high percentage of the nitrogen applied in Illi-
nois is in the ammonium form or converts to ammo-
nium (anhydrous ammonia and urea, for example)
soon after application. Ammonium nitrogen is held
by the soil clay and organic matter and cannot move
very far until it nitrifies (changes from ammonium to
nitrate). In the nitrate form, nitrogen can be lost by ei-
ther denitrification or leaching (Figure 11.07).

Denitrification. Denitrification is believed to be the
main process by which nitrate and nitrite nitrogen are
lost, except on sandy soils, where leaching is the ma-
jor pathway. Denitrification involves only nitrogen
that is in the form of either nitrate (NOp or nitrite
(NO-).

The amount of denitrification depends mainly on
(a) how long the surface soil is saturated; (b) the tem-

11 • SOIL TESTING AND FERTILITY

-^^

Denitrification

Ammonium ^ Nttrfte

NHt *" NO2

Nitrate

Leaching

Figure 11.07. Nitrogen reactions in the soil.

perature of the soil and water; (c) the pH of the soil;
and (d) the amount of energy material available to
denitrifying organisms.

When water stands on the soil or when the surface
is completely saturated in late fall or early spring, ni-
trogen loss is likely to be small because much nitro-
gen is still in the ammonium rather than nitrate form
and because the soil is cool, and denitrifying organ-
isms are not very active.

Many fields in east-central Illinois, and to a lesser
extent in other areas, have low spots where surface
water collects at some time during the spring or early
summer. The flat claypan soils also are likely to be
saturated, though not flooded, during that time.
Sidedressing would avoid the risk of spring loss on
these soils but would not affect midseason loss. Un-
fortunately, these are the soils on which sidedressing
is difficult in wet years.

New scientific procedures now make it possible to
directly measure denitrification losses. Results col-
lected over the past few years indicate that when soils
were saturated for 3 days or longer, 5 percent of the
nitrogen present in the nitrate form was lost per day
of saturation.

Leaching. In silt loams and clay loams, 1 inch of
rainfall moves down about 5 to 6 inches, though some
of the water moves in large pores farther through the
profile and carries nitrates with it.

In sandy soils, each inch of rainfall moves nitrates

down about 1 foot. If the total rainfall at one time is
more than 6 inches, little nitrate will be left within the
rooting depth on sands.

Between rains, some upward movement of nitrates
occurs in moisture that moves toward the surface as
the surface soil dries. The result is that it is difficult to
predict how deep the nitrate has moved based only
on cumulative rainfall.

When trying to estimate the depth of leaching of
nitrates in periods of very intensive rainfall, two
points need to be considered. First, the rate at which
water can enter the surface of silt and clay loams may
be less than the rate of rainfall, which means that
much of the water runs off the surface into low spots
or into creeks and ditches. Second, the soil may be
saturated already. In either of these cases, the nitrates
will not move down the 5 to 6 inches per inch of rain
as suggested above.

Com roots usually penetrate to 6 feet in Illinois
soils. Thus, nitrates that leach only to 3 to 4 feet are
well within normal rooting depth unless they reach
tile lines and are drained from the field.

Nitrification Inhibitors

As Figure 11.07 shows, nitrification converts ammo-
nium nitrogen into nitrate, the form susceptible to
loss by denitrification or leaching. Use of nitrification
inhibitors can retard this conversion. When inhibitors
were properly applied in one experiment, as much as
42 percent of soil-applied ammonia remained in the
ammonium form through the early part of the grow-
ing season, in contrast with only 4 percent that re-
mained when inhibitors were not used. Inhibitors can
therefore significantly affect crop yields. The benefit
from using an inhibitor varies, however, with soil
condition, time of year, type of soil, geographic loca-
tion, rate of nitrogen application, and weather condi-
tions that occur after the nitrogen is applied and be-
fore it is absorbed by the crop.

Considerable research throughout the Midwest has
shown that only under wet soil conditions do inhibi-
tors significantly increase yields. When inhibitors were
applied in years of excessive rainfall, increases in com
yield ranged from 10 to 30 bushels per acre; when
moisture conditions were not as conducive to denitri-
fication or leaching, inhibitors produced no increase.

For the first 4 years of one experiment conducted
by the University of Illinois, nitrification inhibitors
produced no effect on grain yields because soil mois-
ture levels were not sufficiently high. In early May of
the fifth year, however, when soils were saturated
with water for a long time, the application of an in-
hibitor in the preceding fall significantly increased
com yields (Figure 11.08). Furthermore, at a nitrogen

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

application rate of 150 pounds per acre, the addition
of an inhibitor increased grain yields more than did
the addition of another 40 pounds of nitrogen (Figure
11.08). Under the conditions of that experiment, there-
fore, it was more economical to use an inhibitor than
to apply more nitrogen.

Because soils normally do not remain saturated
with water for very long during the growing season
after a sidedressing operation, the probability of ben-
efiting from the use of a nitrification inhibitor with
sidedressed nitrogen is less than from its use with
either fall- or spring-applied nitrogen. Moreover, the
short time between application and absorption by the
crop greatly reduces the potential for nitrogen loss.

The longer the period between nitrogen application
and absorption by the crop, the greater the probability
that nitrification inhibitors will contribute to higher
yields. The length of time, however, that fall-applied
inhibitors remain effective in the soil depends partly
on soil temperature. On one plot, a Drummer soil that
had received an inhibitor application when soil tem-
perature was 55°F retained nearly 50 percent of the
applied ammonia in ammonium form for about 5
months. When soil temperature was 70°F, the soil
retained the same amount of ammonia for only 2
months. Fall application of nitrogen with inhibitors
should therefore be delayed until soil temperatures
are no higher than 60°F; and though temperatures
may decrease to 60°F in early September, it is advis-
able to delay applications until the second week of
October in northern Illinois and the third week of
October in central Illinois.

In general, poorly or imperfectly drained soils
probably benefit the most from nitrification inhibitors.
Moderately well-drained soils that undergo
frequent periods of 3 or more days of flooding in the
spring also benefit. Coarse-textured soils (sands) are
likely to benefit more than soils with finer textures
because the coarse-textured soils have a higher poten-
tial for leaching.

Time of application and geographic location must
be considered along with soil type when determining
whether to use a nitrification inhibitor. Employing in-
hibitors can significantly improve the efficiency of
fall-applied nitrogen on the loams, silts, and clays of
central and northern Illinois in years when the soil is
very wet in the spring. At the same time, currently
available inhibitors do not adequately reduce the rate
of nitrification in the low-organic-matter soils of
southern Illinois when nitrogen is applied in the fall
for the following year's com. The lower organic-
matter content and the warmer temperatures of south-
em Illinois soils, both in late fall and early spring,
cause the inhibitor to degrade too rapidly. Further-

more, applying an inhibitor on sandy soils in the fall
does not adequately reduce nitrogen loss because the
potential for leaching is too high. Fall applications of
nitrogen with inhibitors thus are not recommended
for sandy soils or for soils with low organic-matter
content, especially those found south of Interstate 70.

In the spring, preplant applications of inhibitors
may be beneficial on nearly all types of soil from
which nitrogen loss frequently occurs, especially on
sandy and poorly drained soils. Again, inhibitors are
more likely to have an effect when subsoils are re-
charged with water than when they are dry at the
beginning of spring.

Nitrification inhibitors are most likely to increase
yields when nitrogen is applied at or below the opti-
mum rate. When nitrogen is applied at a rate greater
than that required for optimum yields, benefits from
an inhibitor are unlikely, even when moisture in the
soil is excessive.

Inhibitors should be viewed as soil management
tools that can be used to reduce nitrogen loss. It is not
safe to assume, however, that the use of a nitrification
inhibitor will make it possible to reduce nitrogen rates
below those currently recommended, because those
rates were developed with the assumption that no
significant amount of nitrogen would be lost.

Time of Nitrogen Application

For nitrogen that is fall-applied without a nitrification
inhibitor, farmers in central and northern Illinois

200

180

■ Spring-applied nitrogen, Nitrapyrin (0 lb/A)
o Fall-applied nitrogen, Nitrapyrin (0.5 lb/A)
• Fall-applied nitrogen, Nitrapyrin (0 lb/A)

100 150

Nitrogen (pounds/acre)

200

Figure 11.08. Effect of nitrification inhibitors on com
yields at varying nitrogen application rates, DeKalb.

11 • SOIL TESTING AND FERTILITY

Figure 11.09. Influence of soil temperature on the relative

rate of NO, accumulation in soils.

should apply nitrogen in non-nitrate form in the late
fall after the soil temperature at 4 inches is below 50°F,
except on sandy, organic, or very poorly drained soils.

The 50°F level for fall application is believed to be a
realistic guideline for farmers. Applying nitrogen ear-
lier risks too much loss (Figure 11.09). Later applica-
tion risks wet or frozen fields, which would prevent
application and fall tillage. Average dates on which
these temperatures are reached are not satisfactory
guides because of the great variability from year to
year. Soil thermometers should be used to guide fall
applications of nitrogen.

In Illinois, most of the nitrogen applied in late fall
or very early spring is converted to nitrate by corn-
planting time. Though the rate of nitrification is slow
(Figure 11.09), the soil temperature is between 32''F
and 40° to 45°F for a long period.

In consideration of the date at which nitrates are
formed and the conditions that prevail thereafter, the
difference in susceptibility to denitrification and
leaching loss between late fall and early spring appli-

Table 11.14. Effect on Corn Yield of Ammonia

Knife Spacing with Different Tillage
Systems at Two Illinois Locations

Yield (bu/A)

Injector spacing (in.)

Plow

Chisel

Disk No-till

DeKalb trials

159

157

163 146

158

157

157 143

Elwood trials

• • •

119

121 118

117

125 121

cations of ammonium sources is probably small. Both
are, however, more susceptible to loss than is nitrogen
applied at planting time or as a sidedressrng.

Anhydrous ammonia nitrifies more slowly than
other forms and is slightly preferred for fall applica-
tions. It is well suited to early spring application,
provided the soil is dry enough for good dispersion
of ammonia and closure of the applicator slit.

Sidedress application. Results collected from
studies in Illinois indicated that nitrogen injected
between every other row was comparable in yield to
injection between every row. This finding was true
irrespective of tillage system (Table 11.14) or nitrogen
rate (Table 11.15). This outcome should be expected,
as even with e very-other- row injection, each row will
have nitrogen applied on one side or the other (Fig-
ure 11.10).

Use of wider injection spacing at sidedressing
allows for reduced power requirement for a given
applicator width or use of a wider applicator with the
same power requirement. From a practical stand-
point, the lower power requirement frequently means
a smaller tractor and associated smaller tire, making
it easier to maneuver between rows and causing less
compaction next to the row. With this system, injector
positions can be adjusted to avoid placing an injector
in the wheel track. When matching the driving pat-
tern for a planter of 8, 12, 16, or 24 rows, the outside
two injectors must be adjusted to half-rate applica-
tion, as the injector will go between those two rows
twice if one avoids having a knife in the wheel track.
To avoid problems of back pressure that might be cre-
ated when applying at relatively high speeds, use a
double-tube knife, with two hoses going to each
knife; the outside knives would require only one hose
to give the half-rate application.

Winter application. Based on observations, the risk
of nitrogen loss through volatilization associated with
winter application of urea for com on frozen soils is
too great to consider the practice unless one is assured
of at least 0.5 inch of precipitation occurring within 4

Table 11.15. Effect on Corn Yield of Injector
Spacing of Ammonia Applied at
Different Rates of Nitrogen at DeKalb

Nitrogen (lb /A)

Injector spacing (in.)

120

180

240

= no data collected.

30
60

171

170

yield (bu/A)

176
171

181
182

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Figure 11.10. Schematic of every-other-row, sidedress nitrogen injection. The outside two injectors are set at one-half rate
because the injector runs between those two rows twice.

to 5 days after application. Yield loss of 30 to 40 bush-
els per acre occurred when urea was surface-applied
in late February to frozen soils (Table 11.16). In most
years, application of urea on frozen soils has been an
effective practice for wheat.

Aerial application. Under some conditions, aerial
application of dry urea results in increased yield. This
practice should not be considered a replacement for
normal nitrogen application but rather an emergency
treatment in situations where com is too tall for nor-
mal applicator equipment. Aerial application of nitro-
gen solutions on growing com is not recommended,
as extensive leaf damage likely results if the applica-
tion rate is greater than 10 pounds of nitrogen per acre.

Which Nitrogen Fertilizer?

Most of the nitrogen fertilizer materials available for
use in Illinois provide nitrogen in the combined

form of ammonia, ammonium, urea, and nitrate
(Table 11.17). For many uses on a wide variety
of soils, all forms are likely to produce about the
same yield — provided that they are properly applied.

Ammonia. Nitrogen materials that contain free
ammonia (NH^), such as anhydrous ammonia and
low-pressure solutions, must be injected into the soil
to avoid loss of ammonia in gaseous form. Upon injec-
tion into the soil, ammonia quickly reacts with water
to form ammonium (NH^. In this positively charged
form, the ion is not susceptible to gaseous loss be-
cause it is temporarily attached to the negative
charges on clay and organic matter. Some of the am-
monia reacts with organic matter to become a part of
the soil humus.

On silt loam or soils with finer textures, ammonia
moves about 4 inches from the point of injection. On
more coarsely textured soils, such as sands, ammonia

Table 11.16. Effect of Source, Time, and Rate of Nitrogen Fertilizer on Corn Yield

Nitrogen treatment

Nitrogen (lb /A)

Fertilizer material

Time of application

Method of application

120 180

240

Winter
Spring
Spring

Surface

Incorporated

Injected

uipJH (hnIA )

None (control)

Urea

Anhydrous ammonia

\jiciu \uuir\./

94 123
140 157
149 157

126
165
158

11 • SOIL TESTING AND FERTILITY

Table 11.17. Composition of Various Nitrogen Fertilizers

Material

Total
nitrogen

Percent of total nitrogen as

Ammonia Ammonium Nitrate Urea

Salting out Weight of solu-
temperature tion per gallon

Anhydrous ammonia 82

Ammonium nitrate 34

Ammonium sulfate 21

Urea 46

Urea-ammonium nitrate 28

Urea-ammonium nitrate 32

100

5.90

—

100

—

100

—

-1

10.70

11.05

may move 5 to 6 inches from the point of injection. If
the depth of application is shallower than the dis-
tance of movement, some ammonia may move slowly
to the soil surface and escape as a gas over several
days. On coarse-textured (sandy) soils, anhydrous
ammonia should be placed 8 to 10 inches deep,
whereas on silt-loam soils, the depth of application
should be 6 to 8 inches.

ArJ^iydrous ammonia is lost more easily from shal-
low placement than is ammonia in a low-pressure
solution. Nevertheless, low-pressure solutions con-
tain free ammonia and thus need to be incorporated
into the soil at a depth of 2 to 4 inches.

Ammonia should not be applied to soils having a
physical condition that would prevent closure of the
applicator knife track. Ammonia will escape to the
atmosphere whenever there is a direct opening from
the point of injection to the soil surface.

Seedlings can be damaged if proper precautions
are not taken when applying nitrogen materials that
contain or form free ammonia. Damage may occur
if nitrogen material is injected into soils that are so
wet that the knife track does not close properly. If
the soil dries rapidly, this track may open. Damage
can also result from applying nitrogen material to
excessively dry soils, which allow the ammonia to
move large distances before being absorbed. Finally,
damage to seedlings can be caused by using a shal-
lower application than that suggested in the preced-
ing paragraph. Generally, delaying planting 3 to
5 days after applying fertilizer will cause little, if
any, seedling damage. While it is extremely rare,
damage from fall-applied ammonia to com seeded
the next spring has been observed. The situations
where this has occurred have been characterized by
application in late fall on soils that were wet
enough that serious compaction resulted along the
side walls of the knife track. This was followed by
an extremely dry winter and spring. When the sur-
face soils dried in the spring, the soil cracked along

the knife track and allowed the ammonia to escape
into the seed zone.

Ammonium nitrate. Half of the nitrogen con-
tained in ammonium nitrate is in the ammonium
form, and half is in the nitrate form. The part
present as ammonium attaches to the negative
charges on the clay and organic-matter particles and
remains in that state until it is used by the plant or
converted to the nitrate ions by microorganisms
present in the soil. Because 50 percent of the nitro-
gen is present in the nitrate form, this product is
more susceptible to loss from both leaching and
denitrification. Thus, ammonium nitrate should not
be applied to sandy soils because of the likelihood of
leaching, nor should it be applied far in advance of
the time when the crop needs the nitrogen because
of possible loss through denitrification.

Urea. The chemical formula for urea is CO(NH2)2.
In this form, it is very soluble and moves freely up
and down with soil moisture. After being applied to
the soil, urea is converted to ammonia, either chemi-
cally or by the enzyme urease. The speed with which
this conversion occurs depends largely on tempera-
ture. Conversion is slow at low temperatures but
rapid at temperatures of 55°F or higher.

If the conversion of urea occurs on the soil surface
or on the surface of crop residue or leaves, some of
the resulting ammonia will be lost as a gas to the at-
mosphere. The potential for loss is greatest when the
following conditions exist:

• Temperatures are greater than 55°F. Loss is less
likely with winter or early spring applications, but
results show that the loss may be substantial if the
materials remain on the surface of the soil for sev-
eral days.

• Considerable crop residue remains on soil surface.

• Application rates are greater than 100 pounds of
nitrogen per acre.

100

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 11.18. Effect of Source of Nitrogen on Yield for No-Till Com

Application

Rate

ab/A)

Yield (bu/A)
at Brownstown

(1974-77 avg)

Yield (bu/A)
at Dixon Springs

Nitrogen source

Date

Method

1974 1975

Control

Ammonium nitrate

Urea

Ammonium nitrate

Urea

Early spring
Early spring
Early June
Early June

Surface
Surface
Surface
Surface

0
120
120
120
120

52
96

106

132 160
106 166
151 187
125 132

• The soil surface is moist and rapidly drying.

• Soils have a low cation-exchange capacity.

• Soils are neutral or alkaline in reaction.

Research conducted at both the Brownstown and
Dixon Springs research centers has shown that sur-
face application of urea for no-till com did not yield
as well as ammonium nitrate in most years (Table
11.18). In years when a rain was received within 1 or 2
days after application, urea resulted in as good a yield
increase as did ammonium nitrate (that is, compared
to results from early spring application of ammonium
nitrate at Dixon Springs in 1975). In other studies,
urea that was incorporated soon after application
yielded as well as ammonium nitrate.

Urease inhibitor. Chemical compound N-(n-butyl)
thiophosphoric triamide, commonly referred to as
NBPT and sold under the trade name AgrotaiN, has
been shown to inhibit the urease enzyme that con-
verts urea to ammonia. This material can be added to
urea-ammonium nitrate solutions or to urea. Addi-
tion of this material will reduce the potential for vola-
tilization of surface-applied, urea-containing prod-
ucts. Experimental results collected around the Com
Belt over the last several years have shown an aver-
age increase of 4.3 bushels per acre when applied
with urea and 1.6 bushels per acre when applied with
urea-ammonium nitrate solutions. Where nonvolatile
nitrogen treatments resulted in a higher yield than
unamended urea, addition of the urease inhibitor
increased yield by 6.6 bushels per acre for urea and
by 2.7 bushels per acre for urea-ammonium nitrate
solutions. In a year characterized by a long dry period
in the spring, NBPT with urea resulted in yield in-
creases of 20 bushels per acre as compared to urea
alone in related experiments in Southern Illinois and
Missouri (Tables 11.19 and 11.20). These results clearly
show the importance of proper urea management
techniques in years when precipitation is not received
soon after surface application of urea.

Urease inhibitors have the greatest potential for
benefit when urea-containing materials are surface-
applied without incorporation at 50°F or higher. The
potential is even greater if there is significant residue
remaining on the soil surface. In situations where the
urea-containing materials can be incorporated within
2 days after application, either with a tillage operation
or with adequate rainfall, the potential for benefit
from a urease inhibitor is very low.

Table 11.19. Effect of Nitrogen Source, Rate, and
NBPT on No-Till Com Vield in
Southern Illinois

Yield (bu/A) by nitrogen

source

Ammonium

Urea

N (lb /A)

nitrate

Urea

+ NBPT

114

110

120

118

115

160

114

105

122

Source: Southern Illinois University, Dr. E. C. Varsa. 1992.

Table 11.20. Effect of Nitrogen Source, Rate, and
NBPT on No-Till Com Yield in
Missouri

Yield (bu/A) by nitrogen source

N (lb/A)

Ammonium
nitrate

Urea

Urea
+ NBFf

180

83
164
203

132
173

151
196

Source: University of Missouri.

11 • SOIL TESTING AND FERTILITY

101

Ammonium sulfate. The compound ammonium
sulfate ([NH^ ]2^^4) supplies all of the nitrogen in the
ammonium form. As a result, it theoretically has a
slight advantage over products that supply a portion
of their nitrogen in the nitrate form, because the am-
monium form is not susceptible to leaching or denitri-
fication. However, this advantage is usually short-
lived because all ammonium-based materials quickly
convert to nitrate once soil temperatures are favorable
for activity of soil organisms (above 50°F).

In contrast to urea, there is little risk of loss of the
ammonium contained in ammonium sulfate through
volatilization. As a result, it is an excellent material for
surface application on fields that will be planted no-
till that have high-residue levels. As with any other
ammonium-based material, there is a risk associated
with surface application in years in which there is in-
adequate precipitation to allow for adequate root ac-
tivity in the fertilizer zone.

Ammonium sulfate is an excellent material for
use on soils that may be deficient in both nitrogen
and sulfur. However, applying the material at a rate
sufficient to meet the nitrogen need will cause
overapplication of sulfur. That is not of concern
because sulfur is mobile and moves out of the pro-
file quickly. Fortunately, there is no known environ-
mental problem associated with sufate sulfur in
water supplies.

Most ammonium sulfate available in the market-
place is a by-product of the steel, textile, or lysine in-
dustry and is marketed as either a dry granulated ma-
terial or a slurry.

Ammonium sulfate is more acidifying than any
of the other nitrogen materials on the market. As
a rough rule, ammonium sulfate requires about
9 pounds of lime per pound of nitrogen applied,
compared to 4 pounds of lime per pound of nitrogen
from ammonia or urea. The extra acidity is of no
concern as long as the soil is monitored for pH every
4 years.

In areas where fall application is acceptable, am-
monium sulfate could be applied in late fall (after
temperatures have fallen below SO^F) or in winter on
frozen ground where the slope is less than 5 percent.

Nitrogen solutions. The nonpressure nitrogen so-
lutions that contain 28 to 32 percent nitrogen consist
of a mixture of urea and ammonium nitrate. Typi-
cally, half of the nitrogen is from urea, and the other
half is from ammonium nitrate. The constituents of
these compounds will undergo the same reactions as
described earlier for the constituents applied alone.

Experiments at DeKalb have shown a yield differ-
ence between incorporated and unincorporated ni-
trogen solutions that were spring-applied (Table

Table 11.21. Effect of Source, Method of Application,
and Rate of Spring- Applied Nitrogen on
Corn Yield, DeKalb

Yield (bu/A)

Carrier and

application method

(lb/A)

1976

1977

Avg

None

Ammonia

103

138

120

28% N solution.

incorporated

132

115

28% N solution.

unincorporated

126

106

Ammonia

160

111

164

138

28% N solution.

incorporated

160

107

157

132

28% N solution.

unincorporated

160

155

126

Ammonia

240

112

164

138

28% N solution.

incorporated

240

101

164

132

28% N solution.

unincorporated

240

153

122

LSD,/

9.1

5.2

^Differences greater than the LSD value are statistically
significant.

11.21). This difference associated with method of ap-
plication is probably caused by volatilization loss of
some nitrogen from the surface-appUed solution con-
taining urea.

The effect on yield of postemergence application of
nitrogen solutions and atrazine when com plants are
in the three-leaf stage was evaluated in Minnesota.
The results indicated that yields were generally de-
pressed when the nitrogen rate exceeded 60 pounds
per acre. Leaf bum was increased by increasing the
nitrogen rate, including atrazine with the nitrogen,
and by hot, clear weather conditions.

Phosphorus and Potassium

Inherent Availability

Illinois has been divided into three regions in terms of
the inherent phosphorus-supplying power of the soil
below the plow layer in dominant soil types (Figure
11.11).

High phosphorus-supplying power means that
the soil test for available phosphorus (P, test) is
relatively high and conditions are favorable for good

102

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

root penetration and branching throughout the soil
profile.

Low phosphorus-supplying power may be caused
by one or more factors:

1. A low supply of available phosphorus in the soil
profile because (a) the parent material was low in
phosphorus; (b) phosphorus was lost in the soil-
forming process; or (c) the phosphorus is made un-
available by high pH (calcareous) material.

2. Poor internal drainage that restricts root growth.

3. A dense, compact layer that inhibits root penetra-
tion or branching.

4. Shallowness to bedrock, sand, or gravel.

5. Droughtiness, strong acidity, or other conditions
that restrict crop growth and reduce rooting depth.

Regional differences in phosphorus-supplying
power are shown in Figure 11.11. Parent material and
degree of weathering were the primary factors con-
sidered in determining the various regions.

The "high" region is in western Illinois, where the
primary parent material was more than 4 to 5 feet of
loess that was high in phosphorus content. The soils
are leached of carbonates to a depth of more than SVi
feet, and roots can spread easily in the moderately
permeable profiles.

The "medium" region is in central Illinois, with
arms extending into northern and southern Illinois.
The primary parent material was more than 3 feet of
loess over glacial till, glacial drift, or outwash. Some
sandy areas with low phosphorus-supplying power
occur in the region. In comparison with the high-
phosphorus region, more of the soils are poorly
drained and have less available phosphorus in the
subsoil and substratum horizons. Carbonates are
likely to occur at shallower depths than in the "high"
region. The soils in the northern and central areas are
generally free of root restrictions, whereas soils in the
southern arm are more likely to have root-restricting
layers within the profile. The phosphorus-supplying
power of soils of the region is likely to vary with natu-
ral drainage. Soils with good internal drainage are
likely to have higher levels of available phosphorus in
the subsoil and substratum. If internal drainage is fair
or poor, phosphorus levels in the subsoil and substra-
tum are likely to be low or medium.

In the "low" region in southeastern Illinois, the
soils were formed from IVi to 7 feet of loess over
weathered Illinoisan till. The profiles are more highly
weathered than in the other regions and are slowly or
very slowly permeable. Root development is more re-
stricted than in the "high" or "medium" regions. Sub-

Figure 11.11. Subsoil phosphorus-supplying power in
Illinois.

soil levels of phosphorus may be rather high by soil
test in some soils of the region, but this is partially off-
set by conditions that restrict rooting.

In the "low" region in northeastern Illinois, the
soils were formed from thin loess (less than 3 feet)
over glacial till. The glacial till, generally low in avail-
able phosphorus, ranges in texture from gravelly
loam to clay in various soil associations of the region.
In addition, shallow carbonates further reduce the
phosphorus-supplying power of the soils of the re-
gion. Further, high bulk density and slow permeabil-
ity in the subsoil and substratum restrict rooting in
many soils of the region.

The three regions are delineated to show broad dif-
ferences among them. Parent material, degree of
weathering, native vegetation, and natural drainage
vary within a region and cause variation in the soil's
phosphorus-supplying power. It appears, for ex-

n • SOIL TESTING AND FERTILITY

103

ample, that soils developed under forest cover have
more available subsoil phosphorus than those devel-
oped under grass.

Illinois is divided into two general regions for po-
tassium, based on cation-exchange capacity (Figure
11.12). Important differences exist, however, among
soils within these general regions because of differ-
ences in these factors:

1. The amount of clay and organic matter, which in-
fluences the exchange capacity of the soil.

2. The degree of weathering of the soil material,
which affects the amount of potassium that has
been leached out.

3. The kind of clay mineral.

4. Drainage and aeration, which influence uptake of
potassium.

5. The parent material from which the soil was
formed.

Soils with a cation-exchange capacity less than
12 meq/100 grams are classified as having low capac-
ity. These soils include the sandy soils because miner-
als from which they were developed are inherently
low in potassium. Sandy soils also have very low cat-
ion-exchange capacities and thus do not hold much
reserve potassium.

Silt-loam soils in the "low" area in southern Illinois
(claypans) are relatively older in terms of soil devel-
opment; consequently, much more of the potassium
has been leached out of the rooting zone. Further-
more, wetness and a platy structure between the sur-
face and subsoil may interfere with rooting and with
potassium uptake early in the growing period, even
though roots are present.

Rate of Fertilizer Application

Minimum soil-test levels required to produce opti-
mum crop yields vary depending on the crop to be
grown and the soil type (Figures 11.13 and 11.14).
Near-maximum yields of com and soybeans are
obtained when levels of available phosphorus are
maintained at 30, 40, and 45 pounds per acre for soils
in the high, medium, and low phosphorus-supplying
regions, respectively. Potassium soil-test levels at
which optimum yields of these two crops are at-
tained are 260 and 300 pounds of exchangeable po-
tassium per acre for soils in the low and high cation-
exchange capacity regions, respectively. Because
phosphorus, and on most soils also potassium, will
not be lost from the soil system other than through
crop removal or soil erosion and because these are
minimum values required for optimum yields, it is

Figure 11.12. Cation-exchange capacity of Illinois soils.
The shaded areas are sands with low cation-exchange
capacity.

recommended that soil-test levels be built up to 40,
45, and 50 pounds per acre of phosphorus for soils in
the high, medium, and low phosphorus-supplying
regions, respectively.

Depending on the soil-test level, the amount of
fertilizer recommended may be buildup plus mainte-
nance, maintenance, or no fertilizer. The buildup is
the amount of material required to increase the soil
test to the desired level. The maintenance addition is
the amount required to replace the amount that will
be removed by the crop to be grown.

Buildup plus maintenance. When soil-test levels
are below the desired values, it is suggested that
enough fertilizer be added to build the test to the de-
sired goal and to replace what the crop will remove.
At these test levels, the yield of the crop will be af-
fected by the amount of fertilizer applied that year.

104

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

110

/' Wheat, oats, alfalfa, clover

P region

subsoil

phosphorus

High

Medium

Low

P, test (pounds/acre)

Figure 11.13. Relationship between expected yield and
soil-test phosphorus.

Maintenance. When the soil-test levels are be-
tween the minimum and 20 pounds above the mini-
mum for phosphorus (that is, 40 to 60, 45 to 65, or 50
to 70) or between the minimum and 100 pounds

above the minimum for potassium (260 to 360 or 300
to 400), apply enough to replace what the crop to be
grown is expected to remove. The yield of the cur-
rent crop may not be affected by the fertilizer addi-
tion, but the yield of subsequent crops will be ad-
versely affected if the materials are not applied to
maintain soil-test levels.

No fertilizer. Although it is recommended that
soil-test levels be maintained slightly above the level
at which optimum yield would be expected, it would
not be economical to attempt to maintain excessively
high values. Therefore, it is suggested that no phosphorus
be applied ifP^ values are higher than 60, 65, and 70 for
soils in the high, medium, and low phosphorus-supplying
regions, respectively. No potassium is suggested if test
levels are above 360 and 400 for the low and high cation-
exchange capacity regions, unless crops that remove large
amounts of potassium (such as alfalfa or corn silage) are
being grown. When soil-test levels are between 400
and 600 pounds per acre of potassium and com si-
lage or alfalfa is being grown, the soil should be
tested every 2 years instead of every 4, or mainte-
nance levels of potassium should be added to ensure
that soil-test levels do not fall below the point of
optimum yields.

Oats, wheat

Crop yields

dependent

on K fertilizer

Subsequent I /^ • u

7 , . I Crop yields

crop yields - .^ j »

. . 4. I not dependent

dependent i ^ , ....

w , ^,,. on K fertilizer
on K fertilizer

use

use I

1 ,

100

120

200 260 300

K test, low CEC K region

240 300

K test, high CEC K region

Figure 11.14. Relationship between expected yield and soil-test potassium.

360

400

500

11 • SOIL TESTING AND FERTILITY

105

Consequences of omitting fertilizer. The impact
of eliminating phosphorus or potassium fertilizer on
yield and soil-test level will depend on the initial soil
test and the number of years that applications are
omitted. In a recent Iowa study, elimination of phos-
phorus application for 9 years decreased soil-test lev-
els from 136 to 52 pounds per acre, but yields were
not adversely affected in any year as compared to
plots where soil-test levels were maintained
(Figure 11.15). In the same study, elimination of
phosphorus for the 9 years when the initial soil test
was 29 resulted in a decrease in soil-test level to 14
and a decrease in yield to 70 percent of the yield
: obtained when adequate fertility was supplied.
Elimination of phosphorus at an intermediate soil-
test level had little impact on yield but decreased the
soil-test level from 67 to 26 pounds per acre over the
9 years. These as well as similar Illinois results indi-
cate little if any potential for a yield decrease if phos-
phorus application was eliminated for 4 years on
soils that have a phosphorus test of 60 pounds per
acre or higher.

Phosphorus

Buildup. Research has shown that, as an average for
Illinois soils, 9 pounds of P^Og per acre is required to
increase the Pj soil test by 1 pound. The recom-

140

4 6

Year

Figure 11.15. Effect of elimination of P fertilizer on P^ soil
test

Table 11.22. Amount of Phosphorus (PjOj) Required
to Build Up the Soil

Lb /A of P^Oj to apply each year for soils

with

supplying power rated

P, test

(lb/A)

Low

Medium

High

103

NOTE: Amounts are based on buildup over 4 years. Nine
pounds of PjOj per acre are required to change the Pj soil
test 1 pound.

mended rate of buildup phosphorus is thus nine
times the difference between the soil-test goal and the
actual soil-test value. The amount of phosphorus rec-
ommended for buildup over 4 years for various soil-
test levels is presented in Table 11.22.

Because the 9-pound rate is an average for Illinois
soils, some soils will fail to reach the desired goal in 4
years with P^O^ applied at this rate, and others will
exceed the goal. It is recommended that each field be
retested every 4 years.

In addition to the supplying power of the soil, the
crop to be grown influences the optimum soil-test
value. For example, the phosphorus soil-test level
required for optimum yields of wheat and oats (Fig-
ure 11.13) is considerably higher than that required
for com and soybean yields, partly because wheat

106

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 11.23. Maintenance Fertilizer Required for Various Crop Yields

Yield

per acre

PP3(lb/A)

K^OClb/A)

Yield per acre

PA (lb/A)

K,CH(lb/A)

Com

grain (bu)

Com silage (bu; tons)

90; 18

126

100

100; 20

140

110

110; 22

154

120

120; 24

168

130

130; 26

182

140

140; 28

196

150

150; 30

210

160

170

Wheat (bu)

27b

180

190

200

50
60

54
63

18
21

Oats (bu)

19"

100

110

100

Alfalfa, grass.

110

or alfalfa-grass

120

mixtures (tons)

130

100

140

150

48
60

200
250

Soybeans (bu)

300

350

400

108

450

120

500

104

117

100

130

*If annual application is chosen, potassium application will be 1.5 times the values shown.
"Values given are 1.5 times actual P^Oj removal for wheat and oats.

and com have different phosphorus uptake patterns.
Wheat requires a large amount of readily available
phosphorus in the fall, w^hen the root system is feed-
ing primarily from the upper soil surface. Phospho-
rus is taken up by com until the grain is fully devel-
oped, so subsoil phosphorus is more important in
interpreting the phosphorus test for com than for
vy^heat. To compensate for the higher phosphorus require-
ments of wheat and oats, it is suggested that 1.5 times the
amount of expected phosphorus removal be applied prior to
seeding these crops. This correction has already been in-

cluded in the maintenance values listed for wheat and oats
in Table 11.23.

Maintenance. In addition to adding fertilizer to
build up the soil test, add sufficient fertilizer each
year to maintain a specified soil-test level. The
amount of fertilizer required to maintain the soil-test
value is the amount removed by the harvested por-
tion of the crop (Table 11.23). The only exception to
this guideline is that the maintenance value for wheat
and oats is 1.5 times the amount of phosphorus (PjOg)
removed by the grain. This correction has already

11 • SOIL TESTING AND FERTILITY

107

been accounted for in the maintenance values given
in Table 11.23.

POTASSIUM

As indicated, phosphorus usually remains in the soil
unless it is removed by a growing crop or by erosion;
thus soil levels can be built up as described. Experi-
ence during recent years indicates that on most soils
potassium tends to follow the buildup pattern of
phosphorus, but on other soils, soil-test levels do not
build up as expected. Because of this, options for both
buildup plus maintenance and annual application are
provided.

Producers whose soils have one or more of the fol-
lowing conditions should consider annual application:

1. Soils for which past records indicate that soil-test
potassium does not increase when buildup applica-
tions are applied.

2. Sandy soils that do not have a capacity large
enough to hold adequate amounts of potassium.

3. Agricultural lands having an unknown or a very
short tenure arrangement.

On all other fields, buildup plus maintenance is
suggested.

Rate of Fertilizer Application

Buildup. The only significant loss of soil-applied
potassium is through crop removal or soil erosion. It
is thus recommended that soil-test potassium be built
up to values of 260 and 300 pounds of exchange-
able potassium for soils in the low and high cation-
exchange capacity region, respectively. These values
are slightly higher than that required for maximum
yield, but as in the recommendations for phosphorus,
this will ensure that potassium availability will not
limit crop yields (Figure 11.14).

Research has shown that 4 pounds of K^O is re-
quired on average to increase the soil test by 1 pound.
Therefore, the recommended rate of potassium appli-
cation for increasing the soil-test value to the desired
goal is four times the difference between the soil-test
goal and the actual value of the soil test.

Tests on soil samples that are taken before May 1 or
after September 30 should be adjusted downward as
follows: subtract 30 for the dark-colored soils in cen-
tral and northern Illinois; subtract 45 for the light-
colored soils in central and northern Illinois and for
fine-textured bottomland soils; subtract 60 for the
medium- and light-colored soils in southern Illinois.
Annual rates of buildup of potassium application

Table 11.24. Amount of Potassium (K^O) Required
to Build Up the Soil

Lb /A of K^O to apply each year for soils

with cation

-exchange capacity rated

Ktest^

Low

High

(lb/A)

(< 12 meq/100 g soil) (>12

: meq/100 g soil)

210

250

200

240

190

230

180

220

170

210

100

160

200

110

150

190

120

140

180

130

170

140

120

160

150

110

150

160

100

140

170

130

180

120

190

110

200

100

210

220

230

240

250

260

270

280

290

300

NOTE: Amounts are based on buildup over 4 years. Four
pounds of KjO per acre are required to change the
potassium test 1 pound.

^Tests on soil samples taken before May 1 or after
September 30 should be adjusted downward:

Subtract 30 pounds for dark-colored soils in central and
northern Illinois.

Subtract 45 pounds for light-colored soils in central and
northern Illinois and for fine-textured bottomland soils.

Subtract 60 pounds for medium- and light-colored soils
in southern Illinois.

108

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

recommended for a 4-year period for various soil-test
values are presented in Table 11.24.

Wheat is not very responsive to potassium unless
the soil-test value is less than 100. Because wheat is
usually grown in rotation with com and soybeans, it
is suggested that the soils be maintained at the opti-
mum available potassium level for com and soybeans.

Maintenance. As with phosphorus, the amount of
fertilizer required to maintain the soil-test value
equals the amount removed by the harvested portion
of the crop (Table 11.23).

Annual application. If soil-test levels are below
the desired buildup goal, apply potassium fertilizer
annually at an amount 1.5 times the potassium con-
tent in the harvested portion of the expected yield.
If levels are only slightly below desired buildup
levels, so that buildup and maintenance are less than
1.5 times removal, add the lesser amount. Continue
to monitor the soil-test potassium level every 4 years.

If soil-test levels are within a range from the de-
sired goal to 100 pounds above the desired potassium
goal, apply enough potassium fertilizer to replace
what the harvested yield will remove.

Buildup plus maintenance and annual application
each have advantages and disadvantages. In the short
run, the annual option will likely be less costly. In the
long run, the buildup approach may be more economi-
cal. In years of high income, tax benefits may be ob-
tained by applying high rates of fertilizer. Also, in peri-
ods of low fertilizer prices, the soil can be built to higher
levels that in essence bank the materials in the soil for
use at a later date when fertilizer prices are higher. Pro-
ducers using the buildup system are insured against
yield loss that may occur in years when weather condi-
tions prevent fertilizer application or in years when fer-
tilizer supplies are not adequate. The primary advan-
tage of the buildup concept is the slightly lower risk of
potential yield reduction that may result from lower an-
nual fertilizer rates. This is especially true in years of ex-
ceptionally favorable growing conditions. The primary
disadvantage of the buildup option is the high cost of
fertilizer in the initial buildup years.

Examples of how to figure phosphorus and potas-
sium fertilizer recommendations follow.

Example 1. Continuous com with a yield goal of
140 bushels per acre:

(a) Soil-test results

Soil region

Pj30

High

K250

High

(b) Fertilizer recommendation (Ib/A/year)

Pa03

Buildup 22 (Table 11.22)

Maintenance 60 (Table 11.23)

Total

50 (Table 11.24)
39 (Table 11.23)

Example 2. Corn-soybean rotation with a yield goal
of 140 bushels per acre for com and 40 bushels per
acre for soybeans:

(a) Soil-test results

Soil region

P,20
K200

Low
Low

(b) Fertilizer recommendation (Ib/A/year)

Corn

Buildup
Maintenance

Total

Buildup
Maintenance

Total

68
60

128

68
34

102

Soybeans

60
39

112

Note that buildup recommendations are indepen-
dent of the crop to be grown, but maintenance
recommendations are directly related to the crop to
be grown and the yield goal for the particular crop.

Example 3. Continuous com with a yield goal of
150 bushels per acre:

(a) Soil-test results

Soil region

P, 90
K420

Low

(b) Fertilizer recommendation (Ib/A/year)

Buildup
Maintenance

Total

Note that soil-test values are higher than those sug-
gested; thus no fertilizer is recommended. Retest the
soil after 4 years to determine fertility needs.

n • SOIL TESTING AND FERTILITY

109

Example 4. Corn-soybean rotation with a yield goal
of 120 bushels per acre for com and 35 bushels per
acre for soybeans:

(a) Soil-test results

Soil region

Pj20
K180

Low

Low (soil test
does not increase
as expected)

(b) Fertilizer recommendation (Ib/A/year)

K^O

Corn

Buildup
Maintenance

Total

Buildup
Maintenance

Total

120

68
30

51 (34 X 1.5)

Soybeans

69 (46 X 1.5)

For farmers planning to double-crop soybeans after
wheat, it is suggested that phosphorus and potassium
fertilizer required for both the wheat and soybeans be
applied before seeding the wheat. This practice re-

I duces the number of field operations at planting time
and hastens the planting operation.

The maintenance recommendations for phosphorus

i and potassium in a double-crop wheat and soybean
system are presented in Tables 11.25 and 11.26, respec-
tively. Assuming a wheat yield of 50 bushels per acre
followed by a soybean yield of 30 bushels per acre,
the maintenance recommendation would be 71
pounds of P^Og and 54 pounds of K^O per acre.

Computerized Recommendations

Soil fertility recommendations have been incorpo-
rated into a microcomputer program that utilizes the
soil-test information, soil type and characteristics,
cropping and management history, cropping plans,
and yield goals to develop recommendations for lime,
nitrogen, phosphorus, and potassium. This program,
called Soil Plan, groups similar fertilizer recommenda-
tions and provides a map showing where each recom-
mendation should be implemented within the field.
The user can alter the map to show the desired spread
pattern. The program also indicates the potential im-
pact of altering the recommendation on crop yield.

Table 11.25. Maintenance Phosphorus Required for
Wheat-Soybean Double-Crop System

Wheat yield
(bu/A)

Lb /A of P^Oj required for
desired soybean yield (bu/A)

30
40
50
60
70
80

53
62
71
80
89

53
62
71
80
89
98

61
70
79
88
97
106

69
78
87
96
105
114

105

114

123

Further information about this program may be ob-
tained from IlliNet Software, 548 Bevier Hall, 905 S.
Goodwin Avenue, Urbana, IL 61801.

Time of Application

Although the fertilizer rates for buildup and mainte-
nance in Tables 11.22 through 11.24 are for an annual
application, producers may apply enough nutrients in
any 1 year to meet the needs of the crops to be grown
in the succeeding 2 to 3 years.

Phosphorus and potassium fertilizers may be ap-
plied in the fall to fields that will not be fall-tilled,
provided that the slope is less than 5 percent. Do not
fall-apply fertilizer to fields that are subject to rapid
runoff. When the probability of runoff loss is low, soy-
bean stubble need not be tilled solely for the purpose
of incorporating fertilizer. This statement holds true
when ammoniated phosphate materials are used as well be-
cause the potential for volatilization of nitrogen from am-
moniated phosphate materials is insignificant.

For perennial forage crops, broadcast and incorpo-
rate all of the buildup and as much of the mainte-
nance phosphorus as economically feasible before
seeding. On soils with low fertility, apply 30 pounds
of phosphate (P2O5) per acre using a band seeder. Us-
ing a band seeder, it is safe to apply a maximum of 30
to 40 pounds of potash (K^O) per acre in the band
with the phosphorus. Up to 600 pounds of K^O per
acre can be safely broadcast in the seedbed without
damaging seedlings.

Applications of phosphorus and potassium top-
dressed on perennial forage crops may be made at
any convenient time. Usually this will be after the first
harvest or in September.

110

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 11.26. Maintenance Potassium Required for
Wheat-Soybean Double-Crop System

Lb /A of KjO required for

Wheat yield
(bu/A)

desired

soybean

yield (bu/A)

50 60

74 87

77 90

80 93

83 96

86 99

89 102

High Water Solubility of Phosphorus

The water solubility of the P^Og listed as available on
the fertilizer label is of little importance under typical
field crop and soil conditions on soils with medium to
high levels of available phosphorus when recom-
mended rates of application and broadcast placement
are used. Due to rapid interaction of phosphorus fer-
tilizer with iron and aluminum, phosphorus is tightly
bound in the soil such that water solubility does not
imply great movement or leaching.

For some situations, water solubility is important:

1. For band placement of a small amount of fertilizer
to stimulate early growth, at least 40 percent of the
phosphorus should be water-soluble for applica-
tion to acidic soils and, preferably, 80 percent for
calcareous soils. As shown in Table 11.27, the phos-
phorus in nearly all fertilizers commonly sold in
Illinois is highly water-soluble. Phosphate water
solubility above 80 percent has not been shown to
increase yield any farther than water solubility of
at least 50 percent.

2. For calcareous soils, a high degree of solubility in
water is desirable, especially on soils that are shown
by soil test to be low in available phosphorus.

Phosphorus and the Environment

Phosphorus has been identified as an important pol-
lutant to surface waters. At very low concentrations,
it can increase eutrophication of lakes and streams,
which leads to problems with their use for fisheries,
recreation, industry, and drinking water. Although
eutrophication is the natural aging process of lakes
and streams, human activities can accelerate this pro-
cess by increasing the concentration of nutrients flow-
ing into water systems. Since phosphorus is the ele-
ment most often limiting eutrophication in natural
water bodies, controlling its input into lakes and

streams is very important. At the present time, there
are no established criteria for phosphorus in water.
The United States Environmental Protection Agency
is in the process of developing a strategy to adopt nu-
trient criteria as part of state water quality standards.
There are concerns that agricultural runoff and ero-
sion from soils may be major contributors to eutrophi-
cation. While this loss may not be of economic sig-
nificance to farmers, it may create economic impacts
on water quality. Even though phosphorus loss from
agricultural fields may not be of economic signifi-
cance and even though there are no standards estab-
lished for phosphorus runoff, it is in the best interest
of all in agriculture to minimize the amount of phos-
phorus loss. While additional research will likely lead
to new and better ways to minimize phosphorus loss,
the following practices are already known to help:

1. Do not maintain excessively high phosphorus soil
test levels. Research has demonstrated that the
higher the soil-test level, the greater the loss of dis-
solved phosphorus (Figure 11.16). This relation-
ship does vary somewhat depending on soil type.
Environmental decisions regarding phosphorus ap-
plications should not be made solely on phospho-
rus soil-test levels. Rather, the decision should also
include such factors as distance from a significant
lake or stream, infiltration rate, slope, and residue
cover. Additional work is being done to develop a
system that more accurately predicts the vulner-
ability to phosphorus loss on a field-by-field basis.
At this time, the research database is inadequate to
establish a soil-test level that can be used for envi-
ronmental purposes. Soil-test procedures were de-
signed to predict where phosphorus was needed;

Table 11.27. Water Solubility of Some Common
Processed-Phosphate Materials

Percent

Material

water-soluble

Ordinary

superphosphate 0-20-0

16-22

Triple superphosphate

44-^7

Mono-ammonium

phosphate 11-48-0

46-48

100

Diammonium

phosphate 18-46-0

100 '

Ammonium

polyphosphate

10-34-0, 11-37-0

34-37

100

11 • SOIL TESTING AND FERTILITY

111

Table 11.28. Suggested Soil-Test Levels for
Secondary Nutrients

Levels adequate for crop
production (lb /A)

I Soil type Calcium Magnesium

Sandy
Silt loam

400
800

60-75
150-200

Rating

Sulfur

(Ib/A)

Very low
Low

Response
unlikely

0-12

12-22

they were not designed to predict environmental
problems. One possible problem with using soil-
test values to predict environmental problems is in
sample depth. Normally samples are collected to a
7-inch depth for prediction of nutritional needs.
For environmental purposes, it would often be bet-
ter to collect the samples from a 1- or 2-inch depth,
which is the depth that will influence phosphorus
runoff. Another potential problem is within field
soil-test level variability in relation to the dominant
runoff and sediment-producing zones.

2. Maintain buffer strips at the point where water
leaves the field.

3. Minimize erosion. Although this may not reduce
the potential for loss of dissolved phosphorus, it
will reduce the potential for loss of total phosphorus.

4. Match nutrient applications to crop needs. This
will minimize the potential for excessive buildup of

0.6

0.5
3 0.4

0.3

> 0.2

Cropped land

0.1

Low

Very high

Soil-test value

Figure 11.16. Relationship between soil-test value and
dissolved phosphorus in runoff.

Table 11.29. Average Yields at Responding and

Nonresponding Zinc and Sulfur Test
Sites, 1977-79

Yield

from

zinc-

sulfur-

untreated

treated

plots

Sites

(bu/A)

Responding sites

Low-sulfur soil

140.0

. . •

151.2

Low-zinc soil

150.6

164.7

Nonresponding

sites

147.6

146.2

148.2

phosphorus soil tests and reallocate phosphorus
sources to fields or areas where they can produce
agronomic benefits.

5. Where possible, grow high-yielding, high-phospho-
rus-removing crops on fields that have excessively
high soil-test phosphorus levels. Even when this is
done, it may take several years to reduce very high
soil-test levels to medium to high tests.

Secondary Nutrients

The elements classified as secondary nutrients include
calcium, magnesium, and sulfur. Crop yield response
to application of these three nutrients has been ob-
served on a very limited basis in Illinois. The database
necessary to correlate and calibrate soil-test proce-
dures is thus limited, and the reliability of the sug-
gested soil-test levels for the secondary nutrients pre-
sented in Table 11.28 is low.

Deficiency of calcium has not been seen in Illinois
where soil pH is 5.5 or higher. Calcium deficiency as-
sociated with acidic soils should be corrected by using
limestone that is adequate to correct the soil pH.

Magnesium deficiency has been recognized in iso-
lated situations in Illinois. Although the deficiency is
usually associated with acidic soils, in some instances
low magnesium has been reported on sandy soils that
were not excessively acidic. The soils most likely to be
deficient in magnesium include sandy soils through-
out Illinois and low exchange-capacity soils of south-
em Illinois. Deficiency will be more likely where cal-
cific rather than dolomitic limestone has been used.

Sulfur deficiency has been reported with increas-
ing frequency throughout the Midwest. Deficiencies

112

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

probably are occurring because of (1) increased use
of sulfur-free fertilizer; (2) decreased use of sulfur as
a fungicide and insecticide; (3) increased crop yields,
resulting in increased requirements for all of the es-
sential plant nutrients; and (4) decreased atmo-
spheric sulfur supply. Early season sulfur symptoms
may disappear as rainfall contributes some sulfur and
as root systems develop to exploit greater soil volume.

Organic matter is the primary source of sulfur in
soils, so soils low in organic matter are more likely to
be deficient than soils high in organic matter. Because
sulfur is very mobile and can be readily leached, defi-
ciency is more likely on sandy soils than on finer-
textured soils.

A yield response to sulfur application was ob-
served at 5 of 85 locations in Illinois (Table 11.29).
Two of these responding sites, one an eroded silt
loam and one a sandy soil, were found in northwest-
em Illinois (Whiteside and Lee counties); one site, a
silty clay loam, was in central Illinois (Sangamon
County); and two sites, one a silt loam and one a
sandy loam, were in southern Illinois (Richland and
White counties).

At the responding sites, sulfur treatments resulted
in com yields that averaged 11.2 bushels per acre
more than yields from the untreated plots. At the non-
responding sites, yields from the sulfur-treated plots
averaged only 0.6 bushel per acre more than those
from the untreated plots (Table 11.29). If only the re-
sponding sites are considered, the sulfur soil test pre-
dicts with good reliability which sites will respond to
sulfur applications. Of the five responding sites, one
had only 12 pounds of sulfur per acre, less than the
amount considered necessary for normal plant
growth, and three had marginal sulfur concentration
(from 12 to 20 pounds of sulfur per acre). Sulfur tests

on the 80 nonresponding sites showed 14 to be defi-
cient and 29 to have a sulfur level considered mar-
ginal for normal plant growth. Sulfur applications,
however, produced no significant positive responses
in these plots. The correlation between yield increases
and measured sulfur levels in the soil was very low,
indicating that the sulfur soil test did not reliably pre-
dict sulfur need.

Experiments were conducted over 2 years on a
Cisne silt loam and a Grantsburg silt loam in southern
Illinois to evaluate the effect of sulfur application on
wheat production. Even though increasing rates of
sulfur application increased the sulfur concentration
of the flag leaf and the whole plant, it did not increase
grain yield at either location in either year. Based on
these studies, routine application of sulfur fertilizer
for wheat production does not appear warranted.

In addition to evaluating soil-test values, consider
organic-matter level, potential atmospheric sulfur
contributions, subsoil sulfur content, and moisture
conditions just before soil sampling in determining
whether a sulfur response is likely. If organic matter
exceeds 2.5 percent or if the field in question is down-
wind from industrial operations where significant
sulfur is emitted, use sulfur only on a trial basis even
when the soil-test reading is low. Because sulfur is a
mobile nutrient supplied principally by organic-
matter oxidation, abnormal precipitation (either high
or low) could adversely affect the sulfur status of
samples taken from the soil surface. If precipitation
has been high just before sampling, some samples
may have a low reading due to leaching. If precipita-
tion were low and temperatures warm, some soils
might have a high reading when, in fact, the soil is
not capable of supplying adequate sulfur throughout
the growing season.

Table 11.30. Suggested Soil-Test Levels for
Micronutrients

Micronutrient

Soil-test level (lb /A)

and procedure

Very low

Low

Adequate

Boron

(hot-water soluble)
Iron (DTPA)
Manganese (DTPA)
Manganese (HjPO^)
Zinc (.IN HCl)
Zinc (DTPA)

0.5

1
<4
<2
<10
<7
<1

2
>4
>2

>10

Table 11.31. Effect of Time of Application of
Manganese on Soybean Yield

Treatn\ent

Manganese
(lb /A /application) Times

Application

Dates

0.15

1 6-19

1 7-2

1 7-17

2 6-19, 7-2

3 6-19, 7-2, 7-19

Yield
(bu/A)

56
63
66
66
69
71

11 • SOIL TESTING AND FERTILITY

113

MlCRONUTRIENTS

The elements classified as essential micronutrients in-
clude zinc, iron, manganese, copper, boron, molybde-
num, and chlorine. These elements are classified as
micronutrients because they are required in small (mi-
cro) amounts. Confirmed deficiencies of any of these
micronutrients in Illinois have been limited to boron
deficiency of alfalfa, zinc deficiency of com, and iron
and manganese deficiencies of soybeans.

Similar to the tests for secondary nutrients, micro-
nutrient tests have very low reliability and usefulness
because of the limited database available to correlate
and calibrate the tests. Suggested levels for each test
are provided in Table 11.30. In most cases, micronutri-
ent plant analysis will probably provide a better esti-
mate of micronutrient needs than the soil test.

Manganese deficiency (stunted plants with green
veins in yellow or whitish leaves) is common on high-
pH (alkaline), sandy soils, especially during cool, wet
weather in late May and June. Suggested treatment is
to spray either manganese sulfate or an organic man-
ganese formulation onto the leaves soon after the
symptoms first appear. Broadcast application on the
soil is ineffective because the manganese becomes
unavailable in soils with a high pH.

Foliar application of MnEDTA at rates as low as
0.15 pound Mn per acre in mid-June to beans planted
in early May provided a significant yield increase
(Table 11.31). Delaying application until early July
provided a slightly higher yield than did the mid-
June application. In some cases, multiple applications
may be necessary to optimize yield.

jl Table 11.32. Soil Situations and Crops Susceptible to Micronutrient Deficiency

i Micronutrient

Sensitive crop

Susceptible soil situations

Conditions
favoring deficiency

Zinc (Zn)

Young com

1. Low in organic matter, either
inherently or because of erosion
or land shaping

2. High pH(> 7.3)

3. Very high phosphorus

4. Restricted root zone

5. Coarse-textured (sandy) soils

6. Organic soils

Cool, wet

i Iron (Fe)

Soybeans,
grain sorghum

High pH

Cool, wet

Manganese (Mn)

Soybeans, oats

1. HighpH

2. Restricted root zone

3. Organic soils

Cool, wet

Boron (B)

Alfalfa

1. Low organic matter

Drought

2. HighpH

3. Strongly weathered soils in
south-central Illinois

4. Coarse-textured (sandy) soils

Copper (Cu)

Com, wheat

1. Infertile sand

2. Organic soils

Unknown

Molybdenum (Mo)

Soybeans

Acidic, strongly weathered soils
in south-central Illinois

Unknown

Chlorine (CI)

Unknown

Coarse-textured soils

Excessive
leaching by
low-Cl water

114

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Wayne and Hark soybean varieties or lines devel-
oped from them often show iron deficiency on soils
with a very high pH (usually 7.4 to 8.0). The symp-
toms are similar to those shown with manganese defi-
ciency. Most of the observed deficiencies have been on
Harpster, a "shelly" soil that occurs in low spots in
some fields in central and northern Illinois.

Soybeans often outgrow the sttmted, yellow ap-
pearance of iron shortage. As a result, it has been dif-
ficult to measure yield losses or decide whether or
how to treat affected areas. Sampling by U.S. Depart-
ment of Agriculture scientists indicated yield reduc-
tions of 30 to 50 percent in the center of severely af-
fected spots. The yield loss may have been caused by
other soil factors associated with a very high pH and
poor drainage rather than by the iron deficiency itself.

Research in Minnesota has shown that time of iron
application is critical to attaining a response. Re-
searchers recommend that 0.15 pound of iron as iron
chelate be applied per acre to leaves within 3 to 7
days after chlorosis symptoms develop (usually in the
second-trifoliate stage of growth). Waiting for soy-
beans to grow to the fourth- or fifth- trifoliate stage
before applying iron resulted in no yield increase.
Because iron applied to the soil surface between rows
does not help, applications directed over the soybean
plants were preferred.

A significant yield response to zinc applications
was observed at 3 of 85 sites evaluated in Illinois
(Table 11.29). The use of zinc at the responding sites
produced a com yield that averaged 14.1 bushels per
acre more than the check plots. Two sites were Fayette
silt loams in Whiteside County, and one was a Green
river sand in Lee County.

At two of the three responding sites, tests showed
that the soil was low or marginal in available zinc.
The soil of the third had a very high zinc level but
was deficient in available zinc, probably because of
the excessively high phosphorus level also found.

The zinc soil-test procedures accurately predicted
results for two-thirds of the responding sites. The
same tests, however, incorrectly predicted that 19
other sites would also respond. These results suggest
that the soil test for available zinc can indicate where
zinc deficiencies are found but does not indicate reli-
ably whether the addition of zinc will increase yields.

To identify areas before micronutrient deficiencies
become important, continually observe the most sen-
sitive crops in soil situations in which the elements
are likely to be deficient (Table 11.32).

In general, deficiencies of most micronutrients are
accentuated by one of five situations: (1) strongly
weathered soils; (2) coarse-textured soils; (3) high-pH
soils; (4) organic soils; and (5) soils that are inherently

low in organic matter or are low in organic matter be-
cause erosion or land-shaping processes have re-
moved the topsoil.

The use of micronutrient fertilizers should be
limited to areas of known deficiency, and only the
deficient nutrient should be applied. An exception
to this guideline would be situations in which farm-
ers already in the highest yield bracket try micro-
nutrients experimentally in fields that are yielding
less than would be expected under good manage-
ment, which includes an adequate nitrogen, phos-
phorus, and potassium fertility program and a favor-
able pH.

Method of

Fertilizer Application

With the advent of new equipment, producers have a
number of options for placement of fertilizer. These
options range from traditional broadcast application
to injection of the materials at varying depths in the
soil. Selecting the proper application technique for a
particular field depends at least in part upon the in-
herent fertility level, the crop to be grown, the land
tenure, and the tillage system.

On fields where the fertility level is at or above the
desired goal, there is little research evidence to show
any significant difference in yield that is associated
with method of application. In contrast, on low-testing
soils and in soils that "fix" phosphorus, placement of
the fertilizer within a concentrated band has been
shown to result in higher yields, particularly at low
rates of application. On higher-testing soils, plant
recovery of applied fertilizer in the year of application
is usually greater from a band than a broadcast appli-
cation, though yield differences are unlikely.

Broadcast fertilization. On highly fertile soils, both
maintenance and buildup phosphorus and potassium
are efficiently utilized when broadcast and then
plowed or disked in. This system, particularly when
the tillage system includes a moldboard plow every
few years, distributes nutrients uniformly throughout
the entire plow depth. As a result, roots growing
within that zone have access to high levels of fertility.
Because the nutrients are intimately mixed with a
large volume of soil, opportunity exists for increased
nutrient fixation on soils having a high fixation ability.
Fortunately, most Illinois soils do not have high fixa-
tion rates for phosphorus or potassium.

Row fertilization. On soils of low fertility, placement
of fertilizer in a concentrated band below and to the
side of the seed has been shown to be an efficient
method of application, especially in situations for which
the rate of application is markedly less than that needed

11 • soil TESTING AND FERTILITY

115

I to build the soil to the desired level. Producers who are
not assured of having long-term tenure on the land may
wish to consider this option. The major disadvantages
of this technique are (1) the additional time and labor
required at planting time; (2) limited contact between
roots and fertilizer; and (3) inadequate rate of applica-
tion to increase soil levels for future crops.

For information on the use of starter fertilizer for
no-till, see the description of fertilizer management
related to tillage systems.

Strip application. With this technique, phospho-
rus, potassium, or both are applied in narrow bands
on approximately 30-inch centers on the soil surface,
in the same direction as the primary tillage. The
theory behind this technique is that, after moldboard
plowing, the fertilizer will be distributed in a narrow
vertical band throughout the plow zone. This system
reduces the amount of soil-to-fertilizer contact as
compared with a broadcast application, and thus it re-
duces the potential for nutrient fixation. Because the
fertilizer is distributed through a larger soil volume
than with a band application, the opportunity for
root- fertilizer contact is greater.

Deep fertilizer placement. Several terms have
been used to define this technique, including root-
zone banding, dual placement, knife injection, and
deep placement. With this system a mixture of
nitrogen-phosphorus or nitrogen-phosphorus-
potassium is injected at a depth from 4 to 8 inches.
The knife spacings may vary by crop to be grown,
but generally they are 15 to 18 inches apart for close-
grown crops such as wheat and 30 inches for row
crops. This technique provided a significantly higher
wheat yield as compared with a broadcast applica-
tion of the same rate of nutrients in some, but not all,
experiments conducted in Kansas. Wisconsin re-
search showed the effect of this technique to be
equivalent to a band application for com on a soil
testing high in phosphorus but inferior to a band ap-
plication for com on a soil testing low in phospho-
rus. If this system is used on low-testing soils, it is
advisable to apply a portion of the phosphorus fertil-
izer in a band with the planter.

Dribble fertilizer. This technique applies urea-
ammonium nitrate solutions in concentrated bands
on 30- inch spacings on the soil surface. Results from
several states have shown that this system reduces the
potential for nitrogen loss of these materials, as com-
pared with an unincorporated broadcast application.
However, it has not been shown to be superior to an
injected or an incorporated application of urea-
ammonium nitrate solution.

"Pop-up" fertilization. The term "pop-up" is a
misnomer. The com does not emerge sooner with this

kind of application, and it may come up 1 or 2 days
later. The com may, however, grow more rapidly dur-
ing the first 1 to 2 weeks after emergence. Pop-up fer-
tilizer will make corn look very good early in the sea-
son and may aid in early cultivation for weed control.
But no substantial difference in yield is likely in most
years due to a pop-up application as compared to fer-
tilizer that is placed in a band to the side and below
the seed. Seldom will there be a difference of more
than a few days in the time the root system intercepts
fertilizer placed with the seed as compared to that
placed below and to the side of the seed.

Under normal moisture conditions, the maximum
safe amount of N plus K^O for pop-up placement is
about 10 or 12 pounds per acre in 40-inch rows and
correspondingly more in 30- and 20-inch rows. In
excessively dry springs, even these low rates may
result in damage to seedlings, reduction in germi-
nation, or both. Pop-up fertilizer is unsafe for
soybeans. In research conducted at Dixon Springs,
a stand was reduced to one-half by applying
50 pounds of 7-28-14 and reduced to one-fifth with
100 pounds of 7-28-14.

Site-specific application. Equipment has recently
been developed that uses computer technology to al-
ter the rate of fertilizer application as the truck passes
across the field. This approach offers the potential to
improve yield while minimizing the possibility of
overfertilization. Yield improvement results from ap-
plying the correct rate (not a rate based on average
soil test) to the low-testing portions of the field.
Overfertilization is reduced by applying the correct
rate (in many cases zero) to high-testing areas of the
field. The combination of improved yield and reduced
output results in improved profit.

Foliar fertilization. Researchers have known for
many years that plant leaves absorb and utilize nutri-
ents sprayed on them. Foliar fertilization has been
used successfully for certain crops and nutrients. This
method of application has had the greatest use with
nutrients required in only small amounts by plants.
Nutrients required in large amounts, such as nitrogen,
phosphorus, and potassium, have usually been ap-
plied to the soil rather than the foliage.

The possible benefit of foliar-applied nitrogen fer-
tilizer was researched at the University of Illinois in
the 1950s. Foliar-applied nitrogen increased com and
wheat yield, provided that the soil was deficient in ni-
trogen. Where adequate nitrogen was applied to the
soil, additional yield increases were not obtained from
foliar fertilization.

Research in Illinois on foliar application of nitrogen
to soybeans attempted to supply additional nitrogen
to soybeans without decreasing nitrogen that was

116

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 11.33. Yields of Corsoy and Amsoy Soybeans
After Fertilizer Treatments Were
Sprayed on the Foliage Four Times at
Urbana

Treatment per spraying

(lb/A)

Yield
Corsoy

(bu/A)

N PA

Amsoy

0 0

20 0

0 5

10 5

20 5

30 7.5

1.5

symbiotically fixed. It was thought that if nitrogen ap-
plication were delayed until after nodules were well
established, perhaps symbiotic fixation would remain
active. Neither single nor multiple applications of ni-
trogen solution to foliage increased soybean yields.
Damage to vegetation occurred in some cases because
of leaf "bum" caused by the nitrogen fertilizer.

Although considerable research in foliar fertiliza-
tion had been conducted in Illinois already, new stud-
ies were done in 1976 and 1977. This research was
prompted by a report from a neighboring state that
soybean yields had recently been increased by as
much as 20 bushels per acre in some trials. Research
in that state differed from earlier work on soybeans in
that, in addition to nitrogen, the foliar fertilizer in-
creased yield only if phosphorus, potassium, and sul-
fur were also included. Researchers there thought that
soybean leaves become deficient in nutrients as nutri-
ents are translocated from vegetative parts to the
grain during grain development. They reasoned that

foliar fertilization, which would prevent leaf deficien-
cies, should result in increased photosynthesis that
would be expressed in higher grain yields.

Foliar fertilization research was conducted at sev-
eral locations in Illinois during 1976 and 1977, ranging
from Dixon Springs in the south to DeKalb in north.
None of the experiments gave economical yield in-
creases. In some cases there were yield reductions, at-
tributed to leaf damage caused by the fertilizer. Table
11.33 contains data from a study at Urbana in which
soybeans were sprayed four times with various fertil-
izer solutions. Yields were not increased by foliar
fertilization.

NONTRADITIONAL PRODUCTS

In this day of better- informed farmers, it seems hard
to believe that letters, calls, and promotional leaflets
about nontraditional products are increasing. The
claim made is usually that "Product X" either replaces
fertilizers and costs less, makes nutrients in the soil
more available, supplies micronutrients, or is a natu-
ral product without strong acids that kill soil bacteria
and earthworms.

The strongest position that agronomists can take is
to challenge these peddlers to produce unbiased re-
search results in support of their claims. Testimonials
by farmers are no substitute for research.

Extension specialists at the University of Illinois are
ready to give unbiased advice when asked about pur-
chasing new products or accepting a sales agency for
them.

In addition, each Extension office has the publica-
tion Compendium of Research Reports on the Use of Non-
traditional Materials for Crop Production, which contains
data on a number of nontraditional products that
have been tested in the Midwest. Check with the near-
est Extension office for this information.

Authors

Robert G. Hoeft

Department of Crop Sciences

Theodore R. Peck

Department of Natural Resources
and Environmental Sciences

ne V5

Chapter 12.

Soil Management and Tillage Systems

Soils are a natural resource. In Illinois, the greatest
concern for soil degradation is erosion caused by wa-
ter. The potential for erosion of a specific soil type,
slope, and slope length largely depends on the crops
grown and the number and types of tillage operations
used to produce them. Several techniques are avail-
able to reduce soil erosion, including residue manage-
ment, crop rotation, contouring, grass waterways, ter-
races, and conservation structures. The techniques
adopted must ensure the long-term productivity of
the land, be environmentally sound, and, of course, be
profitable. Residue management, consisting of mulch
tillage and no-tillage farming systems, is recognized
, as a cost-effective means of significantly reducing soil
erosion and maintaining productivity.

Federal conservation provisions focus on reducing
soil erosion. Growing concerns about water quality
are likely to be an issue in hammering out future state
and federal legislation. Many conservation practices
help preserve water quality. Conservation tillage, ter-
races, strip cropping, contouring, grass waterways,
and filter strips all reduce water runoff and soil ero-
sion and thus help preserve water quality.

As indicated earlier, the tillage system selected to
produce a crop has a significant effect on soil erosion,
water quality, and profitability. Profitability, of course,
is determined from crop yield (net income) and costs.
Selecting a tillage system is thus an important man-
agement decision. Before the factors are discussed in
detail, several tillage systems will be defined.

Conservation Compliance

A dramatic step taken to encourage the adoption of
techniques to control soil erosion was the passage of
the 1985 Food Security Act. Conservation require-
ments were also included in the 1990 and 1996 ver-
sions of the Farm Bill. Conservation compliance is a
major provision of the federal legislation. The goal is
to reduce soil erosion to levels that will maintain the
long-term productivity of the land. For a farmer to re-
main eligible for many USDA programs, conservation
compliance provisions of the laws require the farmer
to follow an approved conservation system on highly
erodible fields. Conservation systems must meet
specifications or guidelines of the Natural Resources
Conservation Service Field Office Technical Guide and
must be approved by the local conservation district.
Most conservation compliance systems include use of
mulch tillage or no-tillage. Even though conservation
compliance pertains only to highly erodible fields,
many farmers are adopting conservation tillage sys-
tems not only to reduce soil erosion but because they
reduce labor and equipment costs and can be more
profitable.

Conservation Tillage Systems

The objective of conservation tillage is to provide a
means of profitable crop production while minimiz-
ing soil erosion due to wind and water. The emphasis
is on soil conservation, but the conservation of soil
moisture, energy, labor, and even equipment provides
additional benefits. To be considered conservation till-
age, the system must provide conditions that resist
erosion by wind, rain, and flowing water. Such resis-
tance is achieved either by protecting the soil surface
with crop residues or growing plants or by maintain-
ing sufficient surface roughness or soil permeability
to control soil erosion.

Conservation tillage is often defined as any crop
production system that provides either (1) a residue
cover of at least 30 percent after planting to reduce
soil erosion due to water or (2) at least 1,000 pounds
per acre of flat, small-grain residues (or the equiva-
lent) on the soil surface during the critical erosion
period to reduce soil erosion due to wind.

The term conservation tillage represents a broad
spectrum of tillage systems. However, maintaining an
effective amount of plant residue on the soil surface is

118

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

the crucial issue, which is why the Natural Resources
Conservation Service (NRCS) has replaced conserva-
tion tillage with the term crop residue management.
This term refers to a philosophy of year-round man-
agement of residue to maintain the level of cover
needed for adequate control of erosion. Adequate ero-
sion control often requires more than 30 percent resi-
due cover after planting. Other conservation practices
or structures may also be required.

Conservation tillage or crop residue management
includes a broad spectrum of tillage systems, some of
which are described here.

NO-TiLL

With no-till, the soil is left undisturbed from harvest
to seeding and from seeding to harvest. The only "till-
age" is the soil disturbance in a narrow band created
by a row cleaner, coulter, seed furrow opener, or other
device attached to the planter or drill. Many no-till
planters are now equipped with row cleaners to clear
row areas of residue. No-till planters and drills must
be able to cut residue and penetrate undisturbed soil.
No-till planting of com and no-till drilling or no-till
planting in narrow rows of soybeans have increased
in Illinois.

Strictly speaking, a no-till system does not allow
operations that disturb the soil other than the planting
or drilling operation. However, the basic no- till sys-
tem is sometimes modified by the use of a strip tillage
operation which often includes knife fertilizer
application.

RlDGE-TlLL

With ridge-till, also known as ridge-plant or till-plant,
the soil is left undisturbed from harvest to planting
except for fertilizer application. Crops are planted and
grown on ridges formed in the previous growing sea-
son. Typically, ridges are built and reformed annually
during row cultivation. A planter equipped with
sweeps, disk row cleaners, coulters, or horizontal
disks is used in most ridge-till systems. These row-
cleaning attachments remove 1 to 2 inches of soil, sur-
face residue, and weed seeds from the row area. Ide-
ally, this process leaves a residue-free strip of moist
soil on top of the ridges into which the seed is
planted. Special heavy-duty row cultivators are used
to reform the ridges. Com and grain sorghum stalks
are sometimes shredded between harvest and planting.

Mulch-Till

Mulch-till includes any conservation tillage system
other than no-till and ridge-till. Deep tillage might be

performed with a subsoiler or chisel plow; tillage be-
fore planting might include one or more passes with a
disk harrow, field cultivator, or combination tool. Her-
bicides or crop cultivation, or both together, control
weeds. The tillage tools must be equipped, adjusted,
and operated to ensure that adequate residue cover
remains for erosion control, and the number of opera-
tions must also be limited. At least 30 percent of the
soil surface must be covered with plant residue after
planting.

OTHER Tillage Systems

Conventional Tillage

Conventional tillage is the sequence of tillage opera-
tions traditionally or most commonly used in a given
geographic area to produce a given crop. The opera-
tions used vary considerably for different crops and
different regions. In the past, conventional tillage in
Illinois included moldboard plowing, usually in the
fall. Spring operations included one or more disk
harrowings or field cultivations before planting or
drilling. The soil surface with conventional tillage was
essentially free of plant residue and provided a high
potential for soil erosion. The term clean tillage is also
used for any system that provides a residue-free soil
surface. A soil surface essentially free of residues can
also be achieved with other implements, especially
following a crop such as soybeans that produces frag-
ile, easy-to-cover residue.

SYSTEMS NAMED

BY Major Implement

Several tillage systems are named according to the
major implement used, including moldboard plow,
chisel plow, subsoiler, disk, and field cultivator. These
systems may be "mulch tillage" systems if at least 30
percent of the soil surface is covered with residue af-
ter planting. With these systems, herbicides may be
incorporated into the soil before planting using a disk
harrow, field cultivator, or combination tool. No-till
attachments are not needed on the planter or drill.
Crops planted in rows can be row cultivated.

Minimum Tillage

The term minimum tillage is not very meaningful, but
it is still used by some. Minimum tillage means the
minimum soil manipulation necessary for crop pro-
duction or meeting tillage requirements under exist-
ing conditions. When most people use the term mini-
mum tillage, they mean reduced tillage (defined in the
next section).

12 • SOIL MANAGEMENT AND TILLAGE SYSTEMS

119

REDUCED Tillage

Reduced tillage refers to any system that is less inten-
sive and aggressive than conventional tillage. Com-
pared to conventional tillage, the number of opera-
tions is decreased, or a tillage implement that
requires less energy per unit area is used to replace
an implement typically used in the conventional till-
age system. The term is sometimes used to mean the
same as conservation tillage. However, to be consid-
ered a conservation tillage system, 30 percent of the
soil surface must be covered with residue after plant-
ing. Because it is not specific, the term reduced tillage
is not very useful.

ROTARY-TILL

For the rotary-till system, a powered rotary tiller is
used in the fall or spring before planting. The planter
may be attached directly to the rotary tiller. This sys-
tem is not widely used in Illinois.

Effects of Tillage
ON Soil Erosion

A primary advantage of conservation tillage systems,
particularly no-till, is less soil erosion due to water
on sloping soils. Although wind erosion in Illinois is
not as great a problem as water erosion, conservation
tillage systems also essentially eliminate wind ero-
sion. A bare, smooth soil surface is extremely suscep-
tible to erosion. Many Illinois soils have subsurface
layers that are not favorable for root growth and de-
velopment. Soil erosion slowly but continually re-
moves the topsoil that is most favorable for root de-
velopment, resulting in gradually decreasing soil
productivity and value. Even on soils without root-
restricting subsoils, erosion removes nutrients that
must be replaced with additional fertilizers to main-
tain yields.

An additional problem related to soil erosion is
sedimentation and the nutrients, pesticides, and other
materials carried by the sediment and water. Sediment
and other materials from eroding fields increase water
pollution, reduce storage capacities of lakes and reser-
voirs, and decrease the effectiveness of surface drainage
systems.

Surface residues effectively reduce soil erosion. A
residue cover of 20 to 30 percent after planting re-
duces soil erosion by approximately 50 percent com-
pared to a bare field. A residue cover of 70 percent af-
ter planting reduces soil erosion more than 90 percent
compared to a bare field. On long, steep slopes, con-
servation tillage will not adequately control soil ero-
sion. Other practices are thus required, such as con-

touring, grass waterways, terraces, or structures. For
technical assistance in developing erosion control sys-
tems, consult your district conservationist or the NRCS.

Residue Cover

The percentage of the soil surface covered with resi-
due after planting is affected by the previous crop
grown and the tillage system used. In general, the
higher the crop yield, the greater the residue pro-
duced. More important, however, is the type of resi-
due a crop produces. Types of residue produced by
various crops have been classified as nonfragile or
fragile (Table 12.01). The classification is subjective
and based on the ease with which the residues are de-
composed by the elements or buried by tillage opera-
tions. Plant characteristics such as composition and
sizes of leaves and stems, density of the residues, and
relative quantities produced were considered. The
residues of a crop such as soybeans are considered
fragile because essentially all of the residues are dam-
aged in passing through the combine, the stems and
stubble are small in diameter, and the leaves are small
and fall from the plants well before harvest. In con-
trast, residues from com are classified as nonfragile.

Table 12.01. Types of Residue Produced by
Various Crops

Nonfragile

Fragile

Alfalfa or legume hay

Barley*

Buckwheat

Com

Flaxseed

Forage seed

Forage silage

Grass hay

Millet

Oats*

Pasture

Popcorn

Rye

Sorghum

Triticale*

Wheat*

Canola/rapeseed

Dry beans

Dry peas

Fall-seeded cover crops

Flower seed

Green peas

Potatoes

Soybeans

Vegetables

NOTE: From Estimates of Residue Cover Remaining After
Single Operation of Selected Tillage Machines, developed jointly
by the Soil Conservation Service, USDA, and Equipment
Manufacturers Institute. First edition, February 1992.
*If a combine is equipped with a straw chopper or the straw
is otherwise cut into small pieces, small-grain residue
should be considered fragile.

120

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Cornstalks, leaves, and cobs are individually large in
size and quite durable, and the total mass of residue
produced is greater.

The line-transect method is often used to measure
residue cover. A light rope or tape with 100 equally
spaced knots or marks is stretched diagonally across
the crop rows. Residue cover is measured by counting
each knot or mark that is directly over a piece of resi-
due. The percent residue cover is equal to the number
of knots counted.

Often there is a desire to predict the amount of
residue that will remain on the soil surface using a
particular tillage system. The prediction requires
knowing the amount of residue cover remaining after
each field operation included in the tillage system.
Typical percentages of the residue cover remaining
after various field operations are given in Table 12.02.
The percentages can be used to estimate the residue
cover after each field operation in a tillage system.

A com crop of 150 bushels per acre will usually
provide a residue cover of 95 percent after harvest.
Grain sorghum, most small grains, and lower yield-
ing corn will generally provide a cover of 80 to 90 per-
cent. Following soybean harvest, 70 to 80 percent cover
typically remains. In all cases, the residue must be uni-
formly spread behind the combine. For a tillage system,
a rough approximation of the residue cover remaining
after planting can be obtained by multiplying the initial
percent residue cover by the values in Table 12.02 of
percent cover remaining after each operation. To
leave 30 percent or more residue cover following
com, only one or two tillage operations can be per-
formed. To leave 30 percent cover following soybeans
essentially requires that the no-tillage system be used.

Crop Production with
Conservation Tillage

Crop response to various tillage systems is variable in
both farmers' fields and experimental plots. The vari-
ability is often difficult to explain because so many
aspects of crop production are influenced by tillage.
Crop germination, emergence, and growth are largely
regulated by soil temperature, aeration, and moisture
content; nutrient availability to roots; and mechanical
impedance to root growth.

Soil Temperature

Crop residue on the soil surface insulates the soil
from the sun's energy. In most of Illinois, higher soil
temperatures than normal are desirable for plant
growth in the spring. Later in the season, tempera-
tures cooler than normal are often desirable.

Table 12.02. Residue Cover Remaining on the Soil
Surface After Weathering or Specific
Field Operation

Percent
of residue remaining

Nonfragile Fragile

Climatic effects

Overwinter weathering*
Following summer harvest
Following fall harvest

Field operations

Moldboard plow

V ripper/subsoiler

Disk-subsoiler

Chisel plow with
Straight spike points
Twisted points or shovels

Coulter-chisel plow with
Straight spike points
Twisted points or shovels

Offset disk harrow —
heavy plowing > 10" spacing

Tandem disk harrow
Primary cutting > 9" spacing
Finishing 7" to 9" spacing
Light disking after harvest

Field cultivator
As primary tillage operation
Sweeps 12" to 20"
Sweeps or shovels 6" to 12"

As secondary tillage operation
Sweeps 12" to 20"
Sweeps or shovels 6" to 12"

Combination finishing tool with
Disks, shanks, and

leveling attachments
Spring teeth and rolling baskets

70-90

65-85

80-95

70-80

0-10

0-5

70-90

60-80

30-50

10-20

60-80

40-60

50-70

30-40

50-70

30-40

40-60

20-30

25-50

50-70
70-90

Anhydrous ammonia applicator 75-85

10-25

30-60

20-40

40-70

25-40

70-80

40-50

60-80

55-75

35-75

50-70

80-90

60-75

70-80

50-60

Drill
Conventional
No-till

80-100
55-80

30-50
50-70

45-70

60-80
40-80

12 • SOIL MANAGEMENT AND TILLAGE SYSTEMS

121

Table 12.02. Residue Cover Remaining on the Soil
Surface After Weathering or Specific
Field Operation (cont.)

Percent
of residue remaining

Nonfragile

Fragile

Conventional planter

85-95

75-85

No-till planter with
Ripple coulters
Fluted coulters

75-90
65-85

70-85
55-80

Ridge-till planter

40-60

20-40

*With long periods of snow cover and frozen conditions,
weathering may reduce residue levels only slightly, while
in warmer climates, weathering losses may reduce residue
levels significantly.

Minimum daily temperatures of the soil surface
usually occur between 6 a.m. and 8 a.m., and in
spring they are often the same or slightly higher with
residue cover than without. Maximum daily tempera-
tures of the soil surface occur between 3 p.m. and 5
p.m., and with clean tillage they are 3° to 6°F warmer
than those with residue cover. During the summer, a
complete crop canopy restricts the influence of crop
residue on soil temperature, and soil surface tem-
peratures are about the same with and without sur-
face residue.

During May and early June, the reduced soil tem-
peratures caused by a surface mulch influence early
plant growth. In northern regions of the state, aver-
age daily soil temperatures are often close to the tem-
perature at which com grows, and the reduced tem-
peratures caused by surface residues result in slow
plant growth. In southern regions of the state, aver-
age daily temperatures are usually well above the
temperature at which com grows, and the reduced
temperatures caused by surface residues have little, if
any, effect on early com growth.

The amount of residue influences soil temperature.
Residues from com, wheat, and grass sod maintain
cooler soil than residue from soybeans and other
crops that produce less residue or residue that de-
composes rapidly.

Whether the lower soil temperature and subse-
quent slower early growth result in lower yields de-

pends largely on weather conditions during the sum-
mer. Research shows that lower yields with reduced
tillage systems occur most often on poorly drained
soils and on all soils in northern Illinois in years not
affected by drought. In these situations, soil tempera-
ture, com growth, and yield potential often improve
when residues are removed from the row area. Sev-
eral planter attachments are available for removing
residue from the row area. However, on well-drained
soils in southern Illinois, reduced soil temperature
caused by in-row residues may increase crop growth
and yield.

Allelopathy

Allelopathy refers to toxic effects on a crop due to de-
caying residue from the same crop or closely related
species. Greenhouse studies have shown that toxins
and bacteria from decaying residue affect growth of
new plants. In the field, it is difficult to separate al-
lelopathic effects from soil temperature effects. The
toxic effect is most likely to occur when corn follows
corn, rye, or wheat or when wheat follows rye or
wheat, and when residue is on or near the soil sur-
face near the growing crop. Planter attachments
which remove residue from the row area may reduce
the toxic effect.

MOISTURE

When 30 percent or more of the soil surface is cov-
ered with residues, generally evaporation is reduced
and water infiltration increases, leading to more wa-
ter stored in sloping soils. More stored water may be
advantageous in dry summer periods but may be dis-
advantageous at planting time and during early
growth — especially on soils with poor internal
drainage.

In most years in Illinois, extra water is needed af-
ter the crop canopy closes. In Kentucky, evaporation
and transpiration were estimated for no-till and
moldboard plowed plots. Average annual evapora-
tion was reduced by 5.9 inches with no-till. Thus, it
was concluded that more water is available for tran-
spiration with no-till, often resulting in higher com
yields.

Soil moisture saved through reduced tillage sys-
tems may be important in years with below-normal
rainfall. In the northern half of Illinois excessive soil
moisture in the spring months often reduces crop
growth because it slows soil warming and may delay
planting. However, on soils where drought stress of-
ten occurs during summer months, additional stored
moisture leads to higher yields.

122

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Organic Matter
and aggregation

Soil organic matter tends to stabilize at a certain level
for a specific tillage system. Moldboard plowing bur-
ies essentially all of the residue and increases oxida-
tion of organic matter. With conservation tillage sys-
tems, especially no-till and ridge-till, residue is left on
the soil surface where decomposition is slow, which
then causes organic matter in the upper few inches to
increase after several years.

Both the amount and distribution of organic matter
change with the tillage system (Table 12.03). Com-
pared to moldboard plowing, organic matter with
no-till gradually increases near the soil surface and
is maintained or increased slightly below a depth of
4 inches. It is assumed that with mulch-tillage sys-
tems, organic matter would approach a level between
moldboard plow and no-till systems.

SOIU DENSITY

An increase in soil density is often referred to as
compaction. Excessive soil compaction restricts plant
root growth, impedes drainage, reduces soil aeration,
increases injury potential of some herbicides, and re-
duces uptake of potassium and nitrogen. Unfilled
soil usually has a greater density than tilled soil.
However, after soil is loosened by tillage, density in-
creases due to wetting and drying, wheel traffic, and
secondary tillage operations. By harvest time soil
density is often about equal to that of untilled soil.
Wheel traffic of heavy equipment such as tractors,
combines, and grain carts may cause plant rooting to
be limited or redirected with any tillage system.
In an experiment at the University of Illinois,
com and soybeans have been grown with and with-

Table 12.03. Amount and Distribution of Soil
Organic Matter with Plow and
No-Till Systems*

Sandy

loam

Silty cla;
Depth (in.)

y loam

Tillage system

Depth (in.)

OM (%)

Plow

0-4

1.5

0-3

4.1

4-8

1.5

3-6

4.1

8-12

0.8

6-9

3.7

No-till

0-4

1.9

0-3

4.8

4-8

1.7

3-6

4.2

8-12

0.9

6-9

3.8

out wheel traffic compaction on tilled soil before
planting (Table 12.04). Heavy wheel traffic on the
entire soil surface significantly decreased com yields
when rainfall was adequate or excessive. In years
with excessive rainfall, ponding of water occurred
on plots with the entire surface compacted, and com
yields were reduced significantly. On other plots,
wheel traffic was applied to every other row of the
plot area before planting — which may be more typi-
cal of field conditions. On these plots, yields were
not significantly affected compared to yields from
no-extra-compaction plots.

STAND ESTABLISHMENT

Uniform planting depth, good contact between the
seed and moist soil, and enough loose soil to cover
the seed are necessary to consistently produce uni-
form stands. Planting shallower than normal in the
cool, moist soil common to many conservation tillage
seedbeds may partially offset the disadvantage of
lower temperatures. However, if dry, windy weather
follows planting, germination may be poor, and shal-
low-planted seedlings may be stressed for moisture. A
normal planting depth is thus suggested for all tillage
systems.

For most conservation tillage systems, planters and
drills are equipped with coulters in front of each seed
furrow opener to cut the surface residues and pen-
etrate the soil. Row cleaners can also be mounted in
front of each seed opener. Generally, coulters should
be operated at seeding depth. Row cleaners should be
set to move the residue from the row area and to
move as little soil as possible. Extra weight is often
needed on planters and drills for no-till so that the
soil-engaging components function properly and suf-
ficient weight is ensured on the drive wheels. Heavy-
duty, down-pressure springs may also be necessary
on each planter unit to penetrate firm, undisturbed
soil.

Table 12.04. Effects of Wheel Traffic Compaction
on Soybean and Com Yields
at Urbana

Compaction treatment

11 -year average yields (bu/A)
Soybeans Com

No extra compaction 40.3

Half-surface compaction 40.0

Entire surface compacted 38.8

163
160
150^

^Indiana, after growing continuous com for 7 years.

*Soil compaction caused water to pond after heavy rain in
some years.

12 • SOIL MANAGEMENT AND TILLAGE SYSTEMS

123

FERTILIZER PLACEMENT

See the "Fertilizer Management Related to Tillage Sys-
tems" section in Chapter 11 for discussion of this topic.

WEED CONTROL

Controlling weeds is essential for profitable produc-
tion with any tillage system. With less tillage, weed
control becomes more dependent on herbicides. How-
ever, effective herbicides are available for controlling
most all weeds in conservation tillage systems. Herbi-
cide selection and application rate, accuracy, and tim-
ing become more important. Application accuracy is
especially important with drilled soybeans because
row cultivation is impractical. (For specific herbicide
recommendations, see Chapter 15.)

Perennial weeds, such as milkweed and hemp dog-
bane, may be a problem with conservation tillage sys-
tems. Excellent postemergence controls are now avail-
able for weeds such as johnsongrass, shattercane, and
yellow nutsedge that formerly required incorporated
treatments. Volunteer com is often a potential prob-
lem with tillage systems that leave com lost at harvest
on the soil surface or at a shallow depth. However,
excellent herbicides are now available for control of
volunteer com in soybeans. Unless control programs
are monitored closely, surface-germinating weeds, such
as fall panicum and crabgrass, may also increase with
reduced-tillage systems. Some broadleaf weeds such
as velvetleaf are often less of a problem with no-till.

Surface-applied and incorporated herbicides may
not give optimum performance under tillage systems
that leave large amounts of crop residue and clods on
the soil surface. These problems interfere with herbi-
cide distribution and thorough herbicide incorporation.

Herbicide incorporation is impossible in no-till sys-
tems. Residual or postemergence herbicides are effec-
tive, and mechanical cultivation is usually not done.

Heavy-duty cultivators are available to cultivate
with high amounts of surface residues and hard soil.
High amounts of crop residues interfere with some
rotary hoes and cultivators with multiple sweeps per
row. Cultivators equipped with a single coulter and
sweep plus two weeding disks per row are effective
across a wide range of soil and crop residue conditions.

With the ridge-tillage system, special cultivation
equipment is necessary to form a sufficiently high
ridge and to operate through the inter-row residue.
Weed control is also accomplished as ridges are rebuilt.

NO-TiLL WEED CONTROL

In conventional and most conservation-tillage sys-
tems, existing weeds are destroyed by tillage before

planting. No-till systems may require a knockdown
herbicide like paraquat or Roundup to control exist-
ing vegetation. However, some herbicides, such as
Extrazine, may provide both "bumdown" and re-
sidual control. The vegetation may be a grass or le-
gume sod or early germinating annual and perennial
weeds. Alfalfa and certain perennial broadleaf weeds
are not well controlled by paraquat or Roundup. For
com it may be necessary to treat these weeds with
Banvel or 2,4-D. A combination of 2,4-D and Banvel is
often best to broaden the spectrum of control.
Horseweed and prickly lettuce are often associated
with no-till. A combination of Roundup plus 2,4-D is
often appropriate as a bumdown for such weeds.

Insect Management

Although insect problems and management practices
may be affected by reduced tillage, concern about
insect problems should not prevent a farmer from
adopting conservation tillage practices. With few
exceptions, effective insect-management guidelines
and tactics are available, regardless of the tillage sys-
tem used. Extension entomologists throughout the
north central region of the United States seldom alter
insect-management recommendations for different
tillage systems.

Insect development rates are closely related to tem-
perature. Insects that spend part of their life cycles in
the soil may develop more slowly in conservation till-
age systems. For instance, initial emergence of com
rootworm adults is delayed in no-till com fields. The
type of tillage system may also influence insect sur-
vival during the winter. Research has shown that
survival of com rootworm eggs during the winter is
greater in no-till systems than in more conventional
systems, especially if snow cover is deficient and if
temperatures remain very cold for an extended
period.

Conservation tillage systems may affect other com-
ponents that influence insect populations, such as
weed densities and populations of beneficial insects.
Poor weed management in some tillage systems is
responsible for increasing the densities of cutworms,
for example. On the other hand, some weeds attract
predators and parasitoids that may suppress some
insect pest populations.

The effects of tillage on insects are most prominent
in com. The insects most directly affected are those
that overwinter in the soil and become active during
the early stages of crop growth. Increases in grassy
weed populations, reduced disturbance of soil, and
delayed germination caused by cooler soil tempera-
tures may favor the buildup of white grubs and

124

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

wireworms. Seedcom maggot flies prefer to lay eggs
where crop residue has been partially incorporated
into the soil. No-till com stubble may be less attrac-
tive to egg- laying flies, but cooler, wetter soils shaded
by crop residues may slow germination and increase
the period of vulnerability to seedcom maggot injury.
On the other hand, com rootworms are little affected
by conservation tillage (Table 12.05).

Although soil-dwelling insects are usually affected
more than the foliage-feeding insects, some species
respond to certain weeds. Black cutworm moths pre-
fer to lay eggs in weedy fields and in fields with unin-
corporated crop residues. Ryegrass and other grass
cover crops, hay crops, and grassy weeds are espe-
cially attractive to egg-laying armyworm moths. In
no-till fields, serious damage by stalk borers is most
likely where grasses were present to attract egg-
laying moths during August and September of the
previous year.

Conservation tillage favors greater survival of Eu-
ropean com borers in crop residue, but effects in spe-
cific fields are minor because moths disperse from
emergence sites to lay eggs in suitable fields through-
out the local area. Where reduced tillage leads to later
planting or slower growth, com may be less suscep-
tible to attack by first-generation com borers and
more susceptible to second-generation damage.

Although the potential for insect problems is
slightly greater with conservation tillage than it is in
plowed fields, adequate management guidelines are
generally available (Chapter 17).

Disease Control

The potential for plant disease is greater when mulch
is present than when fields are clear of residue. With
clean tillage, residue from the previous crop is buried
or otherwise removed. Because buried residue is sub-
ject to rapid decomposition, overwintering of patho-
gens is lessened or reduced with clean tillage
systems.

If volunteer com in continuous com is a hybrid
that is susceptible to disease, early infection with dis-
eases such as southern com leaf blight or grey leaf
spot, for instance, will increase.

Although the potential for plant disease is greater
with conservation tillage systems than with clean till-
age, disease-resistant hybrids and varieties can help
reduce this problem. The erosion-control benefit of
conservation tillage must be balanced against the in-
creased potential for disease. Crop rotation or modifi-
cation of the tillage practice may be justified if a dis-
ease cannot otherwise be controlled.

Table 12.05. Potential Effects of Conservation
Tillage Systems on Pests in Corn

Insect

Potential effect*

Armyworm

0 to -K -K -1-

Black cutworm

-h to -h H- 4-

Com earworin

Oto-i-

Com leaf aphid

Com rootworm

European com borer

OtOH-

Hop vine borer

0 to -1- + -1-

Seedcom maggot

Slugs

+ + +

Stalk borer

0 to -(- + -h

Stink bugs

White grubs

Wireworms

* Potential effects depend on cropping sequence, weather
conditions, and presence or absence of weeds. 0 = no effect
in pest population; + = some increase; + + + - substantial
increase.

Crop Yields

Tillage research is conducted at the six University of
Illinois Agricultural Research and Demonstration
Centers (see map on inside front cover) to evaluate
crop yield responses to different tillage systems under
a wide variety of soil and climatic conditions. Crop
yields vary, due more to weather conditions during
the growing season than the tillage system used. Com
and soybean yields are generally higher when the
crops are rotated compared to either crop grown con-
tinuously. It is important with any tillage system that
plant stands be adequate, weeds be controlled, soil
compaction not be excessive, and adequate nutrients
be available.

Comparative yields due to tillage system vary with
soil type (Table 12.06). In general, com and soybean
yields have been found to decrease slightly as tillage
is reduced on poorly drained and somewhat poorly
drained dark soils. An exception is the ridge-till sys-
tem, which frequently produces higher com yields on
these soils. Flanagan silt loam and Drummer silty
clay loam are two examples of poorly drained to
somwhat poorly drained soils.

On well-drained to moderately well-drained,
medium-textured, dark- and light-colored soils, ex-
pected yields with all tillage systems are quite simi-
lar for rotation corn and soybeans. With continuous
com, yields generally decrease as tillage is reduced.

12 • SOIL MANAGEMENT AND TILLAGE SYSTEMS

125

iTama silt loam, which is dark, and Downs-Fayette silt
loam, which is light-colored, are both well-drained to
moderately well-drained and medium-textured.

On somewhat excessively drained sandy soils, con-
I servahon tillage systems that retain surface residues
reduce wind erosion and conserve moisture, typically
producing high yields.

Soils such as Cisne silt loams, which are very
slowly permeable and poorly drained, have a clay
pan that restricts root development with all tillage
systems. On such soils, yields are frequently higher
with less tillage.

PRODUCTION Costs

For evaluating the profitability of various tillage-
planting systems, the related costs are an important
consideration. Various systems may affect the cost of
machinery, labor, fertilizers, pesticides, and seed.
Grain-handling and drying costs are affected if yields
differ. Land cost is norn\ally assumed not to vary with
tillage system.

Machinery and Labor Costs

Machinery-related costs for Illinois farms typically
overshadow all other cost categories except land.

Machinery-related costs include the expenses for
owning and operating machinery and for labor to
operate it. Many factors and assumptions must be
made to estimate these costs for a farm and for vari-
ous tillage systems.

Machinery-related costs were estimated using a
computerized farm machinery selection program that
determines the optimum set of machinery for a farm.
The optimum set of machinery is the one resulting in
the minimum total cost for machinery and labor
which will complete all field operations in a timely
manner with assumed workday probabilities. The
program assumes new machinery is purchased and
used for up to 10 years. Machinery costs include de-
preciation, interest, insurance, housing, repairs, fuel,
and lubrication. The program was used to determine
the optimum machinery set for various tillage sys-
tems and farm sizes. For each machinery set, esti-
mated machinery and labor costs were calculated.
The field operations for the tillage systems are sum-
marized in Table 12.07.

Total costs for machinery and labor per acre de-
crease as the amount of tillage is reduced and as farm
size increases (Table 12.08). For reduced tillage, fewer
implements and field operations are used, and the
necessary power units are often smaller for a given

Table 12.06. Corn and Soybean Yields with Moldboard Plow, Chisel Plow, Disk, and No-Till Systems

Soil type

Flanagan

silt loam

Thorp

Alford

and Drummer Cisne Downs-Fayette

Tama

Tillage system

silt loam

clay loam silt loam silt loam

silt loam

— - mi^fncT^ rrifti Murine Tnllmnivict Ci^MrM>nvic IrMi/A ).. — — — _ — .

UUcfU^C LUm ifli^lUbjUllUiVlfl^ bUyUCUrib \UU/r\/ ■

Moldboard plow

...

146"

160^ . . . 172^

165'

Chisel plow

167^

145

145 138" 170

155

Disk

169

...

154 138 171

165

No-till

165

145

151 133 167

^mipyncTP Qnijhi^nn i/ipl/ic fnllmiiitin- mm (Viit/A \ - -

159

Ui/Cf UVC dUUUcUiI uICIUd JUilUU/lflV LUi fl \UU//\/

Moldboard plow

50 28 44

Chisel plow

• • ■

49 29 47

Disk

• • •

48 ... 46

No-till

48 32 45

'Urbana.

""Dixon Springs.
^DeKalb.

''Brownstown.

Terry.
'Monmouth.

. . . System not included

in experiment.

126

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

farm size. If a reduced tillage system is used on only
part of the land farmed, implements and tractors will
need to be available for other portions, so savings
may be smaller than indicated in Table 12.08.

With reduced tillage systems, labor costs are less
because some fall or spring tillage operations are less
intensive or eliminated. The labor saved in this way
has value only if it reduces the cost of hired labor or if
the saved labor time is directed into other productive
activities, such as raising livestock, working off-farm,
or farming more land.

Using a drill or narrow-row planter for soybeans is
an option for most tillage systems. However, owning
a drill for soybeans and a planter for com often in-
creases the machinery inventory and costs for a corn-
soybean farm. The effects on machinery cost for the
farm depend on farm size and the cost of the drill.
Some no-till drills are quite expensive. For systems
that include row cultivation of planted soybeans, the
cost increase of the drill may be offset by less use of
the planter, row cultivator, and tractor. In comparing
no-till planted soybeans (no row cultivation) with
no-till drilled soybeans, the no-till drill increases esti-
mated optimum machinery and labor costs from $38.60
to $45.60 per acre for a 1,000-acre corn-soybean farm
(Table 12.08).

An extra cost for additional or more expensive pes-
ticides may be associated with some conservation
tillage systems. For example, a "bumdown" herbicide
may be needed with no-till and ridge-tillage systems.
These increases are usually more than offset by re-
duced machinery and labor costs with conservation
tillage. Ridge-till can be cost-effective, especially if
only a band application of herbicide is used.

Costs for com and soybean seeds are usually the
same for all tillage systems. However, when soybeans
are drilled or planted in narrow rows, the seeding rate

Table 12.07. Tillage Operations for Various Systems

Tillage system

Field Field

After soybeans Chisel cultivate cultivate No-till

After com Plow Chisel Disk No-till

Fall

Harvest

S C

S c

Mb plow

Chisel plow

Apply NHg^

Spring

Disk

Field cultivate

* *

Plant

C S

Row cultivate

* *

* ♦

* *

S = soybeans, C = corn.

* Portions of anhydrous ammonia were applied in fall, in

spring, or as sidedress.

is usually increased 10 to 20 percent compared to
planting in rows 30 inches or wider.

Usually the amounts of fertilizers and lime are not
varied with different tillage systems. However, the
forms and application techniques may vary depend-
ing on the tillage system. Any differences in cost
should be considered. A starter fertilizer for com is of-
ten recommended with conservation tillage, espe-
cially with the no-till system. Planter attachments to
apply starter fertilizer in a separate band are an ex-
pense that should be considered.

12 • SOIL MANAGEMENT AND TILLAGE SYSTEMS

127

I Table 12.08. Estimated Machinery-Related Costs for Various Corn and Soybean Farm Sizes and Tillage Systems^

Tractors

Combines

Costs ($/acre)

Farm size and

tillage system^

I'll _^

(no.-Hp)

Machinery

Labor'^

Total

til
1 Corn and soybeans planted

^! 500 acres

Mb plow/chisel

1-120

1-160

77.70

12.30

90.00

. Chisel/disk

1-120

1-160

71.80

10.60

82.40

Disk/field cultivator

2-80

1-160

69.50

11.70

81.20

No-till/no-till

1-80

1-160

52.10

7.00

59.10

750 acres

Mb plow

1-140, 1-80

1-160

64.00

11.90

75.90

Chisel

1-120, 1-80

1-160

59.60

10.75

70.35

Disk/field cultivator

2-80

1-160

52.30

11.70

64.00

No-till/no-hll

1-80

1-160

39.20

7.00

45.20

1,000 acres

Mb plow/chisel

1-160, 1-80

1-220

59.80

9.00

68.80

Chisel/disk

1-160, 1-80

1-220

53.30

8.10

61.40

i Disk/field cultivator

1-160, 1-80

1-220

52.90

7.50

60.40

No-till/no-till

1-100

1-190

36.60

5.30

41.90

1,500 acres

Mb plow/chisel

1-220, 1-100

1-220

55.40

7.22

62.62

Chisel/disk

1-200, 1-100

1-220

50.00

6.50

56.50

Disk/field cultivator

1-220, 1-100

1-220

48.50

6.20

54.70

No-till/no-till

1-100

1-220

33.10

4.40

37.50

2,000 acres

Mb plow/chisel

2-180, 1-120

1-275

55.30

7.00

62.30

, Chisel/disk

1-220, 1-120

1-275

46.90

5.50

52.40

1 Disk/field cultivator

1-220, 1-120

1-275

46.80

5.20

52.00

No-till/no-till

1-120

1-275

31.50

3.30

34.80

Com planted and soyb*

eans drilled

500 acres

' Mb plow/chisel

1-100, 1-80

1-160

76.60

14.70

91.30

Chisel/disk

1-100, 1-80

1-160

72.50

12.70

85.20

1 Disk/field cultivator

2-80

1-160

65.40

12.80

78.20

No-till/no-till

1-80

1-160

55.20

8.20

63.40

1 750 acres

Mb plow/chisel

1-120, 1-80

1-160

59.40

13.40

72.80

Chisel/disk

1-120, 1-80

1-160

58.80

10.50

69.30

Disk/field cultivator

2-80

1-160

50.70

11.50

62.20

No-till/no-till

1-80

1-160

42.80

7.50

50.30

1,000 acres

Mb plow/chisel

1-160, 1-100

1-220

59.10

8.40

67.50

Chisel/disk

1-160, 1-100

1-220

55.70

7.00

62.70

Disk/field cultivator

1-160, 1-100

1-220

54.30

6.80

61.10

No-till/no-till

1-140

1-190

42.00

5.40

47.40

128

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 12.08. Estimated Machinery-Related Costs for Various Corn and Soybean Farm Sizes and Tillage Systems*
(cont.)

T~' • 1

y— t 1 •

Costs ($/acre)

:-1

Farm size and

Tractors

Combmes

tillage system''

(no.-Hp)

Machinery

Labor^

Total

Com planted and soyb

eans drilled (cont)

-i?

1,500 acres

Mb plow/chisel

1-240, 1-160

1-275

54.30

6.20

60.50

Chisel/disk

1-180, 1-140

1-275

47.70

5.80

53.50

Disk/field cultivator

1-180, 1-140

1-275

46.50

5.50

52.00

No-till/no-till

1-140, 1-100

1-275

37.90

3.90

41.80

2,000 acres

Mb plow/chisel

2-200, 1-160

1-275

54.80

6.40

61.20

Chisel/disk

2-180, 1-160

1-275

49.30

5.50

54.80

Disk/field cultivator

2-180, 1-160

1-275

49.20

5.10

54.30

No-till/no-till

1-160, 1-120

1-275

38.30

3.50

41.80

* Optimum sizes and numbers of tractors with matched implements and combines with attached headers were determined

and costs estimated using a computerized Farm Machinery Selection Program. These sizes and numbers should be regarded

as the minimums to perform the operations in a timely manner. Costs for applying potassium and phosphorus fertilizers,

herbicides, and lime are not included.

''Corn-soybean rotation assumed. Operations for each tillage system are given in Table 12.07.

" Labor assumed to cost $10 per hour. 1

Author

John C. Siemens

Department of Agricultural Engineering

Chapter 13.

No TlUUAGE

No-till is a system in which the soil is left undis-
turbed. The only soil disturbance is of a narrow band
by soil-engaging components of the planter or drill. In
addition to double-disk seed furrow openers and
press wheels or firming wheels, soil-engaging compo-
nents often include row cleaners, coulters, or other
devices attached to the planter or drill.

No-till is very effective in reducing the potential for
soil erosion due to wind and water. With no-till, the
maximum amount of plant residue remains on the
soil surface compared to other tillage systems. Surface
residue protects the soil from raindrop impact and thus
reduces splash erosion. In addition, surface residue
slows the speed of water flowing down a slope, allow-
ing more time for the water to infiltrate into the soil.

The trend toward no-till management for crop pro-
duction in Illinois has accelerated since adoption of
the 1985 Food Security Act. Provisions of the act re-
quire farmers to develop and apply an approved con-
servation plan on highly erodible fields. Many plans
include the use of the no-till system. In addition,
many farmers are adopting the no-till because they
find it to be cost-effective.

NO-TiLL PLANTERS

No-till planters are specifically designed to plant in
undisturbed soil with a high percentage of the surface
covered with residue. In addition to field conditions,
planter performance is influenced by planter features,
attachments, adjustment, and operation. Successful
planting in residue-covered and undisturbed fields
depends on planter weight and appropriate down-
pressure springs to transfer the weight to the planting
units and other soil-engaging components in order to
cut the residue and achieve adequate soil penetration.

Row-Cleaning Devices

A pair of spoked wheels is the most popular row
cleaner design. In light residue, such as when follow-

ing soybeans, it is questionable whether a row cleaner
is necessary.

Row cleaners should be adjusted to remove only
the residue from the row area and not a large amount
of soil.

In heavy surface residue, use of row cleaners to
move residue away from the row aids in soil warming
and may improve seed placement and stand estab-
lishment. Early soil warming contributes to faster
early growth, especially in poorly drained soils. Early
soil warming also reduces disease pressure. Several
plant pathogens, especially fungal pathogens such as
Pythium species, are favored by cool, wet soils that
occur under no-till. When combined with fungicide
treatments, the use of row cleaners should result in
more vigorous and uniform seedling emergence.

Row cleaners may also be beneficial in reducing
the toxic effects of allelopathy. The potential for allel-
opathy occurs when the toxins and bacteria from de-
caying residue affect growth of new plants. The toxic
effect is most likely to occur when crops are not ro-
tated— for example, when com follows com.

Coulters

A coulter is usually mounted in front of each row unit
of a no-till planter. The coulter is primarily for cutting
through the residue and loosening the soil in the row
to planting depth. It has little effect on soil warming
or allelopathy. Coulter operating depth in relation to
seeding depth is more consistent when the coulter is
mounted on the planter unit rather than on a separate
toolbar.

Several types of coulters are available for no-till
planters (Figure 13.01). The most commonly used is
the Vi- or 1-inch-wide fluted coulter. Generally, wider
coulters increase tillage action and require more
weight for penetration; a total weight of 400 to 600
pounds per coulter may be required. Wider coulters
also may throw excessive amounts of soil from the row,
especially when operated at higher planting speeds.

130

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Smooth

Rippled

Rippled with
smooth edge

Fluted

Figure 13.01. Common coulter styles.

Compared to fluted coulters, rippled or smooth
coulters perform less tillage, require less weight for
penetration, allow higher planting speeds, and are
preferred for cutting residue.

Seed Furrow Openers

Seed furrow openers create well-defined slits in the
soil where seed is placed at the desired depth.
Planters are commonly equipped with either the
double-disk or staggered double-disk seed furrow
openers.

The staggered double-disk opener is a modification
of the double-disk version. The leading edge of one
disk, slightly in front of the other, provides a definite
cutting edge. The trailing disk helps open the seed
furrow. Planters with staggered double-disk seed fur-
row openers may not require as much weight to
achieve soil penetration, especially if operated with-
out a leading coulter. The double-disk opener will sat-
isfactorily cut well-distributed soybean residue and
penetrate a soft soil without a leading coulter. Re-
search indicates no difference in seed spacing unifor-
mity due to the type of opener.

Seed Covering

Good seed-to-soil contact is essential for seed germi-
nation and seedling emergence. A narrow press wheel
or seed firmer can be attached to planters to improve
seed-to-soil contact. This wheel operates just behind

the seed furrow opener and presses the seed into the
bottom of the furrow.

Commonly used seed covering devices include a
small disk blade on each side of the row, a press
wheel, an angled wheel on each side of the row, or a
combination of these. Currently, there is no combina-
tion of covering devices and press wheels that has
proven to offer a distinct advantage across all soil
conditions.

Weight and Down-Pressure Springs

Additional weight is usually required on no-till
planters to achieve uniform soil penetration. Down-
pressure springs, which transfer weight from the
toolbar to the row units, are usually located on
the parallel linkage supporting the row units and
may need tightening to achieve adequate penetra-
tion of the soil-engaging components. For no-till
planting in hard soil conditions, heavy-duty down-
pressure springs may be required in addition to
extra weight.

Down pressure must be sufficient to cause the soil-
engaging components to function properly and main-
tain a uniform planting depth. However, the planter
must be heavy enough to prevent the springs from
lifting too much weight from the seed-metering drive
wheels, causing excessive wheel slippage and lower
seeding rate.

The operator's manual serves as a guide for setting
the planter. Final adjustments, such as planting depth
and seeding rate, should be made in the field. Also,
soil penetration and residue cutting should be
checked in the field and appropriate adjustments
made to ensure proper seed placement and to en-
hance seed-to-soil contact.

Strip Till

Long-term research and farmer experience in the Mid-
west show that traditional no-till planting (using
planters with one no-till coulter in front of each row)
usually maintains yield potential on well-drained and
very low organic matter soils. However, in some
cases, no-till planting may have a yield disadvantage
compared to full-width tillage systems. One or more
of the following conditions are usually associated
with reduced no-till yields: heavy residue levels, poor
soil drainage, cool soil temperatures, very early plant-
ing, uneven residue distribution, or an uneven soil
surface. Such conditions can result in reduced stand,
uneven emergence, slow early-season growth, and de-
layed maturity — all potential yield-limiting factors.
These negative factors reduce com yield more than
soybean yield, since soybeans have a greater ability to

13 • NO TILLAGE

131

overcome early-season stress and to compensate for
reduced stand.

To offset some of the limitations of traditional no-
till planting, many farmers are now using spiked
wheels as a planter attachment to prepare a residue-
free strip for each row. Another method for improving
the in-row area is to use strip till. Strip till is a system
whereby a narrow strip is tilled, either at planting or
before planting in early spring or the previous fall.
One method involves equipping each planter row
I with two or three staggered, nonpowered fluted
coulters that loosen soil and partially incorporate resi-
, due in a 6- to 8-inch band ahead of planter units. Stag-
! gered coulters and spiked wheels are often used on
the same planter. Another method of loosening soil
includes the use of powered rotary tillers set for strip
tillage, either before planting or with the planter.
A new form of strip tillage involves planting in the
I tilled strips created by an anhydrous ammonia appli-
' cator equipped with special attachments. The attach-
ments include a coulter mounted in front of each
knife to cut residue; each knife is equipped with a
"sealing wing" or "mole knife" and is followed by a
pair of sealing disks. The goal is to form small ridges
in which the crop will be planted. It is common for
anhydrous ammonia to be applied as the ridges are
formed. Attachments are also available to inject P and
K in the same operation. If anhydrous ammonia is ap-
plied in the strip prepared for planting, the operation
should be done in the fall to reduce the potential for
ammonia injury to com seedlings that often occurs if
applied in the spring.

Studies in the northern Com Belt show an advan-
tage for residue-free rows for com. In central Iowa,
maintaining a residue-free band for the row regained
about 80 percent of the yield loss for no-till compared
to a clean-tilled seedbed for continuous com. In Min-
nesota, residue removal from the row area was benefi-
cial for no-till com. However, with the longer growing

season in Kentucky, removing residue from the row
area increased continuous com yield only one year
out of four. Most research has shown only a small
growth or yield response to residue removal or strip
tillage compared to traditional no-till planting of com
in soybean residue.

Since the equipment for most strip tillage methods
including an anhydrous ammonia applicator do a
considerable amount of tillage, the potential for seri-
ous soil erosion may increase compared to traditional
no-till, especially if rows run up and down slope. The
problem may be especially critical on highly erodable
fields following soybeans.

No-TiLL Drills

Erosion control is improved when soybeans are
drilled in row spacings of 10 inches or less, which also
provides a nearly equidistant plant spacing, resulting
in greater yield potential. Narrow rows form a full
canopy sooner, shading the soil earlier and reducing
weed pressure. No-till drilling a crop leaves the field
relatively smooth for easier harvesting and for no-till-
ing the following crop. It is difficult to obtain consis-
tent depth of planting and uniform stand establish-
ment in a field that has a rough surface, which may
have been caused by previous wheel traffic, small
ridges created by tillage, a planter, a row cultivator, or
erosion.

Soil-engaging components of no-till drills are much
like those on no-till planters. They must be able to cut
and handle large amounts of residue, penetrate the
soil, and establish good seed-to-soil contact.

There are two basic types of no-till drills: converted
drills (conventional drills equipped with double-disk
seed furrow openers to which a gang of coulters has
been added) and drills designed specifically for no-
till. For many situations, either type may provide sat-
isfactory performance. However, in fields with heavy

Figure 13.02. Drill mounted on a coulter cart.

Figure 13.03. No-till drill with coulters.

132

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

residue and hard surface soils — and in large-scale op-
erations— a drill designed specifically for no-till can
probably be justified.

A converted drill (Figure 13.02) is usually a three-
point mounted conventional drill on a wheeled car-
rier, equipped with a coulter positioned in front of
each double-disk seed furrow opener. Ripple or fluted
coulters are commonly used (Figure 13.01). Weight
may need to be added to the carrier for sufficient pen-
etration of the coulters. It is important for the seed
openers to track in the coulter slots.

Drills designed specifically for no-till (Figure 13.03)
have all soil-engaging components on a single unit. In
hard soil conditions, additional weight may be
needed to help ensure penetration by these compo-
nents. On some no-till drills, the openers are stag-
gered to allow improved residue flow.

Individual openers should have sufficient down-
pressure and independent depth control with enough
vertical movement to allow all rows to operate at the
desired depth. Depth control is more consistent if
fields are smooth.

Some no-till drills are not equipped with coulters
but use the seed furrow openers to cut the residue
andpenetrate the soil to seeding depth. These drills
often use staggered double-disk seed furrow openers
without a coulter in front. On these drills, the leading
disk, usually about Vi to 1 inch in front of the other,
cuts the residue, and the following disk aids in open-
ing the seed furrow. At least one brand of drill uses a
large-diameter single disk set at a slight angle to cut
through the residue and serve as a seed furrow
opener. This design provides for minimal soil distur-
bance and requires less weight for penetration.

Spacing, Weight, and Down Pressure

A wider row spacing (10 or 12 inches rather than 7 or
8) on a no-till drill provides more clearance for resi-
due flow and requires less weight per unit of drill
width for soil penetration.

Depending on coulter type and width, opener de-
sign, and field conditions, up to 600 pounds per row
may be needed on a drill to provide for adequate pen-
etration. Down-pressure springs on individual rows
must transfer enough weight from the drill frame for
all soil-engaging components to function as intended.
Coulters and seed furrow openers should operate at
the desired seed-depth setting. Depth control devices
and seed-press wheels must be in firm contact with
the soil. As the springs are tightened, especially in
hard soil conditions, they may physically lift the drive
mechanism of the drill off the ground, causing a re-
duced seeding rate due to wheel slippage. In such

conditions, extra weight on the drill frame may solve ' '
the problem.

Press Wheels and Depth Control

With a converted drill, depth of seed placement may
be controlled by the depth of the coulter gang or by
the press wheels behind each seed opener. When
seeding depth is controlled by the coulters, seed-to-
soil contact is obtained with a narrow press wheel
running directly over the seed. Using this method, extra
weight or heavy down-pressure springs are not needed
for the seed furrow openers, but extra weight or load
may be needed on the coulter carrier. A harrow be-
hind the drill is often used to improve seed coverage.

Several no-till drills use coulters to cut residue and
use both the coulters and seed furrow openers to
loosen a strip of soil. A wide press wheel mounted be-
hind each of the seed furrow openers controls depth.
Total weight and down-pressure springs must be suf-
ficient to force the coulters and openers into the soil
the desired planting depth and keep adequate pres-
sure on the press wheels. The press wheels must be
wide enough to ride on firm soil adjacent to the seed
furrow in order to gauge seeding depth and help
cover the seed.

Another option for no-till drills is the use of a pair
of angled press wheels behind each opener to control
planting depth. Clearance between adjacent rows may
prevent the use of angled press wheels in large
amounts of residue.

General Operation

No-till drills must be heavier than conventional drills.
Enough weight and sufficient down-pressure springs
are needed to cause the soil-engaging components to
function properly. Weight is essential for cutting resi-
due and penetrating soil. Adequate weight also keeps
the depth control wheels, the seed press wheels, and
the drive mechanism in firm contact with the soil.

More tractor power is required to lift and pull the
greater weight of a no-till drill, especially at high oper-
ating speeds. High operating speeds may assist residue
flow but also may sacrifice some seed depth uniformity.

Residue flow through the drill is better if the resi-
due is not shredded. When residue is standing and at-
tached to the soil, less of it has to be cut by the drill,
and the soil holds the residue as the drill passes
through it. Leaving concentrations of residue in the
field at harvest should be avoided; well-distributed
residue provides better erosion control and passes
through a drill better. A chaff spreader, especially for
combines with wide headers, is important.

13 'NO TILLAGE

133

WEED Control

No-till systems require a well-designed weed control
program, including proper timing and accurate appli-
cation of herbicides. Effective programs are available
that include the application of herbicides as early pre-
plant, bumdown, preemergence, and postemergence.

Early Preplant Plus Preemergence
OR Postemergence

Early weed growth may be successfully controlled by
applying an early preplant (EPP) herbicide. An EPP
herbicide is usually applied prior to the germination
of most weed seed. However, if the EPP herbicide has
postemergence activity or foliar activity, it can effec-
tively control small emerged weeds. EPP herbicides,
such as Extrazine for com and Canopy for soybeans,
can provide both bumdown and residual control.
However, with some herbicides it is often preferable
to use a treatment including Roundup plus 2,4-D for

j improved control of existing vegetation.

An EPP herbicide application is unlikely to pro-
vide season-long weed control, especially if the appli-

; cation is made relatively early or if the soil is dis-

\ turbed significantly during the planting application.
An additional herbicide treatment may be needed.
One option is to use a split application, with one por-
tion applied EPP and the other soon after planting.

i Another option is to apply an EPP treatment and fol-
low up with a postemergence herbicide program.

The EPP program has several advantages. Perfor-
mance is usually excellent when a herbicide is ap-
plied in March or early April because cool weather
and spring rains enhance performance. Also, the ex-
pense of a "bumdown herbicide" may be eliminated.
The main disadvantage of EPP programs is that for
late-planted crops, preemergence or postemergence
treatments may be needed to maintain season-long
control.

BuRNDOWN Plus Preemergence
OR Postemergence

With no-till, weeds established prior to planting and
weeds that emerge later must all be controlled.
Weeds established before planting can be controlled
with "bumdown" herbicides, such as Roundup and
Gramoxone Extra. With early planting, especially of
com, there may be no weeds present, and a
bumdown herbicide may not be needed. Emerged
weeds, if small, may also be controlled by some
preemergence herbicides applied at planting. If
preemergence herbicides are not used, several excel-
lent postemergence herbicides are available. The
type of herbicide selected and the application rate

will depend on the type of vegetation present and
the crop.

See the section titled "Conservation Tillage and
Weed Control" in Chapter 15 and University of
Illinois College of Agriculture Circular 1306, Weed
Control Systems for Lo-Till and No-Till for addi-
tional information on weed control using a no-till
system.

FERTILIZER IVlANAGEMENT

Since soils are cooler, wetter, and less well-aerated
with no-till, the ability of crops to utilize nutrients
may be altered and adjustments in fertilizer manage-
ment may be important.

Stratification of immobile nutrients, such as phos-
phorus and potassium, with high concentrations near
the soil surface and decreasing concentrations with
depth, has been routinely observed where no-till and
other conservation tillage systems (such as disk and
chisel plow) have been used for at least 3 to 4 years.
This stratification results from both the addition of
fertilizer to the soil surface and the "cycling" of nutri-
ents by plants. Plant roots uptake nutrients from well
below the soil surface; some of these nutrients are
then deposited on the soil surface in the form of crop
residue.

When soil moisture is adequate, nutrient stratifica-
tion has not been found to decrease nutrient availabil-
ity because root activity in the fertile zone near the
soil surface is sufficient to supply plant needs. The
residue enhances root activity near the soil surface by
reducing evaporation of water, which helps keep the
surface soil moist and cool. If the surface dries out
and the shallow roots become inactive, nutrient up-
take could be reduced, especially if the lower portions
of the old plow layer are most likely to be the areas of
lower fertility.

Details on fertility are covered in Chapter 11, "Soil
Testing and Fertility." The key points on fertility man-
agement for no-till are as follows:

A. Liming to neutralize soil acidity is important, espe-
cially with surface applications of nitrogen (N) fer-
tilizer. Lime rates may need to be adjusted and ap-
plications more frequent with no-till. Where
possible, lime should be incorporated as needed
prior to establishing a no-till system.

B. Any phosphorus and potassium deficiencies
should be corrected prior to switching to no-till be-
cause surface applications move deeper into the
soil very slowly.

C. After several years of no-till, it may be desirable to
take samples for nutrient analysis from near the

134

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

soil surface (0 to 3 inches deep) and from lower
portions of the old tillage zone (3 to 7 inches deep).
If depletion of nutrients or accumulation of acidity
in the lower portion occurs and crops show nutri-
ent deficiency, moldboard or chisel plowing can
correct the stratification problem.

D. Starter fertilizer appears to be more important with
no-till, especially for continuous com. More infor-
mation on the use of starter for no-till is provided
in Chapter 11.

E. Nitrogen management is very important to success
with no-till planting of com. Anhydrous ammonia
applied in the spring before planting can severely
injure or kill seedlings if com is planted directly
above it. Anhydrous ammonia can safely be ap-
plied in the fall (sidedressed after planting) or in
the spring before planting (between rows to be
planted). If rain is not received within 3 days after
application, there is a potential for loss of a portion
of the nitrogen surface applied on no-till in the
form of urea or urea-ammonium nitrate solutions.
To minimize this loss potential, apply these prod-
ucts 1 to 2 days ahead of a rain, or use a urease
inhibitor.

SOIL DENSITY

Untilled soil usually has more density (weight per
unit volume) and less air space than tilled soil. The
density of tilled soil is lower after primary tillage, but
with secondary tillage, wheel traffic, and several wet-
ting and drying periods, it becomes nearly equal in
density to untilled soil by harvest.

Soil densities greater than 1.4 to 1.6 g/cc have been
shown to restrict root growth when rainfall is either
more or less than optimum. With no-till, soil density
sometimes reaches this critical level. High soil density
may also reduce soil drainage, soil aeration, and fertil-
izer uptake, while increasing the potential for herbi-
cide injury.

Over time, however, changes occur in the soil lan-
der no-till which may improve the effect of dense soil
on plant rooting: organic matter near the soil surface
may improve aggregation and air movement in the
soil, and old root channels and earthworm burrows
remain as undisturbed pathways for new roots. Thus
high soil density, which may limit rooting in tilled soU,
may not have the same effect in continuous no-till.

Excessive compaction can cause yield decreases
when too much or too little soil moisture is available.
With too much water, compaction reduces drainage,
causes denitrification, and limits the availability of
oxygen to the roots. With too little moisture, the root

system must seek moisture from the subsoil, and ex-
cessive compaction may prevent the roots from get-
ting to that moisture.

SOIL Organic Matter
AND Aggregation

Soil organic matter content tends to stabilize at a cer-
tain level with any tillage system and crop rotation.
With no-till, partially decayed plant material tends to
concentrate near the soil surface because the residue
is left on the surface and plant roots tend to be more
numerous near the surface.

Continuous no-till leads to better soil aggregation.
A high level of aggregation indicates good soil struc-
ture, which improves plant emergence and rooting,
aeration, drainage, and water infiltration. Good soil
structure also decreases the susceptibility of soil to
compaction.

An Indiana study showed that after 5 years of con-
tinuous no-till com, aggregation in the top 2 inches of
soil was increased. However, moldboard plowing the
plots returned the aggregation index near the soil sur-
face to its original level.

Earthworm and root Channels

Physical properties of soil are not determined solely
by mechanical manipulations of the soil or by surface
residue. Biological populations can significantly im-
prove soil physical conditions important to plant
growth and may play a significant role in maintaining
good soil tilth in the absence of tillage.

Channels for water movement and rooting are pro-
vided by earthworms and roots of previous crops.
Tillage tends to reduce earthworm populations by
speeding soil drying and freezing rates, disrupting
earthworm burrows, and burying the plant residue
that worms use for food. Much more research is
needed to explain all of the impact of no-till on soil
biology.

Soil Drainage

Research and farmer experiences during the past 20
years have shown that no-till may increase crop yields
on soils with no drainage problems. Improving drain-
age on poorly drained soil improves crop perfor-
mance, especially with no-till.

Alleviating Soil Compaction

Problems such as compacted layers or "tillage pans,"
excessive traffic areas, ruts from wheel traffic, and
livestock trails are troublesome with no-till. Com-
pacted layers from previous plowing and disking

13 'NO TILLAGE

135

can limit rooting. Natural soil processes such as
freezing and thawing, wetting and drying, and the
channeling of earthworms and roots eventually
loosen or reduce the effects of compacted zones un-
der no-till, but these processes are slow. The use of a
chisel plow or subsoiler before beginning no-till
should speed the process if compaction is not rein-
troduced by subsequent traffic and excessive second-
ary tillage. Benefits from subsoiling can generally be
expected only when it disrupts or loosens a drain-
age- or root-restricting layer. The disruption allows
excess water to drain and plant roots to explore a
greater volume of soil.

Some soils have a natural hardpan or claypan at a
depth of 12 to 18 inches. Generally, the layers below
the pan are also compacted and poorly drained. In
such cases, chiseling or subsoiling is ineffective be-
cause it is impossible to break through to a better-
drained layer.

Soil surface compaction and non-uniformity from
wheel or livestock traffic can cause uneven seed
placement and poor stands in no-till. To the extent
possible, no-till fields should be kept smooth. Where
the soil surface is not smooth, shallow tillage may be
needed to obtain uniform seed placement.

Crop Rotation

In general, crop rotation improves chances for success
with no-till. Several long-term studies show that a
com/soybean rotation improves the yield potential of
no-till com compared to continuous com. With con-
tinuous no-till com, several factors — including lower
soil temperature and allelopathy — may cause the
lower yield potential. Lower yields have been espe-
cially evident on poorly drained soil and high
organic-matter soils.

Small grains such as wheat and rye germinate at a
much lower soil temperature than com (32°F versus
55°F), but they also benefit from crop rotation when
residue is left on the soil surface. For small grains, the
deleterious effects from monoculture are most likely
due to allelopathy and disease buildup.

The use of row cleaners may improve the germina-
tion, early growth rate, and potential yield of no-till
crops planted without rotation.

Adaptability of No-Till
TO Specific Locations

Soil, climate, and crop rotation influence the success
of no-till. In addition, success is influenced by pest
control, fertility practices, and management experi-
ence of the farm operator. The decision to adopt no-
till may be based on net return, potential for reduced
soil erosion, or eligibility for government programs.
Yield potential of crops grown with no-till is an im-
portant consideration.

Several states have classified soils into tillage man-
agement groups for com and soybean production.
Soil types are grouped according to unique soil prop-
erties and their influence on crop yield with no-till
planting. Soil characteristics include drainage, texture,
organic matter, and slope. A summary of the classifi-
cation as might be applied to Illinois follows:

A. Equal yield. In central and northern Illinois, when
crops are rotated and when no-till is used on natu-
rally well-drained soils, or on slopes greater than
6 percent, no-till should provide yield potential
equal to that of other systems for com, soybeans,
and wheat.

B. Higher yield. In southern Illinois, with crop rotation,
well-drained soil, slope greater than 6 percent, or
very low organic-matter soil, no-till should provide
a higher yield potential than other tillage systems.

C. Higher yield. In southern Illinois, on light (very
low organic matter), somewhat poorly drained,
and poorly drained silt loams (that are nearly
level to gently sloping and overlie very slowly
permeable fragipan-like soil layers that restrict
plant rooting and water movement), no-till yield
potential should be higher than with other tillage
systems.

D. Lower yield. On dark, poorly drained silty clay
loams to clay soils with 0 to 2 percent slope,
slightly lower yields are expected with no-till com-
pared to other tillage systems.

An established sod or cover crop must be managed
to avoid excessive water use and mouse and mole prob-
lems prior to no-till planting com or other grain crop.

Author

John C. Siemens

Department of Agricultural Engineering

Chapter 14.

Water Management

A superior water-management program seeks to
provide an optimum balance of water and air in
the soil, which allows full expression of genetic
potential in plants. The differences among poor, av-
erage, and record crop yields generally can be at-
tributed to the amount and timing of the soil's wa-
ter supply.

Improving water management is an important way
to increase crop yields. By eliminating crop-water
stress, you obtain more benefits from improved cul-
tural practices and realize the full yield of the culti-
vars now available.

To produce maximum yields, the soil must be able
to provide water as it is needed by the crop. But the
soil seldom has just the right amount of water for
maximum crop production; a deficiency or a surplus
usually exists. A good water-management program
seeks to avoid both extremes through a variety of
measures. These measures include draining water-
logged soils; making more effective use of the water-
holding capacity of soils so that crops will grow dur-
ing periods of insufficient rainfall; increasing the soil's
ability to absorb moisture and conduct it down
through the soil profile; reducing water loss from the
soil surface; and irrigating soils with low water-hold-
ing capacity.

In Illinois, the most frequent water-management
need is improved drainage. Initial efforts in the nine-
teenth century to artificially drain Illinois farmland
made our soils among the most productive in the
world. Excessive water in the soil limits the amount of
oxygen available to plants and thus retards growth.
This problem occurs where the water table is high or
where water ponds on the soil surface. Removing ex-
cess water from the root zone is an important first
step toward a good water-management program. A
drainage system should be able to remove water from
the soil surface and lower the water table to about 12
inches beneath the soil surface in 24 hours and to 21
inches in 48 hours.

THE BENEFITS OF DRAINAGE

A well-planned drainage system will provide a num-
ber of benefits: better soil aeration, more timely field
operations, less flooding in low areas, higher soil tem-
peratures, less surface runoff, better soil structure,
better incorporation of herbicides, better root devel-
opment, higher yields, and improved crop quality.

Soil aeration. Good drainage ensures that roots
receive enough oxygen to develop properly. When the
soil becomes waterlogged, aeration is impeded and
the amount of oxygen available is decreased. Oxygen
deficiency reduces root respiration and often the total
volume of roots developed. It also impedes the trans-
port of water and nutrients through the roots. The
roots of most nonaquatic plants are injured by oxygen
deficiency, and prolonged deficiency may result in the
death of some cells, entire roots, or in extreme cases
the whole plant. Proper soil aeration also will prevent
rapid losses of nitrogen to the atmosphere through
denitrification.

Timeliness. Because a good drainage system in-
creases the number of days available for planting
and harvesting, it can enable you to make more
timely field operations. Drainage can reduce planting
delays and the risk that good crops will be drowned
or left standing in fields that are too wet for harvest.
Good drainage may also reduce the need for addi-
tional equipment that is sometimes necessary to
speed up planting when fields stay wet for long
periods.

Soil temperature. Drainage can increase soil sur-
face temperatures during the early months of the
growing season by 6° to 12°F. Warmer temperatures
assist germination and increase plant growth.

Surface runoff. By enabling the soil to absorb and
store rainfall more effectively, drainage reduces runoff
from the soil surface and thus reduces soil erosion.

Soil structure. Good drainage is essential in main-
taining the structure of the soil. Without adequate

IJir

14 • WATER MANAGEMENT

137

drainage the soil remains saturated, precluding the
normal wetting and drying cycle and the correspond-
ing shrinking and swelling of the soil. The structure of
saturated soil will suffer further damage if tillage or
harvesting operations are performed on it.

Herbicide incorporation. Good drainage can help
avoid costly delays in applying herbicide, particularly
postemergence herbicides. Because some herbicides
must be applied during the short time that weeds are
still relatively small, an adequate drainage system
may be necessary for timely application. Drainage
may also help relieve the cool, wet-stress conditions
that increase crop injury by some herbicides.

Root development. Good drainage enables plants
to send roots deeper into the soil so they can extract
moisture and nutrients from a larger volume of soil.
Plants with deep roots are better able to withstand
drought.

Crop yield and quality. All of the benefits previ-
ously mentioned contribute to greater yields of
higher-quality crops. The exact amount of the yield
and quality increases depends on the type of soil, the
amount of rainfall, the fertility of the soil, crop -man-
agement practices, and the level of drainage before
and after improvements are made. Of the few studies
that have been conducted to determine the benefits of
drainage, the most extensive in Illinois was initiated
at the Agronomy Research Center at Brownstown.
This study evaluated drainage and irrigation treat-
ments with Cisne and Hoyleton silt loams.

Drainage Methods

A drainage system may consist of surface drainage,
subsurface drainage, or some combination of both.
The kind of system you need depends in part upon
the ability of the soil to transmit water. The selection
I of a drainage system ultimately should be based on
economics. Surface drainage, for example, would be
most appropriate where soils are impermeable and
would therefore require too many subsurface drains
to be economically feasible. Soils of this type are com-
mon in southern Illinois.

Surface Drainage

; A surface drainage system is most appropriate on flat
land with slow infiltration and low permeability and
on soils with restrictive layers close to the surface.

' This type of system removes excess water from the
soil surface through improved natural channels, hu-
man-made ditches, and shaping of the land surface. A
properly planned system eliminates ponding, pre-

I vents prolonged saturation, and accelerates the flow

of water to an outlet without permitting siltation or
soil erosion.

A surface drainage system consists of a farm main,
field laterals, and field drains. The farm main is the
outlet serving the entire farm. Where soil erosion is a
problem, a surface drain or waterway covered with
vegetation may serve as the farm main. Field laterals
are the principal ditches that drain adjacent fields or
areas on the farm. The laterals receive water from
field drains, or sometimes from the surface of the
field, and carry it to the farm main. Field drains are
shallow, graded channels (with relatively flat side
slopes) that collect water within a field.

A surface drainage system sometimes includes di-
versions and interceptor drains. Diversions are chan-
nels constructed across the slope of the land to inter-
cept surface runoff and prevent it from overflowing
bottomlands. Diversions are usually located at the
bases of hills. These channels simplify and reduce the
cost of drainage for bottomlands.

Interceptor drains collect subsurface flow before it
resurfaces. These channels may also collect and re-
move surface water. They are used on long slopes that
have grades of 1 percent or more and on shallow, per-
meable soils overlying relatively impermeable sub-
soils. The location and depth of these drains are deter-
mined from soil borings and the topography of the
land.

The principal types of surface drainage configura-
tions are the random and parallel systems (Figure
14.01). The random system consists of meandering
field drains that connect the low spots in a field and
provide an outlet for excess water. This system is
adapted to slowly permeable soils with depressions
too large to be eliminated by smoothing or shaping
the land.

The parallel system is suitable for flat, poorly
drained soils with many shallow depressions. In a
field that is cultivated up and down a slope, parallel
ditches can be arranged to break the field into shorter
lengths. The excess water thus erodes less soil because
it flows over a smaller part of the field before reaching
a ditch. The side slopes of the parallel ditches should
be flat enough to permit farm equipment to cross
them. The spacing of the parallel ditches will vary ac-
cording to the slope of the land.

For either the random or parallel systems to be
fully effective, minor depressions and irregularities in
the soil surface must be eliminated through land
grading or smoothing.

Bedding is another surface drainage method that is
used occasionally. The land is plowed to form a series
of low, narrow ridges that are separated by parallel.

138

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Random

Parallel

Figure 14.01. Types of surface drainage systems

dead furrows. The ridges are oriented in the direction
of the steepest slope in the field. Bedding is adapted
to the same conditions as the parallel system, but it
may interfere with farm operations and does not
drain the land as completely. It is not generally suited
for land that is planted in row crops because the rows
adjacent to the dead furrows will not drain satisfacto-
rily. Bedding is acceptable for hay and pasture crops,
although it will cause some crop loss in and adjacent
to the dead furrows.

Subsurface Drainage

Many of the deep, poorly drained soils of central and
northern Illinois respond favorably to subsurface
drainage. A subsurface drainage system is used in
soils permeable enough that the drains do not have to
be placed too closely together. If the spacing is too
narrow, the system will not be economical. By the
same token, the soil must be productive enough to
justify the investment. Because a subsurface drainage
system functions only as well as the outlet, a suitable
one must be available or constructed. The topography
of the fields also must be considered because the in-
stallation equipment has depth limitations and a
minimum amount of soil cover is required over the
drains.

Subsurface systems are made up of an outlet or
main, sometimes a submain, and field laterals. The
drains are placed underground, although the outlet is
often a surface drainage ditch. Subsurface drainage
conduits are constructed of clay, concrete, or plastic.

There are four types of subsurface systems: the
random, the herringbone, the parallel, and the double-
main (Figure 14.02). A single system or some combi-
nation of systems may be chosen according to the to-
pography of the land.

For rolling land, a random system is recom-
mended. With this system, the main drain is usually
placed in a depression. If the wet areas are large, the
submains and lateral drains for each area may be
placed in a gridiron or herringbone pattern to achieve
the required drainage.

With the herringbone system, the main or submain
is often placed in a narrow depression or on the major
slope of the land. The lateral drains are angled up-
stream on either side of the main. This system some-
times is combined with others to drain small or
irregular areas. Because two laterals intersect the
main at the same point, however, more drainage than
necessary may occur at that intersection point. The
herringbone system may also cost more because it
requires more junctions. Nevertheless, it can provide

14 • WATER MANAGEMENT

139

Farm main

Field lateral

Farm main

Random

Herringbone

Field
lateral

Farm main

♦

Field lateral

♦

■^

Farm main

Parallel

Double main

Figure 14.02. Types of subsurface drainage systems. The arrows indicate the direction of water flow.

140

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

the extra drainage needed for the heavier soils found
in narrow depressions.

The parallel system is similar to the herringbone
system, except that the laterals enter the main from
only one side. This system is used on flat, regularly
shaped fields and on uniform soil. Variations are often
used with other patterns.

The double-main system is a modification of the
parallel and herringbone systems. It is used where a
depression, frequently a natural watercourse, divides
the field in which drains are to be installed. Some-
times the depression may be wet due to seepage from
higher ground. A main placed on either side of the de-
pression intercepts the seepage water and provides an
outlet for the laterals. If only one main were placed in
the center of a deep and unusually wide depression,
the grade of each lateral would have to be changed at
some point before it reaches the main. A double-main
system avoids this situation and keeps the grade lines
of the laterals uniform.

The advantage of a subsurface drainage system is
that it usually drains soil to a greater depth than sur-
face drainage. Subsurface drains placed 36 to 48
inches deep and 80 to 100 feet apart are suitable for
crop production on many medium-textured soils in
Illinois. When properly installed, these drains require
little maintenance, and because they are underground
they do not obstruct field operations.

For more specific information about surface and
subsurface drainage systems, obtain Circular 1226,
The Illinois Drainage Guide, from your local Extension
adviser. This publication discusses the planning, de-
sign, installation, and maintenance of drainage sys-
tems for a wide variety of soil, topographic, and cli-
matic conditions.

BENEFITS OF IRRIGATION

During an average year, most regions of Illinois re-
ceive ample rainfall for growing crops, but, as shown
in Figure 14.03, rain does not occur when the crops
need it the most. From May to early September, grow-
ing crops demand more water than is provided by
precipitation. For adequate plant growth to continue
during this period, the required amount of water
must be supplied by stored soil water or by irrigation.
During the growing season, crops on deep, fine-tex-
tured soils may draw upon moisture stored in the soil,
if the normal amount of rainfall is received through-
out the year. But if rainfall is seriously deficient or if
the soil has little capacity for holding water, crop yield
may be reduced. Yield reductions are likely to be most
severe on sandy soils or soils with claypans. Claypan
soils restrict root growth, and both types of soils often

M 4

o
-S 3

Potential
water loss

Precipitation

2
1

Jan.

Mar.

May

July

Sept.

Nov.

Figure 14.03. Average monthly precipitation and potential
moisture loss from a growing crop in central Illinois.

cannot provide adequate water during the growing
season.

To prevent crop water stress during the growing
season, more and more producers are using irrigation.
It may be appropriate where water stress can substan-
tially reduce crop yields and where a supply of usable
water is available at reasonable cost. Irrigation is still
most widely used in the arid and semi-arid parts of
the United States, but it can be beneficial in more hu-
mid states such as Illinois. Almost yearly, Illinois com
and soybean yields are limited by drought to some
degree, even though the total annual precipitation
exceeds the water lost through evaporation and
transpiration (ET).

With current cultural practices, a good crop of com
or soybeans in Illinois needs at least 20 inches of wa-
ter. All sections of the state average at least 15 inches
of rain from May through August. Thus satisfactory
yields require at least 5 inches of stored subsoil water
in a normal year.

Crops growing on deep soil with high water-hold-
ing capacity, that is, fine-textured soil with high or-
ganic-matter content, may do quite well if precipita-
tion is not appreciably below normal and if the soil is
filled with water at the beginning of the season.

Sandy soils and soils with subsoil layers that re-
strict water movement and root growth cannot store
as much as 5 inches of available water. Crops planted
on these soils suffer from inadequate water every
year. Most of the other soils in the state can hold more
than 5 inches of available water in the crop-rooting
zone. Crops on these soils may suffer from water defi-
ciency when subsoil water is not fully recharged by
about May 1 or when summer precipitation is appre-
ciably below normal or poorly distributed throughout
the season.

14 • WATER MANAGEMENT

141

I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I

Central

Southern

5 I I i I I I I i I I I I I I I I I I i I I I I I I

10 20 10 20 10 20 10 20 10 20

March

April

May

June

July

I I I I I I I I I I
10 20 10 20

August September

Figure 14.04. Chance of at least one inch of rain in Illinois in one week.

I I I I I I
10 20
October

The probability of getting at least one inch of rain
in any week is shown in Figure 14.04. One inch of rain
per week will not replace ET losses during the sum-
mer, but it can keep crop-water stress from severely
limiting final grain yields on soils that can hold water
reasonably weU. This probability is lowest in all sections
of Illinois during July when com normally is pollinat-
ing and soybeans are flowering.

Water stress delays the emergence of com silks and
shortens the period of pollen shedding, thus reducing
the time of overlap between the two processes. The
result is incomplete kernel formation, which can have
disastrous effects on com yields.

Com yields may be reduced by as much as 40 per-
cent when visible wilting occurs on four consecutive
days at the time of silk emergence. Studies have also
shown that severe drought during the pod-filling
stage causes similar yield reductions in soybeans.

Increasing numbers of farmers are installing irriga-
tion systems to prevent the detrimental effects of wa-
ter deficiency. Some years of below-normal summer
rainfall and other years of erratic rainfall distribution

throughout the season have contributed to the in-
crease. As other yield-limiting factors are eliminated,
adequate water becomes increasingly important to en-
sure top yields.

Most of the development of irrigation systems has
occurred on sandy soils or other soils with corre-
spondingly low levels of available water. Some instal-
lations have been made on deeper, fine-textured soils,
and other farmers are considering irrigation of such
soils.

DECIDING TO Irrigate

The need for an adequate water source cannot be
overemphasized when one is considering irrigation. If
a producer is convinced that an irrigation system will
be profitable, an adequate source of water is neces-
sary. Such sources do not exist now in many parts of
the state. Fortunately, underground water resources
are generally good in the sandy areas where irrigation
is most likely to be needed. A relatively shallow well
in some of these areas may provide enough water to

142

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

irrigate a quarter section of land. In some areas of Illi-
nois, particularly the northern third, deeper wells
may provide a relatively adequate source of irrigation
water.

Some farmers pump their irrigation water from
streams, a relatively good and economical source, if
the stream does not dry up in a droughty year. Im-
pounding surface water on an individual farm is also
possible in some areas of the state, but this water
source is practical only for small acreages. However,
an appreciable loss may occur both from evaporation
and from seepage into the substrata. Generally, 2 acre-
inches of water should be stored for each acre-inch ac-
tually applied to the land.

A 1-inch application on 1 acre (1 acre-inch) requires
27,000 gallons of water. A flow of 450 gallons per
minute provides 1 acre-inch per hour. Thus a 130-acre,
center-pivot system with a flow of 900 gallons per
minute can apply 1 inch of water over the entire field
in 65 hours of operation. Because some of the water is
lost to evaporation and some may be lost from deep
percolation or runoff, the net amount added is less
than 1 inch.

The Illinois State Water Survey and the Illinois
State Geological Survey (both located in Urbana) can
provide information about the availability of irriga-
tion water. Submit a legal description of the site
planned for development of a well and request infor-
mation regarding its suitability for irrigation-well de-
velopment. Once you decide to drill a well, the Water
Use Act of 1983 requires you to notify the local Soil
and Water Conservation District office if the well is
planned for an expected or potential withdrawal rate
of 100,000 gallons or more per day. There are no per-
mit requirements or regulatory provisions.

An amendment passed in 1987 allows Soil and Wa-
ter Conservation districts to limit the withdrawals
from large wells if domestic wells meeting state stan-
dards are affected by localized drawdown. The legis-
lation currently affects Kankakee, Iroquois, Tazewell,
and McLean counties.

The Riparian Doctrine, which governs the use of
surface waters, states that one is entitled to a reason-
able use of the water that flows over or adjacent to his
or her land as long as one does not interfere with
someone else's right to use the water. No problem re-
sults as long as water is available for everybody. But
when the amount of water becomes limited, legal de-
terminations become necessary as to whether one's
water use interferes with someone else's rights. It may
be important to establish a legal record to verify the
date on which the irrigation water use began.

Assuming that it will be profitable to irrigate and
that an assured supply of water is available, how do

you find out what type of equipment is available and
what is best for your situation? University representa-
tives have discussed this question in various meetings
around the state, although they cannot design a sys-
tem for each individual farm. Your local Extension
adviser can provide lists of dealers located in and
serving Illinois. This list includes the kinds of equip-
ment each dealer sells, but it will not supply informa-
tion about the characteristics of those systems.

If you contact a number of dealers to discuss your
individual needs in relation to the type of equipment
they sell, you will be in a better position to determine
what equipment to purchase.

Subsurface Irrigation

Subirrigation can offer the advantages of good drain-
age and irrigation using the same system. During wet
periods, the system provides drainage to remove ex-
cess water. For irrigation, water is forced back into the
drains and then into the soil.

This method is most suitable for land where the
slope is less than 2 percent, with either a relatively
high water table or an impermeable layer at 3 to 10
feet below the surface. The impermeable layer ensures
that applied water will remain where needed and that
a minimum quantity of water will be sufficient to
raise the water table.

The free water table should be maintained at 20 to
30 inches below the surface. This level is controlled
and maintained at the head control stands, and water
is pumped accordingly. In the event of a heavy rain-
fall, pumps must be turned off quickly and the drains
opened. As a general rule, to irrigate during the grow-
ing season, you must deliver a minimum of 5 gallons
per minute per acre.

The soil should be permeable enough to allow
rapid water movement so that plants are well sup-
plied in peak consumption periods. Tile spacing is a
major factor in the cost of the total system and is per-
haps the most important single variable in its design
and effectiveness. Where subirrigation is suitable, the
optimum system will have closer drain spacings than
a traditional drainage system.

IRRIGATION FOR DOUBLE-CROPPING

Proper irrigation can eliminate the most serious prob-
lem in double-cropping: inadequate water to get the
second crop off to a good start. No part of Illinois has
better than a 30 percent chance of getting an inch or
more of rain during any week in July and most weeks
in August. With irrigation equipment available,
double-crop irrigation should be a high priority. If
you are considering irrigating, evaluate the possibility

14 • WATER MANAGEMENT

143

of double-cropping in making your decision. Soy-
beans planted at Urbana on July 6 following a wheat
harvest have yielded as much as 38 bushels per acre
with irrigation. In Mason County, soybeans planted
the first week in July have yielded as much as 30
bushels per acre with irrigation.

While it may be difficult to justify investing in an
irrigation system for double-cropping soybeans alone,
the potential benefits from irrigating other crops may
make the investment worthwhile. Some farmers re-
port that double-cropping is a top priority in their ir-
rigation programs.

Fertigation

The method of irrigation most common in Illinois, the
overhead sprinkler, is the one best adapted to apply-
ing fertilizer along with water. Fertigation permits nu-
trients to be applied to the crop as they are needed.
Several applications can be made during the growing
season with little or no additional application cost.
Nitrogen can be applied in periods when the crop has
a heavy demand for both nitrogen and water. Com
uses nitrogen and water most rapidly during the 3
weeks before tasseling. About 60 percent of the nitro-
gen needs of com must be met by silking time. Gener-
ally, nearly all the nitrogen for the crop should be ap-
plied by the time it is pollinating, even though some
uptake occurs after this time. Fertilization through ir-
rigation can be a convenient and timely method of
supplying part of the plant's nutrient needs.

In Illinois, fertigation appears to be best adapted to
sandy areas where irrigation is likely to be needed
even in the wettest years. On finer-textured soils with
high water-holding capacity, nitrogen might be
needed even though water is adequate. Neither irri-
gating just to supply nitrogen nor allowing the crop to
suffer for lack of nitrogen is an attractive alternative.
Even on sandy soils, only part of the nitrogen should
be applied with irrigation water; preplant and
sidedress applications should provide the rest of it.

Other problems associated with fertigation can be
only mentioned here. These include (1) possible lack
of uniformity in application; (2) loss of ammonium
nitrogen by volatilization in sprinkling; (3) loss of
nitrogen and resultant groundwater contamination by
leaching if overirrigation occurs; (4) corrosion of
equipment; and (5) incompatibility and low solubility
of some fertilizer materials.

Cost and Return

The annual cost of irrigating field com with a center-
pivot system in Mason County was estimated in 1987
to vary from $95 to $140 per acre. The lower figure is

for a leased low-pressure system with a 50-horse-
power electric motor driving the pump. The higher
figure is for a purchased high-pressure system with a
130-horsepower diesel engine. Additional costs asso-
ciated with obtaining a yield large enough to offset
the cost of irrigation were estimated to be about $30
per acre per year, for a total irrigation cost of $125 to
$170 per acre per year. The total investment for the
purchased high-pressure irrigation system, including
pivot, pump and gear head, diesel engine, and a 100-
foot well, amounted to $450 per acre. If the low-pres-
sure system were purchased, the total investment for
the system, including pivot, pump, electric motor, and
a 100-foot well, would be $400.

Irrigation purchases should be based on sound eco-
nomics. The natural soil-water storage capacity for
some soils in Illinois is too good to warrant supple-
mental irrigation. Based on the assumed fixed and
variable costs of about $110 per acre per year, it would
require an annual yield differential of about 50 bush-
els of com ($2.20 a bushel) or 18 bushels of soybeans
($6 a bushel) to break even (Table 14.01). For irrigation
to pay off, these yield differentials would have to be
met on the average over the 10- to 15-year life of the
irrigation system. Some of the deep, fine-textured
soils in Illinois simply would not regularly support
these yield increases.

Irrigation Scheduling

Experienced irrigators have developed their own pro-
cedures for scheduling applications, whereas begin-
ners may have to determine timing and rates of appli-
cation before they feel prepared to do so. Irrigators
generally follow one of two basic scheduling meth-
ods, each of which has many variations.

The first method involves measuring soil water
and plant stress by (1) taking soil samples at various

Table 14.01. Break-Even Yield Increase Needed to
Cover Fixed and Variable Irrigation
Costs

Corn price

Yield increase

Soybean price

Yield increase

($/bu)

(bu)

($/bu)

(bu)

1.50

4.75

1.70

5.00

1.90

5.25

2.10

5.50

2.30

5.75

2.50

6.00

2.70

6.25

2.90

6.50

144

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

depths with a soil probe, auger, or shovel and then
measuring or estimating the amount of water avail-
able to the plant roots; or (2) inserting instruments
such as tensiometers or electrical resistance blocks
into the soil to desired depths and then taking read-
ings at intervals; or (3) measuring or observing some
plant characteristics and then relating them to water
stress.

Although in theory the crop can utilize 100 percent
of the water that is available, the last portion of that
water is not actually as available as the first water
that the crop takes from the soil. Much like a half-
wrung-out sponge, the remaining water in the soil
following 50 percent depletion is more difficult to re-
move than the first half of the plant-available water.

The 50 percent depletion figure is often used to
schedule irrigation. For example, if a soil holds 3
inches of plant-available water in the root zone, then
we could allow V/i inches to be used by the crop be-
fore replenishing the soil's water with irrigation.

Soil Samples

Estimating when the IV2 inches is used, or when 50
percent depletion occurs, can be done by a number of
methods. One of the simplest is to estimate the
amount of depletion by the "feel" method, which in-
volves taking a sample from various depths in the ac-
tive root zone with a spade, soil auger, or soil probe.
It is important to dig a shallow hole to see how the
soil looks at 6 to 12 inches early in the irrigation sea-
son. As the rooting depth extends to 3 feet, it may be
wise to inspect a soil sample from the 9- to 18-inch
level and another from the 24- to 30-inch level. Ob-

serving only the surface can be misleading on sandy
soils because the top portion dries fairly quickly in the
summer. To use this method of sampling, follow the
guidelines shown in Table 14.02 to identify the deple-
tion range you are in.

Tensiometers

Tensiometers are most suitable for sandy or loamy
soils because the changes in soil-water content can be
adequately described by the range of soil moisture
tension in which they operate. As plant roots dry the
soil, soil moisture tension increases and water is
pulled from the tensiometer into the surrounding soil,
thereby increasing the reading on the vacuum gauge.
After irrigation or rainfall, water replenishes the dry
soil and soil moisture tension decreases. The vacuum
developed in the tensiometer pulls water back
through the porous ceramic tip, and the dial gauge
reading decreases. By responding to both wetting and
drying, a tensiometer can yield information on the
effect of crop transpiration or water additions to soil-
water status.

A tensiometer must be installed carefully to ensure
meaningful readings. Improper use may be worse
than not using a tensiometer, because false readings
can result in poorly timed irrigation. Before use, each
tensiometer assembly must be soaked in water over-
night; then the bubbles and dissolved gases must be
removed from the water within the tube and ceramic
cup. This procedure can be done by using boiled wa-
ter and a small suction pump available from tensiom-
eter manufacturers.

Table 14.02. Behavior of Soil at Selected Soil-Water Depletion Amounts

Available water remaining
in the soil

Soil type

Sands

Loamy sand/sandy loam

Soil saturated, wetter than
field capacity

100% available
(field capacity)

75 to 100%

50 to 75%

Less than 50%

Free water appears when soil ball
is squeezed

When soil ball is squeezed, wet
outline on hand but no free water

Sticks together slightly

Appears dry; will not form a ball

Flows freely as single grains

Free water appears when soil ball
is squeezed

When soil ball is squeezed, wet
outline on hand but no free water

Forms a ball that breaks easily

Appears dry; will not form a ball

Flows freely as grains with some
small aggregates

14 • WATER MANAGEMENT

145

The tensiometer should be installed by creating a
hole with a soil probe to within 3 to 4 inches of the de-
sired depth, then pounding a rod with a rounded end
to the final depth. The rod tip should be shaped like
the tensiometer tip to ensure a good, porous cup-to-
soil contact. Placement of tensiometers should be
made according to two principles: (1) the tensiometer
should be readily accessible if it is to be used; and
(2) field placement of tensiometers should be made
to stagger the readings throughout the irrigation
cycle.

Tensiometers are available in lengths ranging from
6 inches to 4 feet. The length required depends on the
crop grown, with lengths chosen to gain accurate in-
formation in the active root zone. For shallow-rooted
vegetable crops, a single tensiometer per station, at a
6- to 9-inch depth, may be sufficient. Multiple-depth
stations for com or soybeans will allow you to track
the depletion and recharge of soil water at several
depths throughout the season. Because the active root
zone shifts as the plant matures, water extraction pat-
terns change as well. If you want to go with a single
depth station, refer to Table 14.03 for the proper
depths of placement.

Tensiometers may require servicing if soil moisture
tension increases to more than 80 centibars. At this
tension, air enters the porous cup and the vacuum is
broken. Tensiometers that have failed in this manner
can be put back into service by filling them with de-
aerated water. Servicing can be done without remov-
ing the tensiometer from the soil. If proper irrigation
levels are maintained, the soil moisture tension
should not rise to levels sufficient to break the vacuum.

Moisture Blocks

Moisture blocks (sometimes referred to as electrical
resistance blocks or gypsum blocks) are small blocks
of gypsum with two embedded electrodes. The block
operates on the principle that the electrical resistance
of the gypsum is affected by water content.

When saturated, the gypsum block has low electri-
cal resistance. As it dries, the electrical resistance in-
creases. The moisture blocks are placed in the soil and
electrical leads coming from the embedded electrodes

Table 14.03. Tensiometer Placement Depth for
Selected Crops

Depth (in.)

Depth (cm)

Soybeans

Com

Snap beans

Cucumbers

46
30
23
23

are allowed to protrude from the soil surface. These
leads are connected to a portable instrument that in-
cludes an electrical resistance meter and a voltage
source.

When a reading is desired, a voltage is applied and
the resulting reading is recorded. The reading is con-
verted to a soil-water content by using a predeter-
mined calibration curve relating resistance to water
content. Soil moisture blocks work well in fine- and
medium-textured soils and are not recommended for
sandy soils. The increase in fine-textured soil irriga-
tion in Illinois, particularly for seed com, may prompt
an increase in the use of moisture blocks. As with ten-
siometers, a good soil contact is absolutely necessary
for meaningful readings. Soil water must be able to
move in and out of the blocks as if the blocks were
part of the soil. Any gap between the block and the
surrounding soil will prevent this movement.

Another method of scheduling, frequently called
the "checkbook method," involves keeping a balance
of the amount of soil water by measuring the amount
of rainfall and then measuring or estimating the
amount of water lost from crop use and evaporation.
When the water drops to a certain level, the field is ir-
rigated. Computer techniques are also available for
estimating water loss, computing the water balance,
and predicting when irrigation is necessary.

Management Requirements

Irrigation will provide maximum benefit only when it
is integrated into a high-level management program.
Good seed or plant starts of proper genetic origin
planted at the proper time and at an appropriate
population, accompanied by optimum fertilization,
good pest control, and other recommended cultural
practices, are necessary to ensure the highest benefit
from irrigation.

Farmers who invest in irrigation may be disap-
pointed if they do not manage to irrigate properly.
Systems are so often overextended that they cannot
maintain adequate soil moisture when the crop re-
quires it. For example, a system may be designed to
apply 2 inches of water to 100 acres once a week. In
two or more successive weeks, soil moisture may be
limiting, with potential evapotranspiration equaling
2 inches per week. If the system is used on one
100-acre field one week and another field the next
week, neither field may receive much benefit. This is
especially true if water stress comes at a critical time,
such as during pollination of com or soybean seed
development. Inadequate production of marketable
products may result.

Currently I suggest that irrigators follow the
cultural practices that they would use for the most

146

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

profitable yield in a year of ideal rainfall. In many
parts of the state, 1975, 1981, and 1982 were such
years. If a farmer's yield is not already appreciably
above the county average for that particular soil type,
he or she needs to improve management of other cul-
tural factors before investing in an irrigation system.

The availability of irrigation on the farm permits
the use of optimum production practices every year.
If rains were to come as needed, the investment in
irrigation equipment would be unnecessary that year,
but no operating costs would be involved. When rain-
fall is inadequate, however, the yield potential can
still be realized with irrigation.

Author

F. William Simmons

Department of Crop Sciences

Chapter 15.

1999 Weed Control

FOR Corn, Soybeans, and Sorghum

This guide is based on the results of research con-
ducted by the personnel of the University of Illinois
Agricultural Experiment Station, other experiment
stations, and the U.S. Department of Agriculture
(USDA). The soils, crops, and weed problems of Illi-
nois have been given primary consideration.

The user should have an understanding of cultural
and mechanical weed control. As these practices
change little from year to year, this publication fo-
cuses on making practical, economical, and environ-
mentally sound decisions regarding herbicide use.

Most of the suggestions in this guide are intended
primarily for ground applications. For aerial applica-
tions, such factors as carrier volume and adjuvant se-
lection may differ.

Precautions

The benefits of chemical weed control must be
weighed against the potential risks to crops, people,
and the environment. Discriminate use should mini-
mize exposure of humans and livestock, as well as de-
sirable plants. Risks can be reduced by observing cur-
rent label precautions.

Current Label

Precautions and directions for use may change. Herbi-
cides classified as restricted-use pesticides (RUP)
must be applied only by certified applicators (Table
15.01). Use of these herbicides may be restricted be-
cause they are toxic or pose environmental hazards.
The degree of toxicity is indicated by the signal word
on the label.

Signal Word

Heed the accompanying precautions. The signal word for
herbicides discussed in this guide is given in Table
15.01. "Danger — Poison" and "Danger" indicate high
toxicity hazards, whereas "Warning" indicates moder-
ate toxicity. Always use personal protective equip-
ment (PPE) as specified on the herbicide label for han-
dling and application. Keep persons or animals not
directly involved in the operation out of the area. Ob-
serve reentry intervals (REI) as specified on the label.
"Agricultural Use Requirement" on the label may re-
quire posting of the treated area. Use special drift pre-
cautions near residential areas.

Environmental Hazards

Groundwater advisories (Table 15.01) must be ob-
served, especially on sandy soils with a high water
table. The threat of toxicity to fish and wildlife is indi-
cated under "Environmental Hazards" on the herbi-
cide label. Hazards to endangered species may be
indicated.

Proper Herbicide Use

Apply only to approved crops at the proper rate and
time. Illegal residues can result from overapplication
or improper timing. Observe the recommended har-
vesting or grazing intervals after treatment.

Proper Equipment Use

Make sure that spray tanks are clean and free of other
pesticide residues. Many herbicide labels provide
cleaning suggestions, which are particularly important

The information in this chapter is provided for educational purposes only. Product trade names have been used for clarity, but reference
to trade names does not imply endorsement by the University of Illinois; discrimination is not intended against any product. The reader is
urged to exercise caution in making purchases or evaluating product information.

Label registrations can change at any time. Thus the recommendations in this chapter may become invalid. The user must read carefully
the entire, most recent label and follow all directions and restrictions. Purchase only enough pesticide for the current growing season.

148

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 15.01. Herbicide and Herbicide Premix Names and Restrictions

Restricted-use

Groundwatei

Trade name(s)

Common (generic) name(s)

pesticide^

advisory''

Signal word*^

Crop \

AAtrex, Atrazine

Atrazine

Yes

Caution

Accent

Nicosulfuron

—

Caution

Accent Gold

Nicosulfuron + rimsulfuron +
flumetsulam + clopyralid

—

Yes

Danger

Aim

Carfentrazone-ethyl

—

Caution

Assure II/Matador

Quizalofop

—

Danger

Authority First

Sulfentrazone

—

Yes

Caution

Axiom

FOE-5043 + metribuzin

—

Yes

Caution

Balance

Isoxaflutole

Yes

Caution

c&s

Banvel/Clarity

Dicamba

—

Warning/Caution

Basagran

Bentazon

—

Yes

Caution

c&s

Basis

Rimsulfuron + thifensulfuron

—

Caution

c j

Basis Gold

Rimsulfuron + nicosulfuron +
atrazine

Yes

Caution

Beacon

Primisulfuron

—

Caution

Bicep 11 Magnum

S-metolachlor + atrazine + safener

Yes

Caution

Bicep Lite 11 Magnum

S-metolachlor + atrazine + safener

Yes

Caution

Bladex, Cy-Pro

Cyanazine

Yes

Warning

Blazer, Status

Acifluorfen

—

Yes

Danger

Broadstrike + Dual

Flumetsulam + metolachlor

—

Yes

Warning

c&s

Broadstrike + Treflan

Flumetsulam + trifluralin

—

Yes

Danger

S 1

Buctril, Moxy

Bromoxynil

—

Warning

Buctril + Atrazine

Bromoxynil + atrazine

Yes

Caution

Bullet

Alachlor + atrazine

Yes

Caution

Butyrac 200/Butoxone

2,4-DB

—

Danger

Canopy

Metribuzin + chlorimuron

—

Yes

Caution

Canopy XL

Sulfentrazone + chlorimuron

—

Yes

Caution

Classic/Skirmish

Chlorimuron

—

Caution

Cobra

Lactofen

—

Danger

Command 3ME

Clomazone

—

Caution

Contour

Imazethapyr + atrazine

Yes

Caution

c i

Detail

Imazaquin + dimethenamid

—

Yes

Danger

DoublePlay

Acetochlor + EPTC + safener

Yes

Warning

Dual 11 Magnum

S-metolachlor + safener

—

Yes

Caution

c&s

Eradicane

EPTC + safener

—

Caution

Exceed

Primisulfuron + prosulfuron

—

Yes

Caution

C '

Extrazine 11, Cy-Pro AT

Cyanazine + atrazine

Yes

Warning

Fieldmaster

Glyphosate + acetochlor +
atrazine + safener

Yes

Caution

FirstRate

Cloransulam

—

Yes

Caution

Flexstar/Reflex

Fomesafen

—

Warning/Danger

Frontier

Dimethenamid

—

Yes

Warning

c&s

FulTime

Acetochlor + atrazine + safener

Yes

Caution

Fusilade DX

Fluazifop

—

Caution

Fusion

Fluazifop + fenoxaprop

—

Caution

Galaxy, Storm

Bentazon + acifluorfen

—

Yes

Danger

Gramoxone Extra

Paraquat

Yes

—

Danger — Poison

c&s

Guardsman/ LeadOff

Dimethenamid + atrazine

Yes

Caution

Harness

Acetochlor + safener

Yes

Warning

Harness Xtra

Acetochlor + atrazine + safener

Yes

Caution

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

149

Table 15.01. Herbicide and Herbicide Premix Names and Restrictions (cont.)

Restricted-use

Groundwatei

Trade name(s)

Common (generic) name(s)

pesticide""

advisory''

Signal word*^

Crop'^

Hornet

Flumetsulam + clopyralid

Yes

Danger

Laddok S-12

Bentazon + atrazine

Yes

Danger

Lasso/Micro-Tech

Alachlor

Yes

Danger/Caution

C&S

Liberty

Glufosinate

—

Warning

C&S

Liberty ATZ

Glufosinate + atrazine

Yes

Caution

i Lightning

Imazethapyr + imazapyr

—

Yes

Warning

Lorox

Linuron

—

Caution

Marksman

Dicamba + atrazine

Yes

Caution

Many trade names

2,4-D amine

—

Danger

Many trade names

2,4-D ester

—

Caution

NorthStar

Primisulfuron + dicamba

—

Yes

Caution

OpTill

Prosulfuron

—

Yes

Caution

Permit

Halosulfuron

—

Caution

Pinnacle

Thifensulfuron

—

Caution

Poast Plus, Prestige

Sethoxydim

—

Caution

Princep, Simazine

Simazine

—

Yes

Caution

Prowl, Pentagon

Pendimethalin

—

Caution

c&s

Pursuit

Imazethapyr

—

Caution

C&S

Pursuit Plus

Pendimethalin + imazethapyr

—

Caution

c&s

Python

Flumetsulam

—

Yes

Caution

C&S

Raptor

Imazamox

—

Caution

Resolve

Imazethapyr + dicamba

—

Warning

Resource

Flumiclorac

—

Warning

C&S

Roundup Ultra

Glyphosate, isopropylamine

—

Caution

C&S

Scepter 70DF

Imazaquin

—

Caution

Scorpion III

Flumetsulam + clopyralid
+ 2,4-D

—

Yes

Danger

Select

Clethodim

—

Warning

Sencor, Lexone

Metribuzin

—

Yes

Caution

S&C

Shotgun

Atrazine + 2,4-D

Yes

Danger

Sonalan

Ethalfluralin

—

Caution

Spirit

Primisulfuron + prosulfuron

—

Yes

Warning

Squadron

Imazaquin -f- pendimethalin

—

Danger

Steel

Pendimethalin + imazethapyr
-1- imazaquin

—

Warning

Stellar

Lactofen -i- flumiclorac

—

Danger

Stinger

Clopyralid

—

Yes

Caution

Surpass/TopNotch

Acetochlor -i- safener

Yes

Warning/Caution

Surpass 100

Acetochlor -i- atrazine + safener

Yes

Danger

Sutan+

Butylate -i- safener

—

Caution

Synchrony STS

Chlorimuron -t- thifensulfuron

—

Caution

Touchdown 5

Glyphosate, trimesium

—

Caution

C&S

Tough

Pyridate

—

Warning

Treflan, Tri-4

Trifluralin

—

Caution

Tri-Scept

Imazaquin + trifluralin

—

Warning

Turbo

Metribuzin -i- metolachlor

—

Yes

Caution

^To be applied by licensed applicator.

"Special precautions in sandy soils.

"Signal word = toxicity signal; indicates need for extra precautions. The signal words "Danger" and "Warning" often indicate

pesticides that can irritate skin and eyes, necessitating protective clothing, gloves, and goggles or faceshield.

■"C = corn; S = soybeans.

150

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

when spraying different crops with the same sprayer
and especially when using postemergence herbicides.
Correctly calibrate and adjust the sprayer before add-
ing the herbicide to the tank.

Proper Drift Precautions

Spray only on relatively calm days when the wind is
light. Make sure the wind is not moving toward areas
of human activity, susceptible crops, or ornamental
plants. Nearby residential areas and fields of edible
horticultural crops deserve special attention. Use spe-
cial precautions with 2,4-D, Banvel or Clarity, Command
3ME, Gramoxone Extra, Hornet, Marksman, Resolve,
Roundup Ultra, Scorpion III, Shotgun, and Stinger, as
symptoms of injury have occurred far from the appli-
cation site.

Precautions to Protect the Crop

Avoid applying a herbicide to crops under stress or
predisposed to injury. Crop sensitivity varies with size
of the crop and climatic conditions, as well as previ-
ous injury from plant diseases, insects, or chemicals.

Proper Recropping Interval

Failure to observe the proper recropping intervals
may result in carryover injury to the next crop. Soil
texture, organic matter, and pH may affect herbicide
persistence. Check Tables 15.02a and 15.02b and cur-
rent labels for recropping restrictions.

Proper Storage

Promptly return unused herbicides to a safe storage
place. Pesticides should be stored in their original, la-
beled containers in a secure place away from unau-
thorized people (particularly children) and livestock
and their food or feed.

Proper Container Disposal

Liquid containers should be pressure- or triple-rinsed.
Properly rinsed containers can be recycled or may be
accepted by some sanitary landfills. Haul paper con-
tainers to a sanitary landfill or bum them in an ap-
proved manner. If possible, use mini-bulk returnable
containers.

Cultural and Mechanical
Control

Good cultural practices that aid in weed control in-
clude adequate seedbed preparation, adequate fertili-
zation, crop rotation, planting on the proper date, us-
ing the optimal row width, and seeding at the rate
required for optimal stands.

Planting in relatively warm soil can help the crop
emerge quickly and compete better with weeds. Good
weed control during the first 3 to 5 weeks is ex-
tremely important for both com and soybeans, as
they will usually compete quite well with most of the
weeds that begin growing later. Narrow rows help
the crop compete better with the weeds. However, if
herbicides alone cannot give adequate weed control,
then keep rows wide enough to allow for cultivation.

If adequate rainfall does not occur after the appli-
cation of a soil-applied herbicide, use the rotary hoe
after weed seeds have germinated but before most
weeds have emerged. Operate it at 8 to 12 miles per
hour, and weight it enough to stir the soil and kill the
tiny weeds. Rotary hoeing also aids crop emergence if
the soil is crusted.

Row cultivators also should be used while weeds
are small. Throwing soil into the row can help
smother small weeds. Proper adjustment of equip-
ment (speed, depth, and angle) is essential for mini-
mizing crop injury and pruning crop roots. Cultiva-
tion may not be needed where herbicides are
adequately controlling weeds, unless the soil is
crusted or needs aeration.

HERBICIDE INCORPORATION

DoublePlay, Eradicane, Sonalan, Sutan-t-, trifluralin,
and Tri-Scept are incorporated to minimize surface
loss. Other soil-applied herbicides may be incorpo-
rated to mininnize dependence on timely rainfall or to
improve control of certain weed species.

Incorporation should place the herbicide uni-
formly throughout the top 1 to 2 inches of soil for the
best control of most weeds. Slightly deeper placement
may improve the control of certain weeds under rela-
tively dry conditions but may dilute the herbicide
and reduce its effectiveness. Incorporation tools usu-
ally distribute most of the herbicide into the soil to
about one-half the depth of operation. Thus, for most
herbicides, the suggested depth of operation is 3 to 4
inches for most tillage tools.

Thorough incorporation often requires two passes,
but the second pass may be delayed if the first pass
adequately reduces surface loss of the herbicide. The
second pass should be at an angle to the first pass and
no deeper. Single-pass incorporation may be ad-
equate, especially if rotary hoeing, cultivation, or sub-
sequent herbicide treatment maintains adequate
weed control.

Accurate application and uniform distribution
help minimize crop injury and carryover problems.
Uniform distribution depends on the type of equip-
ment used, the depth and speed of operation, the
texture of the soil, and the amount of soil moisture.

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

151

able 15.02a. Com-Sorghum Herbicide Recropping Restrictions, Months

ierbicide^

Comments Field com

Sorghum

Wheat

Oats

Rye

Alfalfa

Clover

Soybeans

{cetochlor and its premixes

)oublePlay

w/EPTC

"ulTime

w/atrazine

NY"

iamess

acetochlor

lamess Xtra 5.6L

w/atrazine

Surpass /TopNotch

acetochlor

mrpass 100

w/atrazine

NY"

\trazine and its premixes; simazine

\Atrex, Atrazine

pH < 7.2

NY"

5icep II Magnum

w/metolachlor

NY"

5icep Lite II Magnum w/metolachlor

NY"

5uctril + Atrazine

w/bromoxynil

3ullet

w/alachlor

NY"

ixtrazine

w/cyanazine

NY"

Guardsman/ LeadOfl

F w/dimethenamid

NY"

.addok S-12

w/bentazon

liberty ATZ

w/glufosinate

NY''

NY"

Vlarksman

w/dicamba

NY"

?*rincep

simazine

\-lumetsulam and its premixes; clopyralid

3roadstrike + Dual

w/metolachlor

4.5

26Fba

riomet

w/clopyralid

10.5

26Fba

10.5^

Python

flumetsulam

26n,a

scorpion III

w/clopyralid + 2,4-D

10.5

26Fba

10.5^

stinger

clopyralid

10.5

10.5^

Imazethapyr and its premixes

Contour

w/atrazine

8.5'

9.5

40Fba

9.5

Lightning

w/imazapyr

8.5'

9.5

40Fba

9.5

Pursuit

imazethapyr

8.5'

40Fba

Pursuit Plus

w/pendimethalin

8.5

9.5

40Fba

Resolve

w/dicamba

8.5'

9.5

40Fba

9.5

Sulfonylureas and their

• premixes

Accent

nicosulfuron

10'^

0.5

Accent Gold

(A) + (R) + Hornet

10.5

26Fba

10.5^

Basis

thifensulfuron +
rimsulfuron

0.5

Basis Gold

nicosulfuron +
rimsulfuron +
atrazine

10"

Beacon

primisulfuron

0.5

Celebrity B & G

dicamba + nicosulfuron

10"^

Exceed, Spirit

primisulfuron +
prosulfuron

18«

188

10-18"

NorthStar

primisulfuron+dicamba 0.5

Permit

halosulfuron

"" = field bioassay needed (see label), NY = next year, 2Y = second year, AT = anytime.

^Other com herbicides have no significant recropping restriction; but Banvel, Clarity, Eradicane, and 2,4-D have replanting limits for soybeans.

*'2Y (second year) if applied after June 10 with high atrazine or July 1 with Basis Gold.

j'Concep or Screen seed protectant needed.

{''IS months if pH > 7.5.

'18 months if < 15 inches of rainfall received and if soil has < 2% organic matter.

iMI-corn hybrids may be replanted anytime.

^Exceed or Spirit: pH < 7.8; applied before July 1; rainfall > 12 inches within 5 months and > 1 inch within 4 weeks of application.

1-70 to 1-80: Spirit 10 months. Exceed 18 months or 10 months if STS soybeans. Above 1-80: Exceed or Spirit 18 months.

152

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 15.02b. Soybean Herbicide Recropping Restrictions, Months

Herbicide

Comments

Field

com Sorghum Wheat Oats Rye Alfalfa Clover Soybeans

Chlorimuron and some of its premixes

Canopy^ w/metribuzin 10 12

Classic/Skirmish high chlorimuron 9'' 9^"

Synchrony STS w/thifensulfuron 9'' 9''

10
12"
12''

12
12"
12"

AT
AT
AT

Flumetsulam and its premixes; cloransulam

Broadstrike + Dual w/metolachlor AT 12 4.5 4.5 4.5

Broadstrike + Treflan w/trifluralin 8 12 4 12 4

FirstRate cloransulam 9 9 3 30^"^ 30^^

Python flumetsulam AT 12 4 4 4

Imazaquin and its premixes (full rate = Detail, Squadron, Tri-Scept; Region 3 = north of Peoria)

Detail— Region 2^
Scepter — Region 2^
Scepter — Region 3*^
Scepter — Region 3*^
Squadron — Region 2"^
Tri-Scept — Region 2^

w/dimethenamid

imazaquin

0.5 rate, post

imazaquin

w/pendimethalin

w/trifluralin

9.5<^-^
9.5'^-^

18
9.5'^'^
9.5"^'^

11^

11
11
11^
11^

4^
3^
Fall^
18
4«
4'

IV
lie

18
IV

18
18
18
18
18
18

26Fba
26Fba
30Fba
26Fba

18
18
18
18
18
18

AT
AT
AT
AT

AT
AT
AT
AT
AT
AT

Imazethapyr and its premixes (full rate = Pursuit, Pursuit Plus; Steel = Pursuit Plus + 0.5X Scepter)
Pursuit imazethapyr 8.5' 18 4 18 4 4

Pursuit Plus w/pendimethalin 8.5 18 4 18 9.5 9.5

Steel— Region 2<^ w/pendimethalin + 9.5'''^ 18 4^ 18 40 18

imazaquin

40
40
40

AT
AT
AT

Sulfentrazone alone or plus chlorimuron
Authority First sulfentrazone

Canopy XL^ w/chlorimuron^

Other active ingredients
Command 3ME
Flexstar, Reflex
Raptor

Sencor, Lexone
Turbo

clomazone
fomesafen
imazamox
metribuzin
metribuzin +
metolachlor

16«

168

16«

4.5

Fba _ £jgj(j bioassay needed (see label), NY = next year, 2Y = second year, AT = anytime.

^Midwest states' rate, soil pH < 6.8.

''Extend 2 months if applied after August 1.

■^See label for exact area and Region 3 (northern Illinois) full-use rate.

•^10- to 15-inch annual rainfall is required, or use IMI-corn hybrids.

^15 months if Scepter/Scepter OT. sequence, but 9.5 months or NY for IMI-corn hybrids.

'IMI-designated com hybrids may be planted anytime.

sCover crops may be planted anytime, but stand reductions may occur. Do not graze or harvest for forage for at least 9

months.

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

153

Field cultivators, tandem disks, and disk-chisels or
other combination tools are sometimes used for incor-
, poration. More uniform herbicide distribution is pro-
^ l[ vided by two passes than one, whether with a field
cultivator or tandem disk.

Field Cultivators

Field cultivators used for herbicide incorporation
need at least three rows of shanks equipped with
sweeps (not points) each with an effective working
space of 7 inches or less. Sweeps for C-shank cultiva-
tors should be at least as wide as the effective shank
spacing. Set the equipment to cut in a level position at
3 to 4 inches deep, and operate at a minimum of 5
miles per hour.

Tandem disks

Tandem disks used for herbicide incorporation should
have disk blade diameters of 20 inches or less and
blade spactngs of 7 to 9 inches. Do not use larger disks
for incorporating herbicides. Set the disk to cut 3 to 4
inches deep and operate at 4 to 6 miles per hour or a
speed sufficient to move soil the full width of the
blade spacing. Slower speeds or lack of a leveling de-
vice can result in herbicide streaking.

Combination Tools

Several tillage tools combine disk gangs, field cultiva-
tor shanks, and leveling devices. Many combination
tools can handle large amounts of surface residue
without clogging and yet leave adequate crop residue
on the soil surface for erosion control. Results indicate
that these combination tools may provide more uni-
form one-pass incorporation than a disk or field culti-
vator, but one pass with them is generally no better
than two passes with the disk or field cultivator.

Chemical Weed Control

Plan your weed control program to fit your soils, till-
age program, crops, weed problems, and farming op-
erations. Good herbicide performance depends on the
weather and on wise selection and application. Your
decisions about herbicide use should be based on the
nature and seriousness of your weed problems. The
herbicide susceptibility of common weed species is
indicated in several tables in this guide.

Com or soybeans are occasionally injured by herbi-
cides applied to these crops. To minimize crop injury,
apply the herbicide uniformly, at the stage of crop
growth specified on the label and at the correct rate
(see the section on "Herbicide Rates"). Crop tolerance
ratings for various herbicides are also given in the
tables in this chapter. Unfavorable conditions such as

cool, wet weather, delayed crop emergence, deep
planting, seedling diseases, soil in poor physical con-
dition, and poor-quality seed may contribute to crop
stress and herbicide injury. Hybrids and varieties vary
also in their tolerance to herbicides and environmen-
tal stress factors. Once injured by a herbicide, plants
may be more prone to disease.

Crop planting options for next season also must be
considered when selecting a herbicide program. Com
and soybean herbicides may have restrictive
recropping intervals for some agronomic and many
vegetable crops. Tables 15.02a and 15.02b cover
recropping intervals for the major agronomic crops
grown in Illinois, but always check the label.
Recropping intervals may be extended for previous,
subsequent, or late-summer herbicide applications, as
well as droughty weather or soil pH. Command or
Scepter (in northern Illinois) can restrict planting
wheat after soybeans, whereas atrazine restricts plant-
ing wheat after com. For soybeans, the persistent com
herbicides of concern are atrazine, clopyralid, and
prosulfuron. STS soybeans may help reduce carryover
problem with prosulfuron. Special concerns are rate
and date of application, as well as rainfall amount
and soil pH. When com follows soybeans, the major
concerns are imazaquin and chlorimuron, but
imidazolinone-resistant (IR) hybrids can minimize
this concern (see the label). Be sure that the applica-
tion of persistent herbicides is uniform and properly
timed to minimize injury to wheat or com. Refer to
the herbicide label for information about cropping se-
quence and appropriate recropping intervals.

For some herbicides, different formulations and
concentrations are available under the same trade
name. No endorsement of any trade name is implied, nor is
discrimination against similar products intended.

Weed Resistance to Herbicides

One of the disadvantages of chemical weed control is
that weeds can become resistant to herbicides. Herbi-
cide resistance is not presently a major problem in Illi-
nois, but it could become a problem without proper
management. There are triazine-resistant pigweed,
lambsquarters, and kochia, as well as acetolactate syn-
thase (ALS)-resistant waterhemp, kochia, and cockle-
bur in Illinois. The imidazolinone, sulfonylurea, and
sulfonamide herbicides all have the same mode of ac-
tion, inhibiting the ALS enzyme. In Illinois, ALS-in-
hibiting herbicides are widely used in soybeans, and
their use is increasing in com. This trend, if not man-
aged properly, has the potential to increase the weed
resistance problem in Illinois.

Certain management strategies can help deter the
development of herbicide-resistant weeds:

154

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

1. Scout fields regularly to identify resistant weeds.
Monitor changes in weed populations to restrict
the spread of herbicide-resistant weeds.

2. Rotate herbicides with different modes of action.
Do not make more than two consecutive applica-
tions of herbicides (whether within the same year
or in successive years) with the same mode of ac-
tion against the same weed. Instead, include other
effective management strategies for weed control.
This is especially critical when using herbicide-
tolerant crops.

3. Use multiple modes of action (tank-mix, premix, or
sequential) that will effectively control potentially
resistant weeds.

4. Where practical, use rotary hoeing and cultivation
to control weed escapes. If necessary, use hand
weeding to minimize the spread of herbicide-toler-
ant weeds.

5. Be aware that resistant weeds can spread from total
vegetation control (TVC) programs used along
highway, railroad, or utility rights-of-way areas
near your farm.

For further information on the causes of herbicide
resistance and strategies to minimize it, visit your Ex-
tension Center or see the Illinois Agricultural Pest Man-
agement Handbook, Chapter 19, "Weed Resistance to
Herbicides."

Herbicide Combinations

Herbicide combinations (tank, pre-, or sequential
mix) can control more weed species, reduce
carryover, and reduce crop injury. Some labels allow
split applications (the same herbicide applied at dif-
ferent times) or sequential applications (different her-
bicides applied at different times). Numerous combi-
nations of herbicides are sold as premixes, and some
are tank-mixed. Registered premixes (Tables 15.03
and 15.04) and tank mixes are shown in the tables in
this chapter. Tank-mixing allows you to adjust the ra-
tio of herbicides to fit local weed and soil conditions,
whereas premixes may overcome some of the com-
patibility problems found with tank-mixing. When
using a tank mix, you must follow restrictions for all
products used in the combination.

Problems may occur when mixing emulsifiable
concentrate (EC) formulations with suspendible
herbicides, such as liquid flowable (L) or dry-flowable
(DF) formulations. Proper mixing procedure may
minimize these problems. The label of most soil-
applied herbicides specifies a compatibility test when
a liquid fertilizer carrier is used. First, fill tanks at
least one-fourth full with carrier (water or liquid fer-

tilizer) and start tank agitation. Next, if needed, add
the compatibility agent at the rate indicated by the
test or adjuvant label. Add suspendible herbicide for-
mulations as just described and completely suspend
(thoroughly mix) before adding emulsifiable concen-
trates. Mix ECs with equal volumes of water (thor-
oughly emulsify) before adding them to the tank. Add
soluble formulations (those that do not emulsify or
disperse) last. Empty and clean spray tanks often
enough to prevent accumulation of material on the
sides and the bottom of the tank.

Herbicide Rates

Herbicide rates vary according to the time and
method of application, the soil conditions, the tillage
system used, and the seriousness of the weed infesta-
tion. Rates of individual components within a combi-
nation are usually lower than rates for the same herbi-
cides used alone.

The rates for soil-applied herbicides often vary
with the texture of the soil and the amount of organic
matter the soil contains. For sandy soils, the herbicide
label may specify reducing the rate or not using any if
crop tolerance to the herbicide is marginal. Postemer-
gence rates often vary, depending on the size and spe-
cies of the weeds.

The rates given in this chapter are, unless other-
wise specified, broadcast rates for the amount of for-
mulated product. If you plan to band or direct herbi-
cides, adjust the amount per crop acre according to
the percentage of the area actually treated. Herbi-
cides may have formulations with different concen-
trations of the active ingredient. Be sure to read the
label and make necessary adjustments when chang-
ing formulations.

POSTEMERGENCE HERBICIDE PRINCIPLES

Postemergence herbicides applied to growing weeds
generally have foliar rather than soil action; however,
some may have both. The rates and timing of applica-
tions are based on weed size and climatic conditions.
When weeds are small, they usually can be controlled
with lower application rates. Larger weeds often re-
quire higher herbicide rates. Herbicide penetration
and action are usually greater with warm temperature
and high relative humidity. Rainfall occurring too
soon after application (0.5 to 6 hours, depending on
the herbicide) can reduce weed control.

Translocated herbicides are most effective at lower
spray volumes (5 to 20 gallons per acre), whereas con-
tact herbicides require more complete coverage. Foliar
coverage increases as water volume and spray pres-
sure are increased. Spray nozzles that produce small
droplets "<lso improve coverage. For contact herbicides.

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

155

Table 15,03. Corn Herbicide Premixes, or Co-packs, and Equivalents

Components

If you apply

Herbicide

(a.i./gal or lb)

(per acre) . .

You have applied (a.i.)

An equivalent rate of

|AccentGold83.8WG

0.065 lb nicosulfuron

2.9 oz

0.188 oz nicosulfuron

0.25 oz Accent 75DF

0.065 lb rimsulfuron

0.188 oz rimsulfuron

0.517 lb clopyralid

1.50 oz clopyralid

4.0 fl oz Stinger 3S

0.191 lb flumetsulam

0.554 oz flumetsulam

0.69 oz Python 80WG

|Axiom 68DF

0.544 lb FOE-5043

19 oz

10.34 oz FOE-5043

10.34 oz a.i. FOE-5043

0.136 lb metribuzin

2.58 oz metribuzin

3.45 oz Sencor 75DF

Basis 75DF

0.50 lb rimsulfuron

0.33 oz

0.167 oz rimsulfuron

0.167 oz a.i. rimsulfuron

0.25 lb thifensulfuron

0.083 oz thifensulfuron

0.33 oz Pinnacle 25DF

Basis Gold 89.5DF

0.0134 lb rimsulfuron

14 oz

0.188 oz rimsulfuron

0.188 oz a.i. rimsulfuron

0.0134 lb nicosulfuron

0.188 oz nicosulfuron

0.25 oz Accent 75DF

0.8678 lb atrazine

12.15 oz atrazine

13.5 oz atrazine 90DF

Bicep II 5.9L

3.23 lb metolachlor

2.4 qt

1.94 lb metolachlor

1.0 qt Dual II 7.8EC

2.67 lb atrazine

1.60 lb atrazine

1.6 qt atrazine 4L

Bicep n Magnum 5.5L

2.40 lb S-metolachlor

2.1 qt

1.26 lb S-metolachlor

0.66 qt Dual H Magnum 7.62EC

3.1 lb atrazine

1.63 lb atrazine

1.63 qt atrazine 4L

Bicep Lite Magnum 6L

3.33 lb S-metolachlor

1.5 qt

1.25 lb S-metolachlor

0.66 qt Dual H Magnum 7.62EC

2.67 lb atrazine

1.00 lb atrazine

1.00 qt atrazine 4L

Bicep Lite II 4.9L

3.23 lb metolachlor

2.4 qt

1.94 lb metolachlor

1 qt Dual II 7.8EC

1.67 lb atrazine

1.00 lb atrazine

1 qt atrazine 4L

Broadstrike + Dual

0.20 lb flumetsulam

2.5 pt

1.0 oz flumetsulam

1.25 oz Python 80WG

7.67EC

7.47 lb metolachlor

2.33 lb metolachlor

2.33 pt Dual 8EC

Buctril + Atrazine

1.0 lb bromoxynil

2pt

0.25 lb bromoxynil

1 pt Buctril 2EC

2.0 lb atrazine

0.50 lb atrazine

1 pt atrazine 4L

Bullet 4ME

2.5 lb alachlor

4qt

2.5 lb alachlor

2.5 qt Micro-Tech 4ME

1.5 lb atrazine

1.5 qt atrazine 4L

Celebrity B & G

B=0.70 lb dicamba

6.0 oz

4.2 oz dicamba

8.4 fl oz Clarity 4S

(co-pack)

G=0.75 lb nicosulfuron

0.66 oz

0.5 oz nicosulfuron

0.66 oz Accent 74DF

Contour 3.38L^

0.38 lb imazethapyr

1.33 pt

0.063 lb imazethapyr

4 fl oz Pursuit 2SC

3.00 lb atrazine

0.500 lb atrazine

1.00 pt atrazine 4L

DoublePlay 7EC

1.4 lb acetochlor

5pt

0.875 lb acetochlor

1.1 pt Surpass 6.4EC

5.6 lb EFIC

3.50 lb EPTC

4.2 pt Eradicane 6.7EC

Exceed 57WG

0.285 lb primisulfuron

1 oz

0.285 oz primisulfuron

0.38 oz Beacon 75WG

0.285 lb prosulfuron

0.285 oz prosulfuron

0.5 oz Peak 57WG

1 Extrazine II 4L or

1.0 lb atrazine

1.3 qt

0.33 lb atrazine

0.33 qt atrazine 4L

1 Cy-ProAT4L

3.0 lb cyanazine

0.98 lb cyanazine

1.0 qt cyanazine 4L

Extrazine II 90DF or

0.225 lb atrazine

1.51b

0.33 lb atrazine

0.375 lb atrazine 90DF

Cy-Pro AT 90DF

0.675 lb cyanazine

1.01 lb cyanazine

1.12 lb cyanazine 90DF

Fieldmaster 4.06L

2.0 lb acetochlor

4qt

2.0 lb acetochlor

2.3 pt Harness 7EC

1.5 lb atrazine

3.0 pt atrazine 4L

0.56 lb glyphosate

1.5 pt Roundup 3S

156

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 15.03. Com Herbicide Premixes, or Co-packs, and Equivalents (cont.)

Herbicide

Components
(a.i./gal or lb)

If you apply

(per acre) . . . You have applied (a.i.) An equivalent rate of

FulTime 4CS

2.4 lb acetochlor
1.6 lb atrazine

4qt

2.4 lb acetochlor
1.6 lb atrazine

3.00 qt TopNotch 3.2CS
1.6 qt atrazine 4L

Guardsman 5L or
LeadOff5L

2.33 lb dimethenamid
2.67 lb atrazine

4.5 pt

1.31 lb dimethenamid
1.50 lb atrazine

28 fl oz Frontier 6EC
3.00 pt atrazine 4L

Harness Xtra 5.6L

3.1 lb acetochlor
2.5 lb atrazine

5.0 pt

1.94 lb acetochlor
1.56 lb atrazine

2.21 pt Harness 7E
3.12 pt atrazine 4L

Harness Xtra 6L

4.3 lb acetochlor
1.7 lb atrazine

5.0 pt

2.15 lb acetochlor
0.85 lb atrazine

2.46 pt Harness TEC
1.7 pt atrazine 4L

Hornet 85.6WG

0.231 lb flumetsulam
0.625 lb clopyralid

4oz

0.924 oz flumetsulam
2.50 oz clopyralid

1.16 oz Python 80WG
6.67 fl oz Stinger 3C

LaddokS-12 5L

2.5 lb bentazon
2.5 lb atrazine

1.67 pt

0.52 lb bentazon
0.52 lb atrazine

1.0 pt Basagran 4SC
1.0 pt atrazine 4L

Liberty ATZ 4.3L

3.3 lb atrazine
1.0 lb glufosinate

40floz
(2.5 pt)

1.03 lb atrazine
0.312 lb glufosinate

32 fl oz atrazine 4L
24 fl oz Liberty 1.67

Lightning 70DG^

0.525 imazethapyr
0.175 imazapyr

1.28 oz

0.672 oz imazethapyr
0.224 oz imazapyr

0.96 oz Pursuit 70DG
0.32 oz imazapyr 70DF

Marksman 3.2L

1.1 lb dicamba
2.1 lb atrazine

3.5 pt

0.48 lb dicamba
0.92 lb atrazine

0.96 pt Banvel 4SC
1.84 pt atrazine 4L

Moxy + Atrazine 3L

1.0 lb bromoxynil
2.0 lb atrazine

2pt

0.25 lb bromoxynil
0.50 lb atrazine

1 pt Moxy 2EC
1 pt atrazine 4L

NorthStar 43.8WG

0.075 lb primisulfuron
0.363 lb dicamba (Na)

5oz

0.375 oz primisulfuron
1.815 oz dicamba

0.50 oz Beacon 75WG
3.63 fl oz Banvel 4SC

OpTill 6EC

5 lb dimethenamid
1 lb dicamba

38floz

1.48 lb dimethenamid
0.297 lb dicamba

31.7 fl oz Frontier 6EC
9.5 fl oz Banvel 4SC

Resolve 75SG^

0.187 lb imazethapyr
0.563 lb dicamba

5.33 oz

1.00 oz imazethapyr
3.00 oz dicamba

1.42 oz Pursuit 70DG
6 fl oz Banvel 4SC

Scorpion 111
84.3WDG

0.093 lb flumetsulam
0.25 lb clopyralid
0.50 lb 2,4-D

4oz

0.372 oz flumetsulam
1,00 oz clopyralid
2.00 oz 2,4-D

0.46 oz Python 80WG
2.67 fl oz Stinger 3SC
2.00 oz a.e. 2,4-D

Shotgun 3.25L

2.25 lb atrazine
1 lb 2,4-D

2pt

0.56 lb atrazine
0.25 lb a.e. 2,4-D

1.12 pt atrazine 4L
0.53 pt Esteron 99 3.8EC

Spirit 57WDG

0.428 lb primisulfuron
0.142 lb prosulfuron

1 oz

0.428 oz primisulfuron
0.142 oz prosulfuron

0.57 oz Beacon 75WG
0.25 oz Peak 57WG

Surpass 100 5L

3.0 lb acetochlor
2.0 lb atrazine

2.6 qt

1.95 lb acetochlor
1.30 lb atrazine

1.22 qt Surpass 6.4EC
1.30 qt atrazine 4L

*Use only on IMI-com hybrids (imidazolinone-tolerant, -resistant).

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

157

Fable 15.04. Soybean Herbicide Premixes, or Co-packs, and Equivalents

Components
(a.i./gal or lb)

If you apply

(per acre) . . . You have applied (a.i.)

An equivalent rate of

\xiom 68DF

Broadstrike + Dual
7.67EC

Broadstrike +
Treflan 3.65EC

Canopy 75DF

0.544 FOE-5043
0.136 metribuzin

13 oz 7.07 oz FOE-5043

1.77 oz metribuzin

0.20 lb flumetsulam 2.5 pt

7.47 lb metolachlor

0.25 lb flumetsulam 2.25 pt

3.40 lb trifluralin

0.107 lb chlorimuron 6 oz

0.643 lb metribuzin

1.00 oz flumetsulam
2.33 lb metolachlor

1.12 oz flumetsulam
0.96 lb h-ifluralin

0.64 oz chlorimuron
3.86 oz metribuzin

Canopy XL 56.3DF 0.094 chlorimuron
0.469 sulfentrazone

6.8 oz 0.64 oz chlorimuron

3.19 oz sulfentrazone

7.07 oz a.i. FOE-5043
2.36 oz Sencor 75DF

1.25 oz Python 80 WG
2.33 pt Dual 8EC

1.41 oz Python 80 WG
1.91 pt Treflan 4EC

2.57 oz Classic 25DF
5.14 oz Lexone 75DF

2.57 oz Classic 25DF
4.25 oz Authority 75DF

Conclude B & G
(co-pack)

Detail 4.1 EC

Fusion 2.56EC

Galaxy 3.67SC

Manifest B & G
(co-pack)

'Pursuit Plus 2.9EC

B = (2.67 lb bentazon -i-

1.33 lb acifluorfen)
G =1.5 lb sethoxydim

0.5 lb imazaquin
3.6 lb dimethenamid

2 lb fluazifop
0.56 lb fenoxaprop

3.00 lb bentazon
0.67 lb acifluorfen

1.5 pt

-1-

0.50 lb bentazon
0.25 lb acifluorfen

1.5 pt Storm 4S

-1-

1.5 pt

0.28 lb sethoxydim

1.5ptPoastl.5SC

Iqt

8floz

2pt

B = (3.00 lb bentazon -i- 2 pt

0.67 lb acifluorfen) +

G = 1.5 lb sethoxydim 1.5 pt

0.2 lb imazethapyr 2.5 pt
2.7 lb pendimethalin

2.00 oz imazaquin
14.4 oz dimethenamid

2.00 oz fluazifop
0.56 oz fenoxaprop

0.75 lb bentazon
0.17 lb acifluorfen

0.75 lb bentazon
0.17 lb acifluorfen
0.28 lb sethoxydim

1.00 oz imazethapyr
0.84 lb pendimethalin

2.86 oz Scepter 70DG
19.2 fl oz Frontier 6.0EC

8 fl oz Fusilade DX 2EC
6.7 fl oz Option 11 0.67EC

1.5 pt Basagran 4SC
0.67 pt Blazer 2SC

2 pt Galaxy 3.67SC

-t-
1.5ptPoastl.5SC^

4 fl oz Pursuit 2SC
2.00 pt Prowl 3.3EC

Rezult B & G
(co-pack)

B = 5.0 lb bentazon
G = 1.0 lb sethoxydim

1.6 pt
1.6 pt

1.00 lb bentazon
0.20 lb sethoxydim

2.0 pt Basagran 4SC
1.6 ptPoast Plus ISC

Scepter O.T. 2.5SC

0.5 lb imazaquin
2.0 lb acifluorfen

1.0 pt

1.00 oz imazaquin
0.25 lb acifluorfen

1.44 oz Scepter 70DG
1 pt Blazer 2SC

Squadron 2.33EC

0.33 lb imazaquin
2.00 lb pendimethalin

3.0 pt

1.98 oz imazaquin
0.75 lb pendimethalin

2.83 oz Scepter 70DG
1.82 pt Prowl 3.3EC

Steel 2.59EC

2.25 lb pendimethalin
0.17 lb imazethapyr
0.17 lb imazaquin

3.0 pt

0.84 lb pendimethalin
1.00 oz imazethapyr
1.00 oz imazaquin

2.00 pt Prowl 3.3EC
4 fl oz Pursuit 2SC
1.46 oz Scepter 70DG

Stellar 3.1EC

2.4 lb lactofen
0.7 lb flumiclorac

5floz

1.50 oz lactofen
0.44 oz flumiclorac

6 fl oz Cobra 2EC

4 fl oz Resource 0.86EC

158

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 15.04. Soybean Herbicide Premixes, or Co-packs, and Equivalents (cont.)

Herbicide

Components
(a.i./gal or lb)

If you apply

(per acre) . . . You have applied (a.i.) An equivalent rate of

Storm 4SC

2.67 lb bentazon
1.33 lb acifluorfen

Synchrony STS 42DF 0.318 lb chlorimuron

0.102 lb thifensulfuron

Tri-Scept 3EC

Turbo SEC

0.43 lb imazaquin
2.57 lb trifluralin

6.55 lb metolachlor
1.45 lb metribuzin

1.5 pt

0.5 oz

2.33 pt

2.75 pt

0.50 lb bentazon
0.25 lb acifluorfen

1 pt Basagran 4SC
1 pt Blazer 2SC

0.159 oz chlorimuron 0.64 oz Classic 25DF
0.051 oz thifensulfuron 0.20 oz Pinnacle 25DF

2.00 oz imazaquin
0.75 lb trifluralin

2.25 lb metolachlor
8.00 oz metribuzin

2.86 oz Scepter 70DG
1.50 pt trifluralin 4EC

2.25 pt Dual 8EC
10.0 oz Sencor 75DF

n.5 pt of Poast 1.5SC is equivalent to 2.25 pt of Poast Plus ISC.

labels usually specify to use 10 to 40 gallons of water
per acre for ground application and a minimum of 5
gallons per acre for aerial application. Spray pressures
of 30 to 60 psi are often suggested with flat-fan or hol-
low-cone nozzles to produce small droplets and im-
prove canopy penetration. These small droplets are sub-
ject to drift.

Crop size limitations may be specified on the label
to minimize crop injury and maximize weed control.
If weeds are smaller than the crop, basal-directed
sprays may minimize crop injury because they place
more herbicide on the weeds than on the crop. If the
weeds are taller than the crop, rope-wick or sponge-
type applicators may be used to place the herbicide
on top the weeds and minimize contact with the crop.
Follow the label directions and precautions for each
herbicide.

Herbicide adjuvants, such as crop oil concentrate
(COC), nonionic surfactant (MS), or ammonium fer-
tilizer adjuvant, may be specified on the herbicide la-
bel. Crop oil concentrates spread the herbicide across
the leaf surface, keep the surface moist longer, and aid
penetration into the cuticle. COCs are phytobland oils
with emulsifier (surfactant) added to allow better
mixing with water. The oil may be of petroleum
(POC) or vegetable (VOC) origin. Methylated seed
oils (MSO) are esters of fatty acids formulated to pro-
vide better performance than a conventional VOC.
Most labels allow POC, MSO, or VOC, but Assure II
and Matador specify a POC only. COCs are used at
1 to 3 pints per acre or about 1 percent on a volume
basis. Oils generally have a greater postemergence ef-
fect than surfactants do on both weeds and crops.

Surfactants cause a spreading and wetting action
by decreasing the surface tension of water, allowing
the spray mix to spread over waxy or hairy leaf sur-
faces rather than forming droplets. Because more leaf
surface is covered, more herbicide may be absorbed.
Surfactants may contain fatty acids to improve pen-
etration. Labels may specify that the NIS should con-
tain a minimum of 75 to 85 percent active ingredient
or else you should use a higher surfactant rate. An
NIS usually is applied at 0.25 to 1 pint per acre or Vs to
Vi percent on a volume-to-volume basis.

Ammonium fertilizer adjuvants are added to in-
crease herbicide activity on weed species such as
velvetleaf. Urea ammonium nitrate solution (28-0-0
UAN) is the most common fertilizer adjuvant, al-
though ammonium polyphosphate (10-34-0 APP) or
ammonium sulfate (AMS) may also be specified.
UAN usually is used at 2 to 4 quarts per acre. Contact
herbicide labels may specify that a fertilizer adjuvant
replaces an NIS or COC, while translocated herbicides
usually specify UAN in addition to an NIS or COC.

Drift-reduction agents are added to the spray tank
to reduce small-droplet formation and thus reduce
spray-particle drift. See the adjuvant label for rates, as
drift retardants vary greatly in formulation.

Conservation Tillage
AND WEED Control

Conservation tillage allows crop production while re-
ducing soil erosion by protecting the soil surface with
plant residue. Minimum or reduced tillage refers to
any tillage system leaving crop residue on the soil

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

159

surface, including primary tillage with chisel plows
or disks and the use of field cultivators, disks, or com-
bination tools for secondary tillage. Mulch tillage is
reduced tillage that leaves at least 30 percent of the
soil surface covered with plant residue.

Ridge tillage and zero tillage are conservation till-
age systems with no major tillage prior to planting. In
ridge tillage, conditions are often ideal for banding
preemergence herbicides because cultivation is a part
of the system. "No-till" is actually "slot tillage" for
planting with no overall primary or secondary tillage.
No-till planting conserves moisture, soil, and fuel. It
also allows timely planting of soybeans or sorghum
after winter wheat harvest (double-cropping).

If tillage before planting is eliminated, undesirable
existing vegetation must be controlled with herbi-
cides either before, at, or after planting. The elimina-
tion or reduction of preplant tillage and row cultiva-
tion puts a greater reliance on chemical weed control.
Greater emphasis may be placed on preplant or
postplant soil-applied herbicides that are not incorpo-
rated or on foliar-applied herbicides. Herbicides are
now available to allow "total postemergence" weed
control in com and soybeans.

Where primary tillage is minimized, soil-residual
herbicides applied several weeks before planting may
reduce the need for a "knockdown" herbicide. How-

ever, early preplant (EPP) application may require ad-
ditional preemergence or postemergence herbicides
or cultivation for satisfactory weed control after
planting. See the "Early Preplant Herbicides Not In-
corporated" sections for com and soybeans for more
details.

Com and soybeans are the primary crops in Illi-
nois, and they are often planted in sequence. Modem
equipment allows successful no-till planting in com
and soybean stubble. The use of a disk or chisel plow
on com stubble may still provide adequate crop resi-
due to meet mulch-till requirements.

Soybean stubble is often ideal for minimum- or
zero-tillage production systems. Primary tillage is
rarely needed, and the crop residue, if properly
spread, should not interfere with herbicide distribu-
tion. Early preplant application of preemergence her-
bicides or the use of postemergence herbicides often
provides adequate weed control.

The existing vegetation in com and soybean
stubble is usually annual weeds. If small, weeds often
can be controlled before planting with herbicides that
have both foliar and soil-residual activity. For com,
these include atrazine, premixes containing atrazine,
and Balance. Sencor or Lexone (metribuzin). Canopy
(metribuzin + chlorimuron), and Canopy XL
(sulfentrazone -i- chlorimuron) may be used before

Table 15.05. Control Ratings

for No-Till Herbicides to Control

Existing Vegetation

' Herbicide

Annual grasses

^ c »^
-d 00 5

g _2 o 03

o ^ ^^
J? o >^-§

Annual broadleaves

Perennial broadle

S 2i .1

fO ^ C

< U P

aves

en
a»

cr
£

'C
u

Marestail
(horseweed)

*-•

Ragweed,
common

4->

2
"So

a»

T5
Ol

i-i

.4-'

glyphosate-12^

1 glyphosate-24''

glyphosate -i- 2,4-D

Gramoxone

Gramoxone 4- atrazine

2,4-D ester, 1 pint

1 Banvel/Clarity

! 2,4-D -1- Banvel

Marksman

Atrazine

Balance

Canopy

j Canopy XL

Sencor, Lexone

Control ratings: 9 = excellent, 8 = good, 7 = fair, 6 = poor, 5 or 4 = unsatisfactory. N = Nil or None. Boldface indicates acceptable control,
"glyphosate 12 oz a.e./A = 16 fl oz/A Roundup Ultra or 14.5 fl oz Touchdown 5.
•"glyphosate 24 oz a.e./A = 32 fl oz/A Roundup Ultra or 29.0 fl oz Touchdown 5.

160

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

soybean emergence (see Table 15.05). Do not apply after
soybean emergence. Foliar activity is enhanced by add-
ing a COC or an MS. See the herbicide label for specific
adjuvant recommendations. The use of 28-0-0 UAN as a
carrier also increases annual weed knockdown.

Annual vegetation more than 2 to 3 inches tall at
planting may require a contact or a translocated herbi-
cide (Table 15.05). Gramoxone Extra, Roundup Ultra,
or Touchdown 5 may be used with most preemer-
gence herbicides to control existing vegetation. To
control broadleaf weeds, 2,4-D may be used prior to
planting com or no-till soybeans, and Banvel may be
used in the spring prior to com but not soybeans.

Roundup Ultra or Touchdown 5 (glyphosate) may
be used to control existing vegetation prior to plant-
ing. Small annual weeds can be controlled with 1 to 2
pints of Roundup Ultra or Touchdown 5. Use higher
rates on larger weeds and when mixing with residual
herbicides. Higher rates can also suppress or control
some perennial weeds. Spray volume per acre should
be 10 to 40 gallons. FieldMaster (glyphosate -i-
acetochlor + atrazine) is used in com at 3.5 to 5 quarts
per acre.

Gramoxone Extra'*^'' 2.5S (paraquat) is used at 1.5
to 3 pints per acre to control existing vegetation before
planting. Apply with an NIS or COC in at least 10 to
20 gallons of spray per acre. The addition of a photo-
synthetic inhibitor herbicide such as atrazine or
metribuzin can improve control of smartweeds, giant
ragweed, and marestail (horseweed).

Banvel or Clarity (dicamba) or 2,4-D may be used
in the fall or spring before planting com or in the fall
before planting soybeans to control annual and some
perennial broadleaf plants, including clovers and al-
falfa. A combination of dicamba plus 2,4-D can often
control more weeds at lower cost. 2,4-D also may be
used in the spring before planting no-till soybeans.
See the current 2,4-D label or the "Early Preplant Herbi-
cides Not Incorporated (Soybeans)" section.

Annual cover crops in Illinois are hairy vetch, winter
rye, and winter wheat. Hairy vetch, a winter annual
legume, is easily controlled with 2,4-D or dicamba be-
fore planting com. Winter rye or winter wheat can be
controlled by glyphosate prior to planting com or
soybeans. Cover crops should be controlled prior to
planting crops, but the question is, "How early do we
do this?" If the season is dry, late control depletes soil
moisture for crop establishment, but if the season is
wet, late control helps dry out the soil. Decomposing
residue of small-grain cover crops can sometimes in-
hibit com seedlings.

Perennial sods require a different approach. It is esti-
mated that 65 to 70 percent of the Conservation Re-
serve Program (CRP) acres in the Com Belt may re-
turn to cropland. Many of these acres have been
planted to perennial grass or legume sods. The ques-
tions here are these: What is the best way to control
sod species? What is the best timing for control, and
what are the best cropping choices? Sods should be
killed prior to planting crops into them (Table 15.06).

Table 15.06. Control of Perennial Grass and Legume Sods Before No-Till Crop Production

Rate/

Blue-

Brome,

Clover,

Fescue,

Orchard-

Quack-

Herbicide

acre

Alfalfa

grass

smooth

red

tall

grass

Timothy

glyphosate, fall

48 oz"

glyphosate, fall

24 oz^

+ 1 pt 2,4-D

+ 0.5 pt Banvel

-(- 1 pt Banvel

glyphosate, fall -i- spring

24 oz/24 oz^

9-1-

glyphosate, spring

48 oz^

glyphosate, spring

24 oz a.e.^

+ 1 pt 2,4-D

+ 0.5 pt Banvel

Gramoxone, spring

3pt

Gramoxone, spring

2.0 pt

-1- 2 lb atrazine

Control ratings: 9 = excellent, 8 = good, 7 = fair, 6 = poor, 5 or 4 = unsatisfactory. N = Nil or None. Boldface indicates

acceptable control.

^glyphosate 24 oz a.e./A = 32 fl oz/A Roundup Ultra or 29 fl oz/A Touchdown 5.

''glyphosate 48 oz a.e./A = 64 fl oz/A Roundup Ultra or 58 fl oz/A Touchdown 5.

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

161

Perennial grass sods were planted on much of the
CRP land. Roundup Ultra and Touchdown (glypho-
sate) provide the best "sod grass" control. Fall applica-
tion is more effective than spring. Mowing the sod in late
summer allows adequate regrowth for timely fall ap-
plication. Active regrowth should be 6 to 8 inches be-
fore fall application. Spring applications must be de-
layed to obtain 6 to 10 inches of new growth for
effective control. In the spring, Gramoxone Extra -i-
atrazine is often as effective as glyphosate for control-
ling several grass species (Table 15.06). Preplant gly-
phosate rates may be reduced if followed with atra-
zine at com planting. If grass-legume mixes are
established, the legume component must also be
controlled.

Perennial legume sods must have 6 to 8 inches of new
growth for effective control. Do not take a spring cutting
before controlling legumes, as this delays com planting.
Com will better utilize legume nitrogen and allows
preplant or postemergence use of 2,4-D or dicamba.

Dicamba controls alfalfa better than 2,4-D does, but
both control red clover. When glyphosate is used,
adding dicamba improves alfalfa control and adding
2,4-D improves dandelion control. Roundup Ultra
may be applied before the last alfalfa cutting in the
fall or spring. Clover sods may be controlled by atra-
zine (see Tables 15.05 and 15.06).

HERBICIDES FOR CORN

Herbicides mentioned in this section are registered
for use on field corn. Most are also registered for si-
lage corn. See Tables 15.08, 15.13, and 15.14 for regis-
tered tank mixes. Herbicide suggestions for sweet
corn and popcorn may be found in the Illinois Agri-
cultural Pest Management Handbook, Chapter 10,
"Weed Control for Commercial Vegetable Crops."
Growers producing hybrid seed com should check
with the contracting company or the producer of in-
bred seed about tolerance of the parent lines. Rates of

Table 15.07. Com Herbicides: Preplant or Preemergence Rates Per Acre

1% OM

1-2% OM

3^% OM

5-6% OM

Herbicide

Unit

sandy loam^

silt loam''

silty clay loam"^

silty clay''

Atrazine 4L

2.0

Ah-azine 90DF

2.2

Axiom 68WSG

Balance 75WDG

2-2.5

Banvel 4S

No'i

No"

1.0

Bleep II 5.9L

1.5

1.8

2.4

3.0

Bleep II Magnum 5.5L

1.3

1.6

2.1

2.6

Bicep Lite 4.9L

1.5

1.8

2.4

3.0

Bleep Lite II Magnum 6L

0.9

1.1

1.5

1.9

Broadstrike + Dual 7.67E

1.75

2.00

2.25

2.50

Bullet 4L

2.5

3.0

4.0

4.5

Contour^ 3.38L

1.33

Cyanazine' 4L

l.Os

1.0

Cyanazine' 90DF

l.ls

1.1

DoublePlay 7E

4.5*^-'

4.5*^

4.5^

. 4.5*^

Dual II 7.8E

1.5

2.0

2.5

3.0

Dual II Magnum 7.62L

1.0

1.33

1.67

2.0

Eradicane 6.7E

4.75

4.75*^

4.75''

Extrazine IP 4L

1.3S

1.3

Extrazine IV 90DF

1.58

1.5

Frontier 6.0E

floz

FulTime 4L

2.5'

3.0

4.0

5.0

Guardsman/LeadOff 5L

2.5

3.0

4.5

5.0

Harness 7E

1.5-

2.0

2.5

2.75

Hamess Xtra 5.6L

1.4'

2.0

2.5

3.0

162

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 15.07. Corn Herbicides:

Freplant

or Preemergence Rates Per Acre (cent.)

1
1

1% OM

1-2% OM

3^% OM

5-6% OM

Herbicide

Unit

sandy loam^

silt loam'' ;

5ilty clay loam''

silty clay''

Hornet 85.6WG

3.2

4.0

4.8

Lasso 4E

2.0

2.25

2.75

3.25

Marksman 3.3L

No'i

No'*

3.5

Micro-Tech 4CS

2.0

2.25

2.75

3.25

OpTill 6E

floz

22'

Partner 65WG

3.0

3.5

4.0

5.0

Pentagon 60WG

1.5

2.5

3.0

3.3

Princep 90DF

2.2

2.6

3.3

4.0

Prowl 3.3E

2.0

3.0

4.0

4.8

Pursuit Plus^ 3E

2.5

Python 80WDG

0.88

1.08

1.25

1.33

Surpass 6.4E

1.5'

2.0

2.5

3.0

Surpass 100 5L

1.6'

2.0

2.6

3.3

Sutan+ 6.7E

4.75

4.75*'

4.75*^

4.75^^

TopNotch 3.2CS

2.0'

2.25

2.5

3.0

OM = organic matter in the soil.

^Characteristic of most sandy soils in Illinois.

''Characteristic of many Illinois soils south of Interstate 70.

''Characteristic of many "prairie soils" in northern Illinois.

''If planted to no-till com, may use 0.5 pt Banvel or 2 pt Marksman.

*Use only on IMI-designated com hybrids.

'Cyanazine is sold as Bladex or Cy-Pro.

^May cause crop injury on this soil.

•"Use a higher rate (see label) for heavy infestations and certain weeds.

'Do not use if groundwater is within 30 ft of surface.

Cy-Pro AT is a product similar to Extrazine II.

Table 15.08. Soil- Applied Com Herbicide Tank Mixes and Application Timing

Atrazine Balance

Banvel/Clarity Contour^ or Cyanazine or
or Marksman Pursuit^ Extrazine IP

Hornet Simazine

used alone

1,2,3

1,2

2,3

atrazine

—

1,2

—

Axiom

1,2

—

Balance

1,2

—

DoublePlay

—

Dual 11 Magnum

1,2,3

1,2

2,3

Eradicane, Sutan+

—

Frontier

1,2,3

1,2

2,3

Harness

1,2,3

1,2

2,3

Micro-Tech, Lasso

1,2,3

1,2

2,3

Prowl, Pentagon

2,3

Surpass, TopNotch

1,2,3

1,2

2,3

1,2,3
1,2

1,2,3

2,3

1,2,3

1,2,3^

1,2

2,3^

1,2,3^

1,2,3

1,2

—

1,2

—

1,2

—

1,2

—

1,2

1 = preplant incorporated; 2 = early preplant not incorporated or preemergence; 3 = early postemergence.

*Use only with IMI-designated com hybrids.

''Cy-Pro AT is a similar product.

"Use DF (not 4L) formulation of cyanazine postemergence.

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

163

preplant and preemergence herbicides to use on sev-
eral typical Illinois soils are given in Table 15.07. See
Tables 15.09, 15.10, 15.11, and 15.12 for weeds con-
trolled by the herbicides used in corn.

Early Preplant Herbicides not
incorporated (corn)

Early preplant applications in no-till com programs
are used to minimize existing vegetation problems
and reduce the need for a bumdown herbicide at
planting. Atrazine has both foliar and soil activity, so
it may control small annual weeds (Table 15.05) prior
to planting com, especially if a COC is added to the
spray mix or if 28-0-0 UAN is used as a spray carrier.

Atrazine"*^, Axiom, Bicep II Magnum'*^'',
Bullet'*^'', Dual II Magnum, Frontier, Guardsman'^"^
Hamess'^^'', Harness Xtra'^^^ LeadOff '*^, or Micro-
jgj.j^RUP j^ay i^g applied within 30 days of planting as
a single full-rate application or within 45 days if the
application is split, before and at planting.
Topnotch'*"'' or FulTime'*"'' may be applied within 40
days, and Broadstrike + Dual, Hornet, OpTill, Py-
thon, Surpass'*'^'', or Surpass 100'^^'' within 30 days of
planting com. Contour'^^'' or Pursuit may be applied
within 45 days of planting IMI (imidazolinone-toler-
ant or -resistant) com. Balance'*"'' 75WDG may be ap-
plied 14 days before planting com. These herbicides
are discussed further in the upcoming sections on
soil-applied herbicides.

2,4-D ester, dicamba, Gramoxone Extra'*"'',
Roundup Ultra, or Touchdown should be added to
the spray mix if weeds are over 2 to 3 inches tall
(check label recommendations for individual species).
These herbicides are discussed in the "Conservation
Tillage and Weed Control" section of this chapter. See
Table 15.05 for weeds controlled by these herbicides.

Soil-Applied ^^Grass" Herbicides (Corn)

The common soil-applied grass herbicides are aceta-
mides or thiocarbamates, which are seedling growth
inhibitors. Eradicane (EPTC) and Sutan+ (butylate)
are thiocarbamates, whereas DoublePlay'*"'' 7E is a
premix of EPTC plus acetochlor. They all require in-
corporation into the soil within 4 hours to minimize
surface loss. Apply within 2 weeks of expected plant-
ing date. Rates per acre are in Table 15.07.

Acetamide herbicides for com are acetochlor,
alachlor, dimethenamid, FOE-5043, and metolachlor,
which control annual grasses (Table 15.09) and some
small-seeded broadleaf weeds. To improve broadleaf
weed control, all acetamide herbicides, except FOE-
5043, are formulated as premixes with atrazine, and
all may be tank-mixed with atrazine or some other

herbicides (Table 15.08). Most acetamides may be
used preplant (surface or incorporated), preemer-
gence, and early postemergence. If they are not incor-
porated and adequate rainfall does not occur soon af-
ter applying, consider rotary hoeing or cultivation if
the cropping plan and planting pattern allow.

Dual II 7,8E (metolachlor) is applied at 1.5 to 4
pints per acre, or use 6 to 16 pounds of Dual II 25G.
Bicep IP"'' 5.9L and Bicep Lite IF"'' 4.9L, 5:4 and 2:1
premixes, respectively, of metolachlor:atrazine, are
used at 1.5 to 3 quarts per acre. Magnum formula-
tions contain S-metolachlor, the active isomer. Use
rates per acre are Dual II Magnum 7.64E at 1.5 to 2
pints, Bicep II Magnum'*"'' 5.5L at 1.3 to 2.6 pints, and
Bicep Lite II Magnum'*"'' 6L at 0.9 to 2.2 pints. These
herbicides all contain benoxacor, a safener to mini-
mize com injury.

Harness'*"'' 7E or Surpass'*"'' 6.4E (acetochlor) is
applied at 1.25 to 3 pints of Harness or 1.5 to 3.75
pints per acre of Surpass. TopNotch'*"'' 3.2CS (encap-
sulated) is used at 2 to 3.25 quarts per acre. Surpass
100'*"'' 5L and FulTime 4L, 3:2 premixes of
acetochIor:atrazine, are used at 1.6 to 3.3 quarts and
2.5 to 5 quarts per acre, respectively. Harness Xtra'*"''
5.6L, a 6:5 premix of acetochlor:atrazine, is used at 1.4
to 3 quarts per acre. All acetochlor products contain
crop safeners to minimize com injury. Do not apply
acetochlor to very sandy soils with a high water table. Read
the label closely for further restrictions, including setbacks.

Lasso'*"'' 4E or Micro-Tech'*"'' 4CS (alachlor) is ap-
plied at 2 to 4 quarts per acre, or 16 to 26 pounds of
Lasso II 15G. Bullet'*"'' 4L is a 5:3 premix of
aIachlor:atrazine used at 2.5 to 5 quarts per acre. Bul-
let and Micro-Tech contain encapsulated alachlor to
increase persistence and reduce com injury.

Frontier (dimethenamid) 6E is applied at 18 to 32
fluid ounces per acre. Guardsman'*"'' or LeadOff'*"''
5L, a 7:8 premix of dimethenamid:atrazine, is used at
2.5 to 5 pints per acre. OpTill 6E, a 5:1 dimethana-
mid:dicamba premix, is applied preplant surface at 22
to 38 fluid ounces per acre.

Axiom 68DF (4:1 FOE-5043:metribuzin) is applied
at 13 to 23 ounces per acre. Higher rates are for con-
servation tillage systems. A tank mix with atrazine
will increase broadleaf weed control.

Prowl 3.3E (pendimethalin) is used preemergence
after planting com, but do not use preplant or incorpo-
rate. Com should be planted at least 1.5 inches deep.
The Prowl rate is 1.8 to 4.8 pints per acre alone or 1.8
to 3.6 pints per acre in tank-mix combinations.

Balance'*"'' 75WDG (isoxaflutole) is used preplant
incorporated or preemergence at 1.5 to 3 ounces to
control several annual grasses in com (Table 15.09).
Do not apply after com emergence or on sandy soils.

164

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 15.09. Com Herbicides: Grass and Nutsedge Control Ratings

Annuals

Perennials

Herbicide

«
'So

PL,

13
c2

03
OS

en
C5

V-i

o
U

Soil-applied

Axiom

Dual II Magnum

Frontier

Harness

Lasso/Micro-Tech

Surpass, TopNotch

DoublePlay

Eradicane, Sutan+

Prowl, Pentagon

Balance

Atrazine

Princep

Postemergence

. . Q^c ""

fflb/e 15.11 for maximutr

( grass

C1'7£>C . .

• • JtC .

bl^co ' '

Accent^ or Celebrity^

Accent Gold^

Basis^

Basis Gold^

Beacon^

Lightning''

Resolve''

Poast Plus^

Atrazine + oil

Liberty''

Liberty ATZ''

Roundup Ultra^

Control ratings: 9 = excellent, 8 = good, 7 = fair, 6 = poor, 5 or 4 = unsatisfactory, N = Nil or None. Boldface indicates

acceptable control.

Corn response: 0 = minimal, 1 - possible, 2 = probable, 3 = serious.

*Use of IR (imidazilinone-resistant) com hybrids minimizes insecticide interaction and injury.

''Use only with IMl-designated com hybrids.

'Use only with PP- or SR-designated corn hybrids.

''Use only with Liberty Link or GR-designated (glufosinate-resistant) corn hybrids.

*Use only with Roundup Ready-designated com hybrids.

Soil-Applied "Grass" Herbicides Applied
After Corn Emergence

Atrazine plus Dual II, Frontier, Harness, Micro-Tech,
Surpass, or TopNotch — or their respective premixes
of Bleep II, Guardsman or LeadOff, Harness Extra,
Bullet, Surpass 100, or FulTime — may be applied after

planting iintil com is 5 to 12 inches tall (depending on
the herbicide). Grass weeds should be less than 1.5
inches tall or not exceeding the 2-Ieaf stage unless the
soil-applied "grass" herbicide to minimize problems
with late-emerging grasses is applied with a post-
emergence grass herbicide such as Accent to control

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

165

larger grasses. See labels for com size limitations.
Split applications of Dual II are used in "seed com" to
prevent late-emerging grass problems. Do not use liq-
uid fertilizer as the carrier after corn emergence.

Prowl or Treflan may be applied from the 2-leaf
stage of field com (4 inches tall) up to last cultivation
(layby); this use has been primarily in sandy soils
where shattercane and crabgrass are late-emerging
problems. See the label for exact instructions and the
need for incorporation. Do not use Prowl in corn more
than once per crop season.

Soil-Applied
(Corn)

'Broadleaf" Herbicides

AAtrex'*"'' or Atrazine'^^'' (atrazine), or Princep (si-
mazine), is often incorporated before planting be-
cause solubility is low. Atrazine is used alone at 4
pints of 4L or 2.2 pounds of 90DF (2.0 pounds active
ingredient/a.i.) per acre, except on highly erodible
land (HEL) with less than 30 percent residue cover,
where 1.6 pounds a.i. per acre is the maximum al-
lowed. When mixed with "grass" herbicides (Table
15.08), the atrazine rate to control broadleaf weeds is
2 to 3 pints of 4L or 1.1 to 1.8 pounds of 90DF. A 1:1
mixture of atrazine and simazine is often used in
southern Illinois.

Atrazine or simazine can persist to injure some ro-
tational crops. The risk of carryover is greater with
late application; a cool, dry growing season; or both;
and on soils with pH over 7.2. Soybeans planted the
next year may show injury from atrazine carryover,
especially if atrazine is applied after June 10. Depend-
ing on rate and season, com or sorghum may be a bet-
ter choice. Do not plant small grains, clovers, alfalfa, or
vegetables in the fall or the next spring after using
atrazine.

Bladex'^^'' or Cy-Pro'*"'' (cyanazine) and Extrazine
jjRUP Qj. Cy-Pro AT'*"'' (cyanazine + atrazine) are under
a phaseout program through 2002. Beginning in 1999,
total cyanazine rates allowed per year (all applica-
tions) are 1 lb a.i. per acre, limiting cyanazine's useful-
ness as a soil-applied herbicide. All products contain-
ing atrazine and cyanazine are restricted-use
pesticides because of the risk of groundwater and sur-
face water contamination.

Best management practices (BMP) to protect
groundwater and surface water are mandated on la-
bels of cyanazine or atrazine and all premixes con-
taining atrazine. Required buffer zones (setbacks) are as
follows: No application is allowed within 66 feet of
points where field surface water can enter perennial
or intermittent streams and rivers (if HEL, this 66 feet
must be in crops or grass, i.e., a filter strip) or within
200 feet of lakes and reservoirs. No mixing or loading

is allowed within 50 feet of streams, rivers, lakes, or
reservoirs.

Maximum allowable atrazine rates are lowest for
highly erodible land with less than 30 percent plant
residue cover (HEL < 30 percent PRC), where the
maximum rate is 1.6 pounds a.i./acre soil-applied or
2.0 pounds a.i./acre postemergence. On other soils,
the maximum atrazine rate is 2 pounds a.i./acre and a
total of 2.5 pounds a.i./year for all soils.

Premixes containing atrazine make calculations of
total annual use difficult, especially if both soil-ap-
plied and postemergence premixes are used. Pounds
of active ingredient of atrazine per pound or gallon of
com herbicide premix are listed in Table 15.03. For ex-
ample, if you apply Bicep II 5.9L at 2.4 quarts (1.60
pounds a.i. atrazine) and Marksman 3.2L at 3.5 pints
(0.92 pounds a.i. atrazine) per acre, you have applied
a total of 2.52 pounds a.i. of atrazine per acre. This
combination is slightly above the 2.50 pounds a.i. of
atrazine allowed per year on any soil.

Balance'*"'' 75WDG (isoxaflutole) may be applied
preplant incorporated or preemergence at 1.5 to 2.5
ounces per acre. Do not apply to very sandy soils. Do
not apply after com emergence. Balance may be tank-
mixed with several herbicides (Table 15.08) to increase
grass control.

Python 80WDG (flumetsulam) or Hornet 85.6WG
(flumetsulam + clopyralid) at 0.8 to 1.33 ounces or 3.2
to 4.8 ounces per acre, respectively, may be applied
prior to planting and incorporated or applied after
planting com. They control only broadleaf weeds
(Table 15.10), so they may be tank-mixed with appro-
priate "grass control" herbicides (see Table 15.08). Ob-
serve label precautions on drift and tank cleanup with Hor-
net, as it contains clopyralid, the active ingredient in
Stinger. Broadstrike + Dual 7.67E (flumetsulam -i- me-
tolachlor) is used at 1.75 to 2.5 pints per acre. All
flumetsulam labels have precautions regarding low
and high soil pH as well as soil insecticide use, so
consult the label before applying them. Be sure soil in-
secticides are applied in a 1-band and not placed in-furrow.

Contour'*"'' (imazethapyr + atrazine). Pursuit
(imazethapyr), or Pursuit Plus (imazethapyr +
pendimethalin) may be used only on IMI-com hy-
brids (IR/IMR or IT/PT). Pursuit or Contour may be
applied preplant incorporated or preemergence,
whereas Pursuit Plus may be used only preemergence
on com. Rates per acre are 1.44 ounces of Pursuit
70DG (V2 soluble bag) or 4 fluid ounces of Pursuit 2S
(1 gallon = 32 acres), 2.5 pints of Pursuit Plus, or 1.33
pints of Contour (1 gallon = 6 acres).

Banvel or Clarity (dicamba), or Marksman'*"''
(dicamba + atrazine), may be applied preemergence,
but only on medium- or fine-textured soils containing

166

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

at least 2 percent organic matter, where the rate is
1 pint of Banvel or Clarity or 3.5 pints of Marksman
per acre. On other soils, only if the corn is planted no-till,
use 0.5 pint of Banvel or Clarity, or 2 pints of Marks-
man per acre. Banvel, Clarity, or Marksman may be
tank-mixed with preemergence "grass" herbicides
(Table 15.08), but do not incorporate.

POSTEMERGENCE (FOLI AR-APPLIED)
HERBICIDES (CORN)

Some postemergence herbicides control certain grass
weeds (Table 15.09), whereas others primarily control
broadleaf weeds (Table 15.10). Several postemergence
herbicide tank mixes are registered (Tables 15.13 and
15.14). Many postemergence com herbicides allow or
require the use of an adjuvant to improve activity.
Table 15.16 lists labeled adjuvants, minimum time be-
tween applications and rainfall for optimal herbicide
activity, and required reentry intervals.

Postemergence Grass and Broadleaf
CONTROL (Corn)

Accent, Accent Gold, Basis, Basis Gold, Beacon, Lib-
erty, Liberty ATZ, Lightning, Poast Plus, Pursuit, Re-
solve, and Roundup Ultra are used postemergence in
com to control some small grass weeds (Tables 15.09
and 15.11). Lightning, Pursuit, and Resolve require IMI-
corn hybrids (IT/PT or IR/IMR). IR/IMR-designated
com hybrids are not required but may help minimize
com injury (see upcoming discussion) from sulfony-
lurea or sulfonamide herbicides. Liberty or Liberty
ATZ requires Liberty Link or GR com hybrids. Poast
Plus requires PP (Poast Protected) com hybrids and
controls only grasses. Roundup Ultra requires
Roundup Ready com hybrids. See Tables 15.09 and

15.10 for grass and broadleaf weed control and Tables

15.11 and 15.12 for maximum weed sizes.
Accent, Basis, Beacon, Lightning, and Pursuit are

ALS inhibitors and do not control ALS-resistant
ivaterhemp or other ALS-resistant weeds. Tank mixes
(Tables 15.13 and 15.14) or premixes (Table 15.03) of
herbicides with different modes of action may help
minimize the potential for weeds developing resis-
tance. Tank mixes also improve broadleaf weed con-
trol but may antagonize grass control, increase the po-
tential for crop injury, or both. Before applying tank
mixes of herbicides or insecticides, "read and heed" all
label precautions as to climatic conditions, grass species,
and adjuvants. Do not tank-mix most ALS herbicides
with bentazon or cyanazine, and do not apply them
within 3 to 7 days after applying bentazon or
cyanazine.

Restrictions regarding soil-applied organophosphate
(OP) insecticide (used primarily for rootworm control) are

similar on the labels of several ALS herbicides (see
Table 15.15). Accent, Accent Gold, Basis Gold, or
imazethapyr controls giant foxtail, fall panicum, and
bamyardgrass better than Basis or Beacon (Tables

15.09 and 15.11).

Basis 75WG (rimsulfuron + thifensulfuron) is used
at V3 ounce (Vi soluble packet) per acre on field com up
to the 4-leaf stage or two visible leaf collars (V-2), which-
ever is most restrictive. Cultivation is suggested 10 to 15
days after application. A sequential application of Ac-
cent is allowed. Basis has a potential to select for ALS-
resistant weed biotypes.

Basis Gold'*^'' (rimsulfuron -1- nicosulfuron + atra-
zine) at 14 ounces or Accent Gold (rimsulfuron +
nicosulfuron -t- flumetsulam -1- clopyralid) at 2.9
ounces (Vi soluble packet of either) per acre may be
applied to field com up to 12 inches tall or exhibiting 6
leaf collars, whichever is most restrictive. Cultivate if rain
does not occur within 5 to 7 days. A sequential appli-
cation of Accent is allowed.

Accent 75WG (nicosulfuron) may be applied over
the top of com up to 20 inches tall (freestanding) or
with six visible leaf collars, whichever is most restrictive.
Apply with drop nozzles on com 20 to 36 inches tall.
Do not apply after corn is 36 inches tall or exhibits 10 leaf
collars. Use Vj ounce (Vi soluble bag) per acre. If
needed, a second application can be made 14 to 28
days later, but do not exceed VA ounces per growing
season; observe com size limits. Celebrity is a co-pack
providing a full rate of Accent plus dicamba to im-
prove broadleaf weed control. Accent and Beacon
control quackgrass and johnsongrass. (See upcoming
section on perennials.)

Beacon 75WG (primisulfuron) is applied to 4- to
20-inch com at 0.76 ounce (Vi soluble bag) per acre.
Split applications (see the label) may provide better
control of johnsongrass. The second application must
be made before tassel emergence and be directed with
drop nozzles if com is over 20 inches tall.

Roundup Ultra (glyphosate) used at 1.5 to 2 pints
per acre on Roundup Ready com hybrids controls
several grass and broadleaf weeds. Total in-crop ap-
plications must not exceed 2 quarts. Apply prior to corn
being 30 inches tall or V-8 stage. See Tables 15.09 and

15.10 for weed ratings.

Contour'^^'' (1:8 imazethapyrratrazine) or Resolve
(1:3 imazethapyr:dicamba) is less likely to select for
ALS-resistant weed biotypes than Lightning
(imazethapyr + imazapyr) or Pursuit (imazethapyr).
Use only on IMI-corn hybrids (IR or IT). Rates per acre
are 5.33 ounces (Vs soluble bag) of Resolve, 1.33 pints
of Contour, 1.28 ounces (V2 soluble bag) of Lightning
70DG, 4 fluid ounces Pursuit 2S, or 1.44 ounces (Vi
soluble bag) of Pursuit 70DG. Apply before com is 12

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

167

Table 15.10. Corn Herbicides: Broadleaf Weed Control Ratings

Herbicide

:§

0)
0)

12
Si

cr
B

Momingglories,
annual

Nightshade,
eastern black

en
bO

£
0

u
T3

a»
bO

-t->

'bb

-0

«
-a
a5

tn
t3
01
0)

2
■|

0
C

<-4-l

o»
>

g
0
u

Soil-applied

Atrazine^''

Princep^^

Marksman

Python'^

Hornet

Balance

Postemergence

. ^i3i:> 7/7

b/e 15.12 for maximum

weed

szzes •

' JCt lU

Contact or triazine^

Aim

—

Atrazrne^''

Buctril

Buctril + atrazine

Laddok S-12

Liberty'

Liberty ATZ

1 Resource

1 +

Tough

Plant-growth regulator (PGR)^

Marksman

Banvel/Clarity

1+'

2,4-D

2+'

Stinger

1 Acetolactate synthetase (ALS)^

' Accent*'-"'

Basis'''"-*

Basis Gold''-'

Beacon''-"-'

Exceed''-"-'

Lightning''-"''

Permit"

Spirit''-"-'

ALS + PGRi

Accent Gold''-^

Celebrity''-''

Hornet

1+^

NorthStar

1+^

Resolve''-''

1 +

Scorpion III

1+^

Roundup Ultra''

Control ratings: 9 = excellent, 8 = good, 7 - fair, 6 = poor, 5 or 4 = unsatisfactory, N = Nil or None. Boldface indicates
acceptable control. Corn response: 0 = minimal, 1 = possible, 2 = probable, 3 = serious.

168

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 15.10. Com Herbicides: Broadleaf Weed Control Ratings (cont.)

^These herbicides do not control triazine-resistant biotypes of pigweed, waterhemp, lambsquarters, or kochia.

•"May also control some grass species. See Table 15.09.

•^ALS-resistant waterhemp (pigweed) or kochia is not controlled by these ALS herbicides.

''Adjuvant varies with herbicide.

The response rating increases if an NIS or COC is added to the spray mix.

'Requires use of Liberty Link corn hybrids.

^Use COC or NIS, but NIS only with some tank mixes.

''Requires use of IMI-designated com hybrids.

'Use of IR-designated corn hybrids minimizes insecticide interaction and injury potential.

'Use an NIS and not COC.

''Use Roundup Ready com hybrids.

For herbicide ratings for tank mixes or premixes, see the component parts:

Premix

Grass

Broadleaf

Bicep II

Dual II

atrazine

Bullet

Micro -Tech

atrazine

FulTime

TopNotch

atrazine

Guardsman

Frontier

atrazine

Harness Xtra

Harness

atrazine

Surpass 100

Surpass

atrazine

Broadstrike + Dual

Dual

Python

OpTill

Frontier

Banvel

Table 15.11. Com "Post-Grass" Herbicides: Maximum G

rass Sizes

in Inches

Celebrity G

Accent

Basis

Light

Poast

or Accent

Basis Gold

Gold

Beacon

Liberty^

-ning''

Plus^

Rate/A:

^aoz

Va oz 2.9 oz

14 oz

0.76 oz

28floz

1.28 oz

24floz

Size*^

Size

" Size-^

Size-^

Size<i

Size"

Size''

Size'^

Annual grasses

Bamyardgrass

—

Crabgrass, large

—

Cupgrass, woolly

<1*

—

Foxtail, giant

Foxtail, green

Foxtail, yellow^

Panicum, fall

Sandbur, field

—

3«

Shattercane

Signalgrass, broadleaf

—

Johnsongrass, seedling

—

Perennial grasses or sedge

Johnsongrass, rhizome

8 to 18

—

8 to 16

Muhly, wirestem

—

Nutsedge, yellow^

—

Quackgrass

4 to 10

—

4 to 8

Perennial weeds

Artichoke, Jerusalem

—

Thistle, Canada

—

— = not listed on the label.

*Suppression or reduced competition only.

*Use only with Liberty Link or GR (glufosinate-resistant) corn hybrids.

''Use only with IMI-designated com hybrids.

*^Use only with PP- or SR-designated corn hybrids.

''Height or length of laterals or tillers in inches.
''Requires 30 fluid ounces.
'Requires 36 fluid ounces.

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

169

Table 15.12. Com "Post-Broadleaf" Herbicides: Maximum Broadleaf Weed Sizes in Inches

Cfi

■»->

Herbicide (rate)

C
o

52
1

Momingglorie
annual

Nightshade,
eastern black

03
Pi

"So

Translocated herbicides

2,4-D amine''

—

Accent

—

2-3

—

Accent Gold

—

Banvel/Clarity*'

Basis

—

Basis Gold

—

Beacon (0.38 oz)

—

Beacon (0.76 oz)

1.5*

Beacon^'' + 2,4-D

—

Beacon^ '' + Banvel''

—

Beacon^ '' + Accent^

—

Celebrity B

Exceed (1 oz)

Hornet (2.4 oz)

—

Hornet (3.2 oz)

—

Lightning

—

Marksman'^

NorthStar (5 oz)

Permit (0.67 oz)

—

Permit (1.33 oz)

12*

—

Permit'' + 2,4-D

—

Permit'' + Banvel

Resolve

—

Scorpion III

—

Sencor'' + Banvel

Spirit (1 oz)

Contact herbicides with variable rates

Aim

—

Atrazine^ 4L (2 qt)

—

Basagran 4S (1.5 pt)

—

Basagran 4S (2 pt)

—

1 Buctril (1 pt)

—

1 Buctril (2 pt)

Buctril + Atrazine (1.5 pt)

—

1 Buctril + Atrazine (3.0 pt)

,LaddokS-12 (1.67 pt)

—

Laddok S-12 (2.33 pt)

' Liberty (20 fl oz)

Liberty (28 fl oz)

Liberty ATZ (32 floz)

! Liberty ATZ (40 fl oz)

Resource*^ (6 fl oz)

—

3L*

—

3L*

—

i Resource^'' + atrazine

AR"

—

' Tough 5E'' (1.5 pt)

—

170

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 15.12. Corn "Post-Broadleaf" Herbicides: Maximum Broadleaf Weed Sizes in Inches (cont.)

* = Suppression or partial control only; — = no control or weed not on label.

*Half rate or low rate.

''Herbicide with label for tank mix.

*^No sizes given on label; weed sizes here are best estimates.

•'All weed sizes given in inches, except Resource and Tough use leaf number, "L" designation; for Resource + atrazine,

4R = 2-4 runners up to 10 inches long.

Table 15.13. Com Postemergence Herbicide Tank Mixes: "Broadleaf" + "Grass" Herbicides

ALS-Grass

ACC-ase Grass

Broadleaf

Accent

Accent Gold

Basis

Basis Gold

Beacon

Lightning

Poast Plus

PGRorALS

2,4-D

-/No!

-/-

-/No!

-/Y

Banvel/Clarity

Y/Y

-/Y

Y/Y

-/Y

Y/Y

-/-

Beacon @ 0.5X

Y/-R

-/-

-/No!

-/-

Contour

Y/-K

-/-

-/No!

-/-

Exceed

Y/Y

-/-

-/No!

-/-

Y/-R

-/-

No!/-

Hornet

Y/-

-/-

-/Y

Y/Y

-/-

Marksman

Y/Y

-/Y

-/-

-/Y

-/-

NorthStar

Y/-

-/-

Y/-R

-/-

No!/-

Permit

Y/-

-/-

-/No!

-/-

Y/-

-/-

Pursuit

Y/-R

-/-

-/No!

-/-

Resolve

Y/-R

-/-

-/No!

-/-

Scorpion 111

-/Y

-/-

-/Y

-/-

Spirit

Y/-.

-/-

Y/-K

-/-

No!/-

Contact or triazine

Aim

Y/-

-/-

Y/-

-/-

Y/-

-/-

Atrazine

-/Y

-/-

-/Y

Basagran

-/No!

-/-

-/Y

Buctril

Y/Y

-/-

Y/Y

-/Y

-/-

Buctril + Atrazine

Y/Y

-/-

-/Y

-/-

Laddok S-12

-/No!

-/-

Y/Y

Liberty

Y/-

-/-

Y/-

-/-

Liberty ATZ

Y/-

-/-

Y/-

-/-

Resource

Y/Y

-/-

Y/Y

-/-

Tough

Y/-

-/-

-/Y

Y/-

-/-

Y/- = "broadleaf" label only; Y/-^ = "broadleaf" label only, reduced "grass" rate; -/Y = "grass" label only; -/No! = prohibited
by grass label; No!/- = prohibited by the "broadleaf" label; Y/Y = both labels; -/- = neither label.

inches in height. Do not make more than one application
per growing season of imazethapyr.

Poast Plus IE (sethoxydim) may be used on PP-
com hybrids (Poast Protected) at 24 fluid ounces for
most annual grasses, (Table 15.11) with a higher rate
allowed for larger or perennial grasses (see label).

Liberty 1.67S (glufosinate) is used in Liberty Link
or GR com hybrids at 16 to 28 fluid ounces per acre to

control small annual grass and broadleaf weeds.
Tank-mix with atrazine to improve broadleaf control.

Liberty ATZ 4.3L, a premix of Liberty and atrazine,
is applied to field com less than 12 inches tall at 32 to
40 fluid ounces per acre. See Tables 15.09 to 15.12 for
weed ratings and sizes. A second application of Lib-
erty (not ATZ) is allowed to control later-emerging
weeds.

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM
Table 15.14. Corn Postemergence Herbicide Tank Mixes: Broadleaf + Broadleaf Herbicides

171

PGR-system

ic "broadleaf"

ALS

•-systemic "broadleaf"

Marks-

Morth-

0.5X

Light-

2,4-D

Banvel Clarity

man

Stinger

Star

Beacon

Exceed

ning

Permit

Pursuit

Spirit

Systemic

2,4-D

-/-

-/Y

-/-

-/Y

-/-

-/Y

Banvel

Y/-

-/-

Y/-cr

-/Y

Y/Y

-/Y

Beacon @

Y/-

Y/Y

Y/-

-/-

-/Y

-/-

-/Y

-/-

-/Y

-/-

-/Y

0.5X

Clarity

Y/-

-/-

Y/-CT

-/Y

Y/Y

-/Y

Hornet

Y/-

Y/-CT

-/-

Marksman

-/-

Y/-cr

-/Y

-/-

-/Y

Contact

Aim

Y/-

-/-

Y/-

-/-

Y/-

Basagran

-/-

-/Y

-/-

Buctril

Y/-

-/-

Y/-CT

-/-

Y/Y

-/Y

Y/Y

-/Y

Buctril +

Y/-

-/-

Y/-cr

-/-

-/Y

-/-

-/Y

-/-

-/Y

atrazine

Laddok S-12

Y/-

-/-

Y/-cr

-/-

Liberty-

-/-

Y/-

-/-

Y/-

-/-

Y/-

-/-

Y/-

Liberty ATZ

-/-

Y/-

-/-

Y/-

-/-

Y/-

-/-

Y/-

-/-

Y/-

Resource

Y/-

-/Y

Y/-

-/-

Y/-

-/-

-/Y

Tough

Y/-

Y/Y

Y/-

-/-

-/Y

Y/-

Y/Y

-/-

Y/-

-/-

-/Y

Triazines-contact

Atrazine

-/-

-g/Y

-/-

-/Y

Sencor

Y/-

-/-

Y/-

-/-

■' Triazine

Triazi
AtrazU

^te

Of^r contact herbicides

ie Basagran

Buctril

Laddok

Toug

Aim

Y/-

-/-

No/-

-/-

Atrazine

-/-

-/Y

Liberty

Y/-

Liberty ATZ

Y/-

-/-

Y/-

Resource

Y/-

-/-

Y/-

No!/

Sencor

Y/-

Y/Y

Y/- = "row" herbicide label (on top); -/Y = "column" herbicide label (at left); Y/Y = tank mix on both labels; Y/-^ = Stinger
added for Canada thistle control; -^/Y = atrazine added for grass control; No!/- or No/- = tank mix prohibited.

Atrazine'^"'^ controls certain small (< 1.5 inches)
annual grasses (Table 15.09) at 2.2 pounds of 90DF or
4 pints of 4L per acre and broadleaf weeds (Table
15.10) at 1.3 pounds of 90DF or 2.4 pints of 4L per
acre. Always add 1 quart of COC per acre. After corn
emerges, do not apply in liquid fertilizer carrier or add
2,4-D. Maximum com size allowed is 12 inches tall.

Atrazine does not control triazine-resistant broadleaf
weeds. Best management practices and maximum rate
per year for atrazine are explained in the "Soil-Ap-
plied 'Broadleaf Herbicides (Com)" section. Sequen-
tial applications are allowed, but do not use more
than 2.5 pounds a.i. of atrazine. If atrazine is applied
after June 10, plant only com or sorghum the next year.

172

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 15.15. Herbicide Label Statements: Interactions with Organophosphate (OP) Insecticides

Soil-applied

OP insecticides^

Foliar OP

Counter 20CR

insecticide''

Com herbicide

Furrow

T-Band

Thimet

Lorsban

Days before

Days after

nicosulfuron and rimsulfuron

Accent

JQlCd

TCI

Accent Gold

TCI

Basis

UCI

TCI

Basis Gold

TCP

TCI

Celebrity B & G

JQlcd

TCI

primisulfuron and
Beacon

prosulfuron

UCP

TCI

Exceed

UCP

TCI

NorthStar

UCI

TCI

Spirit

UCI"

TCI

flumetsulam

Broadstrike + Dual No''

No"

TCP

Hornet

No''

No"

TCP

Python

No"

TCP

—

Scorpion III

Is not soil applied

—

imazethapyr and imazapyr

Contour-IT' Yes

Lightning-IT' Yes

Pursuit-IT^ Yes

Resolve-IT' Yes

Yes

TCI

Yes

TCI

Yes

TCI

Yes

TCI

halosulfuron
Permit

Is not soil applied"

No = Do not use this herbicide on com if this insecticide was previously soil applied in this manner.

UCI = Using this herbicide on corn if this insecticide was previously soil applied in this manner may result in unacceptable

crop injury.

TCI = Using this herbicide on com if this insecticide was previously soil applied in this manner may result in temporary corn

injury.

^Fortress and Aztec are soil-applied OP insecticides, but they do appear to interact with ALS herbicides.

Toliar-applied OP = Cygon, Diazianon, DiSyston, Imidan, Lorsban, malathion, or Penncap-M.

•^Herbicide label states crop injury may be unacceptable on soils with < 4% organic matter content.

"Counter CR supplemental labeling allows its use in this manner with this herbicide!

*Do not place Lorsban in-furrow if Broadstrike + Dual, Hornet, or Python are to be soil applied.

'IT = imidazolinone-tolerant hybrids. All soil-applied insecticides can be used on IR or IMR corn hybrids.

POSTEMERGENCE BROADLEAF CONTROL

(Corn)

There are three herbicide modes of action used for
postemergence control of broadleaf weeds in com:
plant growth regulator (PGR), acetolactate-synthase
(ALS) inhibitor, and contact (triazines have post-
emergence contact action). Banvel, Clarity, Stinger,
and 2,4-D are systemic PGR herbicides, whereas
Marksman and Shotgun are premixes of PGR plus tri-

azine herbicides. Beacon, Exceed, Lightning, Permit,
Pursuit, and Spirit are systemic ALS-inhibiting herbi-
cides, whereas Hornet, NorthStar, Resolve, and Scor-
pion III are premixes of ALS plus PGR herbicides.
Atrazine, bromoxynil, bromoxynil + atrazine, Laddok
S-12, Resource, Sencor, and Tough are contact herbi-
cides. Closely observe drift precautions with all post-
emergence herbicides, but drift is often more serious with
systemic broadleaf herbicides.

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

173

Systemic (Translocated) Broadleaf
Herbicides (Corn)

Translocated PGR or ALS herbicides must be applied
at com growth stages specified on the label to mini-
mize com injury and drift potential. Directed sprays
(drop nozzles) are often specified for later applica-
tions to keep the spray out of the com whorl, maxi-
mize spray contact with weeds, and minimize drift
potential. Adding an adjuvant may increase crop in-
jury potential, but many herbicide labels allow or re-
quire the use of an adjuvant to improve activity. See
Table 15.10 for broadleaf weeds controlled and Table
15.14 for tank mixes to improve broadleaf weed con-
trol. Table 15.12 indicates maximum broadleaf weed
size specified for postemergence herbicides used in
com. Table 15.16 lists labeled adjuvants, minimum
time between application and rainfall for optimal her-
bicide activity, and required reentry intervals.

Banvel or Clarity (dicamba) or Marksman'^^''
(dicamba -t- atrazine) may be applied from spike to the
5-leaf or 8-inch stage in com. Use 1 pint of Banvel or
Clarity, or 3.5 pints of Marksman, per acre except on
coarse-textured soils, where the rate is Vi pint of
Banvel or Clarity and 2 pints of Marksman per acre.
Split applications of Banvel and Clarity are allowed if
the com size restrictions are met, but do not exceed
1.5 pints per treated acre per season.

Banvel may be applied at V2 pint per acre to com
that is 8 to 36 inches tall or 15 days before tassels
emerge, whichever comes first. Use drop nozzles on
com over 8 inches tall (especially if Banvel is applied
with 2,4-D) to reduce the risk of com injury, improve
spray coverage, and reduce drift. Do not apply Banvel
to corn over 24 inches tall if nearby soybeans are over 10
inches tall or have begun to bloom. Observe all label pre-
cautions to minimize the risk of Banvel, Clarity, or
Marksman drifting to nearby susceptible crop or or-
namental plants. Both Marksman and Shotgun (see the
next paragraph) contain atrazine and so must meet atra-
zine rate restrictions and set-back restrictions to protect
ground and surface water. See the "Soil-Applied 'Broadleaf
Herbicides (Corn)" section.

Shotgun'^^*' 3.25L (atrazine -1- 2,4-D) may be applied
at 2 to 3 pints per acre to com from spike to the 4-leaf
stage (or 8 inches tall) or up to 12 inches in height if
drop nozzles are used. Do not use over 2 pints on sandy
soils. Because Shotgun contains atrazine and 2,4-D, the
label carries atrazine restrictions as well as 2,4-D protective
equipment requirements.

2,4-D amine or 2,4-D ester may be used from emer-
gence to tasseling of com. Apply with drop nozzles if
com is more than 8 inches tall. The rate is Va to V2 pint
of 2,4-D ester or 1 pint of 2,4-D amine per acre if the
acid equivalent is 3.8 pounds per gallon. If temperatures

exceed 85°F, 2,4-D ester can volatilize and injure nearby
susceptible plants. Spray particles of either 2,4-D ester
or amine can drift and cause injury to susceptible
plants. Observe protective equipment requirements
on the 2,4-D label.

Com is often brittle for 1 to 2 weeks after 2,4-D is
applied and may be susceptible to stalk breakage
from high winds or cultivation. Other symptoms of
2,4-D injury are stalk lodging, abnormal brace roots,
and failure of leaves to unroll. Com hybrids differ in
their sensitivity to 2,4-D. High humidity and tem-
perature increase the potential for 2,4-D injury to
com.

Hornet 85.6WG (flumetsulam -f- clopyralid) may be
applied to field com up to 20 inches tall or V-6 stage
and Stinger 3S (clopyralid) or Scorpion III 84.3WG
(flumetsulam + clopyralid -1- 2,4-D) up to 24 inches
tall. Because Scorpion III contains 2,4-D, use drop
nozzles if com is over 8 inches tall. Rates per acre are
1.6 to 3.2 ounces (V6 to !^ packet) of Homet, V4 to V2
pint of Stinger, or 4 ounces {Vi packet) of Scorpion III.
Homet or Stinger suppresses Canada thistle, and
Stinger at higfier rates controls Canada thistle. See the
label or Tables 15.10 and 15.12 for weeds controlled
and size limits and Table 15.16 for adjuvant selection.
The interval before planting soybeans is 10.5 months after
applying clopyralid.

Spirit 57WDG and Exceed 57WDG, 3:1 and 1:1
premixes of primisulfuron:prosulfuron, respectively,
are applied at 1 ounce (Vi packet) per acre broadcast
over the top of field com between 4 and 20 inches in
height. Use drop nozzles for com 20 to 24 (Spirit) or
30 inches (Exceed) in height or past 6 leaf collars (V-6
stage). Exceed and Spirit have the potential to select for
ALS-resistant weed biotypes.

If rotating to soybeans the next year: Do not apply af-
ter June 30, or on soils with pH over 7.8, because of
concern with prosulfuron carryover. Use Exceed be-
low Interstate (I) 70, or if STS soybeans are grown, be-
tween 1-70 and 1-80. Use Spirit between 1-70 and 1-80
and NorthStar above 1-80.

NorthStar 47.4WDG (primisulfuron + dicamba)
has the same recropping restriction as Beacon. Apply at
5 ounces per acre over the top of com between 4 and
20 inches tall (V-2 to V-6), or with drop nozzles up to
36 inches tall. Exceed, Spirit, and NorthStar control
many annual broadleaf weeds (Tables 15.10 and
15.12), but they can also be tank-mixed with other
herbicides (Tables 15.13 and 15.14). Observe com
height limits for the tank-mix partner. Exceed, Spirit,
and NorthStar labels carry precautions regarding soil in-
secticides use similar to the Beacon label.

Permit 75WG (halosulfuron) may be applied from
spike to the layby stage of field com at a rate of % to

174

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 15.16. Corn "Post" Herbicides: Adjuvant Use Plus Application and Use Restrictions

Rain-free

Reentry

Apply

period

interval

PHI

over the top

Herbicide

Adjuvant and nitrogen

(hr)

days

of com

Use drop nozzles

2,4-D amine

None

6-8

8" to tassel

2,4-D ester

None

1-2

8" to tassel

Accent

COC or NIS^ + NH^

20-/V-6

20" to 36"/V-10

Accent Gold

COC + NH^

12"/V-6

Aim

NIS

8-leaf/V-8

Atrazine

COC

1-2

12"

Banvel

If d^oughty^ NIS or NH^

—

24"^ to 36"

Reduces drift

Basagran

COC + NH^

6'*

Any size?

Basis

NIS or COC + NH^

6"/V-2

Basis Gold

COC + NIL

12"/V-6

Beacon

COC or NIS^ + NH^

4" to 20"

Splits 20" to tassel

Buctril

COC^ or NIS^

Pretassel

Buctril + atrazine

COC^ or NIS^

12"

Celebrity B & G

NIS^ + UAN (no AMS)

—

20"/V-6

20" to 36"/V-10

Clarity

UAN + COC' or NIS"

—

8"; 5" with oil

Contour^

COC or NIS + NH^

12"

Exceed

COC or NIS + NH^

60/30

4" to 20"

20" to 30"

Hornet

NIS or COC + NH^ if dry

20"/V-6

Laddok S-12

COC + NH

12"

Liberty *"

AMS only!

70/60

24"/V-7

24" to 36"

Liberty"^ ATZ

AMS only

70/60

12"

Lightnings

COC or NIS + NH,

18" ideally

Marksman

COC^orNIS^orNH/

—

5-leafor8"

NorthStar

COC* or NIS + NH^

60/45

4" to 20"/V-6

20" to 36"

Permit

COC or NIS + UAN

Layby (36")

Poast Plus'

COC; NH^ optional

60/30

Pretassel

Layby sprays

Pursuit?

COC or NIS + NH^

See PHI.

Resolve?

NIS + NH,

12"

Resource

COC + NH,

2- to 10-leaf

Roundup Ultra''

AMS optional

1-2

7/50

30"/V-8

Scorpion III

NIS + NH "

8" to 24"

Sencor

NIS or NH^

—

Pretassel

See tank-mix
partner.

Shotgun

None

8"/4-leaf

8" to 12"

Spirit

COC or NIS + NH,

4" to 20"/V-6

20" to 24"

Stinger

None

6-8

24"

Tough

None

1-2

See PHI.

Spot treatment only

Roundup Ultra'

AMS optional

1-2

56/14

Pretassel

Touchdown 5'

NIS, AMS optional

1-2

90/35

See PHI.

COC = crop oil concentrate, NIS = nonionic surfactant, NH^ = ammonium fertilizer adjuvant (UAN or AMS), UAN = urea-ammonium nitrate

(28-0-0), AMS = ammonium sulfate (spray grade 21-0-0), PHI = preharvest interval for grain harvest, shorter for silage.

"Use NIS only when Accent or Beacon is mixed with anything except atrazine.

•" Allowed if arid or droughty conditions exist at application.

■"Up to 24 inches if nearby soybeans are over 10 inches or are blooming.

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

175

Table 15.16. Corn "Post" Herbicides: Adjuvant Use Plus Application and Use Restrictions (cont.)

■^Current label: "Rainfall soon after application may decrease the effectiveness."

'Adjuvants allowed if injury is acceptable.

'Use of oils (penetrants) may cause injury "if com is > 5 inches tall."

^Use only with IMI-designated com hybrids.

''Use only with Liberty Link or GR-designated corn hybrids (glufosinate-resistant).

'Use only with PP- or SR (sethoxydim-resistant)-com hybrids.

iCOC allowed only up to 12-inch-tall com.

''Use only on Roundup Ready-designated com hybrids.

'Use only as a spot treatment and not as an overall application in corn.

IVa ounces per acre. Permit controls yellow nutsedge
plus several broadleaf weeds (Tables 15.10 and 15.12).
Permit may be tank-mixed with other herbicides
(Tables 15.13 and 15.14). Permit has the potential to select
for ALS-resistant weed biotypes.

Contact Broadleaf Herbicides (Corn)

Contact herbicides used in com are Aim, bromoxynil,
bromoxynil + atrazine, Laddok S-12, Resource, and
Tough. Sencor is a triazine but does not have the set-
back restrictions or corn-size limits of atrazine or
cyanazine. Atrazine tank mixes or premixes must be
applied before com is 12 inches tall. Contact herbi-
cides require thorough spray coverage, so note label
specifications for spray volume and nozzle type. See
Table 15.10 for broadleaf weeds controlled and Table
15.12 for maximum weed size specified on the label.
Table 15.16 lists maximum com size allowed and po-
tential adjuvant use. Adjuvant use changes with tank
mixes, weed species, and environmental conditions.
Contact herbicides are much more active in warm, hu-
mid weather and much less active in cool, dry
weather.

Aim 40DF (carfentrazone) is used at V3 ounce per
acre on com up to eight leaf collars (V-8 stage). It may
be used in many tank mixes, but not with bromoxynil
! or 2,4-D ester. Apply with MS only.

Buctril or Moxy 2E (bromoxynil) is used at 1 pint
per acre after emergence or up to 1.5 pints per acre af-
ter the 4-leaf stage of com up to tassel emergence, but
while weeds are in the 3- to 8-leaf stage. Larger pig-
weed and velvetleaf may require the higher rate or a
combination with atrazine.

Buctril + Atrazine'*"'' or Moxy +Atrazine'*"'' 3L

! (bromoxynil -h atrazine) is used at 1.5 to 3 pints per

acre. At the higher rate, do not apply until the 4-leaf

, stage of com. Do not apply to corn over 12 inches tall. An

MS or COC may be added, but the potential for com

injury increases.

Laddok'*"'' S-12 5L (bentazon -i- atrazine) is used at

1.33 to 2.33 pints per acre until com is 12 inches in
height.

Tough 5E (pyridate), at 0.75 to 1.5 pints per acre,
controls some small-seeded broadleaf weeds, such as
kochia and pigweed (Table 15.10). Adding atrazine (1
to 2 pints) or Banvel (0.5 to 1 pint) controls more weeds.
Apply when most weeds are at the 1- to 4-leaf stage.

Sencor (metribuzin) may be included in tank mixes
with several postemergence com herbicides (Table
15.14). Do not use a COC with any tank mix. The rate
per acre is 2 to 3 ounces of Sencor 75DF.

Resource 0.86E (flumiclorac) is used primarily at
4 fluid ounces per acre, tank-mixed with atrazine,
2,4-D, or Banvel, to improve control of velvetleaf,
with the tank-mix partner determining maximum
com size and adjuvant (see label). Resource alone
may be used at 4 to 8 fluid ounces plus 1 to 2 pints of
COC per acre, from the 2- to 10-leaf stage of field com.

Directed Postemergence Gramoxone for
Emergencies (Corn)

Gramoxone Extra'*"'' (paraquat) may be applied after
com is 10 inches tall, as a directed spray no higher
than the lower 3 inches of cornstalks. Use 12.8 fluid
ounces of Gramoxone Extra in a minimum of 20 gal-
lons of water per acre. Always add an NIS or COC.
Observe all label restrictions. Direct the spray to the
base of the com plants to minimize injury to the com
while covering the weeds as much as possible. Adjust
rates for banded application.

Corn Preharvest Treatment

Some 2,4-D labels allow preharvest use after the hard-
dough to dent stages of com to control or suppress
broadleaf weeds that may interfere with harvest. Do
not use the com for forage or fodder for 7 days after
treatment. Roundup Ultra (glyphosate) may be used
at 1 quart by air or 3 quarts per acre by ground after
grain moisture is 35 percent or less. Allow at least 7
days between application and harvest.

176

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Herbicides for Sorghum

Atrazine, Basagran, Bleep (all formulations), Buctril,
Dual II, and Permit are registered for use in grain or
"forage" sorghum, but see the label for grazing and
harvesting restrictions. Some other com herbicides
may be used in grain sorghum (milo) but not forage
sorghum. Check the labels for the relevant information as
to rates because they may be lower than those allowed in
corn.

Gramoxone Extra'*^'' (paraquat) or Roundup Ultra
(glyphosate) may be used to control existing vegeta-
tion before planting grain sorghum in reduced-tillage
systems.

Dual II (metolachlor). Frontier (dimethenamid), or
Micro-Tech'*^'' (alachlor) and their respective pre-
mixes with atrazine (Bleep IP^'^ or Bleep Llte'*^'',
Guardsman'*^'' or LeadOff'*^^ or Bullet'*"'') may be
used if the sorghum seed has been treated with Screen or
Concep. Ramrod (propachlor), alone or with atrazine,
does not require a seed safener, but it may be applied
preemergence only.

Atrazine'*'"'' is soil-applied to certain soils (see the
label). Apply atrazine postemergence before sorghum
is 12 inches in height, at 4 pints of 4L per acre without
a COC or at 2.4 pints per acre with a COC for broad-
leaf control only. Use equivalent rates of atrazine
90DF.

Shotgun'*'^'' (atrazine -i- 2,4-D) or 2,4-D alone con-
trols broadleaf weeds in grain sorghum that is 4 to 12
inches (Shotgun) or 24 inches (2,4-D). Use drop
nozzles if the sorghum is over 8 inches in height. Va-
por drift of 2,4-D ester or Shotgun can occur at tem-
peratures above 85°F.

Banvel or Clarity (dicamba) at 0.5 pint per acre or
Marksman'*"'' (dicamba + atrazine) at 2 pints per acre
may be applied to grain sorghum after the 2-leaf
stage until grain sorghum is 8 inches tall. Banvel or
Clarity may be applied with drop nozzles up to the
15-inch stage.

Permit (halosulfuron) may be applied at % ounce
from the 2-leaf stage through layby (but prior to head
emergence). Allow 30 days before grazing or harvest-
ing forage or silage.

Laddok'*"'' S-12 (bentazon -i- atrazine) may be used
postemergence in grain or forage sorghum up to 12
Inches tall. Basagran (bentazon) may be used up to
boot stage.

Buetril or Moxy (bromoxynll) applied alone can be
used from the 3-leaf to boot stages, but apply pre-
mixes or tank mixes with atrazine before sorghum is
12 inches in height.

Prowl (pendimethalln) or Treflan (trlfluralin) may
be applied to grain sorghum from the 4-inch stage

(Prowl) or 8-inch stage (Treflan) up to the layby stage
and incorporated by cultivation. Tank-mixing with
atrazine is allowed until sorghum is 12 inches in
height.

Roundup Ultra (glyphosate) may be applied as a
spot treatment in grain sorghum prior to heading.

HERBICIDES FOR SOYBEANS

Soybeans may be injured by some herbicides; but if
stands have not been significantly reduced, they usu-
ally outgrow early injury with little or no effect on
yield. Significant yield decreases can result when in-
jury occurs during the bloom to pod-fill stages. Shal-
low planting can increase the risk of injury from some
herbicides. Always follow label instructions. Rates per
acre for preplant and preemergence herbicides for
typical Illinois soils are given in Table 15.17. Accurate
rate selection for soil type is essential for Canopy XL,
Canopy, Lexone, Lorox, Sencor, and Turbo. Do not ap-
ply these herbicides after soybeans begin to emerge, or se-
vere injury can result. See Table 15.18 for some preplant
and preemergence tank-mix combinations.

Consider the kinds of weeds expected when you
plan a herbicide program for soybeans. See herbicide
selectivity Tables 15.19, 15.21, and 15.22 for the rela-
tive weed control ratings for various weeds with dif-
ferent soybean herbicides.

Early Preplant Herbicides Not
Incorporated (Soybeans)

Early preplant applications of herbicides are used in
no-till soybeans to control existing vegetation and re-
duce the need for a knockdown herbicide. Most broad-
leaf herbicides used in early preplant application have
both foliar and soil activity, so they may control small
annual weeds (Table 15.5), especially if an NIS or
COC is added to the spray mix. However, if weeds
are over 1 to 2 inches tall, add 2,4-D, Gramoxone
Extra'*"^ Roundup Ultra, or Touchdown 5 to the
spray mix within label guidelines to control existing
vegetation (see the earlier section on "Conservation
Tillage and Weed Control").

Axiom, Command 3ME, Dual, Frontier,
MieroTeeh'*"'', or Prowl may be applied early preplant
for grass control. Application timings before planting
soybeans are as follows: Axiom within 14 days. Prowl
within 15 days. Command 3ME within 30 days, or
Dual II, Frontier, or MicroTech within 30 days of
planting if a single application is made or within 45
days if split-applied preplant plus at planting.

Canopy, Pursuit, Pursuit Plus, Seepter, Squadron,
or Steel may be applied within 45 days; Broadstrike +

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM
Table 15.17. Soybean Herbicides: Preplant or Preemergence Rates Per Acre

177

1% OM

1-2% OM

3^% OM

5-6% OM

Herbicide (form)

Unit

sandy loam^

silt loam''

silty clay loam'

silty clay''

Axiom 68WSG

7-13

Broadstrike + Dual 7.67E

1.75

2.00

2.25

2.50

Broadstrike + Treflan 3.65E

1.5

2.00

2.25

Canopy 75DF

4.0<^

5.0

6.0

7.0

Canopy XL 53.6DF

5.1<i

6.4

6.8

7.9

Command 3ME

2.00

2.67

Detail 4.1E

1.0

1.0^'f

Dual II 7.8E

1.5

2.0

2.5

3.0

Dual II Magnum 7.62

1.0

1.33

1.67

2.0

FirstRate 84SG

0.6

0.75

Frontier 6E

floz

Lasso 4E

2.0

2.25

2.75

3.0

Lexone 75DF

0.33"^

0.50

0.66

Lorox 50DF

0.75'^

1.3

2.0'

3.0'

Micro-Tech 4ME

2.0

2.25

2.75

3.0

Partner 65DF

3.0

3.5

4.0

4.5

Pentagon 60DF

0.90

1.25

2.50

Prowl 3.3E

1.5

2.0

3.6

Pursuit 2S

floz

4.0

Pursuit 70DG

1.44

Pursuit Plus 2.9E

2.5

Python 80WDG

0.80

1.00

1.25

1.33

Scepter 70DG

2.8

2.8^-f

2.8^'

Sencor 75DF

No-^

0.50

0.75

1.00

Sonalan 3E

1.5

2.0

2.5

3.0

Squadron 2.3L

3.0

3.0^'

3.0^f

Steel 2.59E

3.0

3.0^

Treflan/rri-4 4E

1.0

1.5

2.0

Tri-Scept 3S

2.33

2.33^-f

2.33^'

Turbo 8E

1.25"^

2.25

2.75

3.50

OM = percent organic matter in the soil.

^Characteristic of most sandy soils in Illinois.

''Characteristic of many Illinois soils south of Interstate 70.

''Characteristic of "prairie soils" in northern Illinois.

''May cause excess crop injury on these soils.

^Carryover injury to corn may occur on these soils unless IMI-designated corn hybrids are planted.

'May not be suitable on these soils.

Dual, Canopy XL, or Detail within 30 days; or
FirstRate within 4 weeks prior to planting soybeans
for broadleaf weed control.

Assure II, Fusion, Poast Plus, Prestige, and Select

applied preplant at reduced rates can control 3- to 5-
inch annual grasses. Always add a COC. These herbi-
cides may be tank-mixed with 2,4-D to control broad-
leaf weeds prior to planting soybeans (see the next
paragraph).

2,4-D LV Ester may be applied prior to planting no-
till soybeans. See Table 15.05 for weeds controlled. Ap-
ply 1 pint, 3.8 pounds acid equivalent (a.e.) per gal-
lon, 7 days before planting soybeans, or 2 pints per
acre 30 days before planting soybeans. Check the label
for rates of other 2,4-D formulations. To minimize po-
tential injury, plant soybeans 1.5 to 2 inches deep,
and be sure the seeds are covered with soil. Do not
use on sandy soils with less than 1 percent organic matter.

178

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 15.18. Soil-Applied Soybean Herbicides: Tank Mixes and Application Timing

"Broadleaf'V'grass"

Lexone or

herbicide

Canopy XL

Canopy

Cormi\and

FirstRate

Sencor

Lorox

Pursuit

Scepter

Axiom

1,2

Command 3ME^

1%2

—

V,2

EXial 11 Magnum

1,2

Frontier

1,2

P,2

1,2

1,2,3"

Lasso/Micro-Tech

1,2

1%2

1,2

Prowl/Pentagon'^

1,2<^

1,2^

V, 2''

1,2^

1,2=

Sonalan

—

Trifluralin

—

1 = preplant incorporated; 2 = preemergence; 3 = early postemergence.
'Command 3ME may be lightly incorporated, but preemergence is preferred.
''Early postemergence, before first-trifoliate-leaf stage of soybeans.
=Use preemergence in Illinois soybeans only south of Interstate 80.

Table 15.19. Soybean Herbicides (Soil- or Foliar- Applied): Grass and Nutsedge Control Ratings

Volunteer

Annuals

Perennials

crops

Herbicide

re
CO

bO
«
U

1
U

2
'5b

.in

o
o

Cereals, volunteer
(wheat, oats, rye)

Soil-applied*'

Axiom

Dual II

Frontier

Micro-Tech

Conmiand 3ME

Prowl, Pentagon

1-f-

Sonalan

Trifluralin

Postemergence

. . C/j

e Table 15.20 for maximum

grass 5

Assure II

Fusilade DX

8-1-

Fusion

Liberty

8-t-

1-J-

Matador

Poast Plus

Prestige

Select

Pursuit"

Raptor"

Roundup Ultra" <

8-H

S+

Control ratings: 9 = excellent, 8 = good, 7 = fair, 6 = poor, 5 or 4 = unsatisfactory, N = Nil or None. Boldface indicates accept-
able control.

'Soybean response: 0 = minimal, 1 = possible, 2 - probable, 3 = serious.
These herbicides also control some broadleaf weeds. See Table 15.21.
=Use only with Roundup Ready (glyphosate-resistant) soybean varieties.

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

179

Table 15.20. Soybean "Post" Translocated Grass Herbicides: Maximum Grass Sizes and Rates

Assure II

Poast Plus

Raptor

Weed

or Matador
Size'' floz^

Fusion

or Prestige
Size" fl oz

5 floz
Size

Roundup

Size"

Ultra^
floz

Select

Size"

fl oz^

Size"

floz^

Annuals

^ Bamyardgrass

8-^

8-10

4
8

18
24
36«

579

7712

24
32

4
6-8

Brome, downy
Crabgrass"

8^^

6
4

6-8
8-10

6
8

6
18

6
3
6

6-8
4-5
6-8

Cupgrass'', woolly

4
16

8-10
12-14"^

6-8

Foxtail, giant

7-10

12720

12-14"

8
16

24
36,

6-8

Foxtail, yellow

8-10

8
16

24
36,

12720
20

6-8

Johnsongrass, seedling
, Panicum, fall

8
6

7-8

8
6

6-8
8-10

8
4

24
18

8
6

18
6712

24
24

10
4

6-8
4

8718

6-8

36,

Sandbur'', field

7-8

8-10

—

6-8

Shattercane

6-8

Signalgrass, broadleaf

8^^

8-12

8
12

24
36,

5
7

24
32

4
6

5
6-8

Volunteer com

6-^

4-6

6-8

Wheats rye

7-8

8-10

30718+

6-8

Wheat, overwintered

—

Rhizome perennial grass:
Johnsongrass, 1st

Minimum-maximum sizes
10-24 10 8-18 12

15-20

6-12

12-24

32-64

12-24

8-16

2nd

6-10

6-12

—

6-18

6-8

Muhly, wirestem, 1st

4-8

S"*

4-12

—

32-64

4-8

8-16

2nd

4-8

4-12

—

4-8

8-16

Quackgrass, 1st

6-10

10*^

6-10

6-8

4-^

6-8

32-64

4-12

8-16

2nd

4-8

<10

6-8

4-12

8-16

NOTE: For Poast Plus or Prestige 36^ = high

rate for

rescue operations.

*Use only with Roundup Ready-designated soybean varieties.

""Height of grass or length of lateral growth (crabgrass, sandbur) or diameter (cupgrass), in inches.

'Use higher rate if tank-mixed with broadleaf herbicide, if weeds are droughty or have reached maximum size.

''For best results on these grasses, do not tank-mix with a broadleaf herbicide.

*Size is for area south of Interstate 70 in Illinois.

'Volunteer wheat not overwintered, such as in double-cropped soybeans.

180

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 15.21. Soil-Applied Soybean Herbicides: Broadleaf Weed Control Ratings

■b

Herbicide

u
O

T3
o;

en
B

Momingglories,
annual

Nightshade,
eastern black

a»
a;

-0
o»

2
5b

0)
01

■c

C/5

1
cu

(X)

>
1

o»

Soil-applied "grass"

Axiom

IXial II Magnum

Frontier

Micro-Tech

Prowl/Pentagon

Sonalan

Trifluralin

Soil-applied "broadleaf"

Command

Sencor/Lexone

Lorox

Canopy

Canopy XL

Authority First

—

Python*

FirstRate

—

Pursuit

Scepter

Control ratings: 9 = excellent, 8 = good, 7 = fair, 6 = poor, 5 or 4 = unsatisfactory, N = Nil or None. Boldface indicates acceptable

control. ^

^Soybean response: 0 = minimal, 1 = possible, 2 = probable, 3 = serious. ]

*Control is much less on triazine-resistant biotypes of pigweed, lambsquarters, and kochia. '^

For herbicide ratings for tank mixes or premixes, see the component parts: '

Premix

Grass

Broadleaf

Broadstrike +

Dual

Python

Broadstrike +

Treflan

Trifluralin

Python

Detail

Frontier

Scepter

Pursuit Plus

Prowl

Pursuit

Squadron

Prowl

Scepter

Steel

Prowl

Pursuit + Scepter

Tri-Scept

Trifluralin

Scepter

Turbo

Dual

Sencor

2,4-D may be mixed with most other early preplant
herbicides.

Soil-Applied
(Soybeans)

'Grass" Herbicides

Sonalan and trifluralin are soil-applied "grass" herbi-
cides that require mechanical incorporation. Com-
mand 3ME is used primarily preemergence, whereas
Dual, Frontier, Lasso, Pentagon, or Prowl may be

used preplant-incorporated or preemergence. Do not
apply Pentagon or Prowl preemergence north of Interstate
80 in Illinois. Incorporation improves herbicide perfor-
mance if rainfall is limited. For more information, see
the section titled "Herbicide Incorporation" and
Tables 15.19 and 15.21 for the weeds controlled.

Pentagon or Prowl, Sonalan, and trifluralin are
dinitroaniline (DNA) herbicides that control annual
grasses, pigweeds, and lambsquarters. Control of ad-

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

181

Table 15.22. "Post-Broadleaf" Soybean Herbicides: Weed Control Ratings

C/!l

«■

-M

01
(A

Herbicide

o
U

01
CO

to
o

Momingglorie
annual

Nightshade,
eastern black

Oi
01

01
01

•1-H

0»
01

c75

c«

0»
01

•1—1
Ol

re
^-^

c
re

01
Si

Contact-postemergen

/^P . .

• See Table 25 for maximum weed

sizes-

Basagran

Galaxy

Storm

Blazer

Cobra

Reflex

Flexstar

Resource

Stellar

Liberty

Systemic-postemergence •

• See Tfli^/e 25 for maximum weed sizes

Classic^^

8 +

8+"

Pinnacle^^

Skirmish^'^

8+"

FirstRate^^

—

5''

Synchrony STS'^^'^

Pursuit^'^

Raptor^^

—

8+"

Scepter'*'^

Roundup Ultra-^

8''

Control ratings: 9 = excellent, 8 = good, 7 = fair, 6 = poor, 5 or 4 = unsatisfactory, N - Nil or None. — = not on label. Boldface

indicates acceptable control.

'^^^acetolactate synthase herbicides.

"•Soybean response: 0 - mininnal, 1 - possible, 2 - probable, 3 = serious.

''Will not control ALS (acetolactate synthase)-resistant waterhemp or kochia.

■^Use only with STS-designated soybean varieties.

''Use only with Roundup Ready-designated soybean varieties. Control varies with rate and weed size.

ditional broadleaf weeds requires tank mixes (see Table
15.18) or sequential treatments with other herbicides.

If injured by DNA herbicides, soybeans show
symptoms of stunting, swollen hypocotyls, and short,
swollen lateral roots. Such injuries are rarely serious.
{ If incorporation is shallow, or if Pentagon or Prowl is
I applied to the soil surface, soybean stems may be cal-
loused and brittle, which can lead to lodging or stem
breakage.

i DNA herbicides can sometimes injure rotational

crops of com or sorghum. Symptoms appear as re-

I duced stands and stunted, purple plants with poor

' root systems. Under good growing conditions, com

typically recovers from this early season injury. Accu-
rate, uniform incorporation is needed to minimize po-
tential carryover.

Pentagon 60DG or Prowl 3,3E (pendimethalin)
may be applied preplant incorporated up to 15 days
before planting soybeans, but incorporate within 7
days of application. Use 1.2 to 3.6 pints of Prowl or
0.85 to 2.5 lbs of Pentagon per acre. Preplant surface
applications can be made 15 to 45 days (depends on
tank mix or sequential) prior to planting soybeans.
South of Interstate 80 in Illinois, preemergence appli-
cations may be made up to 2 days after planting. Do
not make preemergence applications north of Interstate 80.

182

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Treflan or Tri-4 4E (trifluralin) may be applied
alone anytime in the spring prior to planting. How-
ever, the labels for tank mixes may specify application
closer to soybean planting. Incorporate trifluralin 2 to
3 inches deep within 24 hours after application. If the
soil is warm and moist, it may be beneficial to incor-
porate sooner. The rate per acre is 1 to 2 pints of 4E or
equivalent rates of Treflan lOG. A slightly higher rate
and deeper incorporation may be specified for
shattercane control.

Sonalan 3E (ethalfluralin) may be applied at 1.5 to
3 pints per acre within 3 weeks before planting and
should be incorporated within 2 days after applying.

Command 3ME (clomazone) is used primarily
preemergence and early preplant at 1.22 to 2.66 pints
per acre to control annual grasses and some broadleaf
weeds. This formulation is microencapsulated to re-
duce volatility. Consult the label for recommendations to
minimize spray drift. See the label or Table 15.02b for
minimum recropping intervals. Carryover injury ap-
pears as whitened or bleached plants after emergence.

Axiom (FOE-5043 + metribuzin). Dual (metola-
chlor). Frontier (dimethenamid), or Micro-Tech'^^''
(alachlor) may be applied up to 30 days preplant in-
corporated or preemergence to control armual grasses
and pigweeds. Incorporate to improve yellow nut-
sedge control. Rates per acre are 7 to 13 ounces of
Axiom, 1.5 to 3 pints of Dual II, 1.5 to 2 pints of Dual
II Magnum, 20 to 32 fluid ounces of Frontier 6E, and 2
to 4 quarts of Micro-Tech. See Table 15.17 or the label
for rate selection for soil type.

Soil-Applied "Broadleaf" Herbicides
(Soybeans)

Broadstrike (plus Dual or Treflan), Canopy, Canopy
XL, Cobra, Command, FirstRate, Lexone, Lorox, Pur-
suit, Python, Scepter, and Sencor are soil-applied her-
bicides used for broadleaf weed control in soybeans
(see Table 15.21 for weeds controlled). Cobra or Lorox
should not be incorporated. Broadstrike + Treflan
should be incorporated, and Command 3ME may be
lightly incorporated (see label). The other herbicides
can be used preplant-incorporated or preemergence
after planting soybeans.

Timely rainfall or incorporation is needed for uni-
form herbicide placement in the soil. Incorporation
may improve control of deep-germinating (large-
seeded) weeds, especially when soil moisture is lim-
ited. Accurate and uniform application and incorpo-
ration are essential to minimize potential soybean
injury. These herbicides are meristematic inhibitors
(MSI), photosynthetic inhibitors (PSI), a premix of
MSI (chlorimuron) and PSI (metribuzin), or a premix

of MSI (chlorimuron) plus sulfentrazone, except for Co-
bra and Command. Command 3ME, a pigment inhibi-
tor, may be used as a broadleaf (especially velvetleaf)
herbicide, but it is discussed as a grass herbicide in the
preceding "Soil-Applied 'Grass' Herbicides (Soy-
beans)." Cobra, a contact postemergence herbicide,
may be used preemergence at 12.5 to 19 fluid ounces
per acre to control some small-seeded broadleaf
weeds.

ALS Meristematic Inhibitors

Chlorimuron (in Canopy XL or Canopy), cloransulam
(FirstRate), flumetsulam (Broadstrike or Python),
imazaquin (Scepter), and imazethapyr (Pursuit) are
meristematic inhibitors that inhibit the acetolactate-
synthase (ALS) enzyme. See Table 15.21 for weeds
controlled. Symptoms of ALS herbicide injury include
a temporary yellowing of upper leaves (golden tops)
and shortened intemodes of soybeans. Although
plants may be stunted, yield generally is not affected.
Some of these ALS herbicides may carry over and in-
jure certain sensitive follow crops. Symptoms on com
or grain sorghum are stunted growth, inhibited roots,
and interveinal chlorosis or purpling of leaves. Symp-
toms on small grains are stunted top growth and ex-
cess tillering. ALS herbicides, if used alone, increase selec-
tion pressure for ALS-resistant weed biotypes.

Pursuit (imazethapyr) is used at 4 fluid ounces 2S
per acre (1 gallon per 32 acres) or 1.44 ounces {}/2
soluble bag) 70DG per acre to control broadleaf weeds
(Table 15.21). Grass control is improved by tank-mix-
ing Pursuit with a grass herbicide (Table 15.18). Pur-
suit Plus is a premix of Pursuit and Prowl used at 2.5
pints per acre. Steel, a premix of Pursuit Plus and a
half-rate Scepter, is used at 3 pints per acre for im-
proved cocklebur control. Pursuit and Pursuit Plus or
Steel may be applied up to 45 days prior to planting
soybeans. If sufficient rain does not occur before
planting, then incorporate mechanically. South of Inter-
state 80, Pursuit Plus and Steel may be surface-applied
up to 2 days after soybean planting. See the label or
Table 15.02b for minimum recropping intervals. Pur-
suit controls velvetleaf better than Scepter does, but
Scepter provides better control of cocklebur.

Scepter 70DG (imazaquin) is used at 2.8 ounces (y2
soluble bag) per acre. Preplant applications (surface
or incorporated) may be made up to 45 days before
planting (fewer days with many tank mixes). Scepter
controls many broadleaf weeds (Table 15.21). Incorpo-
ration decreases dependency on rainfall and may im-
prove control of velvetleaf and giant ragweed. Grass
control is improved by mixing with "grass" herbi-
cides (Table 15.18).

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

183

Detail, Squadron, and Tri-Scept are premixes of
Scepter plus Frontier, Prowl, or trifluralin, respectively.
The rate per acre is 1 quart of Detail, 3 pints of Squad-
ron, or 2.33 pints of Tri-Scept (see Table 15.04 for equiva-
lents). Tri-Scept must be incorporated within 24 hours,
with incorporation optional for Detail and Squadron.

A line through Peoria, extending west along Illinois
Route 116 and east along U.S. Route 24, delineates De-
tail, Scepter, Squadron, Steel, and Tri-Scept rotational
crop restrictions in Illinois (Table 15.02b). Region 3 is
north of the line; Region 2 is south. The potential for
carryover is greater on soils with high organic matter
and low pH. Research and field results indicate that,
in Illinois, imazaquin is best adapted to the soils and
weeds south of Interstate 70.

Significant problems have occurred in Illinois with
carryover of imazaquin associated with soil and cli-
matic conditions plus lack of uniformity in applica-
tion. Reduced rates, which can reduce potential
carryover, are allowed for postemergence use of Scep-
ter and in tank mixes with several other products.
Imidazolinone-tolerant or -resistant (IR/IT) hybrids may be
used to minimize carryover problems in corn.

Broadstrike + Dual 7.67E (flumetsulam + metola-
chlor) may be applied at 1.75 to 2.5 pints per acre up
to 14 days prior to or immediately after planting soy-
beans. Broadstrike + Treflan 3.65E (flumetsulam +
trifluralin) is applied at 1.5 to 2.25 pints per acre up to
30 days prior to planting soybeans. Uniformly incor-
porate into the top 2 to 3 inches of soil within 24
hours after application. Python 80WDG (flumetsu-
lam) at 0.8 to 1.33 ounces per acre may be applied pre-
plant incorporated or preemergence.

FirstRate 84SG (cloransulam) may be used at 0.6 to
0.75 ounces per acre up to 4 weeks preplant (surface
or incorporated) or preemergence up to 2 days after
planting. Tank mixes with "grass" herbicides are al-
lowed (see Table 15.18).

Canopy 75DF (metribuzin -i- chlorimuron) is ap-
plied preplant incorporated or preemergence at 4 to 7
ounces per acre. Do not apply Canopy after soybean
emergence. Do not apply Canopy to soils with pH greater
than 6.8. High soil pH may occur in localized areas.
Correct rate selection for the soil and uniform, accu-
rate application and incorporation are essential to
minimize soybean injury and potential follow-crop
injury. Check labels carefully for rotational guidelines.

Canopy XL 56.3DF (5:1 sulfentrazonerchlori-
muron) is applied early preplant, preplant incorpo-
rated, or preemergence at 5.1 to 7.9 ounces per acre. It
may be tank-mixed with grass herbicides (see Table
15.18). Do not apply to soils classified as sands with less
than 1 percent organic matter or to soils with greater than
pH 6.8, and do not apply after soybeans emerge. Authority

First 75DG (sulfentrazone) is sold as a prepack with
Synchrony STS for soil application at 4 ounces per
acre to control black nightshade and ALS-resistant
waterhemp. See Table 15.02b for recropping intervals.

Photosynthetic Inhibitors

Linuron (Lorox) and metribuzin (Sencor or Lexone, in
Canopy and Turbo) are photosynthetic inhibitors
(PSI), which can cause severe soybean injury from fo-
liar application. Do not apply them after soybeans emerge.
They occasionally injure soybeans from soil uptake.
PSI herbicide injury symptoms are chlorosis (yellow-
ing) of the leaf margins and necrosis (dying) of the
lower soybean leaves, usually appearing at about the
first-trifoliate stage. Atrazine carryover or soil pH
over 7.0 can intensify these symptoms. Soybeans usu-
ally recover from moderate early injury. Soybean vari-
eties can differ in their sensitivity to metribuzin.

Sencor or Lexone (metribuzin) may be applied
anytime within 14 days before planting soybeans.
Tank mixes to control annual grasses are shown in
Table 15.18. Turbo 8E contains metolachlor (Dual) to
control annual grasses. Metribuzin rates are adjusted
for soil type (Table 15.17). Do not apply to sandy soil that
is low in organic matter. Do not use on soils with pH greater
than 7.5.

Lorox (linuron) is best suited to silt loam soils that
contain 1 to 3 percent organic matter, where the rate
per acre is 1 to 1% pounds of 50DF. Do not incorporate
or apply after the crop emerges.

POSTEMERGENCE HERBICIDES (SOYBEANS)

Postemergence (foliar) herbicides are most effective
when used in a planned program with timely applica-
tion. Foliar treatments allow the user to identify the
problem weed species and choose the most effective
herbicide. See Tables 15.19 and 15.22 for weed control
ratings with various soybean herbicides.

Rates and timing for foliar treatments are based on
weed size. Early application, when weeds are young,
may allow the use of lower herbicide rates. Treatment
of oversized weeds may suppress growth only tempo-
rarily, and regrowth may occur. A cultivation 7 to 14
days after application but before regrowth can often
improve weed control. However, cultivation during
or within 7 days of a foliar application may cause er-
ratic weed control. Tables 15.20 and 15.23 give the
soybean herbicide rate for labeled weed sizes. Tables
15.24 and 15.25 give tank mixes labeled for
postemergence weed control in soybeans.

A COC or NIS is usually added to the spray mix to
improve the effectiveness of the postemergence herbi-
cide. Fertilizer adjuvants such as 28-0-0 (urea-ammo-
nium nitrate) or ammonium sulfate (AMS) may be

184

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 15,23. Soybean "Post-Broadleaf" Herbicides: Maximum Weed Sizes and Application Rates

Herbicide

Rate

u
O
U

Momingglories, annual
(tall and ivyleaf)

Nightshade,
eastern black

T3
OI
OI

OI
OI

0)
01

-a

en
73
01

1-1
rs

•4-t

ALS translocated^

r>-7/A ■ .

Label weed

height

m inches ■ ■ • ■

0Z//\

Classic /Skirmish 25DF

0.50

—

Classic /Skirmish 25DF

0.75

—

4<^

—

FirstRate 84WDG

0.30

—

Pinnacle 25DF

0.25

—

Pursuit 70DG

1.44^

—

Raptor IS fl oz

4-5

4"^

Scepter 70DF

1.40

—

Scepter O.T. fl oz

16.0

—

Synchrony STS

0.50

—

4*^

—

Other translocated

Roundup Ultra fl oz

—

6'-12

3^-6

Roundup Ultra fl oz

12+

8^-18

18+

4^-12

Contact

nt/A ■ ■

Lflbe/ weed

height

in inches

yi/r\.

Basagran

1.0

—

Basagran

2.0

4-^

—

Blazer, Status

1.0

—

Blazer, Status

1.5

—

Galaxy

2.0

Storm

1.5

—

Liberty

1.25

Liberty

1.75

Contact

nt/A . .

• Uihel weed height

^ f« leaf stage (number

) . . . .

pi//\

/ • • • •

Cobra

0.5

—

Cobra

0.67

—

4L^

Flexstar HL

1.25

2L^

Reflex

1.25

2L^

—

Resource

0.25

—

3L^

2L^

—

2L^

—

Resource

0.50

3L^

3L<^

—

lOL

Stellar

0.31

—

2L^

3L^

—

Stellar

0.44

2L^

3L'^

3L^

—

^Lambsquarters control is erratic with many herbicides.
''ALS-resistant waterhemp is not controlled by ALS herbicides.
■^Suppression or partial control only; may need supplemental control.
''Redroot pigweed only; smooth pigweed and waterhemp only suppressed.
^Use equivalent rate of other formulations.
'Smaller size is used south of Interstate 70 in Illinois.

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM 185

Table 15.24. Soybean Postemergence Herbicide Tank Mixes: "Broadleaf" + "Grass" Herbicides

Prestige or
Assure IP Fusilade DX^ Fusion^ Poast Plus^ Roundup Ultra'' Select^

Basagran

-/Y

Y/Y

Y/-

-/Y

Blazer /Status

-/-

Y/Y

-/Y

Y/Y

Y/-

-/Y

Classic

Y/Y

Y/-

Y/Y

Cobra

Y/-

-/Y

Y/-

Y/Y

FirstRate

Y/-

-/-

Y/-

Y/Y

Flexstar

Y/-

Y/Y

Y/-

Y/Y

Galaxy

-/-

-/Y

Y/Y

-/-

Y/Y

Liberty

-/-

Y/-

-/-

Y/-

Pinnacle

Y/Y

Y/-

Y/Y

No!/-

-/-

Y/-

Pursuit*^''

Y/-

Y/Y

Y/-

Y/Y

Raptor

Y/-

-/-

Y/Y

Reflex

Y/-

Y/Y

-/-

Y/Y

Resource

-/-

-/Y

Y/-

Y/Y

Scepter

Y/-

Y/Y

-/-

Y/-

Skirmish

Y/Y

Y/-

Y/Y

Stellar

-/-

Y/-

Storm

-/-

-/Y

-/-

Y/Y

Synchrony STS^

Y/Y

Y/-

Y/Y

Y/-

-/-

Y/Y

Y/- = tank mix on "broadleaf" label (row); No!/- = label prohibits the tank mix; -/Y = tank mix on "grass" label (column);

Y/Y = tank mix on both herbicide labels; -/- = neither label allows tank mix.

^Check labels for special instructions, as "grass" herbicide rate may increase or sequential application may be preferable.

''Roundup Ultra requires Roundup Ready soybean varieties.

■^Pursuit also controls several grass species, but it tends to antagonize "grass" herbicide's action.

''Label for adding low-rate "grass" herbicide with Pursuit is primarily to improve control of volunteer corn and shattercane.

*Use only with STS-designated soybean varieties.

Table 15.25. Soybean Postemergence

Herbici

de Tank Mixes: "Broadleaf"

+ "Broadleaf" Herbicides

Classic/

Basagran Butyrac^

Skirmish FirstRate

Liberty

Pinnacle^

Pursuit

Raptor

Resource

Scepter

Synchrony''

f Basagran

-/-

Y/Y

Y/-

-/Y

Y/Y

-/-

-/Y

Y/-

-/-

' Blazer

Y/Y

-/Y

Y/-

Y/Y

-/Y

-/-

Y/-

Y/Y

Butyrac^

Y/Y

-/-

Y/Y

-/-

Y/-

-/-

Y/Y

-/Y

Classic/

Skirmish

-/Y

Y/Y

-/-

Y/Y

-/No

-/-

-/Y

-/-

-/Y

Cobra^

Y/-

Y/Y

-/-

Y/-

Y/Y

Y/-

Y/Y

FirstRate

Y/-

-/-

-/Y

Y/-

-/-

-/Y

-/-

. -/-

Flexstar

Y/-

-/-

-/Y

Y/-

-/Y

Y/Y

Y/-

Galaxy

-/-

Y/-

-/-

-/Y

Y/Y

-/-

-/Y

Y/-

-/-

1 Liberty

Y/-

-/-

Y/-

-/-

Y/-

-/-

Pursuit

Y/Y

-/Y

No/-

-/Y

Y/-

-/-

-/Y

Y/-

No/-

Reflex

Y/Y

-/Y

Y/-

Y/Y

-/Y

Y/Y

Y/-

Y/Y

Resource

Y/-

-/-

Y/-

-/Y

Y/-

-/-

Y/-

-/-

Stellar

Y/-

-/-

Y/-

-/-

Y/-

-/-

Y/-

Storm

-/-

Y/-

-/-

-/Y

Y/-

-/Y

-/-

-/Y

-/-

Y/- = tank mix on label in the row (on top); -/Y = tank mix on label in the column (at left); Y/Y = tank mix on both herbicide
labels; -/- - neither label allows tank mix; No/- or -/No = tank mix prohibited.
^Check label closely for rate and adjuvant use with this herbicide in tank mixes.
''Use only with STS-designated soybean varieties.

186

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 15.26. Soybean "Post" Herbicides: Adjuvant Use Plus Use Restrictions

Rain-free

Reentry

Preharvest

Feed/graze

Herbicide

Adjuvants and nitrogen

period (hr)

interval (hr)

interval (days)

forage

No-till burndown

2,4-D amine

None

6-8

2,4-D ester

None

1-2

Gramoxone Extra

COG or NIS

0.5

Roundup Ultra

AMS optional

1-2

Touchdown 5

NIS; AMS optional

2-4

Postemergence grass only

Assure II/Matador

POC or NIS; NH^ optional

No!

Fusilade DX

COG or NIS; NH^ optional

Prebloom

No!

Fusion

COC or MS; NH^ optional

Prebloom

No!

Poast Plus, Prestige

GOG; NH^ optional

Hay?

Select

GOG; UAN optional

No!

Postemergence broadleaf, contact

Basagran

COC; NH^ optional

6»

None

Yes

Blazer, Status

NIS or UAN

No!

Cobra

GOG or NIS; check humidity

0.5

No!

Flexstar HL

GOG + NH,

Prebloom

No!

Galaxy

COC or/and" NH^

No!

Liberty

None

70/Prebloom

No!

Reflex

NIS or GOG^; NH^ optional

Prebloom

No!

Resource

GOG; NH^ optional

No!

Stellar

GOG^; NH^ optional

No!

Storm

GOG or NIS or NH^

6»

No!

Postemergence — broadleaf, systemic

Butyrac (2,4-DB)

None'*

6-8

Yes/PHl

Classic/Skirmish

NIS, POG% or MSO^ + NH^

No!

FirstRate

NIS + NH^ or GOG

65-50% flower

Yes/14 days

Pirmacle

NIS or GOG" ^ + NH^

No!

Pursuit

GOG or NIS + NH^

No!

Raptor

GOG or NIS + NH^

No!

Roundup Ultra^'f

AMS optional

1-2

7714^

Yes/PHI

Scepter

GOG or NIS

No!

Scepter O.T.

NIS or GOG^

No!

Synchrony STS

POG or MSO + NH,

No!

Touchdown 5'

NIS; AMS optional

1-2

60/7

Yes: 7/56:
wiper/spot

Harvest-aid use

Gramoxone Extra

NIS or GOG

0.5

Yes?/15 days

Roundup Ultra

AMS optional

1-2

7/14«

> 25 days

CCXI = petroleum-oil concentrate (POC) or vegetable-oil concentrate (VOC), MSO = methylated seed oil (specialized VOC),

NIS = nonionic surfactant, NH^ = ammonium fertilizer adjuvant = UAN or AMS; UAN = urea-ammonium nitrate (28-0-0),

AMS = ammonium sulfate (spray grade 21-0-0); PHI = preharvest interval.

Klurrent label: "Rainfall soon after application may decrease the effectiveness."

''Use only if droughty conditions exist at application.

■^Penetrant adjuvant allowed but reduces crop tolerance.

''Some tank mixes allow NIS or COC; see the tank-mix partner's label.

*Use as broadcast treatment only with Roundup Ready-designated soybeans.

'Can be used as a spot treatment. Use NIS with wiper applications of Touchdown 5, but not with Roundup Ultra.

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

187

specified on the label to increase control of certain
weed species, such as velvetleaf. Table 15.26 lists
adjuvants labeled with various postemergence soy-
bean herbicides, reentry intervals, and rain-free peri-
ods for optimal postemergence activity Rainfall soon
after application can cause poor weed control. Warm
temperatures and high relative humidity greatly in-
crease foliar herbicide activity. Weeds growing under
droughty conditions are more difficult to control.
ll Postemergence herbicides for soybeans are either
1 translocated (systemic) or contact in action. Translo-
cated herbicides do not require complete spray cover-
age because they move to growing points (meristems)
after foliar penetration. Their action is slow, and
symptoms may not appear for a week after applica-
tion, especially with the "post-grass" herbicides de-
scribed next.

Translocated Herbicides for Control of
Grass Weeds Only (Soybeans)

Assure II or Matador, Fusilade DX, Fusion, Poast Plus
or Prestige, and Select all have the same mode of ac-
tion (ACC-ase inhibition). They control only annual
and perennial grasses in soybeans. Table 15.20 gives
herbicide rates by grass weed heights. Grasses should
be actively growing (not stressed or injured) and not
tillering or forming seed heads. Cultivation within 5
to 7 days before or after application may decrease
grass control. A COC is preferred, especially if weeds
are droughty or maximum weed heights are ap-
proached. However, an NIS is allowed with Assure II,
Fusion, Fusilade, or Matador (but not with Poast Plus,
Prestige, or Select). See Table 15.26 for adjuvant use.

Specified spray volume per acre is 10 to 20 gallons
for ground application or 3 to 5 gallons for aerial ap-
plication. A 1-hour rain-free period after application is
needed. Avoid drift to sensitive crops such as com,
sorghum, and wheat. Apply prebloom and at least 60
to 80 days before soybean harvest.

These herbicides do not control broadleaf weeds.
Most labels allow tank-mixing with certain broadleaf
herbicides (Table 15.24), but limitations are made as to
rate, timing, and spray coverage. Check the label before
applying postemergence grass and broadleaf herbicide tank
mixes or sequences. Control of grass weeds may be reduced,
or increased rates may be specified.

Rates vary by weed heights and species, so consult
the label or Table 15.20 before applying. Rate reduc-
tions may be optional on small weeds or under ideal
conditions, whereas rate increases may be needed for
larger weeds. Johnson grass or quackgrass often re-
quires a follow-up application for control of regrowth.

Assure II or Matador 0.88E (quizalofop) controls
annual grasses at 7 to 9 fluid ounces per acre. Add
1 percent POC or 0.25 percent NIS. Assure is weak on
yellow foxtail. Fusion 2.56E (fluazifop -i- fenoxaprop)
controls annual grasses at 6 to 8 fluid ounces per acre
when used alone or 8 to 10 fluid ounces when tank-
mixed. Add 0.5 to 1 percent COC or 0.25 to 0.5 percent
NIS. Fusilade DX 2E (fluazifop) is applied at 6 fluid
ounces per acre to control volunteer com and shatter-
cane. Add 1 percent COC or 0.25 percent NIS.

Poast Plus or Prestige IE (sethoxydim) controls an-
nual grasses at 24 ounces (1.5 pints) per acre. Always
add 2 pints of COC per acre. Select 2E (clethodim)
controls annual grasses at 4 to 6 fluid ounces per acre
when used alone or 6 to 8 fluid ounces when tank-
mixed. Add 1 percent COC to the spray mix.

Translocated Herbicides for Grass and
Broadleaf Control (Soybeans)

Roundup Ultra (glyphosate) may be applied only to
"Roundup Ready" -designated soybeans from emergence
through the full flowering stage for control of a broad
spectrum of grass and broadleaf weeds. Single and re-
peat in-crop plus preharvest applications are not to ex-
ceed a maximum of 3 quarts per acre per season. This
3-quart limit does not include applications made for
bumdown of existing vegetation prior to planting.
Rates are based on weed height, but consideration
should also be given to species present (Tables 15.19 and
15.22). The rate per acre is 2 pints on weeds 4 to 8
inches tall and 3 pints on weeds 8 to 18 inches tall.
Glyphosate provides no residual control, so repeat ap-
plications may be needed. Applications should be
made in 5 to 20 gallons of water per acre. AMS may
be included for some situations (check label). Exercise
extreme care to minimize drift to susceptible plants.

Roundup Ultra or Touchdown 5 (glyphosate) may
be applied through wiper applicators to control vol-
unteer com, shattercane, and johnsongrass. Hemp
dogbane and common milkweed may also be sup-
pressed (see Table 15.28). Weeds should be at least 6
inches taller than the soybeans. To minimize soybean
injury, adjust the applicator so that the wiper contact
is at least 2 inches above the soybean plants. For
wiper applicators, mix a 1:2 ratio of Roundup
Ultra:water or 1:4 ratio of Touchdown 5:water. Spot
treatments may be made on a spray-to-wet basis using
a 2 percent solution of Roundup Ultra or 1 percent so-
lution of Touchdown 5 in water. Minimize spray con-
tact with soybeans.

Pursuit (imazethapyr) and Raptor (imazamox),
which are sometimes used to control small annual

188

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

grass (Table 15.19) and broadleaf weeds (Tables 15.22
and 15.23), are discussed in the following section.

Translocated Herbicides for

poste mergence control of broadleaf

Weeds (Soybeans)

Classic or Skirmish, FirstRate, Pinnacle, Pursuit, Rap-
tor, and Scepter inhibit the acetolactate-synthase
(ALS) enzyme. They primarily control broadleaf
weeds (Table 15.22), although Pursuit and Raptor
provide some grass control (Table 15.19). Table 15.23
lists herbicide rates by broadleaf weed species and
heights. Weeds should be actively growing (not mois-
ture- or temperature-stressed). Do not make applica-
tions when weeds are in the cotyledon stage. Armual
weeds are best controlled when less than 3 to 5 inches
tall (within 2 to 4 weeks after soybean emergence). A
1-hour rain-free period after application is adequate.

The ALS herbicides inhibit growth of new meri-
stems, so symptoms of weed injury may not be ex-
hibited for 3 to 7 days after application. Injury symp-
toms are yellowing of leaves, followed by death of
the growing point. Death of leaf tissue in susceptible
weeds is usually observed in 7 to 21 days. Less-
susceptible plants may be suppressed, remaining
green or yellow but stunted for 2 to 3 weeks.

Soybeans may show temporary leaf yellowing
("golden tops"), growth retardation (generally in the
form of shortened intemodes), or both symptoms, es-
pecially if soybeans are under stress. Under favorable
conditions, affected soybeans may recover with only
a slight reduction in height and no loss of yield.

Use a minimum spray volume of 10 gallons per
acre and spray pressure of 20 to 40 psi. An NIS is
usually specified at 1 to 2 pints per 100 gallons of
spray. A COC may improve weed control but in-
crease crop injury. Either a UAN or AMS may im-
prove control of some weeds and is often specified
for velvetleaf control. Because tank-mixing these herbi-
cides with postemergence "grass" herbicides may reduce
grass control, sequential applications are often specified.
Tables 15.24 and 15.25 list labeled tank mixes. Table
15.23 provides rates of herbicides for various sizes of
selected weeds. ALS herbicides, used alone, increase the
potential of selecting for ALS-resistant weed biotypes such
as waterhemp and kochia; see the earlier section on
"Weed Resistance to Herbicides."

Raptor IS (imazamox) is used at 4 to 5 fluid ounces
per acre to control annual grasses (see Table 15.19)
and broadleaf weeds (see Table 15.22). (See Tables
15.20 and 15.23 for weed sizes.) Common ragweed is
only suppressed. Add either a COC or NIS plus an NH^
fertilizer adjuvant. Raptor has better lambsquarters and
grass control than Pursuit and has shorter persistence.

Pursuit (imazethapyr) is used at 4 fluid ounces 2S
or 1.44 ounces (Vi soluble bag) 70DG per acre plus a
COC or NIS and a UAN or AMS. Pursuit controls
some small annual grasses (Table 15.19), but tank
mixes may interfere with grass control of Pursuit.
Pursuit does not control ALS-resistant biotypes such
as waterhemp. Make only one application of Pursuit per
year. Applying herbicides containing chlorimuron or
imazaquin the same year as Pursuit increases the po-
tential for crop injury to soybeans and subsequent
crops. Do not apply Pursuit within 85 days of soy-
bean harvest. Recropping interval is 4 months for
wheat and alfalfa, 18 months for grain sorghum or
oats, and 8.5 months for field com, except IMI-com,
which may be planted anytime (Table 15.02b).

Classic or Skirmish 25WG (chlorimuron) is used
at 0.5 to 0.75 ounce per acre, plus an NIS or COC and
NH^ adjuvant. See Table 15.22 for weeds controlled
and Table 15.23 for weed sizes. ALS-resistant
waterhemp is not controlled. Split applications can im-
prove control of burcucumber, giant ragweed, and
annual momingglories. Do not apply chlorimuron
within 60 days of harvest. Applying chlorimuron after
August 1 extends the corn recrop interval by 2 months.
Recropping intervals are 3 months for wheat; 9
months for com; and 9 or 15 months for milo, alfalfa,
and clover, depending on the rate used (Table 15.02b).

Pinnacle 25WG (thifensulfuron) is used at 0.25
ounce per acre to control lambsquarters, pigweeds,
smartweeds, and velvetleaf. See Table 15.23 for weed
heights. Add 1 to 2 pints of an NIS per 100 gallons.
Use a COC only if conditions are droughty. A UAN im-
proves velvetleaf control. Pinnacle is used at lower
rates in some tank mixes to improve lambsquarters
control (Table 15.25). Plant any crop 45 days after ap-
plying thifensulfuron alone; tank mixes or premixes
require longer recropping intervals.

Synchrony STS 42WG (2.4:1 chlorimuron:thifen-
sulfuron) is used on STS-designated soybean varieties
at 0.5 ounce (V4 soluble bag) per acre. Use a COC or
MSO plus an ammonium fertilizer adjuvant, but con-
sult the label when tank-mixing with Cobra or 2,4-DB.
Weed species controlled and heights are listed in
Tables 15.22 and 15.23. Synchrony STS recropping in-
tervals are 3 months for small grains and 9 for field
com (8 months for IR-corn). Recropping intervals for
other crops vary with sequential Classic applications
and soil pH (see the label or Table 15.02b).

FirstRate 84SG (cloransulam) is used postemer-
gence at 0.3 ounce per acre to control several broad-
leaf weeds (Table 15.22) depending on size (Table
15.23). Add either an NIS or COC +/- NH^ adjuvant.
Tank mixes improve the control spectrum. See the la-
bel and Tables 15.24 and 15.25.

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

189

Scepter 70DG (imazaquin) at 1.4 ounces QA
soluble bag) per acre plus an MS or COC controls
cocklebur, wild sunflower, non-IMI volunteer com,
and pigweed (not waterhemp). Scepter O.T.
(imazaquin + acifluorfen) at 1 pint per acre provides
improved control of annual momingglories and
smartweeds. Do not apply Scepter within 90 days of
soybean harvest. Be sure to follow rotational guidelines
on the label.

Contact Herbicides for "Postemergence
Control" of Broadleaf Weeds
(Soybeans)

Basagran, Blazer or Status, Cobra, Flexstar, Galaxy,
Liberty, Reflex, Resource, Stellar, and Storm are con-
tact broadleaf herbicides used in soybeans, so thor-
ough spray coverage is critical. Spray volume for
ground application is 10 to 30 gallons per acre, and
spray pressure should be 30 to 60 psi. Hollow-cone or
flat-fan nozzles provide much better coverage than
flood nozzles.

Low temperatures and humidity reduce contact
herbicide activity. Injury symptoms are usually visible
within a day. Soybean leaves may show contact bum
under conditions of high temperature and humidity.
This leaf bum is intensified by a COC. Soybeans usu-
ally recover within 2 to 3 weeks after application. A
rain-free period of several hours is required for effec-
tive control with most contact herbicides except Cobra.

Apply contact herbicides 2 to 3 weeks after soy-
bean emergence, when weeds are small and actively
growing. Most contact herbicides have little soil re-
sidual activity, so do not apply too early. Larger
weeds may require increased rates but still may re-
cover and regrow. See Table 15.22 for weeds con-
trolled and Table 15.23 for herbicide rates by weed
height.

Basagran (bentazon) is used at 1 to 2 pints per acre.
A UAN or AMS improves velvetleaf control. A COC is
preferred if the major weed species is common rag-
weed or lambsquarters. Split applications can im-
prove control of lambsquarters, giant ragweed, wild
sunflower, and yellow nutsedge. Rezult is a 1:1 co-
pack of Poast Plus and Basagran 5S.

Blazer or Status (acifluorfen) is used at 0.5 to 1.5
pints per acre. Split applications are allowed 15 days
apart, but do not apply more than 2 pints per acre per
season. Acifluorfen may cause soybean leaf burn; how-
ever, soybeans usually recover within 2 to 3 weeks.
Velvetleaf control is improved with the use of a fertil-
izer adjuvant or the addition of bentazon.

Galaxy 3.67S and Storm 4S are 2:3 and 1:1 pre-
mixes of acifluorfen and bentazon, respectively (see

Table 15.04 for equivalents). Galaxy is used at 2 pints
per acre or up to 3 pints per acre for suppression of
larger weeds. Storm is used at 1.5 pints per acre.
Manifest and Conclude are co-pack delivery systems
for Galaxy and Storm, respectively, plus 1.5 pt/A of
Poast 1.5E. Labeled grass sizes are smaller than for
equivalent rates of Poast or Poast Plus alone.

Reflex 2S or Flexstar 1.88S (fomesafen) controls
broadleaf weeds at 1 to 1.25 pints per acre. Reflex may
be used at 1.5 pints per acre south of 1-70. Apply
Flexstar or Reflex before soybeans bloom. Fomesafen
may cause soybean leaf burn; however, soybeans usually
recover within 2 to 3 weeks. Be sure applications are
accurate and even to minimize possible carryover. In
Illinois, do not apply to the same field the following year.
Recropping intervals are 4 months for wheat, 10
months for com, and 18 months for other crops, in-
cluding grain sorghum.

Cobra 2E (lactofen) is applied at 4 to 12.5 fluid
ounces per acre. Reduced rates are used in tank mixes
to control giant ragweed, common ragweed, and
waterhemp. See the Cobra label for details on adju-
vant selection, which varies with relative humidity
(used alone) and with the tank-mix partner. Cobra can
cause severe soybean leaf burn, but soybeans usually re-
cover within 2 to 3 weeks. Apply Cobra no later than
45 days before harvest.

Resource 0.86E (flumiclorac) is used in tank mixes
(Table 15.25) at a rate of 4 fluid ounces per acre to im-
prove velvetleaf control. It may also be applied alone
at a rate of 4 to 12 fluid ounces per acre, the higher
rate used primarily to control larger velvetleaf. When
applied alone, a COC at 1 quart per acre must be in-
cluded; if tank-mixed, adjuvant selection depends on
the tank-mix partner. Stellar 3.1E, a premix of Re-
source and Cobra, is used at 5 to 7 fluid ounces per
acre. Always add a COC or MSO. Do not apply Stellar
or Resource within 60 days of harvest.

Liberty 1.67S (glufosinate) is used in Liberty Link
soybean varieties at 16 to 28 fluid ounces per acre to
control small annual grass and broadleaf weeds. A
second application of Liberty is allowed to control
later-emerging weeds. See Tables 15.19 and 15.22 for
weed ratings.

Soybean Preharvest Treatments

Gramoxone Extra'*^'' (paraquat) may be used prior to
soybean harvest when 65 percent of the seed pods
have reached a mature brown color or when seed
moisture is 30 percent or less. The rate is 12.8 fluid
ounces of Gramoxone Extra per acre. The total spray
volume per acre is 2 to 5 gallons for aerial application
and 20 to 40 gallons for ground application. Add 1

190

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

quart of an NIS per 100 gallons of spray. Do not pas-
ture livestock within 15 days of treatment, and re-
move livestock from treated fields at least 30 days be-
fore slaughter. Gramoxone is a better "harvest-aid"
than Roundup.

Roundup Ultra (glyphosate) may be applied
preharvest in soybeans after soybean pods have set
and lost all green color, but do not expect fast weed
drying. Allow a minimum of 7 days between applica-
tion and soybean harvest. Do not graze or harvest
treated crop for livestock feed within 25 days after a
preharvest application. Roundup may be applied at a
rate of 1 quart per acre by air or ground. Ground ap-
plication at a higher rate is also allowed in non-
Roundup Ready soybeans, but is usually feasible only
for spot treatment of problem weeds such as perenni-
als. In Roundup Ready soybeans, an application of
1 quart per acre may be made up to 14 days before
harvest as long as the total in-crop and preharvest ap-
plications do not exceed 3 quarts per acre. Do not treat
non-Roundup Ready soybeans grown for seed beans as
there may be a reduction in germination or vigor.

Problem Perennial Weeds

Perennials first appear as light infestations, but if left
unattended they can become serious, causing reduc-
tions in yield, grain quality, and harvesting efficiency.
Pei^ennial weed problems are increasing in Illinois due
to less competition from annuals and reduced tillage.
Spreading perennials reproduce from vegetative
propagules, which can be spread by chisel plows or
field cultivators. For tillage to be beneficial, root frag-
ments must be left on the surface and exposed to ei-
ther freezing or desiccation. Repeated tillage or mow-
ing can deplete root food reserves and make the
plants more susceptible to chemical control. Control
of spreading perennials often relies on a combination
of tillage to weaken the plants and the use of translo-
cated (systemic) herbicides.

Translocated Herbicides to Control or
Suppress Perennial Weeds

Translocated herbicides should be applied when
"food" is moving to the roots if control of perennials
is to be effective. Early in the spring, food moves up
from root reserves to support vegetative growth, and
herbicides provide only "top kill." For the majority of
perennials, the most effective applications are at early bud-
to-bloom stage or early in fall, when the plants are re-
plenishing food reserves in the roots. Some of the best
opportunities for perennial control are on land where
no crop is to be harvested. Plants must be actively
growing; do not disturb (cultivate or mow) for at least

10 days after application to allow time for the herbi-
cide to translocate.

Fallow, CRP, and wheat-stubble land offer good
opportunities to work on warm-season perennials.
Because no control program is completely effective,
adequate control may take several years. 2,4-D,
Banvel, Roundup Ultra, and Touchdown 5 have label
sections concerning their application to fallow or
stubble ground, including CRP land. Crossbow use is
limited to permanent grass areas such as CRP ground
or permanent pastures (see Chapter 16). Crossbow is
not cleared for use before cropping or in corn or sorghum.

Banvel may be applied on fallow ground at 1 to 4
pints per acre to control or suppress perennials. Use
2 pints per acre to control curly dock, horsenettle, and
Canada thistle, and 4 pints per acre to control Jerusa-
lem artichoke, field or hedge bindweed, hemp dog-
bane, swamp smartweed, and trumpet creeper. Up-
right perennials should be at least 8 inches tall, and
vining perennials should be at or beyond the full-
bloom stage. Com or soybeans may be planted the
spring after applications made the previous year. Soy-
bean injury may occur if fewer than 30 days have
elapsed per pint of Banvel applied per acre. Wheat
may be planted if 20 days have elapsed per pint of
Banvel. Do not count days when the ground is frozen.

2,4-D 3.8LVE (ester) or 2,4-D 3.8S (amine) at 2 to 6
pints currently may be applied on fallow ground and
crop stubble. Use equivalent rates of other formula-
tions, as 2,4-D is available under many trade names
and in various concentrations. Observe current guide-
lines for 2,4-D application. If possible, spray perenni-
als that are actively growing at the bud-to-bloom
stage. Do not disturb the treated area for at least
2 weeks after treatment. Multiple applications usually
are required for satisfactory control. Perennials listed
include field and hedge bindweed, Canada thistle,
hemp dogbane, curly dock, and Jerusalem artichoke.
Do not plant soybeans or wheat for 3 months after applying
2,4-D at these rates.

Roundup Ultra (2 to 4 quarts per acre) or Touch-
down 5 (1.5 to 3 quarts per acre) may be used on fal-
low or stubble ground to control perennial grasses
and broadleaf weeds. Broadleaf weeds should be ac-
tively growing at late-bud to full-bloom stage (de-
pending on the species; see the label). Lower rates
may be specified for suppression or in tank mixes
with 2,4-D or Banvel. Perennial broadleaf weeds con-
trolled or suppressed include field bindweed, hemp
dogbane, common milkweed, swamp smartweed,
Canada thistle, and trumpet creeper. Perennial grasses
include johnsongrass, quackgrass, and wirestem
muhly. For forage species and CRP land, see the
"Conservation Tillage and Weed Control" section.

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM

191

Preharvest application may suppress or control
' some susceptible perennials, but is usually made to
suppress annual weeds and minimize harvesting
problems. Preharvest treatments often involve aerial
application, but high-clearance ground equipment
can sometimes be used in com. Preharvest applica-
tions of "cleared" translocated herbicides are 2,4-D or
Roundup Ultra for com or wheat (see the Illinois Agri-
cultural Pest Management Handbook, Chapter 3) and
Roundup Ultra for soybeans. Postharvest treatments
in corn, soybeans, and wheat require that the weeds
regrow sufficiently to be in a susceptible stage before
droughty conditions or frost occur. Postharvest
treatments in wheat or oats are possible (see the pre-
ceding discussion of stubble ground) if the field is not
undersown with a forage legume such as alfalfa or

clover and is not double-cropped to soybeans or grain
sorghum.

In-crop treatments offer fewer possibilities for pe-
rennial broadleaf control because rates are often re-
duced and weeds often are not in the most susceptible
stages. Unfortunately, com and soybeans are often in
reproductive stages when most warm-season perenni-
als are in the bud-to-bloom stage. Do not apply translo-
cated or contact herbicides to corn or soybeans during their
reproductive stages. Spot treatment with Roundup Ul-
tra or Touchdown 5 is allowed in com and soybeans
up to reproductive stages. Currently there are more
postemergence herbicides to control perennial broad-
leaf weeds in com than in soybeans. See "Postemer-
gence Broadleaf Control (Com)."

Table 15.27. Corn "Post" Herbicides: Perennial Broadleaf Weed Control Ratings

'4-'

X
u
O

vi-i
73

4-*

c
o

73"

d, honeyvine

glory, bigroo
eetpotato)

ed, swamp
hoestring)

«5

0»

Milkwee
(climbinj

Morning
(wild sw

dj (fl

Herbicide

Com stage

Rate per acre

01
•S

i-i
O

Smartw
(devil's

2,4-D amine

8 in. to tasseP

Ipt

2,4-D ester

Preharvest

2pt

Banvel

8-24 in.^

0.5 pt

Stinger

<24in.

0.5-0.67 pt

Accent -i- BanveP

8-24 in.^

0.67 oz -1- 0.5 pt

Beacon

Pretassel*^

0.76 oz

Beacon -i- BanveP

4-24 in.'*

0.38 oz -1- 0.5 pt

Exceed

4-30 in.^

1.00 oz

Exceed -i- BanveP

8-24 in.-^

1.00 oz + 0.5 pt^

NorthStar

4-36 in.^

5oz

Spirit

4-24 in.=

1.00 oz

Spirit + Banvel*"

4-24 in."^

1.00 oz-h 0.5 pt

Lightning^

Pretassel

1.28 oz

Permit -i- Banvel*"

8-36 in.^

0.67 oz -1- 0.5 pt

glyphosate'

Pretassel

1-2% solution

Roundup^

<24in.

Iqt/a

Liberty*'

<24in.

1.75 pt

—

Control ratings: 9 = excellent, 8 = good, 7 = fair, 6 = poor, 5 or less = unsatisfactory. Boldface indicates acceptable control.

*Use drop nozzles; do not spray over whorl of corn.

■"Use only NTS as adjuvant.

"^Use drop nozzles with Beacon, Exceed, NorthStar, or Spirit in corn over 20 inches.

''Use drop nozzles if com is over 12 inches tall.

^Lightning used on IMI-designated com hybrids.

'Glyphosate (Roundup Ultra or Touchdown 5) used as a spot treatment in com.

^Roundup Ultra used on Roundup Ready corn hybrids.

''Liberty used on Liberty Link or GR com hybrids.

192

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 15.27 lists translocated herbicides for control
or suppression of perennial weeds in com, and weed
control ratings, as well as crop stages and rates per
acre. Multiple low-rate treatments, if allowed, often
are more effective than a single treatment at a high
rate.

Banvel 4S may be applied at Vz pint per acre when
com is 8 to 36 inches tall or up to 15 days before tassel
emergence, whichever is first. A second application of
Banvel may be made after 2 weeks, up to a maximum
of 1.5 pints per season. Do not apply Banvel to corn over
24 inches tall if soybeans growing nearby are over 10
inches tall or have begun to bloom. Use drop nozzles
when applying Banvel tank-mixed with 2,4-D (0.25
pint per acre), when com leaves prevent proper spray
coverage, or when sensitive crops are growing
nearby.

2,4-D amine or LV ester may be applied with drop
nozzles to com over 8 inches tall up to tassel stage.
The rate per acre is 0.5 to 0.75 pint 3.8 LVE (low-vola-
tile ester) or 1 to 1.5 pints 3.8S (amine) or equivalent
rates of other formulations. Do not use esters if tempera-
tures are expected to exceed 85°F the next few days fol-
lowing application. Adhere closely to all label precau-
tions to prevent injury to nontarget plants in the area.
Banvel or 2,4-D at these rates only suppresses perennial
broadleaf weeds.

Stinger (clopyralid) at VS to % pint per acre sup-
presses or controls 6- to 8-inch Canada thistle and up
to 5-leaf Jerusalem artichoke. For spot treatments with
hand-held sprayers, use a spray mix of 1 fluid ounce
per 4 gallons or V3 pint per 25 gallons of water. Make
applications before com is 24 inches tall on a spray-to-
wet basis (not runoff). Hornet (which contains
Stinger) used postemergence at 3.2 to 4 ounces per
acre controls 6- to 9-tnch Jerusalem artichoke or
Canada thistle.

Beacon or Accent controls quackgrass and john-
songrass in com. See the "Postemergence (Foliar-
Applied) Herbicides (Com)" section for discussion
and Table 15.09 for ratings. Beacon also suppresses
small Jerusalem artichoke, Canada thistle, and
horsenettle. Exceed, NorthStar, and Spirit (which
contain Beacon) suppress small bindweed (hedge or
field), Jerusalem artichoke, Canada thistle, and
horsenettle. They also control seedling johnsongrass
and suppress rhizome johnsongrass and quackgrass.
Permit at % ounce per acre suppresses up to 6-inch
pokeweed, and at 1 to IVS ounces controls 4- to 12-inch
yellow nutsedge and suppresses 4- to 12-inch com-
mon milkweed.

Tank mixes of Banvel, Clarity, or 2,4-D are allowed
with Beacon, Exceed, Permit, or Spirit to improve

suppression of several broadleaf species, including
common and honeyvine (climbing) milkweed, hemp
dogbane, Canada thistle, field bindweed, and com-
mon pokeweed (Table 15.27). Use only an MS as an
adjuvant in these tank mixes for perennials. Because
these herbicides are primarily used to control annual
weeds, timing is not always best for control of peren-
nials. The degree of perennial control depends on the
weed species, size, and susceptibility.

Basis Gold'^'^'' or Accent Gold suppresses up to 2-
inch yellow nutsedge, or 4-inch Canada thistle, com-
mon milkweed, hemp dogbane, and pokeweed. Re-
solve, Contour'*^'', Lightning, or Pursuit may be used
in IMI-designated com to control 6- to 10-inch Jerusa-
lem artichoke and suppress up to 3-inch yellow nut-
sedge or Canada thistle.

Roundup may be used on Roundup Ready com
hybrids to control or suppress perennial weeds in
com. Rates are 1.5 to 2 pints per acre, with a second
application allowed as long as application is before
com is 30 inches tall or the V-8 leaf stage. Total in-
crop applications are limited to 2 quarts per acre plus
1 quart allowed preharvest.

Translocated herbicides used in soybeans to sup-
press or control perennial weeds are ALS herbicides.
Roundup, or ACC-ase "grass-only" herbicides. Pur-
suit, Classic, Synchrony STS, and Raptor are ALS her-
bicides used to control broadleaf weeds and suppress
some perennials (Table 15.28).

Pursuit or Raptor controls up to 8-inch Jerusalem
artichoke and suppresses small Canada thistle and
yellow nutsedge. Raptor also suppresses small field
or hedge bindweed.

Classic or Skirmish at % ounce or Synchrony STS
(only in STS-soybeans) at 0.5 ounce per acre controls
2- to 4-inch yellow nutsedge and suppresses up to 6-
inch Jerusalem artichoke and 4-inch Canada thistle.
Synchrony STS also suppresses up to 6-inch common
milkweed or pokeweed plus 6-inch-diameter peren-
nial sow thistle or 8-inch-diameter dandelion.

Roundup Ultra or Touchdown 5 spot treatment
may be used to control perennials (Tables 15.27 and
15.28) in com and soybeans up to the reproductive
stages of the crops. Use a 3 to 5 percent solution for
low coverage and 1 to 2 percent if application is
spray-to-wet (complete coverage). Fallow ground
and preharvest uses are discussed earlier. Wiper ap-
plicators allow Roundup Ultra or Touchdown 5 treat-
ment in soybeans to control or suppress perennial
weeds such as johnsongrass, Jerusalem artichoke,
milkweed, or hemp dogbane growing 6 inches taller
than soybeans; see "Translocated Herbicides for
Grass and Broadleaf Control (Soybeans)."

15 • WEED CONTROL FOR CORN, SOYBEANS, AND SORGHUM
Table 15,28. Soybean "Post" Herbicides for Partial Control or Suppression of Perennial Weeds

193

o
o

ri .

• 1— 1

i ' 1

^
^

03
T3

bO
V X)
T3 Si

? '55

'to

-0

n3
C

r 1

M
^

01 X

3
u

01
01

Ol ^

^ -9

Ol
Ol

•a

TJ -0

-Sd

:^ 6

-4-*

Herbicide

§S

Roundup Ultra^ 1 qt

glyphosate'' 1-2%

Classic/Skirmish'^

—

Synchrony STS^

—

Pursuit

—

Raptor

—

Basagran"^

—

Blazer'

—

Cobras

—

Flexstar^, Reflex

—

Liberty'

—

Control ratings: 9 = excellent, 8 = good, 7 = fair, 6 = poor, 5 or less = unsatisfactory. Boldface indicates acceptable control.

■"Use only with Roundup Ready-designated soybean varieties.

''Spot treatment with 1% Touchdown 5 or 2% Roundup Ultra on a spray-to- wet basis before bloom stage.

'A ropewick applicator with a mix of 20% Touchdown 5 or 33% Roundup Ultra may also control this weed.

"^Use either the high rate or a split application for this degree of control.

•"Use only with STS-designated soybean varieties.

'Label specifies high rate and favorable environmental conditions required for suppression.

^Label specifies the use of COG and a maximum of 6-leaf stage for suppression.

''Flexstar may provide greater suppression than Reflex.

'Liberty is to be used only on Liberty Link-designated soybean varieties.

Roundup Ready soybean varieties allow Roundup
Ultra to be applied for suppression or control of cer-
tain perennial broadleaf and grass weed species.
Roundup Ultra at 2 quarts in 5 to 20 gallons of spray
solution per acre controls or suppresses Canada
thistle, common milkweed, hemp dogbane, horsenettle,
swamp smartweed (Table 15.28), quackgrass, johnson-
grass, or wirestem muhly (Table 15.19). Sequential ap-
plications of 1 quart followed by 1 quart may be more
effective for some species. Do not exceed a total of 3
■ quarts per acre, the maximum total in-crop rate includ-
! ing preharvest treatment.

Assure II or Matador, Fusion, Fusilade DX, Poast
I Plus or Prestige, and Select provide postemergence
! control of johnsongrass, quackgrass, and wirestem
muhly in soybeans. See Table 15.19 for ratings and
Table 15.20 for rates and sizes.

Contact Herbicides to Suppress
Perennial Weeds

Several postemergence contact herbicides used in
com and soybeans suppress certain perermial weeds
by burning off top growth. This treatment may reduce
competition with the crop, but it does not prevent re-
growth from plant roots because contact herbicides
translocate very little. When selecting a contact herbi-
cide to control annual weeds, however, you may want
to select one that suppresses problem perennials.

Buctril, Moxy, Laddok S-12, and Liberty or Liberty
ATZ are contact herbicides used in com; see "Contact
Broadleaf Herbicides (Com)." See the label or Table
15.16 for adjuvants. Buctril or Moxy at 1.5 pints per
acre suppresses 8- inch to bud-stage Canada thistle in
com. A tank mix with Stinger or Banvel controls

194

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Canada thistle, plus Banvel helps suppress field bind-
weed (see the label).

Laddok S-12'*^'' at 2.33 pints per acre suppresses 1-
to 4-inch yellow nutsedge and 8- to 10-inch Canada
thistle or field bindweed. A tank mix with Stinger
controls Canada thistle, whereas a tank mix with
2,4-D LVE may help control field bindweed and
swamp smartweed (see the label). Do not apply Laddok
S-12 after corn is 12 inches tall

Liberty at 28 fluid ounces or Liberty ATZ'^"'' at 40
fluid ounces per acre suppresses most perennial
weeds and provides control of several when followed
by another application of Liberty at 28 fluid ounces.

Basagran, Blazer or Status, Cobra, Flexstar, Liberty,
and Reflex are contact herbicides used in soybeans;
see "Contact Herbicides for 'Postemergence Control'
of Broadleaf Weeds (Soybeans)" and Table 15.28. See
the label or Table 15.26 for needed adjuvants.

Basagran applied at 1.5 to 2 pints per acre plus a
COC suppresses or controls 8-inch Canada thistle and

6-inch yellow nutsedge. A second application or culti-
vation 7 to 10 days later improves control. Basagran
applied at 2 to 3 pints per acre suppresses up to 10-
inch field or hedge bindweed. Blazer or Status at 1.5
pints per acre suppresses field or hedge bindweed,
common milkweed, and trumpet creeper.

Cobra at 12.5 fluid ounces per acre suppresses up
to 6-leaf Canada thistle, common milkweed, bigroot
momingglory (wild sweet potato), swamp smart-
weed, and trumpet creeper. Reflex or Flexstar at 1.25
pints per acre suppresses field or hedge bindweed,
honeyvine milkweed, trumpet creeper, and yellow
nutsedge. Liberty at 28 fluid ounces per acre sup-
presses most perennial weeds and provides control of
several when followed by another application of Lib-
erty at 28 fluid ounces.

Contributions of other weed scientists and staff of the University of
Illinois and at other institutions, as well as the input of industry
weed scientists, are gratefully acknowledged.

Authors

M. McGlamery, A. Hager, and D. Pike

Department of Crop Sciences

I Chapter 16.
1999 WEED Control

^FOR Small Grains, Pastures, and Forages

Good weed control is necessary for maximum pro-
duction of high-quality small grains, pastures, and
forages in Illinois. When properly established, these
crops usually can compete effectively with weeds, so
the need for herbicide applications is minimized.
However, weeds can sometimes become significant
problems and warrant control. For example, wild gar-
lic is considered the worst weed problem in wheat in
southern Illinois. Because its life cycle is similar to
that of winter wheat, wild garlic can establish itself
with the wheat, grow to maturity, and produce large
quantities of aerial bulblets by wheat-harvest time.
Economics often makes it necessary to control wild
garlic in winter wheat to minimize dockage.

In pastures, woody and herbaceous perennials can
become troublesome. Annual grasses and broadleaf
weeds such as chickweed and henbit may cause prob-
lems in hay crops. By proper management, many of
these weed problems can be controlled effectively.

Several herbicide labels carry the following
groundwater warnings under either the environmen-
tal hazard or the groundwater advisory section: "X is
a chemical that can travel (seep or leach) through soil
and enter groundwater that may be used as drinking
water. X has been found in groundwater as a result of
its use as a herbicide. Users of this product are ad-
vised not to apply X where the soils are very perme-
able (that is, well-drained soils such as loamy sands)
and the water table is close to the surface." Table 16.01
lists herbicides that carry this warning. A few labels
also warn against contamination of surface water.

Small Grains

Good weed control is critical for maximum produc-
tion of high-quality small grains. Often, problems

with weeds may be dealt with before the crop is es-
tablished. For example, some broadleaf weeds can be
controlled effectively in the late fall with 2,4-D or
Banvel (dicamba), or with Roundup Ultra (glypho-
sate) after com or soybean harvest, if seeding is not
too late.

Tillage helps control weeds. Although generally
limited to preplant or postharvest operations, tillage
can destroy many annual weeds and help suppress
certain perennials. Good cultural practices such as
proper seeding rate, optimal soil fertility, and timely
planting help to ensure the establishment of an excel-
lent stand and a crop that is better able to compete
with weeds.

Winter annual grasses such as downy brome and
cheat are very competitive in winter wheat. Illinois
wheat producers are often limited to preplant tillage
operations for control of these species, as few herbi-
cides have label clearances for annual grass control in
winter wheat. If there is a severe infestation of downy
brome or cheat, planting an alternative crop or spring
crop may be best for that field.

A decision to use postemergence herbicides for
broadleaf weed control in small grains should be
based on several considerations:

1. Nature of the weed problem. Identify the species
present and consider the severity of the infestation.
Also note the size of the weeds. Weeds are usually
best controlled while small.

2. Stage of the crop. Most herbicides are applied after
full-tiller until the boot stage. Do not apply herbi-
cides from the boot stage to the hard-dough stage
of small grains (see Figure 16.01 for a description of
growth stages of small grains).

196

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 16.01. Herbicides, Formulations, and Special Statements

Groundwater

Trade name

Common name

Formulation

Restricted use

advisory

Key word

2,4-D amine

2,4-D

3.8 lb a.e./gaP

Danger''

2,4-D ester

2,4-D

3.8 lb a.e./gal^

—

Caution

Ally 60DF

metsulfuron

60%

—

Caution

Balan 60DF

benefrn

60%

—

Warning

Banvel

dicamba

4 lb a.e./gal^

—

Warning

Buctril

bromoxynil

2 lb/gal

—

Warning

Butyrac 200

2,4-DB

2 lb a.e./gal^

—

Yes

Danger''

Crossbow

2,4-D -1- triclopyr

2 -1- lib a.e./gaP

—

Yes

Caution

Eptam 7E, lOG

EPTC

7 lb/gal, 10%

—

Caution

Fusilade DX

fluazifop

2 lb a.e./gaP

—

Caution

Gramoxone Extra

paraquat

2.5 lb/gal

Yes

—

Danger''

Harmony Extra 75DF

thifensulfuron -i-

tribenuron 75%

—

Caution

Kerb SOW

pronamide

50%

Yes

Caution

Lexone 75DF

metribuzin

75%

—

Yes

Caution

MCPA

several

—

Warning

Peak 57WG

prosulfuron

57%

—

Caution

Poast Plus

sethoxydim

1 lb/gal

—

Caution

Prowl

pendimethalin

3.3 lb/gal

—

Caution

Pursuit 2AS, 70DG

imazethapyr

2 lb/gal, 70%

—

Caution,
Warning

Roundup Ultra

glyphosate

3 lb a.e./gaP

—

Caution

Sencor 75DF

metribuzin

75%

—

Yes

Caution

Sinbar SOW

terbacil

80%

—

Caution

Spike 20P

tebuthiuron

20%

—

Yes

Caution

Stinger

clopyralid

3 lb a.e./gaP

—

Yes

Caution

Select

clethodim

2 lb/gal

—

Warning

Treflan

trifluralin

4 lb/gal, 5 lb/gal.

lOG —

—

Warning

Velpar L

hexazinone

2 lb/gal

—

Danger''

Weedmaster

dicamba -i- 2,4-D

1 + 2.87 lb/gal

—

Danger**

^a.e. = acid equivalent for these herbicides. All others are active ingredient (a.i.) formulations.
''Danger. Check label for safety equipment and precautions.

Herbicide activity. Determine crop tolerance and weed
susceptibility to herbicides by referring to Tables
16.02 and 16.03. The lower rates in Table 16.03 are for
more easily controlled weeds and the higher rates for
the more difficult-to-control species. Tank mixes may
broaden the weed spectrum and thereby improve
control; check the herbicide label for registered
combinations.

Presence of a legume underseeding. Usually 2,4-D ester
formulations and certain other herbicides listed in
Table 16.03 should not be applied because they may
damage the legume underseeding.

5. Economic justification. Consider the treatment cost
in terms of potential benefits, such as the value of
increased yield, improved quality of grain, and
ease of harvesting the crop.

Table 16.03 outlines current suggestions for weed-
control options in wheat and oats, the two small
grains most commonly grown in Illinois. Please refer
to Table 16.04 for grazing-restriction information con-
cerning herbicides used in small grains. Always con-
sult the herbicide label for specific information about
the use of a given product.

16 • 1999 WEED CONTROL FOR SMALL GRAINS, PASTURES, AND FORAGES

197

Stage 1
Seedling

Stages 4 to 5
Tillering

Stage 7
Joint

Stage 10
Boot

Stages 10.1 to 10.5
Heading

Figure 16.01. Growth stages of small grains.

Seedling

Stage 1. The coleoptile, a protective sheath that sur-
rounds the shoot, emerges. The first leaf emerges
through the coleoptile, and other leaves follow in suc-
cession from within the sheath of the previously
emerging leaf.

Tillering

Stages 2 to 3. Tillers (shoots) emerge on opposite
sides of the plant from buds in the axils of the first
and second leaves. The next tillers may arise from the
first shoot at a point above the first and second tillers
or from the tillers themselves. This process is repeated
until a plant has several shoots.

Stages 4 to 5. The leaf sheaths lengthen, giving the
appearance of a stem. The true stems in both the main
shoot and the tillers are short and concealed within
the leaf sheaths.

Jointing

Stage 6. The stems and leaf sheaths begin to elon-
gate rapidly, and the first node (joint) of the stem is
visible at the base of the shoot.

Stage 7. The second node (joint) of the stem is vis-
ible. The next-to-last leaf is emerging from within the
sheath of the previous leaf but is barely visible.

Stage 8. The last leaf, the "flag leaf," is visible but
still rolled.

Stage 9. Preboot stage. The ligule of the flag leaf is
visible. The head begins to enlarge within the sheath.

Stage 10. Boot stage. The sheath of the flag leaf is
completely emerged and distended due to the enlarg-
ing but not yet visible head.

Heading

Stages 10.1 to 10.5. Heads of the main stem usually
emerge first, followed in turn by heads of the tillers in
order of their development. Heading continues until
all heads are out of their sheaths. The uppermost
intemode continues to lengthen until the head is
raised several inches above the uppermost leaf sheath.

Flowering

Stages 10.5.1 to 10.5.3. Flowering progresses in or-
der of head emergence. Unpollinated flowers result in
no kernels.

Stage 10.5.4. Premilk stage. Flowering is complete.
The inner fluid is abundant and clear in the develop-
ing kernels of the flowers pollinated first.

Ripening

Stage 11.1. Milk stage. Kernel fluid is milky white
from the accumulating starch.

Stage 11.2. Dough stage. Kernel contents are soft
and dry (doughy) as starch accumulation continues.
The plant leaves and stems are yellow.

Stage 11.3. The kernel is hard, difficult to divide
with the thumbnail.

Stage 11.4. The kernel is ripe for cutting and frag-
ments when crushed. The plant is dry and brittle.

198

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 16.02. Effectiveness of Herbicides on Weeds in Small Grains

This table compares the relative effectiveness of herbicides on individual weeds. Ratings are based on labeled ap-
plication rate and weed size or growth stage. Performance may vary due to weather and soil conditions or other
variables.

Susceptibility to herbicide

Weed

2,4-D

Banvel

Buch-il

Harmony Extra

MCPA

Peak

Stinger

Winter annual

Buckwheat, wild

Chickweed, common

Henbit

Horseweed (marestail)

Lettuce, prickly

Mustard spp., annual

Pennycress, field

Shepherd's purse

Summer annual

Lambsquarters, common

Pigweed spp.

Ragweed, common

Ragweed, giant

Smartweed, Pennsylvania

Perennial

Dandelion

Garlic, wild

Aerial bulblets

Underground bulbs

Thistle, Canada

9 = 90 to 100%, 8 = 80 to 89%, 7 = 70 to 79%, 6 = 60 to 69%, 5 = 50 to 59%, 0 = less than 50% control or not labeled.
*2,4-D ester at maximum use rate.

For annual broadleaf weeds, postemergence herbi-
cides such as 2,4-D, Banvel, Buctril (bromoxynil), and
MCPA can provide good control of susceptible spe-
cies (Table 16.02). Herbicides must be applied during
certain growth stages of the crop to avoid crop injury
and for optimal weed control. Refer to Figure 16.01
for a description of the growth stages of small grains.

Some perennial broadleaf weeds may not be con-
trolled satisfactorily with the low herbicide rates used
in small grains, and higher rates are not advisable be-
cause they can cause serious injury to crops. To con-
trol perennial weeds, translocated herbicides such as
2,4-D, Banvel, or Roundup Ultra, in combination
with tillage after small grain harvest or after soybean
harvest but before establishing small grains, may be
the best approach.

Stinger (clopyralid) may be used to control broad-
leaf weeds in wheat, oats, and barley. Stinger controls

Canada thistle, as well as a number of annual broad-
leaf weeds (Table 16.02).

Wild garlic continues to be a serious weed problem
in winter wheat. Harmony Extra (thifensulfuron +
tribenuron), applied in the spring at 0.3 to 0.6 ounce
of 75DF per acre, effectively controls wild garlic aerial
bulblets and some underground bulbs as well. Har-
mony Extra also helps control chickweed, henbit,
common lambsquarters, smartweed, and several spe-
cies of mustard. See Tables 16.02 and 16.03 for more
information on controlling weeds in small grains.

Roundup Ultra may be used as a preharvest treat-
ment in wheat for control of annual and certain peren-
nial weed species. Applications should be made only
after the hard-dough stage of the grain (30 percent or
less grain moisture) and at least 7 days before harvest.
Roundup Ultra may be applied at a maximum rate of
1 quart per acre using ground or aerial application

16 • 1999 WEED CONTROL FOR SMALL GRAINS, PASTURES, AND FORAGES

199

Table 16.03, Weed Control in Small Grains

Herbicide

Broadcast
rate/acre

Remarks (see Table 16.04 for grazing restrictions)

Oats and wheat with legume underseeding

2,4-D amine
(3.8 lb a.e.)

Buctril 2E

Vi to iy2 pt Winter wheat more tolerant than oats. Apply in spring after full tiller but before
joint stage. Do not treat in the fall. Use lower rate if underseeded with legume.
Some legume damage may occur. May be used as preharvest treatment at
1 to 2 pt per acre during hard-dough stage.

1 to 1.5 pt Apply Buctril alone to fall-seeded small grains in the fall or spring before the

boot stage. Weeds are best controlled before the 3- to 4-leaf stage. Buctril 2E may
be applied at 1 to V/i pt per acre to small grains underseeded with alfalfa.

MCPA amine '/4 to 1.5 pt Less likely than 2,4-D to damage oats and legume underseeding. Apply from 4-

leaf stage to joint stage. Rate varies with crop and weed size and presence of le-
gume underseeding.

Oats and wheat without legume underseeding

Banvel, 4 lb a.e. 4 fl oz Do not use with legume underseeding. In fall-seeded wheat, apply before jointing

stage. In spring-seeded oats, apply before oats exceed 5-leaf stage.

Harmony Extra
75DF

0.3 to 0.6 oz Do not use with legume underseeding. Make applications to wheat after the crop is
in the 2-leaf stage, but before the flag leaf is visible. For spring oats, make appli-
cations after the crop is in the 3-leaf stage but before jointing. The use rate for
spring oats is 0.3 to 0.4 oz per acre. Wild garlic should be less than 12 in. tall,
with 2 to 4 in. of new growth. Annual broadleaf weeds should be past the cotyle-
don stage, actively growing, and less than 4 in. tall or across. Nonionic surfactant
at 0.25% volume per volume (v/v) should be included in the spray mixture.
When liquid fertilizer is used as the carrier, use V\6-Vi% v/v surfactant. Tempo-
rary stunting and yellowing may occur when Harmony Extra is applied using
liquid fertilizer solution as the carrier. These symptoms are intensified with the ad-
dition of surfactant. Without surfactant addition, wild garlic control may be erratic.
Do not plant any crop other than wheat or oats within 60 days after application.

Peak 57WG 0.38 to 0.5 oz Do not use with legume underseeding. Apply Peak to actively growing small grain

crops from the 3-leaf stage to before the second node is detectable in stem elon-
gation. Applications made to small grains before the 3-leaf stage increase likeli-
hood of crop injury. Do not make a foliar or soil application of an organophos-
phate insecticide within 15 days before or 10 days after applying Peak. Always
include a COC (1 to 4 pints per acre) or NIS (1 to 2 quarts per 100 gallons) in the
spray mix, and apply in at least 10 gallons of water per acre. Do not harvest
grain until 60 days after application, and apply no more than 1 ounce of Peak
per growing season. Do not plant soybeans until 10 months after application.

Stinger, 3 lb a.e. 1/4 to V3 pt

Wheat only

2,4-D ester,
3.8 lb a.e.

Roundup Ultra
3 lb a.e. /gal

Vi to 1 pt

1 to 2 pt

Do not use with legume underseeding. Apply to small grains from the 3-leaf stage
up to the early boot stage. For control of Canada thistle, V3 pt per acre should be
used. For control of additional weeds, 2,4-D, Banvel, Buctril, Harmony Extra,
Sencor, or MCPA may be tank-mixed with Stinger.

Do not use with legume underseeding. Apply in the spring after full-tiller but before
joint stage. For preharvest treatment, apply 1 to 2 pt per acre during hard-dough
stage. For control of wild garlic or wild onion, apply 1 to 2 pt in the spring when
wheat is 4 to 8 in. tall, after tillering but before jointing; these rates may injure
the crop and only suppress wild garlic.

Do not use with legume underseeding. Apply as a preharvest treatment only after
the hard-dough stage of grain (30% or less moisture) and at least 7 days before
harvest. It is not recommended that wheat being grown for seed be treated with
Roundup Ultra because a reduction in germination or vigor may occur.

200

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 16.04. Grazing Restrictions for Small Grain Herbicides

Days

after treatment before use

Herbicide

name

Graze

green

Feed

Withdraw

Trade

Common

Crops

Applied

Beef

Dairy

straw

for meat

Banvel

dicamba

wheat, oats, barley

Prejoint

Buctril

bromoxynil

wheat, oats, rye, barley

Preboot

Harmony

2:1 mixture of

triticale

Before flagleaf

Yes

Extra

thifensulfuron
+ tribenuron

wheat, barley,
spring oats

Prejoint

Many

2,4-D

wheat, oats, rye, barley

Prejoint

Many

2,4-D, late

wheat, oats, rye, barley

Before harvest

Many

MCPA

wheat, oats, rye, barley

Prejoint

Peak

prosulfuron

wheat, oats, rye, barley

Prior to sec-
ond node

Roundup Ultra

glyphosate

wheat

Before harvest

Stinger

clopyralid

wheat, oats, barley

Preboot

*No withdrawal information available.

equipment. It is not recommended that wheat being
grown for seed be treated with Roundup because a
reduction in germination or vigor may occur.

GRASS PASTURES

Unless properly managed, broadleaf weeds can be-
come a serious problem in grass pastures. They can
compete directly with forage grasses and reduce the
nutritional value and longevity of the pasture. Certain
species, such as white snakeroot and poison hemlock,
are also poisonous to livestock and may require spe-
cial consideration.

Perennial weeds are of great concern in pasture
management. They can exist for many years, repro-
ducing from both seed and underground parent
rootstocks. Occasional mowing or grazing helps con-
trol certain annual weeds, but perennials can grow
back from underground root reserves unless long-
term control strategies are implemented.

Certain biennials can also flourish in grass pas-
tures. The first year, they exist as a prostrate rosette,
so that even close mowing does little to control their
growth. The second year, biennials produce a seed
stalk and a deep taproot. If these weeds are grazed or
mowed at this stage, root reserves can enable the
plant to grow again, thereby increasing its chance of
surviving to maturity.

In general, the use of good cultural practices such
as maintaining optimal soil fertility, rotational graz-
ing, and periodic mowing can help keep grass pas-
tures in good condition and more competitive with

weeds. Where broadleaf weeds become troublesome,
however, 2,4-D, Banvel, Stinger, or Weedmaster
(dicamba -i- 2,4-D) may be used. Roundup Ultra also
may be used as a spot treatment, and Crossbow
(2,4-D -t- triclopyr) and Ally (metsulfuron methyl) are
labeled for control of broadleaf and woody plant spe-
cies in grass pastures. Spike 20P (tebuthiuron) also
may be used in grass pastures for control of brush
and woody plants (see Tables 16.05 and 16.06 for ad-
ditional information).

Proper identification of target weed species is im-
portant. As shown in Table 16.05, weeds vary in their
susceptibility to herbicides. Timing of herbicide appli-
cation also may affect the degree of weed control. An-
nuals and biermials are most easily controlled while
young and relatively small. A fall or early spring her-
bicide application works best if biennials or winter
annuals are the main weed problem. Summer annuals
are most easily controlled in the spring or early sum-
mer. Apply translocated herbicides to control estab-
lished perennials when the weeds are in the bud-to-
bloom stage. Perennials are most susceptible at this
reproductive stage because translocated herbicides
can move downward with food reserves to the roots,
thus killing the entire plant.

For control of woody brush, apply 2,4-D, Banvel,
or Crossbow when the plants are fully leafed and ac-
tively growing. Where regrowth occurs, a second
treatment may be needed in the fall. During the dor-
mant season, oil-soluble formulations of 2,4-D,
Banvel, or Crossbow may be applied in fuel oil to the
trunk. Spike controls many woody perennials and

Table 16.05. Effectiveness of Herbicides on Weeds in Grass Pastures

16 • 1999 WEED CONTROL FOR SMALL GRAINS, PASTURES, AND FORAGES

201

Susceptibility

' to herbicide

Weed

2,4-D

Ally

Banvel

Crossbow

Roundup^

Stinger

Winter annual

Horseweed (marestail)

Pennycress, field

Summer annual

Ragweed, common

Ragweed, giant

Biennial

Burdock, common

Hemlock, poison

Thistle, bull

Thistle, musk

Perennial''

Daisy, oxeye

Dandelion

Dock, curly

Goldenrod spp.

Hemlock, spotted water

Ironweed

Milkweed, common

Nettle, stinging

Plantain spp.

Rose, multiflora'^

Snakeroot, white

Sorrel, red

Sowthistle, perennial

Thistle, Canada

9 = 90 to 100%, 8 = 80 to 89%, 7 = 70 to 79%, 6 = 60 to 69%, 5 = 50 to 59%, 0 = less than 50% control or not labeled.

^Spot treatment only.

''Perennial weeds may require more than one application.

■^Spike also is an effective herbicide for multiflora rose control (weed susceptibility = 9).

should be applied to the soil in the spring. Spike re-
quires rainfall to move it into the root zone of target
species. Ally as a spot treatment controls multiflora
rose, Canada thistle, and blackberry (Rubus spp.) and
controls several annual broadleaf weeds when ap-
plied as a broadcast treatment at the lower rate range.

The weed control options in grass pastures are
shown in Table 16.06. Refer to Table 16.07 for informa-
tion concerning grazing restrictions for herbicides
used in grass pastures. Be cautious with any pesticide,
and always consult the herbicide label for specific in-
formation about the use of a given product.

FORAGE LEGUMES

Weed control is important in managing forage le-
gumes. Weeds can reduce the vigor of legume stands,
reducing yield and forage quality. Good management
begins with weed control that prevents weeds from
becoming serious problems.

Establishment

To minimize problems, prepare the seedbed properly
so that it is firm and weed free. Select an appropriate
legume variety. If you use high-quality seed and follow

202

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 16.06. Broadleaf Weed Control in Grass Pastures

Herbicide

Rate/acre

Remarks (see Table 16.07 for grazing restrictions)

2,4-D, 3.8 lb a.e.
(amine or low-
volatile ester)

Ally 60DF

Banvel, 4 lb a.e.

Crossbow

Roundup Ultra

2 to 4 pt

0.1 to 0.3 oz

Annuals: 0.5 to

iy2pt
Biennials: Vi to

3pt
Perennials: 2 to

4pt

Annuals: 1 to 2 qt
Biennials and

herbaceous

perennials:

2 to 4 qt
Woody perennials:

6qt

1 to 2% solution
(spot
treatment)

Broadleaf weeds should be actively growing. Higher rates may be
needed for less-susceptible weeds and some perennials. Spray bull or
musk thistles in the rosette stage (spring or fall) while they are actively
growing. Spray perennials such as Canada thistle in the bud stage or
the fall regrowth stage. Spray susceptible woody species in the spring
when leaves are fully expanded. Do not apply to newly seeded areas or
to grass when it is in boot-to-milk stage. Be cautious of spray drift.

Apply in the spring or early summer before annual broadleaf weeds
are 4 in. tall. As a spot application for control of multiflora rose, black-
berry, or Canada thistle, apply Ally at 1 oz per 100 gal of water and
spray foliage to runoff. Include a nonionic surfactant of at least 80% ac-
tive ingredient at 1 pt to 1 qt per 100 gal spray solution {Vs% to V4%
v/v). Bluegrass, bromegrass, orchardgrass, timothy, and native grasses
such as bluestem and grama have demonstrated good tolerance. Blue-
grass, bromegrass, orchardgrass, and timothy should be established for
at least 6 months and fescue for 24 months at the time of application, or
injury may result. Application to fescue may result in stunting and
seedhead suppression. Do not apply to ryegrass or pastures containing
desirable alfalfa or clovers. Ally is persistent in soil, and crop rotation
guidelines on the label must be followed.

Use lower rates for susceptible annuals when they are small and ac-
tively growing and for susceptible biennials in the early rosette stage.
Use higher rates for larger weeds, for less susceptible weeds, for estab-
lished perennials in dense stands, and for certain woody brush species.
Be cautious of spray drift.

Apply to foliage during warm weather when brush and broadleaf
weeds are actively growing. When applying as a spot spray, thoroughly
wet all foliage. See herbicide label for more specific rate recommenda-
tions. Be cautious of spray drift. Best control of multiflora rose occurs
when application is made during early to mid-flowering stage.

Controls a variety of herbaceous and woody brush species, such as
multiflora rose, brambles, poison ivy, and quackgrass. Spray foliage of
target vegetation completely and uniformly, but not to point of runoff.
Avoid contact with desirable nontarget vegetation. Consult label for
recommended timing of application for maximum effectiveness on tar-
get species. No more than Vio of any acre should be treated at one time.
Further applications may be made in the same area at 30-day intervals.
Use only where livestock movement can be controlled to prevent graz-
ing for 14 days. Treated areas may be reseeded after 14 days.

16 • 1999 WEED CONTROL FOR SMALL GRAINS, PASTURES, AND FORAGES 203

Table 16.06. Broadleaf Weed Control in Grass Pastures (cont.)

Herbicide

Rate/acre

Remarks (see Table 16.07 for grazing restrictions)

Spike 20P

10 to 20 lb

Stinger, 3 lb a.e. % to IV3 pt

For control of brush and woody plants in rangeland and grass pastures.
Requires sufficient rainfall to move herbicide into root zone. May kill or
injure desirable legumes and grasses where contact is made. Injury is
minimized by applying when grasses are dormant. Do not apply on or
near field crops or other desirable vegetation. Do not apply where soil
movement is likely. Refer to product label for additional restrictions.

Apply when weeds are young and actively growing. Grasses are toler-
ant, but new grass seedlings may be injured. For Canada thistle, apply
to thistle at least 4 in. tall but before thistle reaches bud stage. Do not
spray pastures containing desirable forbs, such as alfalfa or clover, un-
less injury can be tolerated. Do not use hay or straw from treated areas
for composting or mulching on susceptible broadleaf crops. Refer to
product label for additional precautions.

Table 16.07. Restrictions on Herbicides Used

in Permanent Grass

Pastures

name

Days

after treatment before

use

Herbicide

Grazing

Grass hay

Slaughter
withdrawal

Trade

Common

Beef

Dairy

Beef

Dairy

Ally

metsulfuron

Banvel < 4 pt

dicamba

7 to 40^

37 to 70^

Crossbow

triclopyr -1- 2,4-D

365

Many

2,4-D

7 to 14^

3 to 7"

Stinger*^

clopyralid

Roundup

glyphosate

Spot-treat

Renovation

Spike 20P

tebuthiuron

(spot treatment)

< 20 lb/acre

365

> 20 lb /acre

Do not u<iP fnr

livestock for 1
37

year. .

Weedmaster

dicamba -1- 2,4-D

"Varies with rate used per acre — see label.

''Labels vary (withdrawal unnecessary if more than 14 days after treatment).

•^Do not transfer livestock onto a broadleaf crop area within 7 days of grazing treated area.

••No information available.

the recommendations for liming and fertility, the le-
gume crop may compete well with many weeds and
reduce the need for herbicides.

In fields where companion crops such as oats are
used to reduce weed competition, seed the small
grain at half the rate for grain production to ensure
that the legumes become established with minimum
stress. If the legume is seeded without a companion
crop (direct-seeded), the use of an appropriate herbi-
cide is suggested.

Preplant-Incorporated
Herbicides

Balan (benefin), Eptam (EPTC), and Treflan (triflura-
lin) are registered for preplant incorporation for le-
gumes that are not seeded with grass or small-grain
companion crops. These herbicides control most an-
nual grasses and some broadleaf weeds. In fall
plantings, the weeds controlled include winter annu-
als such as downy brome and cheat. In spring

204

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 16.08. Effectiveness of Herbicides on Weeds in Legume and Legume-Grass Forages

Gramoxone

Poast

Round-

Sencor/

Weed 1

3alan

Buctril

Butyrac

Eptam

Extra

Kerb

Plus

Pursuit

up^^

Select

Lexone^

Sinbar

Velpar

Winter annual

Brome, downy

Chickweed,

common

Henbit

Mustard, wild

Pennycress, field

9 1

Shepherd's purse

9 '

Yellow rocket

Summer annual

€

Bamyardgrass

Crabgrass spp.

Foxtail spp.

Lambsquarters,

common

*■

Nightshade spp.^

Panicum, fall

Pigweed spp.

Ragweed,

common

Smartweed,

Pennsylvania

Perennial

Canada thistle

Dandelion

Dock, curly

Nutsedge, yellow

Orchardgrass

Quackgrass

9 = 90 to 100%, 8 = 80 to 89%, 7 = 70 to 79%, 6 = 60 to 69%, 5 = 50 to 59%, 0 = less than 50% control or not labeled.

^Lexone, Roundup, and Sencor are labeled for use in mixed legume-grass forages. No other herbicides are cleared for this use.

''Spot treatment only.

■^Control of different species may vary.

plantings of legumes, the summer annual weeds con-
trolled include foxtails, pigweeds, lambsquarters,
crabgrass, and fall panicum. Eptam can help suppress
johnsongrass, quackgrass, yellow nutsedge, and
shattercane, in addition to controlling many annual
grasses and some broadleaf weeds. These herbicides
do not effectively controls mustards, smartweed, or
established perennials.

Balan, Eptam, and Treflan must be thoroughly in-
corporated soon after application to avoid herbicide
loss. They should be applied shortly before the le-

gume is seeded to remain effective as long as possible
into the growing season.

Weeds that emerge during crop establishment
should be evaluated for their potential as problems. If
they do not reduce the nutritional value of the forage
or if they can be controlled by mowing, they should
not be the primary focus of a postemergence herbi-
cide application. For example, winter annual weeds
do not compete vigorously with the crop after the first
cutting in the spring. Unless they are unusually dense
or production of weed seed becomes a concern, these

16 • 1999 WEED CONTROL FOR SMALL GRAINS, PASTURES, AND FORAGES

205

Table 16.09. Weed Control in Legume Forages

Herbicide

Legume

Time of
application

Broadcast
rate/acre

Remarks (see Table 16.10 for haying restrictions)

Seedling year

Balan 60DF

Alfalfa, birdsfoot Preplant 2 to 2.5 lb

trefoil, red clover, incorporated
ladino clover,
alsike clover

Buctril 2E

Alfalfa only

Postemergence 1 to 1.5 pt

Butyrac 200 or
Butoxone 200

Eptam 7E, 20G

Alfalfa, birdsfoot Postemergence 1 to 3 qt
trefoil, ladino clover, (amine)

red clover, alsike
clover, white clover

Alfalfa, birdsfoot
trefoil, lespedeza,
clovers

Gramoxone Extra Alfalfa only

Preplant
incorporated

Between
cuttings

3'/2 to 4V2 pt
(7E)
15 lb (20G)

12.8 fl oz

Kerb 50W

Alfalfa, birdsfoot Postemergence 1 to 3 lb

trefoil, crown vetch,

clovers

Poast Plus

Alfalfa only

Postemergence l'/8to2'/4pt

Pursuit 2AS
or 70DG

Alfalfa

Postemergence 3 to 6 fl oz
(2AS)
1.08 to
2.16 oz
(70DG)

Apply shortly before seeding. Do not use with
any companion crop of small grains.

Apply in the fall or spring to seedling alfalfa
with at least 4 trifoliate leaves. Apply to weeds
at or before the 4-leaf stage or 2 in. in height
(whichever is first). May be tank-mixed with
2,4-DB for improved control of pigweed; how-
ever, crop burn may occur from this mixture, es-
pecially under warm, humid conditions. Eptam,
previously used, may enhance Buctril burn to
alfalfa. Do not apply when temperatures are
likely to exceed 70°F during or for 3 days follow-
ing application or when the crop is stressed. Do
not add a surfactant or crop oil.

Use when weeds are less than 3 in. tall or less
than 3 in. across if rosettes. Use higher rates for
seedling smartweed or curly dock. May be tank-
mixed with Poast Plus. Do not use on sweet clover.

Apply shortly before seeding. Do not use with
any companion crop of small grains.

Apply within 5 days after cutting and before al-
falfa regrowth is 2 in. Add surfactant according
to label instructions. Do not apply more than
twice during seedling year. Gramoxone Extra is a
restricted-use pesticide.

In fall-seeded legumes, apply after legumes
have reached trifoliate stage. In spring-seeded
legumes, apply the next fall. Kerb SOW is a re-
stricted-use pesticide.

Best grass control is achieved when applications
are made prior to mowing. If tank-mixed with
2,4-DB, follow 2,4-DB harvest and grazing re-
strictions and add no additives with this tank
mix. Do not apply more than a total of 9.75 pt of
Poast Plus per acre in 1 season.

Apply when seedling alfalfa is in the second-
trifoliate stage or larger and when the majority
of weeds are 1 to 3 in. tall. For low-growing
weeds, apply before the rosette exceeds 3 in. in
diameter. Always include a nonionic surfactant

206

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 16.09. Weed Control in Legume Forages (cont.)

Herbicide

Legume

Time of Broadcast

application rate/acre

Remarks (see Table 16.10 for haying restrictions)

Seedling year (cont.)

Pursuit 2AS Alfalfa

or 70DG (cont.)

Select 2EC

Alfalfa

Postemergence 3 to 6 fl oz
(2AS)
1.08 to
2.16 oz
(70DG)

Postemergence 6 to 8 fl oz

Treflan HFP,

Alfalfa only

Preplant

Itol.Spt

TR-10

incorporated

(HFP)
5 to 7.5 lb
(TR-10)

Established stands

Butyrac 200 or

Alfalfa only

Growing

1 to 3 qt

Butoxone 200

(amine)

Gramoxone

Alfalfa only

Between

12.8 fl oz

Extra

cuttings

Gramoxone
Extra

Alfalfa, Clover

Dormant

or crop oil concentrate and a liquid nitrogen fer-
tilizer solution, and apply in 10 or more gallons
of water per acre. When applied to seedling al-
falfa. Pursuit may cause a temporary reduction in
growth. Do not apply more than 6 fl oz or
2.16 oz per acre per year

May be applied to seedling or established alfalfa
grown for seed, hay, silage, green chop, or direct
grazing. If tank-mixed with 2,4-DB, follow 2,4-DB
grazing and harvest restrictions. Do not plant rota-
tional crops until 30 days after Select application.

May be applied as a preplant incorporated treat-
ment for preemergence control of certain grass
and small-seeded broadleaf species. Some crop
stand reduction and stunting may occur

Spray when weeds are less than 3 in. tall or less
than 3 in. wide if rosettes. Fall treatment of fall-
emerged weeds may be better than spring treat-
ment. May be tank-mixed with Poast Plus.

Between cuttings, treatments should be applied
immediately after hay removal, within 5 days after
cutting and with less than 2 in. of growth. Weeds
germinating after treatment are not controlled.
Gramoxone Extra is a restricted-use pesticide.

13 to 24 fl oz For dormant season, apply after last fall cutting or
before spring growth is 2 in. tall. Weeds should be
succulent and growing at the time of application.
Do not apply if fall regrowth is more than 6 in.
Gramoxone Extra is a restricted-use pesticide.

Kerb SOW

Poast Plus IE

Alfalfa, birdsfoot
trefoil, crown
vetch, clovers

Alfalfa

Growing or
dormant

1 to 3 lb

Postemergence iVs to 2V4 pt

Pursuit 2AS
or 70DG

Alfalfa only

3 to 6 fl oz
(2 AS);

1.08 to
2.16 oz
(70DG)

Apply in the fall after last cutting, when weather
and soil temperatures are cool. Kerb SOW is a
restricted-use pesticide.

Best grass control is achieved when applications
are made prior to mowing. If tank-mixed with
2,4-DB, follow 2,4-DB grazing and harvest restric-
tions. Do not apply more than a total of
9.75 pt of Poast Plus per acre in 1 season.

Apply in the fall or spring to dormant or semi-
dormant alfalfa (less than 3 in. of regrowth), or
between cuttings. Do not apply Pursuit to alfalfa
during the last year of the stand. Always include
a nonionic surfactant or crop oil concentrate and
a liquid nitrogen fertilizer solution, and apply in
10 or more gallons of water per acre.

16 • 1999 WEED CONTROL FOR SMALL GRAINS, PASTURES, AND FORAGES

207

Table 16.09. Weed Control in Legume Forages (cont.)

Herbicide

Legume

Time of Broadcast

application rate/acre Remarks (see Table 16.10 for haying restrictions)

Roundup

Select 2EC

Sencor or
Lexone 750F

Sencor 75DF

Sinbar SOW

Treflan
TRIO
4EC

Alfalfa

Alfalfa, clover,
and alfalfa or
clover-grass
mixtures

Alfalfa

Alfalfa and

alfalfa-grass

mixtures

Alfalfa

Alfalfa only

Alfalfa

Velpar L

Alfalfa only

Postemergence 1 to 2%
Growing solution

(spot
treatment)

Last cutting 1 to 2 pt

Postemergence 8 fl oz

Dormant 1/2 to iVa lb

Postdormant 1 to I'/a lb

Dormant Vz to V/i lb

Dormant or

201b

after a

4pt

cutting

during the

growmg

season

Dormant 1 to 3 qt

No more than '/lo of any acre should be treated
at one time. Further applications may be made
in the same area at 30-day intervals. Avoid con-
tact when desirable, nontarget vegetation be-
cause damage may occur. Refer to label for
recommended timing of application for maxi-
mum effectiveness on target species.

For use in declining alfalfa stands prior to crop
rotation. Apply before last cutting in fall or
spring for control of certain perennial grass and
broadleaf weed species. Do not use for alfalfa
grown for seed.

For control of annual grasses in established al-
falfa use a minimum of 8 fl oz/acre. If tank-
mixed with 2,4-DB, follow 2,4-DB grazing and
harvest restrictions.

Apply once in the fall or spring before new
growth starts. Rate is based upon soil type and
organic-matter content. Higher rates may injure
grass component. Do not use on sandy soils or
soils with pH greater than 7.5.

May be applied postdormant but prior to 3 in.
of alfalfa top growth when impregnated on dry
fertilizer.

Apply once in the fall or spring before new
growth starts. Use lower rates for coarser soils.
Do not use on sandy soils with less than 1 per-
cent organic matter. Do not plant any crop for

2 years after application.

A single rainfall or overhead sprinkler irrigation
of 0.5 in. or more, flood irrigation, or furrow irri-
gation after application is required to achvate
the herbicide. If activation does not occur within

3 days after application, incorporate using
equipment that provides thorough soil mixing
with minimum damage to the established al-
falfa. Treflan 4EC may be surface-applied or ap-
plied by chemigation. Do not apply Treflan TR-
IO by chemigation.

Apply in the fall or spring before new growth
exceeds 2 in. in height. May also be applied to
stubble after hay crop removal but before re-
growth exceeds 2 in. Do not plant any crop ex-
cept com within 2 years of treatment. Corn may
be planted 12 months after treatment, provided
deep tillage is used.

208

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 16.10. Herbicides Used in Forage Legumes and Restrictions

Herbicide name

Applied

on /at

Days before
Graze

use

Trade

Common

Forage^

When^

Hay

Seedling legumes

Balan

benefin

AL, CL,

PPI

Eptam

EPIC

AL, CL,

PPI

. . .''

Treflan

trifluralin

PPI

Butyrac 200, Butoxone

2,4-DB

AL, CL,

Post

Buctril

bromoxynil

Postfall

Postspring

Gramoxone Extra

paraquat

After cut^

Poast Plus

sethoxydim

Post

Pursuit

imazethapyr

Post

Select

clethodim

AUBT

Post

Established legumes

Many

2,4-DB

Post

Gramoxone Extra

paraquat

After cut'

Poast Plus

sethoxydim

Post

Pursuit

imazethapyr

Post

Roundup Ultra

glyphosate

AL, CL,

Spot-treat

Roundup Ultra

glyphosate

AL, CL,

Renovate

Roundup Ultra

glyphosate

Last cutting

Gramoxone Extra

paraquat

Dormant

Kerb

pronamide

AL, CL,

Dormant

120

Lexone

metribuzin

Dormant

Sencor

metribuzin

Dormant

Sencor

metribuzin

Predormant/
postdonnant'^

Select

clethodim

AL,BT

Post

Sinbar

terbacil

Dormant

Treflan

trifluralin

Dormant or
after cutting

Velpar

hexazinone

Dorrr\ant

^AL = alfalfa, CL = clover (red, alsike, or ladino), BT = birdsfoot trefoil, PPI = preplant-incorporated.

''No grazing information on label.

■^Between cuttings (less than 5 days after cut with less than 2 in. regrowth).

''If impregnated on dry fertilizer.

weeds may not be a significant problem. Some weeds
such as dandelions are palatable and may not require
control if the overall legume stand is dense and
healthy, but undesirable weeds must be controlled
early to prevent their establishment.

POSTEMERGENCE HERBICIDES

Poast Plus (sethoxydim) or Select (clethodim) may be
applied to seedling alfalfa for control of annual and
some perennial grass weeds after weed emergence.

Grasses are more easily controlled when small.
Butyrac (2,4-DB) controls many broadleaf weeds and
may be applied postemergence in many seedling for-
age legumes. Pursuit (imazethapyr) may be applied
postemergence to seedling alfalfa for control of sev-
eral broadleaf and grass weed species. Buctril (bromo-
xynil) may be used to control broadleaf weeds in
seedling alfalfa. Be sure to apply Buctril while weeds
are small, and use precautions to avoid an adverse
effect on the crop. (See Table 16.08 for specific weed
control ratings and Table 16.09 for rates and remarks.)

16 • 1999 WEED CONTROL FOR SMALL GRAINS, PASTURES, AND FORAGES

209

Established Legumes

The best weed control practice in established forage
legumes is maintenance of a dense, healthy stand
with proper management techniques. Chemical weed
control in established forage legumes is often limited
to late fall or early spring applications of herbicide.
Sencor or Lexone (metribuzin), Sinbar (terbacil), and
Velpar (hexazinone) are applied after the last cutting
in the fall or in the early spring. These herbicides con-
trol many broadleaf weeds and some grasses, too.
Kerb (pronamide) is used for grass control and is ap-
plied in the fall after the last cutting. The herbicide
2,4-DB controls many broadleaf weeds in established
alfalfa; it should be applied when the weeds are small
and actively growing. Pursuit may be applied
postemergence to established alfalfa stands to control
certain broadleaf and grass weed species. Refer to

Tables 16.08 and 16.09 for additional remarks and
weed control suggestions.

Once grass weeds have emerged, they are particu-
larly difficult to control in established alfalfa. Poast
Plus or Select may be used in established alfalfa for
postemergence control of annual and some perennial
grasses. Optimal grass control is achieved if Poast
Plus is applied when grasses are small and before the
weeds are mowed.

Table 16.08 outlines current suggestions for weed
control options in legume forages. The degree of con-
trol often varies with weed size, application rate, and
environmental conditions. Select the correct herbicide
for the specific weeds to be controlled (Table 16.08). Re-
fer to Table 16.10 for grazing and harvesting restrictions
for forage legumes. Always consult the herbicide label
for specific informahon about using a given product.

AUTHORS

A. Hager

Department of Crop Sciences

with contributions by
M. McGlamery

Department of Crop Sciences

Chapter 17.

Management of Field Crop Insect Pests

This chapter focuses on pest management guidelines
for insects that attack com, soybeans, alfalfa, and
wheat in Illinois. Practical, nonchemical control mea-
sures that have proven effective are discussed and
strongly encouraged. However, insecticides often are
the only efficient tool for responding to insect pest
outbreaks. We recommend that insecticides be used
only to supplement a completely integrated pest man-
agement (IPM) program that also includes the use of
host plant resistance and cultural, mechanical, and
biological control tactics.

IPM has been defined as a comprehensive ap-
proach to pest control that uses combined methods to
reduce pest densities to tolerable levels while main-
taining a quality environment. In this context, insecti-
cides should be used only after all other effective in-
sect control alternatives have been considered.
Although the use of insecticides has become a stan-
dard practice for reducing insect densities, certain
problems arise from the sole reliance on insecticides,
such as insect resistance to insecticides and threats to
the environment and public health. A balanced mix of
pest management tactics should avert these types of
problems. More than ever, IPM is vital for both a sus-
tainable agriculture and environmental protection.

Scouting and Economic Thresholds

Two principles of an insect management program are
scouting fields and basing control decisions on eco-
nomic thresholds. Growers must understand the im-
portance of these principles and incorporate both
regular scouting and the use of economic thresholds
into their crop management plans.

A scouting trip through a field reveals which insect
pests are present, the stage of growth of the insect
pests and the crop, whether the insects are parasitized
or diseased, whether an infestation is increasing or
decreasing, and the condition of the crop, all of which
can be used to determine the need for a control mea-
sure. A scouting program also requires accurate, writ-

ten records of the field location, current field condi-
tions, a history of insect pest infestations and insecti-
cide use, and a map locating infestations. Records en-
able a grower to keep track of each field and antici-
pate or diagnose pest problems and crop conditions.

Insect pests can be monitored in several ways. Usu-
ally the insects are counted or the amount of crop in-
jury is estimated. Counts of insects commonly are ex-
pressed as number per plant, per foot of row, per
sweep, or per unit area (square foot or acre). Estimat-
ed crop injury usually is expressed as a percentage.
Methods of scouting for insects include collecting in-
sects with a sweep net, shaking the crop foliage and
counting dislodged insects, counting insects on
plants, and capturing insects with traps.

Representative surveys of a field are essential. A
field is a unit of land that has been treated the same
way agronomically (same planting date, same vari-
ety, same crop rotation, same fertility level, etc.). For
example, if a 40-acre field has been planted to two
corn varieties, 20 acres planted to each variety, the
two 20-acre units should be scouted as different fields.
Fields should be scouted at least weekly, and inspec-
tions should be made in several representative areas
of each field. Avoid scouting the edges of a field un-
less specifically looking for an insect that first invades
field edges (grasshoppers, spider mites, stalk borers).

Results from a scouting trip through a field should
reveal numbers of insect pests or the percentage of
plants that are injured by the pests. A decision to use
an insecticide should be made only when an insect
population has reached or exceeded an economic
threshold — that level of a pest population at which
control should be implemented to prevent economic
loss (that is, the projected cost of damage is greater
than the cost of control). Economic thresholds may be
expressed as numbers of insects (such as average
number of bean leaf beetles per foot of row) or as a
level of damage (5 to 10 percent of soybean pods in-
jured within a field).

17 • MANAGEMENT OF FIELD CROP INSECT PESTS

211

Environmental and econoniic conditions are un-
stable, so several factors may alter an economic
threshold: value of the crop (as the price paid for the
crop increases, the economic threshold decreases);
cost of control (as the cost of control increases, the
economic threshold also increases); and crop stress (as
the amount of stress on a crop increases, the economic
threshold may decrease). For example, an insecticide
may be justified economically for an insect pest den-
sity that is below the economic threshold if the crop is
under stress from a lack of moisture, severe weed
pressure, a plant disease, or a lack of proper fertility.
Economic thresholds should be adjusted to reflect
changes in market prices, cost of control, and crop
stress.

Although economic thresholds generally have re-
duced excessive use of insecticides, economic thresh-
olds do not reflect any of the potential environmental
hazards associated with a pesticide treatment, such as
reduced densities of beneficial insects, pesticide resi-
dues on food products, pesticide contamination of
surface and groundwater supplies, and wildlife kills.
Before deciding to apply an insecticide, a grower
should weigh the risks to human health and safety
and environmental risks against the economic ben-
efits. If a particular insecticide poses significant risks
to human health or the environment, a grower should
select another product or another tactic.

Insect Management Tactics

The judicious use of insecticides is accomplished most
often by blending insect control tactics. Insect man-
agement programs may include cultural, mechanical,
physical, biological, genetic, regulatory, and chemical
control methods. Some common tactics used in field
crop insect-management programs in Illinois are
(1) planting insect-resistant crop varieties; (2) rotating
crops; (3) changing tillage practices; (4) altering plant-
ing or harvest times; (5) conserving biological control
agents; and (6) applying insecticides.

Insect-resistant crops. Certain varieties of field
crops offer some level of resistance or tolerance to
specific insect pests. For example, conventional breed-
ing efforts have produced com hybrids with degrees
of tolerance or resistance to leaf feeding by first-gen-
eration European com borers and sheath-collar feed-
ing by second-generation borers. Resistant or tolerant
varieties also are available for the following insects:
com rootworms in com; bean leaf beetle, Mexican
bean beetle, potato leafhopper, and twospotted spider
mite in soybeans; Hessian fly in wheat; and alfalfa
weevil, aphids, and potato leafhopper in alfalfa.

Recent developments in genetic engineering have
produced crop varieties that impart resistance to in-

sect pests. Specifically, gene transfer techniques have
been used to produce com plants that contain a gene
taken from the bacterium Bacillus thuringiensis, often
abbreviated as Bt. The Bt gene has been inserted di-
rectly into the com genome. The gene produces a
crystal protein that is toxic to certain caterpillars, in-
cluding the European com borer and southwestern
com borer. After the caterpillar ingests the protein, the
crystal breaks down and releases a toxin that attacks
the gut lining. The insects stop feeding within a few
hours and die within a couple of days. The presence
of this Bt toxin in com provides season-long protec-
tion against European com borers and southwestern
com borers and some protection against com ear-
worms and stalk borers. "Bt-com" offers an opportu-
nity to control one of our most economically damag-
ing com insect pests without the use of conventional
insecticides. Biotechnology likely will continue to pro-
duce crop hybrids that are resistant to many of our
most important insect pests of field crops.

As a first step in managing insect pests in field
crops, consider resistance or tolerance when selecting
a crop variety. At the very least, solicit from the seed
dealer information about the variety selected and its
ability to resist or tolerate insect infestations.

Crop rotation. Crop rotation greatly influences
whether a soil insect problem may occur. The complex
of insect pests changes according to the types of crops
rotated, the sequence of the crop rotation, and the
amount of time devoted to the production of a par-
ticular crop before planting a new crop. The brief
summaries that follow should help producers deter-
mine the likelihood of an insect outbreak in different
crop rotation schemes.

Corn after soybeans. The potential for soil insect
problems in com after soybeans generally is low, and
the use of a soil insecticide typically is not recom-
mended. This recommendation remains true for all
areas of Illinois except east-central Illinois where
western com rootworm larvae recently have injured
roots in fields of com planted after soybeans (see
"Com rootworms" on page 216).

Corn after corn. The potential for rootworm damage
exists wherever com is planted after com in Illinois.
Rootworn\ soil insecticides are applied to approxi-
mately 90 percent of continuous com acreage, even
though economic infestations generally occur in only
half of all continuous com fields.

Corn after legumes. Cutworms, grape colaspis, white
grubs, and wireworms occasionally damage com
planted after clover or alfalfa. Adult northern com
rootworms sometimes are attracted to legumes or to
weed blossoms in legumes for egg laying, especially
in years when beetles are forced to leave adjacent

212

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

fields of drought-stressed com to seek food. The use
of a seed treatment is recommended, but producers
may consider the use of a soil insecticide for this crop-
ping sequence.

Corn after small grain. There is a slight potential for
injury caused by wireworms, seedcom beetles, and
seedcom maggots in com after small grain, particu-
larly wheat. In most instances, a diazinon + lindane
planter-box seed treatment is adequate. However, ex-
cessive weed cover in small-grain stubble may have
been attractive to northern com rootworm beetles for
egg laying if the adults moved from adjacent fields of
drought-stressed com.

Corn after grass sod. Com billbugs, sod webworms,
white grubs, and wireworms may cause stand reduc-
tions when com is planted after bluegrass, brome, fes-
cue, rye, or wheat. If a producer plants com into an
established field of grass sod, an insecticide, applied
either before or at planting, should be considered for
the control of wireworms and white grubs. Rescue
treatments applied after the damage is noticed are not
effective. If a stand is being thinned severely by wire-
worms or white grubs, the only options are to accept
the reduced stand or replant and apply an insecticide
during replanting.

Corn after sorghum. A planter-box seed treatment of
diazinon or diazinon + lindane will protect the seeds
from seedcom maggots.

Tillage. The type of equipment and the timing (fall
or spring), depth, and frequency of tillage operations
can influence the survival of some insect species. Till-
age operations may alter soil temperature, soil mois-
ture, aeration, organic matter content, and bulk den-
sity of the soil, each of which may have a direct effect
on some insects' survival and development. Often of
greater importance to an insect population are the in-
direct effects occasionally associated with certain till-
age systems. For example, poor weed control in some
tillage systems increases the potential for infestation
of some insects (black cutworms, stalk borers). How-
ever, sweeping predictions about how all insects re-
spond to a certain tillage practice are not appropriate.

Insects that may cause problems in mulch-till,
ridge-till, or no-till com can be divided into two cat-
egories: soil insects and foliage-feeding insects. Soil
insects include billbugs, com rootworm larvae, cut-
worms, seedcom beetles, seedcom maggots, white
grubs, and wireworms. Foliage-feeding insects in-
clude armyworms, brown and onespotted stink bugs,
European com borers, and stalk borers.

The insects most affected by changes in tillage
practices are those that overwinter in the soil and be-
come active during the early stages of crop growth.
Soil- and litter-dwelling insects are affected more than

the foliage-feeding insects. In most instances, a
greater diversity of insects is present in reduced-
tillage systems, but this greater diversity does not al-
ways result in predictable increases or decreases in
crop injury because both pests and their natural en-
emies respond to tillage practices.

Much less is known about the influence of various
cultural practices on insects in soybeans. Most soy-
bean insect pests are defoliators or pod feeders. They
often are very mobile; some immigrate from other re-
gions of the country, and most move readily from
field to field. The effect of a single soybean producer's
tillage practices on the potential for injury caused by
defoliators is insignificant. However, slugs, which are
not insects, occasionally cause significant injury to no-
till soybeans. Densities of slugs are often highest in
no-till systems where crop residue is greatest; their
densities are lowest where no residue is present. Due
to the residue cover and inclusion of soybeans in no-
till rotational systems, slug problems are expected to
increase as conservation tillage becomes more common.

Altering planting or harvest times. The time of
planting influences the development of infestations of
several pests on several crops. For example, European
com borer moths laying eggs for the first generation
are attracted to fields with the tallest com. Conse-
quently, com that is planted early should be moni-
tored closely during June and early July for signs of
whorl feeding by com borer larvae. However, late-
planted com fields are most susceptible to economic
infestations of the second generation of com borers.

The time of planting com also affects the potential
for infestation by black cutworms and com root-
worms. Early planted com usually escapes infesta-
tions by black cutworms but supports infestations by
com rootworm larvae. Late-planted com is more
likely to be attacked by black cutworms but may es-
cape severe root-feeding injury caused by rootworm
larvae. However, late-planted com also attracts egg-
laying rootworm beetles late in the season, which in-
creases the potential for larval injury the next year.

For some specific insect pests, altering planting or
harvest dates can be used as a management tactic
without adversely affecting crop performance. For ex-
ample, wheat can be planted after "fly-free dates" to
control Hessian fly (see "Hessian fly" on page 225),
and alfalfa can be harvested early to manage alfalfa
weevils or potato leafhoppers.

Biological control. Certain insects and diseases
naturally suppress populations of pest insects without
our help. For example, European com borer densities
are often reduced by Beauvaria bassiana, a fungus, or
by Nosema pyrausta, a protozoan. Natural control by
predators, parasitoids, and pathogens may alter pest-

17 • MANAGEMENT OF FIELD CROP INSECT PESTS

213

management decisions. An abundance of predators or
parasitoids or a significant percentage of diseased
pests may suggest that an insecticide application is
not necessary. Producers should make every effort to
conserve natural enemies by avoiding unnecessary
applications of insecticides.

Through a process called applied biological control,
predators, parasitoids, or disease pathogens are intro-
duced into a field. Although considerable research has
been conducted, the introduction of beneficial insects
and disease pathogens into com and soybean fields to
control pest insects has not been very effective. Field
crop environments change constantly, so beneficial or-
ganisms have a difficult time becoming established.

The use of microbial insecticides offers more poten-
tial within an IPM program. Microbial insecticides are
made of microscopic living organisms (viruses, bacte-
ria, fungi, protozoa, or nematodes) or the toxins pro-
duced by them. These insecticides can be formulated
to be applied as sprays, dusts, or granules. Their chief
advantage is an extremely low toxicity to nontarget
animals and humans. The most familiar microbial in-
secticides (DiPel and similar products) are those that
contain toxins produced by Bacillus thuringiensis.

Applying insecticides. Insecticides should be used
only after all other effective insect control alternatives
have been explored. The decision to use an insecticide
should be based upon (1) information obtained from
scouting; (2) knowledge of economic thresholds; and
(3) an awareness of the potential benefits and risks as-
sociated with a treatment. If used improperly, insecti-
cides can cause detrimental effects to the applicator,
the crop, or the environment. Insecticides can provide
effective control, but they should be used judiciously
and in combination with nonchemical methods that
can be incorporated into the cropping system. After a
decision to use an insecticide has been made, several

i aspects of the insecticide should be considered: Is it
labeled for control of the target insect? Is it effective
against the target insect? What is the rate of applica-
tion? How toxic is the insecticide? Is it classified as
general use or restricted use? What environmental

I hazards are posed by use of the insecticide? What hu-
man health hazards are posed by use of the insecti-
cide? Answers to these questions will help producers
select the most appropriate insecticide for the use in-

I tended and the current conditions.

Key Field Crop Insect Pests

This section contains discussions of some of the key
insect pests in field crops in Illinois, including de-
scriptions, life cycles, current economic thresholds,
and current management suggestions. However, a

complete list of insecticides that can be used to control
all of the potential insect pests has not been included.
Tables that provide specific information about insecti-
cides and their use for all of the insect pests that at-
tack com, soybeans, alfalfa, grain sorghum, small
grains, and pasture are published in Chapter 1, "In-
sect Pest Management for Field and Forage Crops," in
the current year's edition of the Illinois Agricultural
Pest Management Handbook. Color photographs and
more information about scouting are published in the
Field Crop Scouting Manual.

Insect Pests of Alfalfa

Due to its lush growth, alfalfa is an excellent habitat
for many insects: species destructive to alfalfa and
other crops; species that inhabit the alfalfa but have
little or no effect on the crop; pollinating insects; inci-
dental visitors; and predators and parasitoids of other
insects. Many species overwinter in alfalfa because it
grows perenially.

More than a hundred species of insects and mites
are capable of reducing alfalfa yield, impairing forage
quality, or reducing the vitality and longevity of the
crop. However, only two insect species are considered
key pests: the alfalfa weevil and the potato leafhopper.

Alfalfa weevil

Description. The mature alfalfa weevil larva is about
% inch long and has a black head. The curved body of
the larva is green, with a white stripe along the center
of the back. The adult alfalfa weevil is about V4 inch
long and has a distinct snout. It is light brown, with a
darker brown stripe along the center of the back.

Life cycle and damage. In southern Illinois, when
temperatures permit, adult weevils lay eggs through-
out the fall and winter and into the spring. Because
eggs begin to hatch about the time alfalfa is beginning
its spring growth, larval injury occurs early in the
spring. In northern Illinois, most eggs are deposited
in the spring. By the time larvae emerge, alfalfa is
usually 6 to 10 inches tall and can tolerate more wee-
vil feeding than the southern crop.

Newly hatched larvae feed in the growing tips.
An early sign of injury is pinholes in newly opened
leaves. As larvae grow larger, they shred and skel-
etonize the leaves. Heavily infested fields appear
frosted because of the loss of green leaf tissue.
Anything that slows spring alfalfa growth increases
the impact of weevil injury.

When weevil larvae finish feeding, they spin
netlike cocoons on the plants or in soil debris and pu-
pate. After several days, the adults emerge and feed
on alfalfa for a few weeks. They cause leaves to ap-
pear "feathered," and they scar the stems of the alfalfa

214

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

plants. In addition, both surviving larvae and newly
emerged adults may affect regrowth after the first cut-
ting. They remove early shoot growth, depleting food
reserves in the roots and reducing the stand.

The adults eventually leave alfalfa fields to enter
summer dormancy in sheltered sites. In the fall, most
adults return to alfalfa, where they feed for a while
before "hibernating." In southern counties, the adults
mate and lay eggs, and both adults and eggs overwin-
ter. Alfalfa weevils complete one generation each year.

Management suggestions. The key to effective man-
agement of alfalfa weevils is timely monitoring.
Growers in southern and central Illinois should in-
spect their fields closely in April, May, and June.
Growers in northern counties should look carefully
for larval injury during May and June. All growers
should examine the stubble after the first cutting of
alfalfa has been removed. Treatment for control of al-
falfa weevils on the first crop of alfalfa may be war-
ranted when there are 3 or more larvae per stem and
25 to 50 percent of the tips have been skeletonized,
depending on the height of the crop and the vigor of
growth. Tall, rapidly growing alfalfa can tolerate con-
siderable defoliation without a subsequent loss in
yield. After harvest, control may be warranted when
larvae and adults are feeding on more than 50 percent
of the crowns and regrowth is prevented for three to
six days.

Parasitic wasps and a fungal disease may regulate
alfalfa weevil populations in the spring. When scout-
ing for alfalfa weevils, look for signs of parasitism
and for diseased weevils (discolored, moving slowly,
or moving not at all). When natural enemies and
pathogens suppress weevil numbers, insecticide treat-
ments may not be necessary.

Potato leafhopper

Description. The adult potato leafhopper is a green,
wedge-shaped insect about Vs inch long. Nymphs re-
semble the adults but are smaller and wingless. Both
have piercing, sucking mouthparts and are very ac-
tive. The adults hop or fly, and the nymphs move rap-
idly, either sideways or backward, when disturbed.

Life cycle and damage. Potato leafhoppers do not
overwinter in Illinois. Prevailing spring winds carry
adults northward from the Gulf Coast states, and leaf-
hoppers first appear in alfalfa fields in Illinois in late
April or early May. The adults mate and begin laying
eggs in stems and leaf veins. Nymphs emerge in about
a week and begin feeding. Several generations may oc-
cur before cold temperatures kill the leafhoppers.

Both nymphs and adults suck fluids from alfalfa
plants. Nymphs cause more damage than adults. Ini-
tial injury is characterized by a V-shaped yellow area
at the tips of the leaflets, often called "hopperbum" or

"tipbum." As the injury progresses, the leaves turn
completely yellow and may turn purple or brown and
die. Severely injured plants are stunted and bushy.
Leafhopper injury also causes plants to produce more
sugars and less protein and vitamin A, resulting in
lower-quality alfalfa. If leafhoppers deplete root re-
serves of the late-season growth of alfalfa, the plants
will be less hardy and may not survive the winter.

Injury by potato leafhoppers often is confused with
boron deficiency, plant diseases, or herbicide injury.
The presence of the insect often is the key to diagnos-
ing the problem.

Management suggestions. Sampling with a 15-inch-
diameter sweep net is the best method for monitoring
populations of potato leafhoppers in alfalfa. Economic
thresholds are based on the number of leafhoppers
per sweep of the sweep net.

When alfalfa is regrowing after a cutting, scouting
for leafhoppers is critical. Tender, regrowing alfalfa is
very susceptible to leafhopper injury. Taller, more ma-
ture alfalfa can tolerate more leafhopper injury, and
the economic thresholds vary accordingly. An insecti-
cide may be warranted for alfalfa up to 3 inches tall
when there is an average of 0.2 leafhopper per sweep.
The economic thresholds for 3- to 6-inch alfalfa, 6- to
12-rnch alfalfa, and alfalfa taller than 12 inches are 0.5,
1, and 2 leafhoppers per sweep, respectively.

Sampling is very important. By the time symptoms
of potato leafhopper injury appear, considerable yield
and nutritional quality may have been lost. Monitor-
ing should begin after first harvest and continue on a
regular basis throughout the summer.

Within the past couple of years, some seed compa-
nies have released glandular-haired alfalfa that is re-
sistant to potato leafhoppers. Glandular-haired alfalfa
seems to be resistant to moderate densities of leafhop-
pers. However, it does not seem to prevent leafhopper
infestations during the first year of seeding, during
seedling regrowth immediately after cutting, or dur-
ing years when leafhopper infestations are severe.
The overall utility of these resistant alfalfa varieties
has yet to be determined.

Insect Pests of Corn

Insects that attack com generally are separated into
two categories: those that attack the plant below
ground and those that attack the plant above ground.
Populations of below-ground insects are difficult to
predict; responsive "rescue" treatments are ineffective
for most. Consequently, many com producers prevent
infestations with crop rotation or application of soil
insecticides. A list of soil insecticides that are sug-
gested for control of com rootworms, cutworms, wire-
worms, and white grubs is presented in Table 17.01.

17 • MANAGEMENT OF FIELD CROP INSECT PESTS

Table 17.01. Insecticides Suggested for Control of Some Soil Insects in Illinois

215

Insecticide

Rootworms

Cutworms

Wireworms

White grubs

*Ambush 2E
*Asana XL
*Aztec 2.1G
*Counter CR
*Force 3G

*Fortress 5G'
Lorsban 15G
Lorsban 4E
*Pounce 1.5G
*Pounce 3.2EC

*Regent 4SC
*Thimet 20G
*Warrior lEC
*Warrior T

* Use restricted to certified applicators only.

— = The most economical rate and application of this insecticide is not labeled for control of this insect, or labeled only for
suppression or aid in control of the insect.

• = The most economical rate and application of this insecticide is labeled for control of this insect. Refer to label for rate,
timing, and placement of application.

^Available only in the SMARTBOX, a closed handling and application system.

Most below-ground insect pests in Illinois feed on un-
derground parts of the com plants. Com rootworm
larvae feed on and prune the roots; white grubs and
grape colaspis larvae feed on the root hairs and the
roots; wireworms, seedcom beetles, and seedcom
maggots attack the planted seeds; wireworms also
will tunnel into the underground portion of the stem.
Young cutworms feed on the leaves of seedling com
plants; older cutworms cut off the plants at, just be-
low, or just above the soil surface. Webworms cause
injury similar to that caused by cutworms. Hop vine
borers drill into the underground portion of the stem
and tunnel upward. Billbugs and stink bugs feed at
the bases of the cornstalks; billbug larvae feed inside
the lower portion of the stalk.

Above-ground insect pests include stalk-boring in-
sects such as the European com borer, southwestern
com borer (southern Illinois), and stalk borer, and in-
sects that feed primarily on the leaves, such as army-
: worms, fall armyworms, flea beetles, and grasshop-
pers. Chinch bugs, com leaf aphids, spider mites, and
i thrips suck the fluids from the plants at different
I times of the growing season. Com rootworm beetles,
Japanese beetles, and woollybear caterpillars clip com
silks, interfering with pollination. Larvae of com ear-
worms, European com borers, and fall armyworms
feed on the ear.

Black cutworm

Black cutworms occur sporadically as pests of com in
Illinois. When an outbreak develops, however, the re-
sulting damage may be extensive. Black cutworms
feed on seedling com, which is very susceptible to
any type of injury.

Description. Black cutworm larvae vary in color
from light gray to black, and are about V/i inches long
when fully grown. Numerous convex skin granules of
different sizes give the cutworm a somewhat "greasy"
and rough appearance. The moths (adults) have a ro-
bust body and a wingspan of about IVi inches. They
are dark gray, with a black, dagger-shaped marking
toward the outer edge of the forewing.

Life cycle and damage. Black cutworms probably do
not overwinter in large numbers in Illinois. Evidence
suggests that the moths fly into the Midwest from
southern states early in the spring. Some people use
sticky traps baited with synthetic female sex phero-
mone to monitor moth flight in the spring. Results
from trap captures may help timing of insecticide ap-
plications, if necessary.

Female moths lay eggs primarily on weedy vegeta-
tion, preferably on winter armuals. After the eggs
hatch, the small larvae feed on these host plants.
When herbicides or tillage destroys the weeds, the lar-
vae begin feeding on com seedlings.

216

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

The larvae pass through six or seven instars (stages
of larval development). Their rate of development de-
pends upon temperature: the larvae develop more
quickly when the weather is warm. The first three in-
stars are very small, and the larvae feed on the com
leaves. This injury, which is not economic, appears as
small holes or bites in the leaves. The fourth through
seventh instars cut the plants off at or just below the
soil surface. If the soil is dry and crusted, the larvae
remain below the surface and drill into the base of the
plant. If the growing point is destroyed or the plant is
cut below the growing point, the plant will not sur-
vive. Large numbers of black cutworms can drasti-
cally reduce the plant population in a field.

After the larvae finish feeding, they pupate. The
moths then emerge from the soil and begin mating
and laying eggs for the next generation. There may be
three or four generations each year, but the later gen-
erations rarely injure taller com.

Management suggestions. Although some growers
apply soil insecticides to prevent an infestation of
black cutworms, it usually is not justified economi-
cally. Because black cutworm populations are so spo-
radic and difficult to predict, a wait-and-see approach
to cutworm management is recommended.

Field monitoring is the key to effective manage-
ment of black cutworms. To determine the need for a
rescue treatment, scout the fields during plant emer-
gence, particularly those considered to be at high risk.
Check the field for leaf feeding, cut plants, wilted
plants, and missing plants. A rescue treatment may be
warranted if 3 percent or more of the plants are cut
and cutworms are present. A single cutworm will cut
three or four plants if the plants are in the two-leaf
stage or smaller. After com plants reach the four-leaf
stage, a single cutworm will cut only one or two
plants during the remainder of its larval stage.

Control of cutworms may be poor regardless of the
insecticide used if the topsoil is dry and crusted and
the worms are feeding below the soil surface. Cut-
worm control may be enhanced by cultivating or run-
ning a rotary hoe over the field before or after spray-
ing. This disruption causes the worms to move
around and come into contact with the insecticide.
Insecticides registered for control of black cutworms
are presented in Table 17.01.

Com rootworms

Com rootworms are the most economically important
pests of com in Illinois. Com rootworms include three
species: western, northern, and southern. Southern
com rootworms do not overwinter in the Midwest,
however, so the western and northern species are the
only injurious species in Illinois.

Description. The background color for both male
and female western com rootworms is yellow-tan, but
the two sexes differ somewhat in their markings. On
males, nearly the entire front half of each wing cover
is black; only the tips of the wing covers are yellow-
tan. Females are slightly larger and have three distinct
black stripes on the wing covers, one near each outer
edge and one in the middle. Northern com root-
worms have no distinct markings. Newly emerged
northern com rootworms are cream or tan in color,
but they become green as they age. Both species are
about Va inch long. The larvae of both species are
creamy white with a brown head and tail plate.

Life cycle and damage. Western and northern com
rootworms overwinter as eggs in the soil. Eggs begin
hatching in May. If com has been planted in the field,
the larvae feed on the roots. Rootworms survive only
on the roots of com and a few grasses. They cannot
survive on the roots of soybeans and other broadleaf
plants.

Larvae chew on and tunnel inside or along the
roots. As they feed, the larvae prune roots back to the
stalk. Extensive feeding weakens the root system. In-
jured plants cannot take up water and nutrients effi-
ciently and are susceptible to lodging. Yield losses are
a result of both root pruning and lodging.

When the larvae finish feeding, they pupate within
small earthen cells. The pupa transforms into the
adult stage in about one week, and beetles begin
emerging in late June or early July.

Rootworm beetles will feed on com leaves and
weed blossoms but prefer com silks and pollen. They
clip fresh, green silks off at the ear tip, an injury that
may interfere with pollination, so some kernels never
form. An average of 5 or more beetles per plant is
usually sufficient to cause economic damage if they
are clipping silks to within V2 inch of the ear tip.

Beetles mate in July and August, and the females
lay eggs in cornfields in the top 4 inches of soil. West-
em and northern com rootworms complete one gen-
eration each year.

Management suggestions. Acorn-soybean rotation usu-
ally provides excellent control of com rootworm lar-
vae because the larvae survive only on com roots;
rootworms complete only one generation each year;
and rootworm beetles, except for western com root-
worm adults in east-central Illinois, generally do not
lay eggs in soybeans. A corn-soybean rotation may
fail to control com rootworms when volunteer com
plants in a soybean field attract egg-laying beetles or
when rootworms exhibit prolonged diapause, a bio-
logical phenomenon that allows some rootworm eggs,
primarily those of northern com rootworms, to re-
main dormant in the soil for more than one winter.

17 • MANAGEMENT OF FIELD CROP INSECT PESTS

217

Also, in some east-central Illinois counties, western
com rootworms have adapted to a corn-soybean rota-
tion and are prone to lay eggs in both soybeans and
com.

Since 1993 the incidence and severity of com root-
worm larval injury in first-year com fields (primarily
com rotated with soybeans) throughout much of east-
central Illinois have increased. Producers in the fol-
lowing counties have been affected most often:
Champaign, Ford, Grundy, Iroquois, Kankakee,
Livingston, McLean, Vermilion, and Will. Producers
in the following counties may be at some risk: Clark,
Coles, DeWitt, Douglas, Edgar, Kendall, LaSalle, Lo-
gan, Macon, Moultrie, Peoria, Piatt, and Woodford.
Growers throughout the northern half of Indiana and
in southern Michigan and western Ohio also have re-
ported similar rootworm problems in com rotated
with soybeans.

Producers in east-central Illinois who have experi-
enced rootworm larval injury in first-year com and
have found western com rootworm adults in adjacent
soybean fields should consider using a soil insecticide
in com rotated with soybeans. An economic threshold
for adult western com rootworms in soybeans has
been developed to help producers determine whether
a soil insecticide is needed to protect com the next
year. Growers can sample for western com rootworm
adults by placing 12 unbaited Pherocon AM traps
(yellow sticky traps) systematically throughout the in-
terior of a soybean field. If the number of western
com rootworm adults from the last week of July
through the third week of August exceeds an average
of two to seven beetles per trap per day, economic
damage caused by larvae to com roots the next year is
likely. The lower threshold (two beetles per trap per
day) suggests a level of root injury that may be eco-
nomic. The higher threshold (seven beetles per trap
per day) suggests a level of root injury that likely will
be economic. A planting-time application of a soil in-
secticide to com should be considered if numbers of
western com rootworm adults exceed one or the other
of these thresholds in soybeans during the previous
summer. More detailed information about western
com rootworms is provided in Insect Information 1:
Western Corn Rootworm, a fact sheet published by the
Department of Crop Sciences at the University of
Illinois. The fact sheet is also available on the Web at
<http://www.aces.uiuc.edu/~ipm/field/com/insect/
wcr.html>.

Growers outside of east-central Illinois are encour-
aged not to use a soil insecticide on first-year com for
rootworm control. As of 1998, the new "strain" of
western com rootworm had not been detected in
counties other than the 22 mentioned previously.

Corn planted after corn is susceptible to injury by
com rootworm larvae, depending upon the size of the
rootworm population. Most producers who grow
com after com usually apply a soil insecticide at
planting to protect the com roots from larval-feeding
injury. Most growers apply granular insecticides in ei-
ther a 7-inch band directly over the row or directly
into the seed furrow (Tables 17.01 and 17.02). Some
liquid formulations of soil insecticides are also labeled
for control of com rootworm larvae (Tables 17.01 and
17.02). Trials conducted by entomologists at the Uni-
versity of Illinois have revealed that Aztec, Counter,
Force, and Lorsban provide the most consistent con-
trol of com rootworm larvae.

By counting western and northern com rootworm
beetles from mid-July into September, growers can
figure out the potential for rootworm larval injury the
following year. If the average is 0.75 or more beetles
per com plant for any sampling date, plan to rotate to
a nonhost crop, or apply a rootworm insecticide if
com will be planted the following year. If the average
is fewer than 0.75 beetle per com plant, the probabil-
ity of economic damage the next year is low, and a
soil insecticide is not necessary.

Another com rootworm management tactic is to
control the adults in July or August or both months to
prevent them from laying eggs. If this tactic works, a
soil insecticide is not needed the following year. Both
conventional insecticides and insecticide baits are
used to control the beetles before they lay eggs. How-
ever, the prerequisites for a successful beetle-suppres-
sion program are complex. It is necessary to identify
both species (western and northern), distinguish be-
tween the sexes, and determine whether the females
are ready to lay eggs. Frequent scouting trips and pre-
cise scouting techniques also are required.

An adult management approach to prevent egg
laying by western com rootworms in soybeans cur-
rently is not recommended. Until sampling strategies
and economic thresholds can be developed, growers
are encouraged not to attempt this strategy to prevent
corn rootworm larval injury in com planted after
soybeans.

Spraying to kill adult western com rootworms in
soybeans one year and also treating com with a soil
insecticide to control larvae the next year is strongly
discouraged. Treating two stages (adults and larvae)
of the same insect is a quick way to develop insecti-
cide resistance within the insect population.

Planning your rootworm management program. A
management plan for rootworms should be long-
range (not a year at a time) and include crop rota-
tion, soil insecticides if needed, and scouting to de-
termine the need for rootworm control.

218

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 17.02. Soil Insecticides for Rootworm Control in Illinois, 1999

Time of application

Ozof

product per

1,000 ft of row

Amount of product per acre^

Insecticide

40" rows

38" rows

36" rows

30" rows

*Aztec 2.1G
Counter CR
*Force 3G

At planting

At planting or cultivation

At planting

6.7

4-5

5.51b

4.91b

3.3^.1 lb

5.81b

5.21b

3.4^.3 lb

6.11b

5.41b

3.6^.5 lb

7.31b

6.51b

4.4-5.5 lb

*Fortress 5G''
*Furadan 4F
Lorsban 15G

At planting

At cultivation

At planting or cultivation

2.5 fl oz

2.51b

2pt

6.51b

2.61b

21/8 pt

6.91b

2.75 lb
2y4pt
7.31b

3.25 lb
2y4pt
8.71b

Lorsban 4E
*Regent 4SC
Thimet 20G

At cultivation

At planting

At planting or cultivation

2.5 fl oz

0.24 oz

2pt
3.1 oz
4.91b

2Vs pt
3.3 oz
5.21b

2y4 pt
3.5 oz
5.41b

2y4 pt
4.2 oz
6.51b

* Use restricted to certified applicators only.

^ Do not exceed the following amounts of specific products per acre per season: 7.3 lb of Aztec 2.1G; 6.5 lb of Counter CR;
13.5 lb of Lorsban 15G; 4.2 oz of Regent 4SC. The minimum row spacing of com to which Thimet 20G can be applied is 30 in.
''Available only in the SMARTBOX, a closed handling and application system.

• Alternate com with another crop when possible,
particularly in fields where rootworm beetles aver-
aged 0.75 or more per com plant last summer, or if
the soil insecticide did not adequately protect the
roots during the previous growing season.

• If the plan is to grow com after com and if root-
worm beetles averaged 0.75 or more per plant in
com after com or 0.5 per plant in first-year com
last summer, apply a rootworm soil insecticide at
planting time.

• If the plan is to grow com after soybeans in east-
central Illinois and if rootworm beetles averaged
two to seven or more per yellow sticky trap per
day in soybeans last summer, apply a rootworm
soil insecticide at planting time.

• Consider a cultivation-time application of a root-
worm soil insecticide if the intent is to plant in
early April or if the planting-time insecticide does
not provide adequate root protection.

• Scout for rootworm beetles from mid-July through
early September to determine the potential for root-
worm larval damage for the next growing season.

Other soil insects in com

In addition to com rootworms and black cutworms,
several other insects attack the underground portions
of the com plant early in the season. Wireworms and
seedcom maggots occasionally injure seeds and seed-
lings. White grubs and grape colaspis larvae feed on

the roots. Other insects — including billbugs, other
species of cutworms, and webworms — feed on com
seedlings at or just above or below the soil surface.

Wireworms. Most wireworm larvae are yellowish or
reddish brown, hard-shelled, and wirelike. However,
"soft-bodied" species are creamy white except for a
reddish brown head and tail section. Wireworms at-
tack the seed or drill into the base of the stem below
ground, damaging or killing the growing point.
Above-ground symptoms are wilted, dead, or weak-
ened plants and spotty stands. Several species of
wireworms attack com, and they may live for 2 to 5
years in the larval stage.

The adults (click beetles) prefer to lay eggs in
grassy fields or small-grain stubble. Injury in a field in
a particular year usually can be attributed to the con-
dition of the field two to four years earlier when the
adults were laying eggs. Fields with a com-soybean-
small-grain rotation and fields of com planted after
sod have the greatest potential for wireworm damage.

Although wireworm infestations are difficult to
predict, solar bait stations will trap wireworm larvae
early in the spring. Establish bait stations early in the
spring by placing a mixture of com and wheat seed in
a 4- to 6-inch hole in the ground, covering the seeds
with soil, then covering the soil with plastic. The plas-
tic warms the soil and induces germination. Wire-
worm larvae are attracted to the germinating seeds.
After the baits have been in the ground for 10 to 14
days, dig them up and count the wireworms. An aver-
age of one or more wireworms per bait station sug-

17 • MANAGEMENT OF FIELD CROP INSECT PESTS

219

gests that an economically damaging population is
present in the field. The grower can apply a soil insec-
ticide that controls wireworms.

White grubs. True white grubs have 3-year life
cycles. Peak levels of injury usually occur during the
year following large flights of May beetles, the adult
stage of white grubs. The beetles prefer to lay eggs in
ground covered with vegetation, for example, weedy
soybean fields, and sod. At least one species lays its
eggs in soybean fields.

The C-shaped white grub has a brown head and is
about an inch long. The grubs chew on the roots and
root hairs. Symptoms of white grub injury visible
above ground are irregular emergence, reduced
stands, and stunted or wilted plants. Injured plants
often cannot take up phosphorus efficiently, so the
plants may turn purple. Injury is generally spotty
throughout the field.

Rescue treatments applied after injury caused by
wireworms or white grubs are not effective. An insec-
ticide seed treatment protects the seed from attack by
wireworms but does not protect the seedling plant
from wireworms and white grubs.

Several soil insecticides are registered for the con-
trol of wireworms and white grubs (Table 17.01). The
percentage of fields affected in Illinois is so small, how-
ever, that the widespread use of soil insecticides to pre-
vent injury by these pests is not justified economically.

European com borer

The European com borer is one of the most destruc-
tive pests of com in the United States. The larvae tun-
nel inside the com plants and disrupt the flow of wa-
ter and nutrients to the developing ear. Extensive
tunneling may cause stalks to break or lodge. Tunnel-
ing in the ear shank may result in ear drop. Com
borer feeding also provides an avenue into the plant
for infection by stalk-rot organisms.

Description. Com borer larvae are cream- to flesh-
colored, with small, raised, dark spots (tubercles) on
each body segment. The head is dark brown. Full-
grown larvae are Va to 1 inch long. The female moth is
buff-colored, with wavy, olive-brown bands on the
wings and a wingspan of an inch. The male moth is
slightly smaller and darker than the female.

Life cycle and damage. Two or three generations of
European com borers occur every year, depending
upon the location in the state and the weather. The
third generation is most common in southern Illinois.
European com borers overwinter as mature larvae,
usually inside the stalk. Spring development starts
when temperatures exceed 50°F. The larvae begin pu-
pating in May, spend about two weeks in the pupal
stage, and emerge as moths in late May and June.

Moths laying eggs for the first generation seek the
tallest (earliest planted) com. The female lays eggs in
masses on the undersides of com leaves near the mid-
rib. Each mass contains 15 to 30 eggs (average 23) that
are flat and overlapping like the scales of a fish. Dur-
ing development, the eggs change from white to a
creamy color. Immediately before hatching, the black
heads of the larvae are visible through the shells.

After the eggs hatch, the tiny larvae begin to feed
on the leaf surfaces on their way to the whorl. The
small feeding scars look like "window panes." Their
feeding in the whorl results in "shot holes" in the
leaves. By the third stage (instar) of development, the
larvae begin tunneling into the leaf midribs; the
fourth and fifth (last) stages bore into the stalks.
When they finish feeding, the larvae pupate inside the
stalk. Transformation to the adult (moth) stage occurs
within the pupa, then the moth emerges to mate and
lay eggs. Com borers require three to four weeks to
develop from egg to adult.

Moths laying eggs for the second generation seek
later-maturing fields with fresh pollen and silks. They
usually deposit their eggs on the undersides of leaves
between the ear zone and the tassel. Newly hatched
larvae feed primarily on leaf-collar tissue and pollen
that accumulates in the leaf-collar areas. More mature
larvae tunnel into the stalks, ear shanks, and ears.

Injury to com by first- generation larvae is prima-
rily physiological. The yield loss caused by this gen-
eration is a result of interference with the transport of
nutrients and water in the stalk and leaves. Injury by
the second generation is both physiological and
physical. Most of the yield loss is caused by second-
generation com borers feeding in the stalks from just
before pollination until the ears are filled. Stalk break-
age, ear feeding, and ear drop also contribute to yield
reduction. Physical damage is amplified when stalk
rot weakens the plant.

Managing corn borers with Bt-corn. As a first step in
managing European com borers, growers should con-
sider selecting a hybrid that is resistant or tolerant.
Some "conventional" hybrids are resistant to first-
generation com borers, and others have some degree
of tolerance to com borer injury. Genetically trans-
formed hybrids that express the Bt gene {Bt-com) that
produces the toxic protein should provide season-
long control of European com borers. (See the section
on "Insect resistant crops.") However, the decision to
plant Bt'Com hybrids should be based on long-term
economic benefits, accompanied by considerations for
managing the potential for the development of com
borer resistance to the Bt gene.

Economic benefits of Bf-com will be realized only
during years when densities of com borers are large

220

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

enough to cause economic yield loss. In years when
com borers occur in subeconomic numbers, producers
will not realize an economic return on their invest-
ment in Bt-com. Therefore, growers must base their
decision to manage com borers with Bt-com on the
frequency of economic infestations of com borers in
their area. In areas where economic infestations of
com borers are relatively frequent (for example, 7 or 8
years out of 10), Bt-com is probably a wise invest-
ment. In areas where economic infestations of com
borers are relatively infrequent (for example, 2 or 3
years out of 10), growers should question whether
purchasing and planting Bt-com is necessary.

If com hybrids containing a Bt protein are planted
widely, European com borer populations eventually
will develop resistance to this very specific insect
toxin. Consequently, producers who grow B^com
should implement a resistance-management plan to
slow down the potential onset of resistance. Refuges
where com borers are not exposed to the Bt toxin are
the most practical resistance-management tactic. In
theory, high doses of the Bt toxin in Bf-com will kill
virtually 100 percent of the com borers. However, if
any borers survive in Bf-com, you want to ensure that
the surviving adults will mate with adults from areas
in which the borers are still susceptible to the Bt toxin.
These refuges should provide the source of suscep-
tible com borers.

Refuges include all fields of non-Bf-com and the
more than 200 species of plants (including several
crops and weeds) on which com borers can develop.
However, resistance-management strategies most of-
ten are based upon managed refuges, including entire
fields planted to non-B^com specifically to provide a
source of susceptible com borers. Alternatives include
planting a block of non-Bf-com within a field of Bf-
com or planting non-Bf-com in a designated percent-
age of rows throughout the field.

Refuge fields should be adjacent to fields of Bf-
com, and an in-field refuge should make up at least
25 percent of the field. Consult current published in-
sect management recommendations and newsletters
to obtain more specific recommendations for imple-
menting resistance-management tactics. North Cen-
tral Regional Extension Publication NCR 602, Bt-Corn
and European Corn Borer: Long-Term Success Through
Resistance Management, provides a detailed discussion
about this management strategy for com borers.

Managing corn borers with insecticides. Management
of European com borers in conventional hybrids be-
gins with scouting. Scout for first-generation com bor-
ers and injury during June. The percentage of plants
with whorl feeding and the average number of larvae
per infested plant are critical. Borers can be located by
unrolling the whorls of several plants.

Scout for second-generation com borers by count-
ing egg masses. Start checking when moth flight is
under way, usually from July through mid-August.

Entomologists have developed management
worksheets for both first- and second-generation Eu-
ropean borers to aid in making decisions about con-
trol. See the worksheets provided. The level of infesta-
tion (obtained from scouting), the expected yield, the
anticipated value of the grain, and the cost of control
are required to complete the worksheet. Enter these
data into the worksheet to calculate the gain or loss if
an insecticide is applied.

For example, assume a 40 percent infestation (40 of
100 plants with whorl-feeding injury caused by first-
generation borers) of early whorl-stage com, with an
average of 1.5 com borer larvae per plant. Expected
yield is 160 bushels per acre, and the com price is
$2.50 per bushel. Also assume 80 percent control with
granules and cost of control is $12 per acre. Enter this
information into the worksheet for first-generation
com borers, as indicated on the example worksheet.
Obviously, 40 percent infestation in this example does
not warrant a treatment ($9.60 per acre preventable
yield loss - $12 per acre control cost = -$2.40 per acre,
a loss if the field is treated). However, if the percent-
age infestation were 60 percent, control would be eco-
nomically justified ($14.40 per acre preventable yield
loss - $12 per acre control cost = $2.40 per acre, a
gain). Typically, if expected yield, price per bushel of
com, or anticipated percentage control increases, eco-
nomic justification for control is more likely. Con-
versely, if expected yield or price per bushel of com
decreases, or if cost of control increases, economic jus-
tification for control is less likely.

Much of the information and suggested guidelines
on the worksheets were derived from research trials
conducted over many years in numerous locations
throughout the Com Belt. However, if your experi-
ence or environmental conditions in your area suggest
that other figures might be more accurate, use them
instead. For example, if you believe you can achieve
90 percent control with a certain insecticide, use 90
percent instead of 80 percent (our average guideline).
If you estimate that survival is less or more than 20
percent (for whatever reason), multiply the percent-
age survival (decimal point) by 23 (average number of
eggs in a mass) to obtain an estimated average num-
ber of borers per plant.

For the most effective com borer control, apply
treatments soon after egg hatch to kill the young
larvae before they bore into the plant. The larvae
begin tunneling into stalks about 10 days after hatching.

Managing corn borers with tillage. Fall plowing and
shredding stalks significantly reduce the number of
com borers that overwinter within a given field.

17 • MANAGEMENT OF FIELD CROP INSECT PESTS

111

However, there will be little effect on the likelihood of
borer injury the following year if nearby fields are not
shredded or plowed. Moths that emerge from fields
not shredded or plowed may fly to nearby fields to
lay eggs, especially if the nearby fields were planted
earlier. As a consequence, fall plowing or stalk shred-
ding will not guarantee a reduction in problems in in-
dividual fields.

Insect Pests of Soybeans

Although many insects and mites feed on soybeans,
annual problems with insects and mites are infre-
quent in Illinois. Only a few reach outbreak propor-
tions in Illinois, usually in conjunction with extreme
weather patterns. Twospotted spider mites caused se-
rious yield reductions during the drought of 1988, for
example.

Some of the most common insect pests are defolia-
tors, including bean leaf beetles, blister beetles, grass-
hoppers, green cloverworms, Japanese beetles, thistle
caterpillars, webworms, and woollybear caterpillars.
General economic thresholds have been established
for these pests. Soybeans can tolerate considerable de-
foliation without yield reduction, although tolerance
to defoliation depends upon the stage of plant growth
and stress to the plant. While the plants are growing
and producing new leaves, and again after the seeds
are completely filled, soybeans can withstand consid-
erable leaf-feeding injury. Defoliation must exceed 30
to 40 percent before yield is affected. Soybean plants
are more susceptible to yield-reducing injury during
the blooming and pod-filling stages, so the economic
threshold during these stages is 20 percent defoliation.

A few pests of soybeans suck fluids from the
plants: potato leafhoppers, spider mites, and thrips.
Of these, only spider mites are capable of being a seri-
ous threat. Some insects, like cutworms, grape
colaspis, and seedcom maggots, attack the under-
ground parts of soybean plants. Pod feeders include
bean leaf beetles, com earworms, grasshoppers, and
stink bugs.

Bean leaf beetle

Description. Bean leaf beetles are about Vi inch
long, with considerable variation in color pattern. The
background color may be yellow, green, tan, or red.
Most beetles' wing covers have four black spots and
black stripes along the edges, although these mark-
ings may be absent. A black triangle is always present
at the base of the wing covers just behind the protho-
rax, the "neck" area between the head and wing covers.

Life cycle and damage. The beetles overwinter under
debris in protected areas. When temperatures warm
in the spring, the beetles fly into alfalfa and clover

fields to feed but do not lay eggs there. As soon as
soybeans begin emerging, the beetles abandon alfalfa
and clover fields to colonize soybean fields. They feed
on the cotyledons, leaves, and stems of emerging soy-
beans and lay eggs in the soil. The eggs hatch in a few
days, and the larvae feed on the roots and nodules of
the plants. The larvae are white, with dark-brown ar-
eas at both ends. When the larvae finish feeding, they
pupate.

Adults of the first generation begin to emerge in
July, but the peak occurs in late July or early August.
The beetles feed on the soybean foliage, leaving small
holes in the leaves. If the infestation is severe, soybean
plants may be completely riddled with holes.

The beetles again lay eggs in soybean fields, and a
second generation occurs. Adults of the second gen-
eration begin emerging in September. They do not lay
eggs, but they remain in the soybeans as long as there
are tender plant parts on which to chew. They may
chew on pods after the leaves become old, and their
feeding creates scars that provide an avenue for entry
of spores of various fungal diseases that normally are
blocked by the pericarp. Mild infection results in seed
staining; severe infection results in seed contamina-
tion. As the temperatures decrease, the beetles seek
overwintering sites in wooded areas.

Management suggestions. Monitoring for bean leaf
beetles should begin when soybean seedlings emerge
and resume when first-generation adults are feeding
on the leaves in July and August. The pod-filling
stage is considered the most critical stage of growth.
Economic damage does not occur until beetle density
exceeds 16 per foot of row early in the seedling stage
of development and 39 per foot of row at stage V-2+.
Consequently, an insecticide application for control of
bean leaf beetles attacking seedling soybeans prob-
ably is rarely justified. However, an insecticide spray
may be economically justified during the pod-filling
stage if defoliation exceeds 20 percent.

Recent research from the University of Nebraska
indicates that economic thresholds for bean leaf
beetles for R5-R6 soybeans in 30-inch rows range
from 3.97 to 6.05 per foot of row, depending on the
value of the soybeans and cost of control. Economic
thresholds for bean leaf beetles for R5-R6 soybeans in
7-inch rows range from 0.93 to 1.41 per foot of row. As
the value of soybeans decreases and the cost of con-
trol increases, the economic threshold increases. As
the value of soybeans increases and the cost of control
decreases, the economic threshold decreases.

The economic threshold for beetles that are damag-
ing pods is 10 or more beetles per foot of row and 5 to
10 percent injured pods.

222 ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Management Worksheet for
First-Generation Com Borer

. % of 100 plants infested x average no. borers/infested plant = borers/plant

(use a decimal)

. borers/plant x % yield loss /borer* = % yield loss

(do not use a decimal)

. % yield loss x expected yield (bu/acre) = bu/acre loss

(use a decimal)

bu/acre loss x $ price/bu = $ loss/acre

$ loss/acre x % control = $ preventable loss/acre

(80% for granules) (use a decimal)
(50% for sprays)

$ preventable loss/acre - $ cost of control/acre =

$ gain (+) or loss (-) per acre if treatment is applied

* 5% for com in the early whorl stage; 4% (late whorl); 6% (pretassel).

Management Worksheet for
First-Generation Com Borer

t^ % of 100 plants infested x /« J average no. borers/infested plant = ^» fe borers/plant
(use a decimal)

O* fe borers/plant x 5 % yield loss/borer* = sJ » ^ % yield loss

(do not use a decimal)

*^ ^ % yield loss x I ^O expected yield (bu/acre) = » * O bu/acre loss
(use a decimal)

* * P bu/acre loss x $ i^»3^ price/bu = $ ls^»uO loss/acre

$ {m*00 loss/acre x ^O % control = $ v»6^ preventable loss/acre

(80% for granules) (use a decimal)
(50% for sprays)

$ A qO preventable loss/acre - $ f 7^*00 cost of control/acre =

•** $ ^» ^G gain (+) or loss (-) per acre if treatment is applied

* 5% for com in the early whorl stage; 4% (late whorl); 6% (pretassel).

17 • MANAGEMENT OF FIELD CROP INSECT PESTS

223

Management Worksheet for
Second-Generation Corn Borer

. number of egg masses/plant x 4 borers /egg mass* =
(cumulative counts, taken a few days apart)

_ borers/plant x _

_ % yield loss x _
(use a decimal)

_ bu/acre loss x $

loss /acre x 75

3% yield loss/borer**
(do not use a decimal)

expected yield =

borers/plant
% yield loss

bu/acre loss

price/bu $

loss/acre

.% control = $

preventable loss/acre

(use a decimal)

preventable loss/acre - $ cost of control/acre =

$ gain (+) or loss (-) per acre if treatment is applied

* Assumes survival rate of 20 percent (4 borers/egg mass).

** 5% for com in the early whorl stage; 4% (late whorl); 6% (pretassel); 4% (pollen shedding); 3% (kernels
initiated). Use 3% per borer per plant if infestation occurs after silks are brown. The potential economic
benefits of treatment decline rapidly if infestations occur after com reaches the blister stage.

Other pod feeders

In addition to bean leaf beetles, com earworms, grass-
hoppers, and stink bugs may injure soybean pods in
Illinois; however, the occurrence of com earworms in
soybeans in Illinois is infrequent.

Grasshoppers. Grasshoppers cause more direct in-
jury to the soybean seeds. Because they have strong
chewing mouthparts, grasshoppers often chew
through the pod wall and take bites out of or devour
entire seeds. If more than 5 to 10 percent of the pods
are injured by grasshoppers, an insecticide applica-
tion may be warranted.

Stink bugs. Green stink bugs overwinter as inactive
adults in wooded areas or under leaf litter. During the
early months of summer, the adults feed on berries in
trees, especially dogwoods. Stink bugs are first found
in soybean fields during August. They undergo in-
complete metamorphosis (immature bugs resemble
the adults), which requires approximately 45 days
from egg hatch to adult emergence. There is usually
only one generation of green stink bugs per year in
Illinois.

Immature stink bugs (nymphs) have a flashy dis-
play of black, green, and yellow or red colors and

short, stubby, nonfunctional wing pads. The adults
are large (about Vs inch long), light-green, shield-
shaped bugs with fully developed wings. Both adults
and nymphs have piercing and sucking mouthparts
for removing plant fluids.

Stink bugs feed directly on pods and seeds; how-
ever, their injury is difficult to assess because their
piercing, sucking mouthparts leave no obvious feed-
ing scars. Stink bugs use their mouthparts to pen-
etrate pods and puncture the developing seeds. They
inject digestive enzymes into seeds, and the feeding
wound provides an avenue for diseases to gain entry
into the pod. Seed quality also is reduced by stink bug
feeding, and beans are more likely to deteriorate in
storage. An insecticide application for control of stink
bugs may be warranted when the level of infestation
reaches one adult bug or large nymph per foot of row
during pod fill.

Other species of stink bugs also occur in soy-
beans. The brown stink bug has feeding habits and
biology similar to those of the green stink bug. The
brown stink bug should not be confused with the
beneficial spined soldier bug. These two species can
be distinguished from each other by examining the

224

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

feeding beak and underside of the abdomen. The
beak of the brown stink bug is slender and embed-
ded between the lateral parts of the head. The base
of the beak of the spined soldier bug is stout and
free from the lateral parts. In addition, the spined
soldier bug has a dark round spot located centrally
on the underside of its abdomen (belly). Be aware of
the species present in a soybean field before making
a control decision.

Spider mites

Description. The most common mite species found
in soybean fields in Illinois is the twospotted spider
mite. These tiny mites (0.002 inch), related to spi-
ders, have four pairs of legs in the adult stage and
range in color from pale yellow to brown.

Life cycle and damage. Spider mites hatch from very
small eggs. Larvae with six legs emerge from the eggs
and progress through two nymphal stages, each with
eight legs. After the last nymphal molt, the eight-
legged adults emerge. Spider mites complete a gen-
eration in 1 to 3 weeks, depending on environmental
conditions (primarily temperature).

Spider mites may be blown into soybean fields or
carried in by equipment or animals. They also crawl
from weed hosts to soybean plants, so infestations
usually appear first along field edges or in spots
within a field. Mites can move throughout fields by
"ballooning," that is, by spinning webs and moving to
a position on a leaf from which they can be blown
aloft. They can also move from row to row by bridg-
ing (moving across leaves in contact) when the
canopy is nearly closed.

Spider mites have piercing, sucking mouthparts
with which they puncture plant cells and remove
plant juices. Damaged plant cells do not recover. Ini-
tial injury results in a yellow speckling of the leaves.
Heavy infestations cause leaves to wilt and die. An-
other sign of the presence of spider mites is the
webbing they produce on the undersides of the
leaves.

Outbreaks of spider mites are associated with hot,
dry weather; populations usually peak by mid- to late
season. If the soybeans have an adequate supply of
moisture, the mites usually do not cause any eco-
nomic damage.

Management suggestions. A miticide for control of
spider mites might be warranted when 20 to 25 per-
cent discoloration is noted before pod set or when 10
to 15 percent discoloration is noted after pod set.
Watch field margins closely for symptoms of mite in-
jury as early as late June, but especially during late
July and August. Confining the miticide application
to border rows and other areas of confirmed infesta-
tion is recommended.

Insect Pests of Wheat

In Illinois, few insects cause economic damage to
wheat. However, when outbreaks of insects coincide
with the head-filling stage of wheat growth, yield
losses can be serious. Most of the potential pests are
defoliators, such as armyworms and cereal leaf
beetles, that may cause extensive injury to the flag
leaves. Other pests include Hessian flies and several
species of aphids.

Armyworm

The armyworm feeds on several field and forage
crops. Armyworms prefer grasses and grain crops
such as wheat and com but occasionally can be found
in forage legume crops.

Description. Newly hatched larvae are pale green
with longitudinal stripes and a yellow -brown head.
Fully grown larvae are about I'A inches long and
green-brown, with two orange stripes on each side.
Several longitudinal stripes mark the remainder of the
body. Each proleg (the false, peglike legs on the abdo-
men of a caterpillar) has a dark band. The moth is tan
or gray-brown and has a V/i -inch wingspan. A small
white dot in the center of each forewing is a distin-
guishing mark.

Life cycle and damage. Few armyworms overwinter
in Illinois, but some partly grown larvae probably sur-
vive the winter under debris in southern counties. Pu-
pation occurs in April; the moths emerge and begin
laying eggs in May. Moths that migrate from southern
states into Illinois add to the resident population.

Moths prefer to lay eggs on grasses or grains. The
eggs hatch in about a week, and the larvae begin to
feed on foliage. Young larvae scrape the leaf tissues;
older larvae feed from the edges of the leaves and
consume all of the tissue. Larvae feed only at night or
on cloudy days. After feeding, the larvae pupate un-
der debris or in the soil, and the moths emerge to be-
gin another cycle. There are two or three generations
each year in Illinois.

Armyworm moths may lay numerous eggs in
wheat fields, and the larvae feed until the grain ma-
tures or the wheat is harvested. The larvae feed on
the leaves, working their way up from the bottom of
the plants. Injury to the lower leaves causes no eco-
nomic loss, but injury to the upper leaves, especially
the flag leaf, can result in yield reduction. After ar-
myworms devour the flag leaves, they often chew
into the tender stem just below the head, causing the
head to fall off. After the grain matures or is har-
vested, the larvae will migrate into adjacent corn-
fields. Large numbers of larvae can destroy com
plants within a day or two.

17 • MANAGEMENT OF FIELD CROP INSECT PESTS

225

Management suggestions. Early detection of an ar-
myworm infestation is essential for effective manage-
ment. Examine dense stands of wheat for larvae. If
the number exceeds 6 nonparasitized worms Va to VA
inches long per foot of row, an insecticide may be
justified.

Weather and natural enemies are the major causes
of reductions in armyworm numbers. Hot, dry
weather promotes the development of parasitoids and
diseases, reducing populations of armyworms. Cool,
wet weather is most favorable for an outbreak.

Cereal leaf beetle

Cereal leaf beetles annually cause some injury to
wheat in southern and central Illinois. Mild winters
and lush fall growth create excellent overwintering
conditions for the beetles.

Description. The cereal leaf beetle adult is hard-
shelled and about V^e inch long. Its wing covers and
head are metallic blue-black; its legs and the front seg-
ment of its thorax (just behind the head) are red-or-
ange. The larva is slightly longer than the adult and
resembles a slug. Its skin is yellow to yellow-brown,
but the larva carries a moist glob of fecal material on
its back that makes it look black.

Life cycle and damage. Adults overwinter in clusters
in sheltered areas. In the spring, the beetles fly to
fields of winter wheat and other small grains. When
spring oats emerge, the beetles quickly infest the
young plants. They feed for about 2 weeks before they
lay eggs. Eggs usually hatch in 5 days, and the larvae
grow and feed for about 10 days. After they finish
feeding, the larvae descend to the ground and pupate
in the soil. New beetles emerge after 2 to 3 weeks.
These beetles often fly to the edges of cornfields and
feed on the leaves. After feeding for about 2 weeks,
the beetles enter summer hibernation.

The larvae eat only the surface of wheat leaves, so
injured plants are silvery in appearance. Severely
damaged fields appear frosted. Yield losses occur
when the larvae feed on the flag leaves.

Management suggestions. Control may be warranted
when the combination of eggs and larvae average 3 or
more per stem or there is an average of 1 or more
large larvae per stem.

Adults eat longitudinal slits between the veins;
they eat completely through the leaves of both wheat
and com. Com plants usually recover from this injury.

Hessian fly

Although Hessian flies have not caused economic
damage to wheat in Illinois for many years, their con-
tinuing presence and development of new biotypes
pose a constant threat to wheat growers. In fact, many
growers have become complacent about managing

Hessian flies because resistant varieties have kept
them under control for several years. However, the
recent development of a new biotype indicates that
management of Hessian flies is still important.

Description. The damaging stage is the larva, or
maggot, which is reddish when it first emerges from
the egg, and then turns glistening white. A Hessian
fly maggot {Vie inch long) has no head or legs, and its
body is tapered toward the front end, which contains
mouth hooks for feeding. A Hessian fly adult re-
sembles a very small (Vs inch) mosquito and is sooty
black with one pair of wings. The small (Vs inch),
elongated, brown puparium, commonly called a
"flaxseed," can be found behind leaves next to the
stem.

Life cycle and damage. The Hessian fly overwinters
as a full-grown maggot inside a puparium. In the
spring, maggots change into pupae inside the puparia
and emerge as adults. After females have mated, they
lay eggs in the grooves on the upper sides of wheat
leaves. After hatching from eggs, the maggots move
behind the leaf sheaths and begin feeding on the
stem. The maggots feed for about 2 weeks and then
form a puparium in which they pupate, usually well
before harvest time. They remain in this stage in the
stubble throughout the summer. Flies emerge again in
late summer and seek egg-laying sites on volunteer
wheat plants or on fall-seeded wheat. After the eggs
hatch, the fall generation of maggots begins feeding
on the seedling plants.

Wheat infested in the fall usually is stunted, and
the leaves are dark blue-green, thickened, and more
erect than healthy leaves. Severely damaged plants
may die during the winter. In the spring, injured
plants appear much like they do in the fall. In addi-
tion, infested plants often break over when the heads
begin to fill.

Management suggestions. Because chemical controls
are neither a practical nor a reliable solution to Hes-
sian fly problems in wheat, the following tactics are
recommended to manage this pest:

• Destroy wheat stubble and volunteer wheat.

• Plant resistant or moderately resistant wheat
varieties.

• Plant wheat after the fly-free date (Table 17.03).

Some producers continue to plant winter wheat
before established fly-free dates. By not adhering to
these dates, growers are placing greater pressure
upon the ability of resistant wheat varieties to with-
stand Hessian fly infestations. Consequently, the po-
tential longevity and usefulness of Hessian fly-resis-
tant wheat varieties will be shortened. The dates

226

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

listed in Table 17.03, ranging from September 17 at the
Wisconsin border to October 12 at the southern tip of
Illinois, are the earliest dates that wheat should be
seeded to avoid egg laying by the fall generation of
Hessian fly females. Where wheat is seeded on or af-
ter the fly-free date for a specific location, Hessian fly
adults usually emerge and die before the crop is out
of the ground.

Hessian flies in Illinois have developed a new bio-
type (L) that has overcome the resistance genes in
commercially available wheat hybrids. Consequently,
planting wheat after fly-free dates is even more criti-
cal because reliance upon formerly resistant wheat
varieties will not provide adequate control of Hessian
flies.

Table 17.03. Average

Date of Seeding Wheat for the Highest Yield

Average date of

seeding wheat for

County

the highest yield

County

the highest yield

Adams

Sep. 30-Oct. 1

Lee

Sep. 19-21

Alexander

Oct. 12

Livingston

Sep. 23-25

Bond

Oct. 7-9

Logan

Sep. 28-Oct. 3

Boone

Sep. 17-19

Macon

Oct. 1-3

Brown

Sep. 30-Oct. 2

Macoupin

Oct. 4-7

Bureau

Sep. 21-24

Madison

Oct. 7-9

Calhoun

Oct.4-«

Marion

Oct. 8-10

Carroll

Sep. 19-21

Marshall-Putnam

Sep. 23-26

Cass

Sep. 30-Oct. 2

Mason

Sep. 29-Oct. 1

Champaign

Sep. 29-Oct. 2

Massac

Oct. 11-12

Christian

Oct. 2^

McDonough

Sep. 29-Oct. 1

Clark

Oct. 4-^

McHenry

Sep. 17-20

Clay

Oct. 7-10

McLean

Sep. 27-Oct. 1

Clinton

Oct. 8-10

Menard

Sep. 30-Oct. 2

Coles

Oct. 3-5

Mercer

Sep. 22-25

Cook

Sep. 19-22

Monroe

Oct. 9-11

Crawford

Oct. 6-^

Montgomery

Oct. 4-7

Cumberland

Oct. 4-5

Morgan

Oct. 2-4

DeKalb

Sep. 19-21

Moultrie

Oct. 2-4

DeWitt

Sep. 29-Oct. 1

Ogle

Sep. 19-21

Douglas

Oct. 2-3

Peoria

Sep. 23-28

DuPage

Sep. 19-21

Perry

Oct. 10-11

Edgar

Oct. 2^

Piatt

Sep. 29-Oct. 2

Edwards

Oct. 9-10

Pike

Oct. 2-4

Effingham

Oct.5-«

Pope

Oct. 11-12

Fayette

Oct. 4-8

Pulaski

Oct. 11-12

Ford

Sep. 23-29

Randolph

Oct. 9-11

Franklin

Oct. 10^12

Richland

Oct. 8-10

Fulton

Sep. 27-30

Rock Island

Sep. 20-22

Gallatin

Oct. 11-12

St. Clair

Oct. 9-11

Greene

Oct. 4-7

Saline

Oct. 11-12

Grundy

Sep. 22-24

Sangamon

Oct. 1-5

Hamilton

Oct. 10-11

Schuyler

Sep. 29-Oct. 1

Hancock

Sep. 27-30

Scott

Oct. 2-4

Hardin

Oct. 11-12

Shelby

Oct. 3-5

Henderson

Sep. 23-28

Stark

Sep. 23-25

Henry

Sep. 21-24

Stephenson

Sep. 17-20

Iroquois

Sep. 24-29

Tazewell

Sep. 27-Oct. 1

Jackson

Oct. 11-12

Union

Oct. 11-12

17 • MANAGEMENT OF FIELD CROP INSECT PESTS

227

Table 17.03. Average Date of Seeding Wheat for the Highest Yield (cont.)

County

Average date of

seeding wheat for

the highest yield

County

the highest yield

Oct. 6-8

Vermilion

Sep. 28-Oct. 2

Oct. 9-11

Wabash

Oct. 9-11

Oct. 6-8

Warren

Sep. 23-27

Sep. 17-20

Washington

Oct. 9-11

Oct. 10-12

Wayne

Oct. 9-11

Sep. 19-21

White

Oct. 9-11

Sep. 22-25

Whiteside

Sep. 20-22

Will

Sep. 21-24

Sep. 23-27

Williamson

Oct. 11-12

Sep. 17-20

Winnebago

Sep. 17-20

Sep. 19-24

Woodford

Sep. 26-28

Oct. 8-10

Jasper

Jefferson

Jersey

JoDaviess

Johnson

Kane

Kankakee

Kendall

Knox

Lake

LaSalle

Lawrence

Authors

Kevin L. Steffey

Department of Crop Sciences

' Michael E. Gray

Department of Crop Sciences

Chapter 18.

Disease Management for Field Crops

Successful management of field crop diseases that are
found in Illinois is based on a thorough understand-
ing of factors influencing disease development and
expression. Strategies should include measures to re-
duce losses in the current crop as well as consider-
ations for future plantings.

The interaction of four factors influences the de-
velopment of all plant diseases: (1) the presence of a
susceptible host crop; (2) a pathogen (disease-caus-
ing agent) capable of colonizing the host; (3) an en-
vironment that favors the pathogen and not the
host; and (4) adequate time for economic damage
and loss to occur. All plant disease management is
directed toward disrupting one or more of these
factors.

Among measures used to manage plant diseases
are crop rotation, genetic resistance, fungicides, and
cultural (agronomic) practices. The success of these
measures depends on how carefully crops are scouted
and diseases assessed. Regular scouting of crops in-
creases the likelihood that disease management will
be properly applied and can reduce the unnecessary
use of pesticides. Pesticides are best used only when
there is threat of an epidemic deemed uncontrollable
through the use of other measures.

FUNGICIDES

Fungicide Application

At present, aircraft are the best vehicles for applying
foliar fungicides to agronomic crops. Some aircraft
may not be equipped or calibrated to do this job, so it
is important to select an aerial applicator who is fa-
miliar with disease control and whose aircraft has
been properly calibrated for uniform, thorough cover-
age of all above-ground plant parts. With the equip-
ment now available, a reasonable job of applying fun-
gicides requires a minimum of 5 gallons of water
carrier per acre. Superior coverage may be obtained
with more water, but the cost may be prohibitive.

Conversely, a lower volume (less than 3 to 4 gallons
per acre) gives correspondingly poorer control. Five
gallons of water can be applied uniformly using about
30 to 70 properly spaced nozzles, depending on the
aircraft. The nozzles should be D-8 to D-12, hollow
cone, with No. 45 or No. 46 cores. The final decision
on nozzle number, size, swath width, and placement
depends on the air speed, pressure, and volume de-
sired. Droplet size is also important. Ideally, droplets
should measure 200 to 400 microns for thorough and
uniform coverage.

USE OF Adjuvants

When it is compatible with the product label, the ad-
dition of a spray adjuvant (surfactant) to the spray
mix is suggested. Adjuvants can help disperse fungi-
cides and improve coverage. They are especially help-
ful for com and small grains.

Nematicide Application

Granular nematicides/ insecticides registered for use
on field crops may be used as in-furrow or band treat-
ments, depending on the product label. In general,
band applications have given more consistent control
than in-furrow applications. Follow the manufac-
turer's suggestions on incorporation. Nematicides are
not designed to replace crop rotation and the use of
resistant crop varieties in a management program.
Successful nematode management is based on a com-
bination approach that may include pesticides. How-
ever, pesticides alone will not provide adequate con-
trol and may produce additional environmental
problems.

Fungicide Guidelines

Seed treatments. The greatest benefits of fungicide
seed treatments will be found (1) where low seeding
rates are used; (2) where seed that is of poor quality
because of fungal infection must be used; and (3)

18 • DISEASE MANAGEMENT FOR FIELD CROPS

229

where seed is planted in a seedbed in which delays in
germination or emergence are likely.

Fungicide seed treatments are not a substitute for
high-quality seed and will not improve the perfor-
mance of seed that is of low quality due to mechanical
damage or physiological factors. Treated seed of low
quality will not produce stands or yields equal to
those of untreated high-quality seed. Only high-qual-
ity seed should be considered for planting.

Disease Management
OF Specific Crops

Although disease management recommendations
vary depending on the host crop, many techniques
are applicable to all field crops. For specific disease
control recommendations, consult the current edition
of the Illinois Agricultural Pest Management Handbook
and other chapters in this publication.

Integrated pest Management
Alfalfa Disease Management

Alfalfa is subject to a number of seedling blights, root
and crown rots, and leaf blights. Losses can be mini-
mized by an integrated management approach in-
cluding these steps:

1. Growing winter-hardy, disease-resistant varieties.

2. Planting high-quality, disease-free seed produced
in an arid area.

3. Providing a well-drained, well-prepared seedbed.

4. Using crop rotation with nonlegumes.

5. Cutting in a timely manner to minimize losses
to foliar blights.

6. Using proper fertilization practices and maintain-
ing proper pH.

7. Avoiding cutting or overgrazing during the
last 5 or 6 weeks of the growing season.

8. Controlling insects and weeds.

9. Cutting only when foliage is dry.

10. Destroying unproductive stands.

11. Following other suggested agronomic practices.

Table 18.01 lists the most common diseases in lUi-
nois and the effectiveness of various management
methods. No control measures are necessary or practi-
cal for several of the conunon alfalfa diseases, includ-
ing bacterial blight or leaf spot, bacterial stem blight.

downy mildew, and rust. For other diseases, produc-
ers should select resistant varieties. Specific recom-
mendations are found in this handbook in Chapter 8,
"Hay, Pasture, and Silage."

Planting disease-resistant varieties. Many newer
varieties offer resistance to bacterial wilt, Fusarium
wilt, Verticillium wilt, common leaf spot, Lepto (pep-
per) leaf spot, spring black stem, anthracnose, and
Phytophthora root rot. However, no variety is resis-
tant to all common diseases. Alfalfa producers should
identify the common pathogens in their areas and se-
lect varieties according to local adaptability, high-
yield potential, and resistance to those common
pathogens.

Choosing planting sites and crop rotation. The
choice of planting site often determines which dis-
eases are likely to occur because most pathogens sur-
vive between growing seasons on or in crop debris,
volunteer alfalfa, and alternate host plants. Pythium
and Phytophthora seedling blights, for example, are
more common in heavy, compacted, or poorly
drained soils and survive in infected root tissues. Leaf
blighting fungi survive in undecayed leaf and stem
tissues. These pathogens die out once residues decay.

Other pathogens are dispersed by wind currents
and can be found in almost any field. Alfalfa mosaic
viruses are transmitted by aphids that may be blown
many miles. Thus, planting site selection alone will
not ensure a healthy crop.

Rotating crops. The diseases strongly associated
with continuous alfalfa production include bacterial
wilt, anthracnose, a variety of fungal crown and root
rots, Phytophthora root rot, Fusarium wilt, Verticil-
lium wilt, spring and summer black stem, common
and Lepto leaf spots, bacterial leaf spot, and Stagno-
spora leaf and stem spot. Rotating crops and using
tillage to encourage residue decomposition before the
next alfalfa crop is planted will help reduce the inci-
dence of many diseases.

Since most alfalfa pathogens do not infect plants in
the grass family, rotation of 2 to 4 years with com,
small grains, sorghum, and forage grasses will help
reduce disease levels.

Cutting of alfalfa in the mid- to late-bud stage.
Cutting heavily diseased stands before bloom and
before the leaves fall will maintain the quality of the
hay and remove the leaves and stems that are the
source of infection (primary inoculum) for later dis-
ease. This will help ensure that succeeding cuttings
have a better chance of remaining healthy. Cutting in
the mid- to late-bud stage, harvesting at 30- to 40-
day intervals, and cutting the alfalfa short are prac-
tices that help to control most leaf and stem diseases
of alfalfa.

230

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 18.01. Alfalfa Diseases That Reduce Yields in Illinois and the Relative Effectiveness
of Various Control Measures

Planting

Having a

Avoiding

winter-

Using

well-

Employing

Achieving

Cutting

late

rank

Maintaining

hardy.

high-

drained

correct

adequate.

in mid- to

cutting

growth

insect

resistant

quality

soil, pH

crop

balanced

late-bud

and

and high

and weed

Disease

varieties

seed

6.5 to 7

rotation

fertility

stage

planting

stubble

control

Bacterial wilt

Dry root and crown

rots, decline

Phytophthora root rot

Fusarium wilt

Verticillium wilt

Anthracnose

Spring black stem

Summer black stem

Common or Pseudo-

peziza leaf spot

Stemphylium or zonate

leaf spot

Lepto or pepper

leaf spot

Yellow leaf blotch

Stagnospora leaf

and stem spot

Rhizoctonia stem bUght

Seed rot, seedling

blights, damping-off

Sclerotinia crown

and root rot

Mosaics

1 = Highly effective control measure; 2 = moderately effective; 3 = slightly effective. A blank indicates no effect.

Cutting only when foliage is dry. This practice
minimizes the spread of fungi and bacteria that cause
leaf and stem diseases, wilts, and crown and root rots.

Controlling insects. Insects commonly provide
wounds by which wilt, crown- and root-rotting fungi,
and bacteria enter plants. Insects also reduce plant
vigor, increasing the risk of stand loss from wilts and
root and crown rots.

Controlling weeds. Do not allow a thick growth of
weeds to mat around alfalfa plants. Like rank, tall
plant growth, weeds also reduce air movement; they
slow the drying of the foliage and lead to serious crop
losses from leaf and stem diseases. Seedling stands
under a thick companion crop, such as oats, are com-
monly attacked by leaf and stem diseases. Weeds also
may harbor viruses that can be transmitted to alfalfa
by the feeding of aphids. Keep down broadleaf weeds
in fence rows and drainage ditches, along roadsides.

and in other waste areas. Such places serve as a
source of mosaic viruses. Whenever possible, do not
grow alfalfa close to other legumes, especially clovers,
garden peas, and beans. Many of the same viruses
that infect alfalfa attack these and other legumes.

Soybean Disease Management

Soybean disease management is based upon an inte-
grated system using resistant varieties, crop rotation,
tillage (where feasible), fungicides, balanced soil fer-
tility, high-quality seed, scouting, and proper insect
and weed control. The use of several of these manage-
ment practices will help disrupt the combination of
factors necessary for disease development. Table 18.02
summarizes the effect of these practices.

Variety selection. All soybean disease management
programs should begin with the selection of a variety
with resistance to the most common pathogens in the

18 • DISEASE MANAGEMENT FOR FIELD CROPS

231

Table 18.02. Soybean Diseases That Reduce Yields in Illinois and the Relative Effectiveness of Various
Control Measures

Disease

Resistant

or tolerant

varieties

Crop
rotation

Clean
plow-
down

High

seed

quality

Phytophthora
root rot

Pythium,

Phytophthora,
Rhizoctonia, and

Fusarium

seedling blights
and root rots

Charcoal root rot

Fungicides Other controls and comments

Soybean cyst
nematode

Pod and stem
blight,
anthracnose,
stem canker

Cercospora leaf
blight (purple
seed stain),
Septoria brown
spot, frogeye
leaf spot

Bacterial bUght,
bacterial pustule,
wildfire

Numerous races of the fungus are
known. Avoid poorly drained areas
and soil compaction.

Plant high-quality seed in a warm
(55 to 60°F), well-prepared seedbed.
Shallow planting may help establish
uniform, vigorous stands.

Early planting, deep and clean plow-
ing, balanced fertility, narrow rows,
and avoiding moisture stress pro-
vides some control. Avoid high seed-
ing rates.

3 Early planting and eliminating sus-

(nemati- ceptible weeds aids in control. Avoid
cides) moving contaminated soil from field
to field by equipment, water, or other
means. Crop rotations of 3 years or
more may be necessary even when
using resistant varieties. Maintain
balanced fertility. Soil analysis
should be used in decision making.

Fungicides are suggested to aid in
producing high-quality seed. Grain
producers may have higher yields in
warm, wet seasons. Plant full-season
varieties.

These diseases may be more impor-
tant in narrow-row culture systems.

Seed should not be saved from fields
that are heavily infected with these
diseases.

232

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 18.02. Soybean Diseases That Reduce Yields in Illinois and the Relative Effectiveness of Various
Control Measures (cont.)

Disease

Resistant

or tolerant

varieties

Crop
rotation

Clean High
plow- seed
down quality

Fungicide Other controls and comments

Downy mildew

Sclerotinia white
mold

Powdery mildew

Soybean mosaic,
bean pod
mottle,

and bud blight
viruses

Brown stem rot

Sudden death
syndrome

This disease, which primarily affects
seed quality, may become more im-
portant in narrow-row culture systems.

The effectiveness of fungicide sprays
is unknown at this time. Varietal dif-
ferences are known, but no resistant
soybeans have been released.

Plant seed produced in fields with a
low incidence of soybean mosaic.
Damage from bud blight may be re-
duced by bordering, soybean fields
with 4 to 8 rows or more of com or
sorghum. This may be especially
helpful where soybean fields border
alfalfa or clover fields. Before plant-
ing, apply herbicides to kill broadleaf
weeds in fencerows, ditch banks,
grass pastures, and the like.

Rotations of 2 to 3 or more years are
necessary for control. Soybeans
planted as end rows on cornfields aid
in carrying over the disease. Early
maturing varieties are generally less
affected than late-maturing varieties.
Resistant varieties act as nonhost
crops in rotations.

See comments for soybean cyst nema-
tode. Early planted or early maturing
varieties appear to be more susceptible.

1 = Highly effective control measure; 2 = moderately effective; 3 = slightly effective. A blank indicates no effect.

area. Many high-yielding public and private soybean
varieties are available with resistance to important
diseases such as Phytophthora root rot, soybean cyst
nematode, and brown stem rot. Other, less important
diseases can also be controlled with resistant varieties.
See Chapter 3 in this handbook for more information
on variety selection.

One major concern for soybean producers is the
possible appearance of new or unexpected races of a
pathogen, particularly for Phytophthora root rot and

the soybean cyst nematode. A race is simply a patho-
gen population with the ability to infect and colonize
a normally resistant host plant. Thus, growers lose the
expected protection of the resistance genes and essen-
tially have "susceptible" plants. Different races are
known to occur in Illinois for both Phytophthora root
rot and soybean cyst nematode. If growers experience
losses in fields where resistant varieties are planted
and other causes can be ruled out, an unusual patho-
gen race should be suspected.

18 • DISEASE MANAGEMENT FOR FIELD CROPS

233

For Phytophthora root rot, there is the option of se-
lecting resistant or tolerant seed sources. Resistant
soybeans contain one or more genes with resistance to
specific races of the pathogen. This type of resistance
is active from the time of planting until full maturity.
It fails only where unusual races occur that are not
controlled by the genes in the plant.

Tolerance provides a broad form of resistance to all
races of the pathogen. However, it may not provide
the level of protection needed where pathogen popu-
lation levels are extremely high. The major advantage
is the protection against all races. However, tolerance
is not active in the early seedling stage, and plants are
considered susceptible to Phytophthora until one or
two true leaves have developed. An application of
Apron seed treatment or Ridomil in-furrow is advised
to protect tolerant varieties in the early season.

Agronomic characteristics affecting disease
development. The relative maturity of soybean culti-
vars can have a dramatic impact on disease develop-
ment. Early-maturing varieties are more commonly
damaged by pod and stem blight, anthracnose, purple
seed stain, and Septoria brown spot. The longer the
time from maturity to harvest, the greater the likeli-
hood of damage by these diseases. However, early-
maturing varieties are generally less affected by
brown stem rot.

Soybean growth habit can also affect disease devel-
opment. Tall, bushy varieties, for example, are more
affected by Sclerotinia white mold than shorter, more
compact varieties. However, the shorter varieties may
also be more prone to damage by water-splashed
pathogens such as Septoria brown spot, pod and stem
blight, and purple seed stain. Differences in indi-
vidual variety resistance may negate the effects of
plant height on disease development.

Planting date also affects diseases. Early planted
beans typically have a greater incidence of seedling
blights if not protected by a fungicide. Conditions in
early spring favor these pathogens and may delay the
rapid emergence of soybeans. Early planting also in-
creases the incidence of sudden death syndrome
when compared to later plantings.

Crop rotation and tillage are very important prac-
tices in controlling most diseases of soybeans. Practi-
cally all soybean pathogens depend on crop residues
for overwintering and do not colonize other hosts.
Therefore, when crop residues are removed or are
thoroughly decayed and /or when rotation with
nonhosts (com, sorghum, small grains) is used, patho-
gen population levels decline.

Programs which promote residue decay through
tillage or rotations will help reduce such diseases as
pod and stem blight, anthracnose, stem canker, pow-

dery and downy mildew, brown stem rot, Sclerotinia
white mold, and soybean cyst nematode.

With the increasing acceptance of reduced and no-
till practices, the practice of total residue incorpora-
tion is declining. Where residues remain on or near
the soil surface, it is important to emphasize all other
means of control. The presence of residues does not
significantly increase disease levels where resistance
and crop rotation are practiced.

Row spacing is another factor that can influence
disease. Diseases that thrive in cool, wet conditions
typically increase where soybeans are planted in nar-
row rows. If previous soybean crop residue is also
present, earlier and more severe epidemics may occur.
Diseases such as downy mildew and Sclerotinia white
mold are greatly affected by high humidity levels.
Narrow rows increase both humidity and disease lev-
els. If tall beans are also planted, there may be little air
circulation within the canopy. Where white mold or
downy mildew are problems, wider rows or shorter
beans will help reduce disease levels.

Wheat Diseases

Wheat disease management is based upon an inte-
grated control program using resistant varieties, high-
quality seed, fungicide treatments, proper planting
time and site, crop rotation, tillage (where feasible),
high fertility, and other cultural practices. Table 18.03
summarizes these measures and the diseases controlled.

Disease-resistant varieties. Growing resistant vari-
eties is the most economical and efficient method of
controlling diseases. Resistance to stem rust, leaf rust,
loose smut, Septoria diseases, powdery mildew, soil-
borne wheat mosaic, barley yellow dwarf, wheat
streak mosaic, and wheat spindle streak (wheat yel-
low mosaic) is of major importance in Illinois. No
single wheat variety is resistant to all major diseases.
Thus, varieties should be selected according to their
local adaptability, high-yield potential, and resistance
to the most common and serious diseases.

High-quality seed. Seed that has been improperly
stored (bin-run) will lose vigor and may develop
problems in the seedling stage that continue through-
out the season and result in reduced crop yield and
quality. Diseases such as bunt, loose smut, basal
glume rot, black chaff, ergot, Septoria diseases,
Helminthosporium spot blotch or black point, and
scab may be carried on, with, or within the seed.

Planting site. The choice of a planting site often de-
termines which diseases are likely to occur because
many pathogens survive on or in crop debris, soil,
volunteer wheat, and alternate host plants. This is
most important in the control of Septoria leaf and
glume blotches, Helminthosporium spot blotch, tan or

234

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

Table 18.03. Relative Effectiveness of Various Methods of Controlling the Major Wheat Diseases in Illinois

Resistant

Crop

Clean
plow-

Balanced

Planting
after the
fly- free

Fungicides
Seed Foliar

Other 1
controls 1
and T

Disease

varieties

rotation

down

fertility^

date

treatment

sprays

comments

Stem rust

Leaf rust

Loose smut

Bunt or stinking smut
Septoria leaf blotches

1
3

Septoria glume blotch

■

Scab

Avoid *

planting f

adjacent to

com

stubble or

following

com.

Take-all

Control

virus

diseases.

Tan or yellow spot

Cephalosporium

stripe

Powdery mildew

Seedling blights

Helminthosporium

spot blotch

Soilbome wheat

mosaic virus

Wheat streak

mosaic virus

Barley yellow

dwarf virus

Wheat spindle

streak virus

1 = highly effective control measure; 2 = moderately effective; 3 = slightly effective. A blank indicates no effect.
*See Table 18.04 for the effect of the form of nitrogen used.

yellow leaf spot, scab, ergot, take-all, Fusarium and
Helminthosporium root rots, crown or foot rots,
Cephalosporium stripe, bunt or stinking smut,
downy mildew, eyespot or strawbreaker, Pythium
and Rhizoctonia root rots, sharp eyespot, soilbome
wheat mosaic, and wheat spindle streak mosaic or
wheat yellow mosaic. Other diseases are not affected
by choice of planting site, including airborne and in-
sect-transmitted diseases. These include barley yel-
low dwarf virus, wheat streak mosaic virus, and rusts.

Crop rotation. Crop rotation is an extremely im-
portant means of reducing carryover levels of many
common wheat pathogens. Diseases strongly associ-
ated with continuous wheat production include take-
all, Helminthosporium spot blotch, tan or yellow
spot, crown and foot rots, root rots, head blights,
Septoria leaf and glume blotches, black chaff, pow-
dery mildew, Cephalosporium stripe, soilbome wheat
mosaic, wheat streak mosaic, scab, downy mildew,
eyespot and sharp eyespot, ergot, and anthracnose.

18 • DISEASE MANAGEMENT FOR FIELD CROPS

235

With many common wheat diseases, crop debris
provides a site for pathogen populations to survive
adverse conditions. Many of these pathogens do not
survive once crop debris is decomposed. Rotations of
2 or 3 years with nonhost crops (such as com, sor-
ghum, alfalfa, and clovers), coupled with other prac-
tices that promote rapid decomposition of crop resi-
due, will reduce the carryover populations of these
pathogens to very low levels. Soilbome wheat mosaic
and wheat spindle streak or wheat yellow mosaic in-
crease when wheat is planted continuously in the
same field. To control these diseases, rotations must
cover at least 6 years. Using highly resistant varieties
is the best way to control losses from these types of
diseases.

Replanting the same field to winter wheat follow-
ing an early summer harvest does not constitute an
adequate rotation.

Tillage. Although a clean plow-down is of great
help in disease control, the losses to soil erosion
should be carefully weighed against potential disease
losses. Pathogens dispersed short distances by wind
and splashing water may infect crops early and cause
more severe losses where debris from the previous
wheat crop remains on the soil surface. The need for
clean tillage is thus based on the prevalence and se-
verity of diseases in the previous crop, other disease-
control practices available, the need for erosion con-
trol, rotation plans, and related factors.

If conservation tillage is to be implemented, strict
attention must be paid to all other disease-control
practices.

Fertility. The effect of fertility on wheat diseases is
quite complex. Adequate and balanced levels of nitro-
gen, phosphorus, potassium, and other nutrients —
based on a soil test — will help reduce disease losses,
particularly from take-all, seedling blights, powdery
mildew, anthracnose, and Helminthosporium spot
blotch. Research has shown that the level and form of
nitrogen both play an important role in disease sever-
ity. The severity of certain diseases is decreased by us-
ing ammonia forms of nitrogen (urea and anhydrous
ammonia) and is increased by using the nitrate forms
of nitrogen. In other cases, the reverse is true. The
general effect on disease severity caused by the form
of nitrogen used is given in Table 18.04.

Planting time. Planting time can greatly influence
the occurrence and development of a number of dis-
eases. Early fall planting and warm soil (before the
"fly-free" date) promote the development of certain
seed rots and seedling blights, Septoria leaf blotches,
leaf rust, powdery mildew, Cephalosporium stripe,
Helminthosporium spot blotch, wheat streak mosaic,
soilbome wheat mosaic, barley yellow dwarf, and

Table 18.04. Effect of the Form of Nitrogen on
Various Wheat Diseases

Disease

Nitrogen form
Nitrate Ammonium

Root and crown diseases

Take-all Increase

Fusarium root rot Decrease

Helminthosporium diseases Decrease

Decrease
Increase

Foliar diseases

Powdery mildew
Leaf and stem rust
Septoria leaf blotch

Increase
Increase
Increase

Decrease

= No effect or data not available.

wheat spindle streak mosaic. Wheat that is planted
early often has excessive foliar growth in the fall,
which favors the buildup and survival of leaf rust,
powdery mildew, and the Septoria diseases. Disease
buildups in the fall commonly favor earlier and more
severe epidemics in the spring. Many of these prob-
lems can be avoided if planting is delayed until after
the "fly-free" date.

Planting after the "fly-free" date is an effective
means of limiting the transmission of viruses and
yield losses from virus diseases such as wheat streak
mosaic and barley yellow dwarf. The cooler tempera-
tures usually limit the activity of mites and aphids
that transmit these viruses. Since fall infections result
in the greatest yield losses, serious virus problems can
be avoided by late planting. See the nearest Extension
office for information on fly-free dates.

Seed treatment. Seed treatment trials in Illinois
during the past 17 years have increased yields 3 or
more bushels per acre by controlling diseases such as
bunt, loose smut, Septoria diseases, seed rots, and
seedling blights. Failure to control seedling blights
may result in serious winterkill of diseased seedlings.

No single fungicide controls all of the diseases just
listed. A combination of fungicides is necessary to ob-
tain broad-spectrum seed protection. Since some
seedbome pathogens are more difficult to control
than others, the full recommended label rate should
always be used.

Foliar fungicides. Septoria leaf and glume
blotches, powdery mildew, and rusts may occur every
year regardless of the precautions taken. These dis-
eases are favored by rainy, windy weather and heavy
dews, and they are a threat whenever such weather
prevails from tillering to heading.

236

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Rusts, powdery mildew, and Septoria diseases can
be controlled by timely and proper applications of
fungicides. The decision to apply fungicides should
be based on the prevalence of disease, disease sever-
ity, and the yield potential of the crop. As a general
guideline, the upper two leaves (flag and flag-1)
should be protected against foliar pathogens since
head-filling depends largely on the photosynthetic ac-
tivity of these two leaves. Loss of leaves below flag-1
usually causes little loss in yield.

Weekly scouting for foliar diseases should begin
no later than the emergence of the second node
(growth stage 6). If diseases are present at this time
and weather conditions favor continued disease de-
velopment (cool and rainy), a fungicide application
should be considered. Be certain that diseases are
correctly diagnosed to ensure proper fungicide selec-
tion. With protectant fungicides the first application
should be at early boot stage followed by a second
spray 10 to 14 days later, depending on the weather.
Systemic fungicides can be applied when diseases
become evident on the upper leaves and provide
protection for about 18 days. A protectant fungicide
may be needed at heading time for late-season dis-
ease control.

Corn Disease Management

To prevent losses from disease, it is necessary to fol-
low a comprehensive, integrated program of com dis-
ease management. Such a program should include
the use of disease-resistant hybrids, crop rotations,
various tillage practices, balanced fertility, fungicides,
insect and weed control, and other cultural practices.
These practices should relate to the risk potential of
the various diseases and the life cycles of disease-
causing organisms (pathogens).

Table 18.05 lists those diseases known to cause
yield losses in Illinois and the relative effectiveness of
various control measures.

Disease-resistant hybrids. The use of resistant hy-
brids is the most economical and efficient method of
disease control. Although no single hybrid is resistant
to all diseases, hybrids with combined resistance to
several major diseases are available. Com producers
should select high-yielding hybrids with resistance or
tolerance to major diseases in their area.

Crop rotation. Many common pathogens require
the presence of a living host crop for growth and re-
production. Examples of such com pathogens include
the leaf diseases ("Helminthosporium" leaf diseases,
Physoderma brown spot, Goss's bacterial wilt, gray
leaf spot, yellow leaf blight, eyespot) and nematodes.
Rotating to nonhost crops (e.g., soybeans, alfalfa, clo-

vers, and canola) "starves out" these pathogens, re-
sulting in a reduction in inoculum levels and the se-
verity of disease. Continuous com, especially in com-
bination with conservation tillage practices, which
promote large amounts of surface residue, may result
in severe outbreaks of disease. In such cases it is
highly advisable to utilize all other disease-control
measures.

Tillage. Tillage programs that encourage rapid resi-
due decomposition, before the next com crop is
planted, help reduce populations of pathogens that
overwinter in or on crop debris. Although a clean
plow-down is an important disease-control practice,
the possibility of soil loss from erosion must be con-
sidered. Other measures can provide effective disease
control if conservation tillage is implemented. Ex-
amples of diseases partially controlled by tillage in-
clude stalk and root rots, "Helminthosporium" leaf
diseases, Physoderma brown spot, Goss's bacterial
wilt, gray leaf spot, anthracnose, ear and kernel rots,
yellow leaf blight, eyespot, and nematodes.

Balanced fertility. Adequate balanced fertility
plays an important role in checking the development
of such diseases as Stewart's bacterial wilt, seedling
blights, leaf blights, smut, stalk rots, ear rots, and
nematodes. Diseases are often most severe where
there is excess nitrogen and a lack of potassium, or
both. Healthy, vigorous plants are more tolerant of
diseases and better able to produce a near-normal
yield.

Foliar fungicides. One or more "Helmintho-
sporium" leaf blights and rust diseases may occur ev-
ery year regardless of the precautions taken. If ex-
tended periods of moist, overcast weather occur be-
fore or shortly after tasseling, these diseases may
cause losses of 10 to 30 percent. If significant disease
occurs earlier than 2 weeks after tasseling, the appli-
cation of foliar fungicides may be justified, especially
in seed production fields. The decision to apply fungi-
cides should be based on the prevalence and severity
of leaf diseases. Leaf blights generally are first seen on
the lower leaves. Rusts first appear on the upper
leaves.

In general, fungicide applications are economi-
cally feasible only in seed-production fields or other
specialty com crops. Weekly scouting for
"Helminthosporium" leaf blights and rusts should
begin at least 2 weeks before tasseling. If diseases
are present and weather conditions favor continued
disease development (rainy and overcast), fungicide
applications should be considered. Add a label-
recommended spreader-sticker (surfactant) to the
spray tank to ensure more uniform coverage.

18 • DISEASE MANAGEMENT FOR FIELD CROPS 237

Table 18.05. Com Diseases That Reduce Yields in Illinois and the Relative Effectiveness
of Various Control Measures

Disease

Resistant Clean

or tolerant Crop plow- Balanced
hybrids rotation down fertility Fungicides

Other controls and comments

Stewart's bacterial wilt 1

Seed rots and seedling 2
blight

"Helminthosporium"
leaf blights; Northern
leaf blight. Northern
leaf spot, Helmintho-
sporium leaf spot.
Southern leaf blight

Physoderma brown
spot

Yellow leaf blight and
eyespot

Gray leaf spot

Anthracnose

Crazy top and sorghum
downy mildew

Goss's bacterial wilt

Smut

Common and southern
rusts

Early control of com flea beetles may
be helpful on susceptible hybrids.

Sow injury-free, plump seed. Plant
seed in soils 50° to 55°F or above. Pre-
pare seedbed properly and place fer-
tilizer, herbicides, and insecticides
correctly.

Fungicide applications are generally
justified only in seed production
fields and only if the lower three
leaves up to 2 weeks after tasseling
are infected.

See comments for "Helmintho-
sporium" leaf blights.

Avoid low wet areas, and plant only
downy mildew-resistant sorghums in
sorghum-corn rotations. Control of
shattercane (an alternate host) is very
important.

Rotations of 2 or more years provide
excellent control.

Avoid mechanical injuries to plants.
Control insects.

Fungicides may be justified in seed-
production fields.

1 = Highly effective control measure; 2 = moderately effective; 3 = slightly effective. A blank indicates no effect.
^Not affected by crop rotation or tillage.

238

ILLINOIS AGRONOMY HANDBOOK, 1999»2000

Table 18.05. Com Diseases That Reduce Yields in Illinois and the Relative Effectiveness
of Various Control Measures (cont.)

Disease

Resistant Clean

or tolerant Crop plow- Balanced
hybrids rotation down fertility

Fungicides Other controls and comments

Stalk rots:
Diplodia
Charcoal
Gibberella
Fusarium
Anthracnose
Nigrospora

Ear and kernel rots:
Diplodia
Fusarium
Gibberella
Physalospora
Penicillium^
Aspergillus^
Others

Plant adapted, full-season hybrids at
recommended populations and fertil-
ity. Control insects and leaf diseases.
Survey at 30 to 40 percent moisture
to determine potential losses.

Control stalk rots and leaf blights.
Hybrids that mature in a downward
position with well-covered ears usu-
ally have the least ear rot. Ear and
kernel rots are increased by bird, in-
sect, and severe drought damage.

Storage molds:
Penicillium
Aspergillus, etc.

Maize dwarf mosaic

Wheat streak mosaic

Nematodes:
Lesion
Needle
Dagger
Sting
Stubby-root

Store undamaged com for short peri-
ods at 15 to 15.5 percent moisture.
Dry damaged com to 13 to 13.5 per-
cent moisture prior to storage. Low-
temperature-dried com has fewer
stress cracks and storage mold prob-
lems if an appropriate storage fungi-
cide is used. See a local Extension
office for details. Com stored for 90
days or more should be dried to 13
to 13.5 percent moisture. Inspect
weekly for heating, crusting, and
other signs of storage molds.

Control Johnsongrass and other
perennial grasses (alternative hosts)
in and around fields.

Plant winter wheat (an alternative vi-
rus host) after the fly-free date and
control volunteer wheat. Separate
com and wheat fields. See Report on
Plant Diseases No. 123.

Clean plow-down helps reduce win-
ter survival of nematodes. Nemati-
cides may be justified in some situa-
tions. See your Extension adviser for
information on chemical control.

1 = Highly effective control measure; 2 = moderately effective; 3 = slightly effective. A blank indicates no effect.
A blank indicates no effect.

18 • DISEASE MANAGEMENT FOR FIELD CROPS 239

NOTE: Descriptions of diseases of field crops can be found in the following publications:

• Various Compendia of Plant Diseases (corn, soybeans, and alfalfa), published by the American Phytopathological Society,
3340 Pilot Knob Road, St. Paul, MN 55121.

• Reports on Plant Diseases, published by Plant Pathology Extension, Department of Crop Sciences, University of Illinois.
These bulletins provide in-depth information for farmers, consultants, and others needing information about specific plant
diseases and their management.

Author

H. Walker Kirby

Department of Crop Sciences

Chapter 19.
On-Farm Research

Many farmers have become actively involved in one
or more on-farm research projects. These farmers have
become involved with such research and the produc-
tion of new knowledge for several reasons, including
(1) the increasing complexity of crop production prac-
tices; (2) the declining support for applied research
conducted by universities; and (3) the proliferation of
products and practices whose benefits are difficult to
demonstrate. Such on-farm research projects have in-
cluded hybrid or variety strip trials conducted in co-
operation with seed companies, tillage comparisons,
evaluations of nontraditional additives or other prod-
ucts, and nutrient rate studies, as well as other man-
agement practice comparisons.

SETTING Goals

FOR ON-FARM research

The stated purpose of most on-farm research is "to
prove whether a given product or practice works
[normally meaning that it returns more than its cost]
on my farm." While this may seem an obvious goal,
the person conducting or considering conducting on-
farm research should understand several implications
of such a goal:

1. Like it or not, Illinois farmers operate in a vari-
able environment, with large changes in weather
patterns from year to year and with differences in
soils within and among fields. These factors may
in practice force the operator to modify the on-
farm research goal from "proving whether some-
thing works" to "finding out under what condi-
tions something works or does not work" or
"finding out how often something works." Both
of these modifications require that particular tri-
als be run over a number of years and in a num-
ber of fields. The key objective of any applied re-
search project — on-farm or not — is to be able to
predict what will happen when we use a practice
or product in the future. The variable conditions

under which crops are produced make such pre-
dictions difficult.

2. All fields are variable, meaning that a measure-
ment of anything (such as yield) in a small part of a
field (a plot) does not perfectly represent that field,
much less the whole farm. Such variability can be
assessed using the science of statistics: for example,
the statistician might look at the yields of six strips
of Hybrid A harvested separately and state, "The
average yield of Hybrid A in these strips was 155
bushels per acre. But due to the variability among
the harvested strips, we can only say that we are 95
percent certain that the actual yield of Hybrid A in
this field was between 150 and 160 bushels per
acre." In other words, variability means that it is
not possible to be completely precise in measuring
the effects of a particular treatment. Replicating
(treating more than one strip with the same treat-
ment) more times can help narrow the range of
unpredictability, but the range will never be zero.
Some uncertainty will always be present.

If a whole field is harvested using an accurate
yield monitor, the exact yield (for that year) is
known, and we also know the range in yields. With
on-farm research, it is necessary to apply treat-
ments to only parts of the field since no compari-
sons are possible if the whole field is treated the
same. Suppose the farmer stripped the whole field,
with Hybrid A in one side of the planter and Hy-
brid B in the other side. After the strips of each hy-
brid were harvested separately, the statistician
might be able to state, "Based on the strips chosen
to represent Hybrid B, this hybrid yielded 140
bushels per acre, and it is 95 percent certain that
the yield of Hybrid B was between 135 and 145
bushels per acre." In this case, since the "confi-
dence intervals" (150 to 160 for Hybrid A; 135 to
145 for Hybrid B) of the two hybrids do not over-
lap, it is possible to state that the yields of the two
hybrids were significantly different. But in this realis-

19 • ON-FARM RESEARCH

241

tic example, note that the yields of the two hybrids
differed by 15 bushels per acre, and still the confi-
dence intervals came within 5 bushels of overlap-
ping. Now with yield monitors, we can measure
yields of the two hybrids, and we can produce a
"difference map," which tells us which hybrid
yielded more in different parts of the field.

3. Because of the uncertainty, it is necessary to ac-
cept that, when measuring yield (or anything else)
in applied field research, it is virtually impossible
to ever "prove" that some practices or products
work or do not work. Even with the most precise
trials done in the most uniform fields, it takes a
yield difference of at least 2 or 3 bushels per acre
(1 to 2 percent) between treatnients to allow the
researcher to state with confidence that the treat-
ments produced different yields. As a rather silly
example, suppose a farmer went out into a com
field, divided the field into twenty 12-row strips,
then carefully cut one plant out of every 500
plants in 10 of the strips but did nothing to the
other 10 strips. It would be absolutely certain that
the farmer's treatment (cutting out 0.2 percent of
the plants) affected the yield of the treated strips,
but it would also be certain that the farmer would
not be able to measure a significant yield differ-
ence between the two treatments, unless perhaps
by accident. The variability between strips in a
case like this would simply overwhelm a very
small but real treatment effect (the physical re-
moval of the plants by the farmer). Similarly, a
crop additive or other practice may give small
yield increases or decreases, yet never be proven to
work or not to work.

Types of On-Farm Trials

A number of different categories of research have
been popular as on-farm projects, each with its own
challenges. These are discussed below.

Fertilizer Rate Trials

Fertilizer is an expensive input, so rate trials designed
to determine a "best" rate, or the effect of reducing
rates, have been common. Fertilizer rate is what is
called a "continuous" variable — two rates for com-
parison could differ by 50 pounds per acre, 5 pounds
per acre, or 1 pound per acre; the researcher chooses
the rates. Whether or not different rates will produce
significantly different yields depends, of course, on
what rates are selected. This makes the typical "rate
reduction" trial difficult to interpret: 140 pounds of
nitrogen per acre might or might not produce a differ-

ent yield from the "normal" 160 pounds of nitrogen
per acre, but as was just discussed, a field experiment
often will not pick up a small difference. As a result,
many rate reduction studies are "successful" in that
lower rates do not produce significantly lower yields.
But the response to fertilizer rate needs to be gener-
ated by using a number of rates — more than just two.
And the results should be used to produce a curve
showing the response to fertilizer, rather than com-
paring the yields produced by the various rates. Re-
member that the researcher or operator chooses the
fertilizer rates, and the chance of just stumbling on
the "best possible" rate is low.

To illustrate, consider the following com yields
produced in a nitrogen fertilizer rate trial:

Nitrogen

rate

Yield (bu/A)

100

142

120

164

180

163

240

140

Many people looking at these numbers would con-
clude that 120 pounds of nitrogen must have been the
"best" rate, since it gave the highest yield. Figure
19.01 is another way to look at the same data. The
curve, generated by a computer, fits the data quite
well in this case.

When the data are presented this way, it is easy to
see that the "best" rate was not in fact 120 pounds of
nitrogen per acre; the rate that would have given the
highest yield was actually 148 pounds per acre. It was
only by chance that the researcher did not use that

180

100

60 120 180

Nitrogen rate (lb/acre)

240

Figure 19.01. A curve fitted to yields from a nitrogen rate
trial on com.

242

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

(best) rate, but with only one best rate (one highest
point on the curve), the chance of actually using that
best rate is low. Because nitrogen fertilizer has a cost,
the best economic rate — the rate producing the high-
est income — is less than the rate that gives the top
yield. How much less depends on the prices of nitro-
gen and com. In this example, if com is $3 per bushel
and nitrogen costs 20 cents per pound, then the nitro-
gen rate providing the best return would be about 137
pounds of nitrogen per acre. With lower com prices
or higher N costs, the optimum N rate decreases.

A curve to present data is used for a fertilizer ex-
ample here, but the same principle applies for any in-
put for which rates are chosen. Examples of such fac-
tors include plant population, seed rate, and row
spacing.

Hybrid or Variety Comparisons

Hybrid or variety comparisons are very common
and are usually done in cooperation with a seed
company. Comparisons have very good demonstra-
tion value, and when results are combined over a
number of similar trials, they can provide reasonable
predictions of future performance. Most of these tri-
als are done as single (unreplicated) strips in a field.
The results of a single trial do not predict future per-
formance very well. For example, a hybrid that hap-
pens to fall in a wet spot in the field may yield
poorly only because of its location, not its genetic
potential. Seed companies are increasingly averaging
the results of multiple strip trials, thereby providing
better predictions and making the trials more useful.
A farmer who participates in such trials should be
sure to ask the company for results from other loca-
tions as well.

Many people who work with hybrid or variety
strip trials are convinced that the effects of variability
can be removed by using "check" strips of a common
hybrid or variety planted at regular intervals among
the varieties being tested. The yields of such check
strips are often used to adjust the yields of nearby hy-
brids or varieties, on the assumption that the check
will measure the relative quality of each area in the
field, thus justifying inflation of yields in low-yielding
parts of the field and deflation of yields in high-yield-
ing parts. If all variation in a field occurred smoothly
and gradually across the field, such adjustments
would probably be reasonable. But variation does not
occur that way, so it is often unfair to adjust yields of
entries simply because the nearby check yielded dif-
ferently than the average of all of the checks. The use
of such checks can provide some measure of variabil-
ity in the field, but it also takes additional time and
space to plant the trial when checks are used. The

only way to know for certain whether performance of
a variety or hybrid in a strip trial was "typical" is to
look at data from a number of trials to see whether
performance was consistent.

Tillage

Tillage trials are difficult and often frustrating, in
large part because tillage is really not a well-defined
term. One farmer's "reduced tillage," for example,
may be very different from another farmer's. The
same is true for "conventional tillage" and even for
"no-tillage" due to the large number of attachments
and other equipment innovations. Motivations may
also differ substantially: while no-tillage versus con-
ventional tillage may seem like a straightforward
comparison, an attitude of "I know I can make no-till
work" might produce a very different research out-
come from an attitude of "I really don't think no-till
yields are as good as in conventional tillage, and I can
prove it." This may be an extreme example, but there
are indications that tillage trials often are not con-
ducted in a strictly "neutral" research environment.
It is possible to make on-farm comparisons of till-
age practices. Treatments for comparison have to be
selected carefully, keeping in mind that "if you al-
ready know what the results will be, there's very little
reason to do research." Because soil type usually af-
fects tillage responses, it is always useful to do tillage
trials in several different soil types, either on one farm
or among several farms. Replication (to sample soil
variation in each field) is also necessary.

Herbicide Trials

Herbicide and herbicide rate trials are subject to large
variations among years and fields due to the fact that
soil, weather, crop growth (and sometimes variety),
and weed seed supply and growth all can affect the
outcome. This makes it very difficult to prove conclu-
sively that a particular herbicide, combination, or rate
will be predictably better than another. The use of her-
bicide additives throws another variable into the mix
and makes choosing a "best treatment" even more
difficult. Trials in which different herbicides and rates
need to be mixed and applied to strips are often very
time-consuming.

Management Practices

It can be relatively easy to compare different plant
populations or planting rates, although calibration of
equipment — knowing how many seeds per acre or
pounds per acre of seed are produced by a particular
planter or drill setting — can be difficult. Changing the
rates also needs to be done during the busy planting

19 • ON-FARM RESEARCH

243

season, but this can be made easier if calibration is
done beforehand. As discussed in the section on fertil-
izer rate trials, two planting rates that differ only
slightly may often produce similar yields, and finding
a "best" planting rate is difficult. By careful replica-
tion of two or three different rates in a number of
fields over several years, however, it might be pos-
sible (with little risk) to tell whether increased plant-
ing rates would increase yields.

"Interaction" and "Systems" Trials

Many crop production factors interact; that is, the re-
sponse to one factor (plant population, for example)
may depend on choices made related to other factors
(hybrid, for example). While this is known in prin-
ciple, it is difficult to design research to help apply
this knowledge. The short life of many hybrids and
varieties adds to this dilemma: once the research is
done to determine the best population for a particular
hybrid, that hybrid will likely no longer be available.
An alternative is to try to identify hybrids that are
"typical" for some characteristic and can thus repre-
sent a lot of other hybrids, both present and future.
From a practical standpoint, this is virtually impos-
sible, since it is not possible to know for certain that a
hybrid is really typical, and the definition of a typical
hybrid changes over time.

Interaction trials by definition also require more
treatments than do one-factor trials. The simplest in-
teraction trial has four treatments — two levels of one
factor times two levels of another. And such a mini-
mal number of treatments may not always tell re-
searchers much. What would be learned, for example,
if two plant populations were used with each of two
hybrids? Farmers will learn that the hybrids react ei-
ther the same or differently in relation to plant popu-
lations, but a "best" population will not be identified
for either hybrid. It may well be more efficient to
choose one hybrid as the better of the two, then use
three or four different populations to try to see how to
increase its yield. In this type of tradeoff, knowledge
is limited to one hybrid, but the knowledge about it
becomes much better.

Another example of the problem of measuring the
effects of interactions is seen in "systems" research.
In many such studies, several factors are changed si-
multaneously, typically ending up with only two
treatments: the "conventional" system and the "new"
system. While the simplicity of such trials is appeal-
ing, it is often impossible to separate out the effects of
any of the changes the farmer made in going to the
new system. In other words, it may be possible to
compare the overall profitability of the two systems,
but it is not possible to optimize — choose the best

combination of inputs for — the system. Systems trials
can be modified by including more treatments and
leaving out one component of the new system for
each treatment. This will tell how much, if any, each
component contributes to the whole system, and will
allow elimination of changes that are not necessary.

Risk Considerations

On-farm research trials should be selected and de-
signed so that they carry little risk of loss. Many trials,
such as those comparing hybrids or varieties, usually
include only treatments that yield relatively well —
and so represent little risk. It is probably best to avoid
entries in such trials that are certain not to perform
very well, unless there is special interest, for ex-
ample, in knowing how modem varieties compare to
old varieties.

Some types of trials involve considerable risk of
yield loss, and the farmer should be aware of this. A
good example is nitrogen rate trials that include the
use of no nitrogen as one of the treatments. This treat-
ment helps us determine if there is any response to ni-
trogen, but is probably not necessary to find the best
rate; some nitrogen is usually needed for best yields.
Thus researchers might use 60, 90, 120, 150, and 180
pounds of nitrogen per acre in a rate trial instead of
using 0, 50, 100, 150, and 200 pounds. This will reduce
the loss associated with rates that are too low. The
closer spacing of rates will — as long as the range is
wide enough to include the optimum rate — often do a
better job of determining a best rate.

Another example in which untreated "checks" can
cause yield losses would be herbicide trials, where the
use of no herbicide might cause visually dramatic re-
sults but might be an impractical alternative. As these
examples illustrate, it is probably better to restrict
most on-farm research treatments to those necessary
to identify the most practical treatment or rate, rather
than to try to cover the whole range of possibilities,
including treatments that may never be used on a
field scale.

Getting Started with
On-Farm Research

While there is a perception that on-farm research
takes a lot of time and effort, the very large numbers
of variety strip trials prove that farmers will take the
necessary time to do such trials if the rewards are suf-
ficient. Such rewards might be material — for example,
additional seed often is given to variety strip trial co-
operators — or intangible, such as cooperation in a
group project that is expected to provide good infor-
mation useful to all group members.

244

ILLINOIS AGRONOMY HANDBOOK, 1999*2000

No matter what the perceptions about time and ef-
fort required to conduct on-farm research, it is essen-
tial that the work be clearly specified and assigned be-
fore the research begins. To do this, it is most useful to
write down everything that will have to be done,
when each task must be completed, and who will do
each task. The important work gets done this way,
and participants can see beforehand what they will
need to do throughout the season to make the project
work.

From a practical standpoint, it is best to undertake
projects that do not interfere greatly with ongoing
farming operations, particularly at planting and har-
vesting times. For example, it may be easier to apply
nitrogen rates after planting than to delay planting in
order to put on different rates. Work such as hybrid
trials or planting rate trials that must be done at
planting time can be planned for fields that are usu-
ally ready to plant first (or last) or by trying other
ways to work around the main farm operations.

The following steps initiate on-farm research:

1. Decide what type of research is preferred. It is of-
ten better if this decision can be made by a group,
perhaps a "club," operating with similar goals. It
may also be prudent to ask advice from an experi-
enced researcher at this stage. Such researchers
may help to ask questions that focus the goal, and
they may know of previous work that might pre-
vent wasted effort.

2. Formulate specific objectives. For example, rather
than "We want to compare different ways to plant
soybeans," the objective might read, "We want to
see how soybeans in 30-inch rows yield compared
to those in 7-inch rows."

3. Formulate a research plan to answer questions in-
cluding these:

• how many locations and years the research will
be conducted in

• who will actually conduct the comparisons

• what soil type restrictions (if any) there will be

• what equipment, herbicide, or variety re-
strictions (if any) there will be

• what data (for example, yield) will be taken

• who will summarize the results

Several meetings — field days, progress discussions,
results discussions — should be scheduled as part of
the plan. Make sure the plan is practical and that
everyone understands his or her role and has the
right equipment to do the work.

4. Pay attention to work underway, thus providing
encouragement and accountability to individuals

in the group. Field days help do this, along with
coffeeshop meetings during the season. Set dead-
lines for assembling results, and telephone those
who are late to keep everyone on schedule as much
as possible.

5. Have an off-season progress meeting to summarize
results. Plans can be modified for the next season,
but remember that changing treatments or objec-
tives partway through a project is often a fatal
blow: the goals become fuzzy, and participants
may feel that their work has been wasted. It is cer-
tainly inadvisable to stop short of the goal because
the first year's results do not "prove" what people
had hoped they would.

6. Have a final meeting to present and discuss results
from the whole study. While members may choose
their own interpretations of the results, such dis-
cussions are often educational and useful. New
projects often come from discussions of completed
ones.

A WORD ABOUT Statistics

As explained earlier, statistical analysis involves as-
sessing the variability that is always present, then
making reasonable, mathematics-based judgments as
to whether or not observed effects are due to chance
or to treatments. When it is concluded that a reason-
able chance exists that differences in production out-
comes were in fact due to treatments, then it is said
that treatment had a significant effect. This conclusion
does not mean that it has been proven that the treat-
ments caused differences, only that researchers are
satisfied that they probably did so.

When researchers are unable to draw the conclu-
sion that treatments differed, they say that the treat-
ments were not significantly different. This does not
mean that treatment had no effect. Rather, it says that
the research trials were not able to detect such an ef-
fect. There are two possibilities here: either the treat-
ments really did not have an effect, or they did have
an effect, but the experiment was not adequate to de-
tect it. Note the earlier indication that small effects are
very difficult to prove. This is because unexplained
variation ("background noise") will usually "drown
out" small effects.

What can farmers and researchers do when they
think treatments should have differed, but the re-
search results fail to show that? If this occurs in one
trial in one field in one year, then the obvious conclu-
sion is that the research needs to be done again. Due
to the nature of statistics, combining the results of a
number of trials, even when each trial shows only

19 • ON-FARM RESEARCH

245

a small difference, may well show a significant treat-
ment effect. The more replications (years, fields, strips
within fields), the better — provided that each com-
parison is done carefully and that the conditions of
each comparison are reasonably similar. Such combin-
ing of results provides much more confidence for
making a final conclusion, whether or not it agrees
with what research had previously predicted.

Doing statistical analysis is not always simple, and
it may often be advisable to work with a researcher to
get results analyzed. Remember that statistical analy-
sis cannot improve on the research; no amount of
analysis will rescue a trial where the research was
done sloppily or was improperly designed. Many
projects have been made useless by poor designs

which do not allow proper analysis and thus do not
allow conclusions that are supported by solid
research.

Above all, keep an open mind: Research designed
"to prove what we already know" is not research but
a rather sterile exercise. At the same time, applied re-
search almost always represents "work in progress."
Researchers and farmers can benefit a great deal from
the confidence such research in progress provides for
a decision to adopt new production practices or con-
tinue more traditional ones. The increased knowledge
that can be obtained from careful observation of a
growing crop and its responses to evolving manage-
ment practices benefits farming in general and society
at large.

Author

Emerson D. Nafziger

Department of Crop Sciences

Selected Publications

Readers interested in reading more about a particular topic are referred to these publications, some of which were
mentioned in the handbook. Many of the publications are available from a local Extension office. Many of them
are also available for purchase from the College of Agricultural, Consumer and Environmental Sciences (ACES)
ITCS, University of Illinois, 1917 South Wright Street, Champaign, Illinois 61820; (800)345-6087. Addresses for
publications from other sources are also indicated.

Chapter 1. Agricultural Climatology

Field Crop Scouting Manual: A Guide to Identifying
& Diagnosing Pest Problems, X880b (available from
the College of Agricultural, Consumer and Environ-
mental Sciences (ACES) ITCS, University of Illinois,
1917 South Wright Street, Champaign, Illinois 61820)

Pest Management & Crop Development Bulletin (dis-
tributed weekly throughout the growing season; sub-
scriptions are available from the University of Illinois,
ACES Newsletter Service, College of Agricultural,
Consumer and Environmental Sciences (ACES), Uni-
versity of Illinois, 1917 South Wright Street, Cham-
paign, Illinois 61820; (800)345-6087)

Chapter 2. Corn

S.R. Aldrich, W.O. Scott, and R.G. Hoeft. Modem Com
Production, Third Edition. A & L Publications,
Champaign, Illinois

Com and Sorghum Hybrid Test Results in Illinois
(published annually and available each year after har-
vest from Department of Crop Sciences, N-305 Turner
Hall, University of Illinois, 1102 South Goodwin Av-
enue, Urbana, Illinois 61801, or a local Extension office)

Com Planting Date and Plant Population. Jour. Prod.
Agr. 7:59-62, 1994

Soils of Illinois, B778 (available from ACES ITCS)

Chapter 3. Soybeans

Managing Deficient Soybean Stands, CI 31 7 (available
from ACES ITCS; offered free with $5 purchase only)

Performance of Commercial Soybeans in Illinois (avail-
able from Department of Crop Sciences, N-305 Turner
HaU, University of Illinois, 1102 South Goodwin Av-
enue, Urbana, Illinois 61801, or a local Extension office)

Chapter 4. Small Grains

Wheat Performance in Illinois Trials (published an-
nually and available from Department of Crop Sci-
ences, N-305 Turner Hall, University of Illinois, 1102
South Goodwin Avenue, Urbana, Illinois 61801, or a
local Extension office)

Chapter 5. Grain Sorghum

Chapter 6. Cover Crops and Cropping
Systems

G.A. Bollero and D.G. Bullock. Cover Cropping Sys-
tems for the Central Com Belt. Jour. Prod. Agr. 7:55-
58, 1994

Chapter 7. Alternative Crops

Alternative Field Crops Manual (available from the
Center for Alternative Plant and Animal Products, 352
Alderman Hall, 1970 Folwell Avenue, St. Paul, MN
55108)

Chapter 8. Hay, Pasture, and Silage

Hay That Pays: Hay Marketing, LW8 (available from
ACES ITCS)

Illinois Seed Law publication, updated as there are
changes in the law (available from Illinois Department
of Agriculture, Bureau of Agricultural Products In-
spection, P.O. Box 19281, State Fair Grounds, Spring-
field, Illinois 62794)

The Land Under Cover: Hay and Pasture Manage-
ment, LW7 (available from ACES ITCS)

1999 Illinois Agricultural Pest Management Hand-
book, IAPM-99 (available from ACES ITCS)

Returning to Grass Roots: Hay and Pasture Estab-
lishment, LW6 (available from ACES ITCS)

Chapter 9. Seed

SELECTED PUBLICATIONS

247

Chapter 10. Water Quality

50 Ways Farmers Can Protect Their Groundwater,
NCR-522 (available from ACES ITCS)

Protecting Your Water Supply from Ag Chemical
Backflow, E2349 (available from ACES ITCS)

Water Quality and the Hydrologic Cycle: How Water
Movement Affects Quality, LW13 (available from
ACES ITCS)

Chapter 1 1. Soil Testing and Fertility

Illinois Voluntary Limestone Program Producer In-
formation (an annual publication available from Illi-
nois Department of Agriculture, Bureau of Agricul-
tural Products Inspection, P.O. Box 19281, State Fair
Grounds, Springfield, Illinois 62794)

Color Chart for Estimating Organic Matter in Min-
eral Soils in Illinois, AG-1941 (available from ACES
ITCS)

Soil Plan (available from IlliNet Software, 548 Bevier
Hall, Urbana, Illinois 61801)

Compendium of Research Reports on the Use of Non-
traditional Materials for Crop Production, NCR-103
(available from Publications Distribution, Printing
and Publishing Building, lov^a State University,
Ames, Iowa 50011, or your local Extension office)

Chapter 12. Soil Management and
Tillage Systems

The Residue Dimension — Managing Residue to Con-
trol Erosion, LW9 (available from ACES ITCS)

J. Siemens, K. Hamburg, and T. Tyrrell. A Farm Ma-
chinery Selection and Management Program. Jour.
Prod. Agr. 3: 212-219, April-June 1990

Chapter 13. No Tillage

Conservation Tillage Systems and Management: Crop
Residue Management with No-Till, Ridge-Till,
Mulch-Till, MWPS-45 (available from MidWest Plan
Service, Department of Agricultural Engineering, Uni-
versity of Illinois, 332 AESB, 1304 West Pennsylvania
Avenue, Urbana, Illinois 61801)

Weed Control Systems for Lo-Till and No-Till, C1306
(available from ACES ITCS)

Chapter 14. Water Management

Illinois Drainage Guide, C1226 (available from ACES
ITCS)

Chapter 16. 1999 Weed Control for
Small Grains, Pastures, and Forages

1999 Illinois Agricultural Pest Management Hand-
book, IAPM-99 (available from ACES ITCS)

Herbicide-Resistant Weeds, NCR-468 (available from
ACES ITCS)

Illinois Drainage Guide, C1226 (available from ACES ITCS)

Quackgrass Control in Field Crops, NCR-219 (avail-
able from ACES ITCS)

Weed Control Systems for Lo-Till and No-Till, C1306
(available from ACES ITCS)

Weeds of the North Central States, B772 (available
from ACES ITCS)

Chapter 17. Management of Field Crop
Insect Pests

1999 Illinois Agricultural Pest Management Hand-
book, IAPM-99 (available from ACES ITCS)

Bt-Com and European Com Borer: Long-Term Success
Through Resistance Management (available from
ACES ITCS)

Conservation Tillage Systems and Management: Crop
Residue Management with No-Till, Ridge-Till, Mulch-
Till, MWPS-45 (available from MidWest Plan Service,
Department of Agricultural Engineering, University of
Illinois, 332 AESB, 1304 West Pennsylvania Avenue,
Urbana, Illinois 61801)

Com Insect Pests: A Diagnostic Guide (available from
ACES ITCS)

Field Crop Scouting Manual: A Guide to Identifying &
Diagnosing Pest Problems, X880b (available from
ACES ITCS)

Chapter 18. Disease Management for
Field Crops

1999 Illinois Agricultural Pest Management Hand-
book, IAPM-99 (available from ACES ITCS)

Various reports on plant diseases (available from De-
partment of Crop Sciences, N-305 Turner Hall, Univer-
sity of Illinois, 1102 South Goodwin Avenue, Urbana,
Illinois 61801)

{

4b4 07/02 n I

99Q0Q JJI If

To convert
column 1
into

colunin 2,
multiply
by

0.621
1.094
0.394
16.5

0.446
0.891
0.891
0.016
0.015

Useful Facts and Figures

Column 1

Column 2

Length

kilometer, km
meter, m
centimeter, cm
rod, rd

mile, mi
yard, yd
inch, in.
feet, ft

Area

Volume

Mass

Yield

Plant Nutrition Conversion

P (phosphorus) x 2.29 = Pp^
K (potassium) x 1.2 = K^O

PPj X .44 == P

Kp X .83 = K

To convert
column 2
into

column 1,
multiply
by

1.609
0.914
2.54
0.061

0.386

kilometer^, km^

mile^ mi^

2.59

247.1

kilometer^, km^

acre, acre

0.004

2.471

hectare, ha

acre, acre

0.405

0.028

liter

bushel, but

35.24

1.057

liter

quart (liquid), qt

0.946

0.333

teaspoon, tsp

tablespoon, tbsp

0.5

fluid ounce

tablespoon, tbsp

0.125

fluid ounce

cup

29.57

fluid ounce

milliliter, ml

0.034

pint

cup

0.5

pint

fluid ounce

0.063

1.102

ton (metric)

ton (English)

0.907

2.205

kilogram, kg

pound, lb

0.454

0.035

gram, g

ounce (avdp.), oz

28.35

ton (metric) /hectare

ton (English) /acre

2.24

kg/ha

lb /acre

1.12

quintal/hectare

hundredweight/acre

1.12

kg/ha-com, sorghum, rye

bu/acre

62.723

kg/ha-soybean, wheat

bu/acre

67.249

Temperature

Celsius

Fahrenheit

5/9(F-

ppm X 2 = lb/A (assumes that an acre plow depth of 6 V^ inches weighs 2 million
pounds)

Speed (mph)

Useful Equations

distance (ft) x 60
time (seconds) x 88

1 mph = 88'/min

Area = a x b

Area = V, (a x b)

Area = Tir^
71 = 3.1416

lb/ 100 ft^ =

Example: 10 tons/acre

lb /acre
435.6

20,000 lb
435.6

46 lb/100 ft^

lb/acre

oz/100 ft^ = X 16

435.6

100

Example: 100 lb/acre = x 16 = 4 oz/100 ft^

435.6

gal /acre

tsp/100 ft^ = X 192

435.6

Example: 1 gal/acre = x 192 = .44 tsp/100 ft^

435.6

Water weight = 8.345 lb/gal
Acre-inch water - 27,150 gal

ISBN l-aa3D^7-E2-3

UNIVERSITY OF ILLIN0I9-URBANA

^'*. "r I

Leading the way for agriculture to the year 2000
The New

1999-2000 Illinois Agronomy Handbook

♦ reliable research

♦ field and forage crop production guides

♦ soil management, testing and fertility

♦ expected crop yields

♦ farm safety information

New this year:

listing of all soil insecticides now labeled for control of
corn rootworms, cutworms, white grubs and wireworms
increased focus on the problem with western corn root-
worms in corn planted after soybeans
improved information about managing European corn
borers with Bt-corn

effects of El Nino and La Nina on Illinois corn and soybean
yields

update on phosphorus and the environment: its impact
on water quality
the pros and cons of strip tillage for your corn

■^•'4.^''^^5!!!S

"llJll'v|^

., ^?a^ ,r ,. .^v-^

Internet Archive Audio

Featured

Top

Images

Featured

Top

Software

Featured

Top

Books

Featured

Top

Video

Featured

Top

Mobile Apps

Browser Extensions

Archive-It Subscription

Save Page Now

Full text of "Illinois agronomy handbook, 1999-2000"

See other formats