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,f*0^,Tj*f A STATE LIBRARY

3 0864 0014 aoal 5

Agricultural Plant Pest Control

A Study Manual for

Commercial and Governmental

Pesticide Applicators

This manual is intended for applicators who apply pesticides to agricultural crops or
rangeland. The Agricultural Plant Pest applicator must demonstrate practical knowl-
edge of crops grown, their specific pests, and the pesticides used for their control. Prac-
tical knowledge is required concerning pesticidal activity in soil and %ater, pre-harvest
intervals, re-entr}^ intervals, phytotoxicit}', potential for environmental contamination,
non-target injury, and community problems resulting from the use of pesticides in agri-
cultural areas.

The Appendices in tliis manual are additional reference materiaL The test will not in-
clude information from Appendix A - C. The information is only added for your ben-
efit to identify pests in the field or for reference in the future. y ||

To simplify information, trade named products and equipment have been mentioned.
No endorsement is intended, nor is criticism implied, of similar products or equipment
which are not mentioned. ^,^^,,-, .-

A special thank you to Susan Kedzie-Webb at Montana State University for the illustra-
tions in the Weeds - Part 11 section of this manual. Also acknowledgments to all those
behind the scene, thank you for your help. -J

Developed by the Montana Department of Agriculture:

Laura Hinck Kim Johnson Barbra Mullin

Entomologist Training & Development State Weed Coordinator

Agricultural Sciences Division, Technical Services Bureau, P.O. Box 200201,
Helena, Montana 59620-0201, (406) 444-5400

Digitized by the Internet Archive

in 2011 with funding from

IVIontana State Library

http://www.archive.org/details/agriculturalplan1998mont

PLANT DISEASES - PART I

THE NATURE AND CAUSES OF DISEASE IN PLANTS

H Introduction

There are an estimated 1 00,000 parasitic plant diseases. Fortunately, about 80 percent occur rarely or
on a limited scale and are considered relatively unimportant. The annual cost of plant diseases in the
United States is five billion dollars.

Plant diseases are the result of the right combination of susceptible host plants, a virulent pathogen
(disease causing agent), and suitable climatic conditions experienced during the growing season (Fig-
ure I-l). Variations fi'om characteristic or normal climatic patterns are often responsible for sudden
outbreaks of certain diseases that would not normally occur. Regional climatic conditions are a major
factor in determining crops that can be grown profitably and the prevalence of diseases on these crops.

Plant diseases are divided into parasitic or nonparasitic:
Non-parasitic or physiological diseases include:

♦ nutrient deficiencies or excesses,

♦ environmental extremes,

♦ air pollution and pesticide injury,

♦ drought,

♦ genetic abnormalities, and

♦ other physiological disorders.

Environment
Parasitic diseases are caused by living organisms which can multiply and spread from infected to
healthy plants. Organisms commonly causing parasitic plant diseases sre fungi, bacteria, vi-
ruses, mycoplasmas, and nematodes.

Figure I-l

B Fungi

Fungi are simple microorganisms that lack chlorophyll and are unable to manufacture their own food.
Fungi obtain their food from living plants and animals or from decaying organic matter. There are about
8,000 parasitic fungi causing 80,000 of the known 100,000 plant diseases.

Most disease-causing fiangi are inconspicuous and can be seen
only with the aid of a microscope. Commonly recognized fungi
include yeast, mildews, and mushrooms.

Fungi may enter a plant through wounds, natural openings, or by
penetrating directly through the epidermis - outer plant tissue (Fig-
ure 1-2).

Figure 1-2. Penetration
of a stomate of a wheat
leaf by a fungus. ^'■•-

1

Mycelium of
a fungus

Stomate guard cells

Epidermis

Figure 1-3

Developing fungal spores.

Vegetative growth (mycelia, hyphae) of the fungus usually gives
rise to reproductive structures producing fungal spores (Figure I-
3) which act to spread the disease from infected to healthy plants.
The life cycles of certain fungi are extremely complex and may
involve a number of different spore stages and more than one
plant host (Figure 1-4).

Fungi cause local or general disintegration of plant cells or tissue,
stunting of plant organs or entire plants, or abnormal vegetative
growth, all of which are detrimental to the plant and may result in
its eventual death.

Fungi may affect plant growth by:

♦> Removing or blocking the movement of nutrients essential to plant growth.
<♦ Producing and secreting certain substances [enzymes or toxins] which affect the
structural and metabolic activity of plants.

Fungal pathogens can spread spores and mycelium through plant materials, wind, water, ani-
mals, and insects. Below is a disease cycle of bunt smut of wheat.

Binucleate
secondary
sporidium

Primary sporidia
fuse to form
H-shaped
structures

Mycelium reaches and
follows growing point of
'\. [,. plant

Secondary
sporidium
germinates

Mycelium pen-
Dikaryotic mycelium f^^^' ^^^^Img
from secondary ^^^^^^^V ^"'^ g™^^

sporidium attacks between cells
wheat seedling

Uninucleate
primary sporidia

y Basidium
Germinating teliospore

Zygote

Teliospores on
prminating
wheat
kernel

Smutted kernels break
upon harvest and
contaminate healthy

wheat kernels

Healthy wheat
head

w, /i' K.CII1C1 Hn

..'It C0#

Intercellular
mycelium

Mycelium grows

through spike
and into wheat
kernels

Mycelium becomes
intracellular in
kernels

Mycelia cells
are transformed
into telipspores

Figure 1-4. Disease
cycle of bunt smut
of wheat.

Smutted
wheat head

Smutted wheat kernel
full of teliospores

nucleoid

■ Bacteria

Bacteria are one-celled microorgan-
isms (Figure 1-5) found in air, soil,
and water and are common on or in
all plants, animals, and humans. In-
dividual cells can be seen only with
a high powered (900 x) microscope.
There are over 170 species of bac-
teria causing diseases in plants.

plasma membrane
ribosomes
mesosome
cell wall
slime layer

Figure 1-5. Illustra-
tion of a bacteri cell.

cell septum

Bacteria reproduce by simple cell division at extremely rapid rates. If a single bacterium divided to
produce two new cells and all its descendants did likewise every 20 minutes for just 12 hours, 70 billion
bacteria would be produced. In 24 hours, 2,000 tons of bacteria would be derived from just a single cell.
It's no wonder that flowers, fruits, and vegetables sometimes rot and wilt so quickly. Fortunately,
bacterial reproduction is limited by nutrients, temperature, and availability of space.

Bacteria enter plant tissue through wounds or natural openings such as the stomata of leaf surfaces.
Once inside, pathogenic bacteria multiply rapidly, kill cells or cause them to grow abnormally, break
down tissue, and often migrate throughout the plant. Certain bacteria, such as fire blight, produce
chemical toxins that poison the plant.

Bacteria are spread by people through cultivation, pruning and transporting diseased plant material,
such as seeds, bulbs, nursery stock, or transplants. Animals, insects, mites, nematodes, splashing rain,
flowing water, and windblown dust are also common disseminating agents for bacteria.

■ Viruses

Viruses are complex macro-molecules composed of ribonucleic acid (RNA) with a protective protein
"overcoat" (Figure 1-6). They resemble the chromosomes present in all living plant and animal cells -
both are self-reproducing nucleoproteins. Viruses can only function and reproduce in a living cell.

Viruses divert normal growth and development processes in plant cells, causing stunting, yellowing,
mosaic, ringspot, or streak symptoms. Identification of viral diseases usually requires the inoculation of
specific indicator plants or special laboratory techniques.

Some plant viruses, such as potato mosaic viruses, are very infectious and can
be spread easily from diseased to healthy plants by contact. Others are trans-
mitted by vectors, such as the wheat curl mite spreading wheat sfreak mosaic
virus. Most viruses can be spread by grafting or budding or by vegetative
propagation (e.g. cuttings, root division). Viruses are also disseminated through
infected seed or plant pollen. Viruses often overwinter in weeds or in the
bodies of insects or mites.

Protein coac -

RNA

Figure 1-6. Maize
mosaic virus

'Trrrr nv^

■ Mvcoplasma-Like Organisms dMLOs)

MLOs are microorganisms of an intermediate size between viruses and bacteria, generally without cell
walls. They possess many virus-like properties and are not visible with a light microscope. MLOs are
made up of RNA + DNA strands with ribosomes and a unit membrane. They are spherical or pleomor-
phic (i.e. exist in different forms or shapes). Spiroplasmas are similar to MLOs but are spiral in form.
Rickettsia-like bacteria are similar to MLOs, but bacilliform.

Most of these organisms cause "yellow" or "witches' broom" type symptoms in plants. Antibiotic
drugs, including tetracycline, are effective in controlling aster yellows and other diseases caused by
MLOs. Plant infecting MLOs have been found in leafhoppers. This insect is the principle vector of
certain yellows-type diseases.

■ Nematodes

Nematodes are microscopic, unsegmented roundworms (Figure 1-7). They occur in water and soil.
Most are harmless, feeding primarily on decomposing organic material and soil organisms.

Parasitic nematodes injure plants by sucking out plant juices through hollow, spear-like
mouth parts (stylet). Nematode feeding lowers natural resistance, reduces the vigor and
yield of plants, and affords easy entrance for wilt or rot producing fungi and bacteria.
Nematode-damaged plants are often more susceptible to winter injury, drought, dis
ease, and insect attack.

Some nematodes enter plant tissues to complete th.eir life cycle, while others remain
(^ outside with only their feeding parts attached to the
roots. All plant-parasitic nematodes reproduce by
laying eggs. Larvae hatch from the eggs and initiate
disease during their feeding (Figure 1-8).

E^f)^':i:i\k?;i;s!;t*.k*^5^!W\'."-<^

Nematodes generally take
several years to build up
damaging population lev-
els in soils. They are easily
spread by any agent that
moves infested soil, plant
parts, or contaminated objects.
Nematode damage is often diag-
nosed based on plant symptoms but cor-
rect identification is done by a trained nema-
tologist working in a well-equipped laboratory
with a compound microscope.

Figure 1-8. Potato cyst nematode life cycle.
1 ) cyst showing enclosed eggs; 2) enlarged egg showing
enclosed, coiled larva; 3) larvae entering root; 4) and
5) swollen females feeding in root; 6) mature female
breaking through root surface.

THE PRINCIPLES OF PLANT DISEASE CONTROL

■ Tntroduction

Effective plant disease control is based on thorough knowledge of diseases likely to appear in an
area, the plants susceptible to attack, plus an early and accurate diagnosis of the problem.

Control measures must start at the early onset of disease - preferably before symptoms appear.
Control starts with the purchase of the best seed or planting materials available, continues with
proper seedbed preparation, and is maintained throughout the growing season.

Five fundamental principles of plant disease control are recognized. These are: Exclusion,
Eradication, Protection, Host Resistance, and Biological. Often there is considerable overlap among
and between these principles. All five may be used alone or concurrently to protect plants.

■ Exclusion

Exclusion is the prevention of disease-causing organisms from entering and becoming established
where susceptible plants are growing - in a garden, locality, state, or country - through federal and
state embargoes, quarantines, inspections, and disinfection of plants, seeds, and other propagative
plant parts. More than 150 countries now have established quarantine regulations.

About 650 USDA plant quarantine inspectors are our first line of defense against alien pests. Each
year, at a cost of about $40 million, these technically trained people intercept some 650,000 lots of
prohibited plant material through inspection of people, baggage, mail packages, plus ship and
airplane stores.

More than 50 percent of the major plant diseases and pests in the United States have been introduced
from foreign countries. Since 1912, our plant quarantine system has saved America billions of
dollars by reducing sharply the rate at which destructive plant pests have gained entry from other
countries and offshore islands. Examples of alien pests include chestnut blight, Dutch elm disease,
and white pine blister rust. These diseases and other pests cause losses of several billion dollars each
year in the United States.

Other methods of exclusion include certification of plants, cuttings, and seed. This may include heat
or chemical disinfection of small plants, seed, bulbs, corms, and other parts by producers or
governmental agencies before shipment (see under Eradication below), fridexing to ensure planting
stock is free of fungi, bacteria, and viruses is also an important exclusion practice.

Sometimes restricted entry of planting material is allowed. The plants are grown in isolation and
are inspected frequently over one to two years before distribution is permitted.

■ Eradication

Eradication is the elimination of the disease-causing agent or pathogen after it has become
established by rotation; removal of diseased plants or infected parts; destruction of wild or other
overwintering host plants; seed or plant freatment; surgery; soil treatment; and a variety of sanitary
measures.

• Crop Rotation

Continuous culture of one kind of plant provides an opportunity for the perpetuation and
increase of pathogens and build up of disease. This is prevented by rotating annuals or
biennials in seed and flower beds and by growing the same or closely related plants in the
same soil only once in three to five years. This practice "starves out" most host specific
pathogens. These organisms normally persist in soil only as long as host plant residues
persist, usually only a year or two. Rotation is not effective against common soil inhabitants
- fimgi and bacteria that survive in soil up to 10 years or more in the absence of host plants.
Many root-rot and wilt-producing fungi (e.g. Aphanomyces. Fusarium, Phytophthora,
Pythium, Rhizoctonia, and Verticillium) may survive indefinitely in soil, making eradication
by rotation impractical.

• Destruction of Overwintering Hosts

Perennial and biennial weeds are often a source of disease-causing pathogens. Eradication
of these weeds breaks the life cycle of the pathogen and helps control disease. Examples
include a wide range of virus and mycoplasma diseases of all types of plants. Aphids, leaf-
hoppers, and thrips feed on weed hosts, pick up the virus or mycoplasma, fly to host plants,
feed, and infect them. Chokecherries, wild plums, and other Pninus species are the primary
source of infection to flowering cherries, plums, and almonds. Viruses and mycoplasmas
causing cucumber mosaic, aster yellows, tobacco mosaic, spotted wilt, plus tomato and
tobacco ringspots infect hundreds of different weeds, crops, and landscape plants alike.
Control of weeds by cultivation, mulches, and herbicides is an important practice. Volunteer
crop plants can also serve as an overwintering host and should be destroyed.

• Seed or Plant Treatment

Control of pathogens within seed, bulbs, corms, and other parts, by wet or dry heat or a
systemic plant health product, is common. Hot water dips are used to kill root knot and other
nematodes in roots of numerous plants. Such treatment of dormant plants or propagative
parts also controls a wide range of organisms causing seed, bulb, corm, stem, rhizome and
root rots, wilts, and leaf spots, mites as well as insects.

Successfiil eradication by hot water is dependent on killing pathogens and pests at a certain
temperature and time which causes little or no injury to the treated plant or part. Effective
hot water treatment must be done with properly calibrated equipment to prevent injury to the
host plant.

Systemic fungicides, such as carboxin (Vitavax), thiophante (Topsin), and thiophanate
methyl (Fungo-50) are used for eradicating fimgi within plant tissues. Streptomycin is useful
as an aid to prevent fire blight and some other bacterial infections.

• Surgery

Pruning and removal of twigs and branches of woody plants affected with fire blight and
other bacterial or fungal cankers is widely practiced. Other examples include removal of
wood-decay in tree trunks and limbs, excision of crown gall-diseased tissue, and cutting out
bacterial soft rot in iris rhizomes. Proper sanitation of cutting utensils and disposal of
diseased materials is important to prevent the spread of disease.

• Soil Treatment

This method is useful for potted plants, seed beds, greenhouses, and certain outdoor
plantings. Annual treatment is usually necessary to control nematodes, soil-borne fungi and
bacteria, insects, mites, and other pests. Preplant soil fumigants that control a wide range of
soil-home organisms and pests include methyl bromide, chloropicrin, and metam-sodium
(Vapam). Dazomet (Basamid) is used as a soil sterilant.

Steam or dry heat is widely used to pasteurize soil for potted plants, greenhouses, and some
outdoor beds. Soil treated with steam or certain fumigants needs to be covered with plastic
to retain the steam or chemical in soil for the required time. It is then important not to
contaminate treated soil with untreated soil or plant material that may be infected.

• Sanitation

Sanitation practices include a clean and deep plowdown, disinfection of tools, machinery and
storage facilities, plus destruction of diseased plant refuse.

>- Clean plowing or burial of plant dehris helps reduce the overwintering or
oversummering inoculum of pathogens causing foliar and fhiit diseases. It works
best for low-growing annuals or biennials that can be shredded to facilitate complete
burial in the soil.

>^ Disinfecting machinery and tools with steam, hot water under pressure, or methyl
bromide is essential to prevent spread of soilbome pathogens from one greenhouse
or flower bed to another.

y^ Disinfecting storage areas, crates, baskets, and sacks helps prevent carryover
from one season to the next of various storage-rot fungi and bacteria in bulbs, corms,
rhizomes, tubers, and roots. Sweeping the storage area clean, followed by thorough
spraying of all surfaces with copper sulfate is very effective. If the storage area is
air-tight, chloropicrin or tear gas may be used. Wait at least 12 to 24 hours - or until
all chemical odor has gone - between treatment and storage of fresh plant materials.

>■ The destruction of plant refuse is valuable for preventing the over-wintering of
bacteria, leaf, stem and flower-infecting fiingi, and insects, mites, nematodes, and
other pests.

>- Eradication of alternate hosts is successful in special situations and aids in
reducing the development of new races of rust fungi. Examples of this practice
include programs to eradicate Rihes spp. (currants and gooseberries), which are
alternate hosts of white pine blister rust and eradicate junipers and red cedars, the
altemate host of a rust fimgus that will also attack chokecherry, crab apple, hawthorn,
mountain ash and other useful tree species. Probably the most well known
eradication program in Montana was eradication of the barberry, an altemate host to
the stem mst found on small grains. Destmction of the less desirable host plants is
usually needed for a distance of several hundred yards or more around the crop to be
effective.

■ Protection

Placement of a. protective barrier between the susceptible part of the host plant and the disease agent
or pathogen is a common method of disease control. This method assumes that the pathogen is
likely to be or is already present where susceptible host plants are grown. Protection usually means
application of sprays or dusts to the plant before air, water, or insect-borne fiingal spores arrive. The
spores germinate in drops of water into which some fiingicide has dissolved. The spores are thus
killed before entrance into the plant can occur. Protection also includes killing of insects, mites, or
other inoculating agents before these pests can feed and infect plants with pathogens carried on or
in their bodies.

To be successful, protective chemicals must be specific to the pest (fungi, bacteria, mycoplasma,
nematode) and applied at the recommended label rate and the appropriate time. Several applications
are usually needed to keep new leaf and fhiit tissue covered with a protective film. Most modem
fungicides have a short residual of 7 to 10 days. Rain also washes some pesticide away and reduces
control.

Creation of an unfavorable environrnent for the pathogen during growth, storage, and shipment
is an effective means of protection. It includes such practices as:

^ Producing crop seed in low rainfall areas where moisture is supplied by furrow
irrigation. Under these dry conditions fiingi and bacteria are not as likely to infect host
plants. The result is healthy, pathogen-free seed.

^- TTie time and depth of planting often helps prevent certain diseases. Soil moisture and
temperatures that favor plant growth and not the pathogen can help prevent disease
development. Examples: Deep planting may result in excessive Phytophthora crown rot to
woody plants, pre-emergence, damping off of seedlings, and decay or shoot blight of
flowering bulbs. Early or late plantings often escape migrations of virus and mycoplasma-
carrying insects from weeds to crops. As a general rule, it is advisable to plant cool season
crops in cool soil and warm season crops in warm soil to minimize soil-borne diseases.

^- Excessive soil moisture in the field commonly increases seed decay, damping off, and
root rot diseases. Where possible, avoid planting annuals and most perennials in areas where
soil drainage is poor or where water stands for several days following rains.

^' Fertilize based on soil or tissue tests. Essential macro- and micro-elements, when kept
in balance, increase plant resistance to many fungal and bacterial infections. For example,
excessively high applications of nitrogen, when available potassium and calcium are low,
greatly increases losses from such diseases as fire blight, stem and storage decays, Botrytis
blights, powdery and downy mildews, many leaf spots, and rusts. A deficiency of an
essential element such as boron, copper, iron, magnesium, manganese, and zmc may be
involved directly in the development of noninfectious diseases.

8

'^ Control of temperature mid moisture when po.s,siNe can prevent development of leaf,
flower, and fruit diseases as well as foliar nematodes. Free water on the foliage from
careless watenng late in the day, is necessary for infection by most bacteria and fiingi i well
as all nematodes. High relative humidity, unless controlled by heat and increased air
circulation, favors development of powdery mildews, Botrytis blights, leaf molds and other
diseases. Wider spacmg of plants in flower beds and landscape plantings promotes rapid
drying following wet penods and thus checks development of foliage, flower and fruit
diseases.

'T ^Q^g '>' hand/ifig plants and nropamive nnrts durm^ hnrv^.t n.H .f^ra^e ^-Hp-i drrrcacc
disease problems. Sorting out bruised, cut, or rotted bulbs, cornis, roots, and tubers at
harvest prevents storage rots, especially when combined with temperature and humiditv
control. ^

'♦ Chemotherapy, the treatment of disease by chemicals working internally to kill
mactivate, or protect against the pathogen without injuiy to the host plant, is another method
ot control. Systemic ftingicides are absorbed and transported within plants to confrol certain
diseases for several weeks or months. To be effective, a chemical must be taken up by the
seed, leaves, roots, or stems and be transported in an active state to where infection occurs
Some fungicides with systemic activity include benomyl, chloroneb, TBZ carboxin
oxycarboxin, and propiconazole.

■ Host Resisfanee

Development of resistant host vaneties is usually the most effective and economical means of
controlling plant diseases. Plant species, evolving over countless centunes, are normally highlv
resistant to prevalent native pathogens. When people introduce hosts or pathogens into new areas
widespread devastation is not uncommon. Good examples are Dutch ehn disease and chestnuJ
blight, both native to the Orient but devastating to landscape trees in the United States.

The primary objective developing resistant plants is to combine disease resistance with other
desirable agronomic or horticultural qualities. A few examples: new bluegrass cultivars resistant
0 Helminthosporium leaf spots; vanous flowers resistant to Fusarium wilt; crepe myrtles resistant
to powdery mildew; and firethoms resistant to scab. One of the most successfiil breeding programs
has been the development of stem rust resistant wheat varieties.

■ Biologioal Tpntr^l

Biological control can be defined as the regulation of pest organisms by their natural enemies
Classical biological control is the control of pests by introduced natural enemies. Natural biological
control IS confrol of a species havmg the potential of becoming a serious pest but failing to do so
because they are restrained by natural enemies. The preservation and augmentation of naturally-
occumng biological confrol agents is a key consideration in pest management.

One area of biological control is competition of soil microbe antagonists with soil-borne plant
pathogens. Soil is ennched with orgamc matter and nonpathogenic soil organisms that can

successfully compete and replace several common soil-bome plant pathogens. An example of this
is the use of the fungus Trichoderma that competes with Sclerotinia, Pythium, Fusarium,
Rhizoctonia, and Thielaviopsis . This is often referred to as "suppressive soil." Several biological
products are labeled to suppress soil microorganisms. An example is, Mycostop (Streptomyces) for
Fusarium wilt. In addition, Kodiak (Bacillus) is a labeled seed treatment and soil drench.

Another successful biological control program is the control of crown gall (Agrobacterium
tumefaciens) by a highly competitive, non-pathogenic strain oi Agrobacterium radiobacter. This
bacterium produces a protein (bacteriocin) which acts as an inhibitor of related bacterial strains, thus
preventing crown gall infection of young nursery stock through ecological exclusion. Research for
bacteriocins of other important plant pathogens continues. Bacteriocins have potential as excellent
biological control agents because they tend to have a narrow host range and testing is fairly simple.
They are common proteins and should, therefore, be environmentally safe.

Some microorganisms are also found that produce antibiotics against other organisms. This
phenomenon is not clearly understood but it has potential as another biological control tool. In
general, antibiotics are not as host specific as bacteriocins.

■ Tntegrated Control of Plant Diseases

Integrated control of plant diseases involves the same practices utilized in integrated insect pest
management. Plant disease management includes selection of adapted, resistant varieties;
environmental manipulation; biological control; and the use of protectant chemicals based on
economic thresholds of the disease level. Effective use of these management principles requires
detailed knowledge of the host, the pathogen, and the environmental effect on their interaction.

Integrated pest management is probably used more than many people realize. Many growers use
different types of control methods without realizing that they are using an integrated pest
management program. Development of integrated plant disease management is hampered by the
formation of new races or biotypes of plant pathogens; weather conditions that are conducive to
epidemics; absence of records on disease occurrence, spread, severity and estimated crop losses; lack
of adequate biological controls; lack of personnel trained in field diagnosis; and the absence of data
on the economic thresholds of plant diseases.

There is tremendous potential for improving integrated plant disease management. There is need
for more plant disease research followed by educational efforts, regulatory work by state and federal
agencies, and input from the private fanner or grower regarding requirements to produce and protect
quality food and fiber.

10

PROCEDURES IN FIELD DIAGNOSIS ON
AN UNKNOWN PLANT DISEASE

■ Tntroduction

Plant disease diagnosis is based upon observation of symptoms and signs. Some basic information
is needed for accurate diagnosis, including:

(D Know what a normal, healthy plant looks like. Be acquainted with the major
varieties and their growth habits.

® Know what diseases have been described as occurring in the crop.

(D Know which of these diseases commonly occur in your area.

® Know the symptoms that will be useful in distinguishing between the different
diseases that you are likely to encounter.

® Look for signs of rodent, insect, or other animal damage that may be causing the
injury.

® Mineral deficiencies cause many plant diseases, usually when they are lacking or tied
up in forms unavailable to the plant.

® Check the water table, particularly if it is near the surface. High water tables may
cause a "physiological drowning out", or salt injury. A soil auger is essential for
such determinations. The plant, on the other hand, may be declining from lack of
water. Here again, an auger may be useful. The quality of the water must also be
considered. Does it contain toxic quantities of salts, factory wastes, or other
contaminants, such as pesticides?

■ Field Diagnostic Factors

The following are some questions and points that must be considered when investigating a disease
in the field:

■^ The Distribution of the Disease

/ Is it over the entire field or does it occur in spots?

/ If it occurs in spots, what is different about these spots? Are they in low or high ground
or could there be some other difference such as a sand or gravel layer near the surface, or soil
dumping area, soil compaction, poor drainage, etc?

"^ Tlie Crop History and the Method of Handling

/ Is this the first time for this crop to be planted in this location, or has the crop been
planted continuously in this same location?

11

/ What about the fertiHzation practices, spray program, irrigation program, or unusual
weather conditions during the past month or season?

/ Has anything unusual been done in the field during the past few years?

/ Have herbicides or soil sterilants been used?

/ Have insecticides or fungicides been applied?

/ Has there been smog or other toxic gases in the area?

/ What was the source of planting stock or seed? Was this seed certified, registered, or
inspected?

■^ Make a Thorough Examination of a Number of Infected Plants

y Examine infected plants throughout the entire field or area in a systematic pattern.
Observe the symptoms.

«/ Are the symptoms systemic, as in the case of root rots, wilts, and certain physiological
disorders associated with nutrition?

y Are the symptoms localized, such as on the leaf margins or along the veins, or scattered
at random over the leaf surface?

/ How does the diseased plant differ from the healthy plant in color, size, and degree of
maturity?

y Are there signs of the cause of the trouble, such as fungal fruiting bodies, mycelium,
sclerotia, molds, mildew, and rust or perhaps indications of insect injury such as chewed
leaves, tunnels in stems or roots, droppings (frass), holes, or mite eggs?

/ Are the terminal shoots, blossoms, or fruits wilted, discolored, or rotted?

"^ Examine Symptoms in Detail
♦ Foliar

Study the injury, observing its color, size, shape (angular or circular) and note the margins,
observing whether they are definite or indefinite.

/ Is there a water-soaked appearance, a velvety growth or discrete black spots on the injured
tissue? Note whether the disease spot of the leaf is cut out, resulting in a shot-hole condition
and whether there are accompanying symptoms such as yellowing of the diseased leaves.

/ Are there malformations or overgrowths on the leaves, stems, or roots?

12

/ Has defoliation occurred, partially or fully?

/ What is the color of the damaged leaves at the time defoliation occurred?

♦ Stem Cankers

Check the extent of the area covered by the canker, either large or small, and whether the
dead area extends deep into the stem or occurs only near the surface. Note whether the
surface is smooth, rough, or scaly. On some cankers, fruiting bodies of the fungus may be
seen resembling blisters or nailheads or small pimple-like dots.

♦ Fruit Rots

y Does the rot occiu- on immature fruit or only on ripening fruit near harvest?

/ What is the size and location of the spot (lesion) on the fruit?

/ Is the tissue sunken and is there evidence of fiingal fruiting bodies?

/ Is the rot dry, watery, soft, pithy, or spongy?

♦ Root Rots

Declines in plants often result from infection by certain soil fiingi. These are seldom
discovered until the above ground part of the plant begins to show disease symptoms. Such
foliage may be wilted and light colored, either on one side or over the entire plant. Check
for fungus growth beneath the bark or for discolored vascular system.

"^ Consider All the Symptoms and Information Availahle

y Have similar symptoms been seen before either in this crop or related crops?

y Can you pick out one or more key symptoms such as mottling, yellowing, or necrosis that
might suggest a recognized virus or deficiency?

/ Is there a pronounced wilting or a dying of the crown or terminal leaves?

/ What is the condition of the root system?

■ Laboratory Aids to Correct Diagnosis

After a thorough examination of specimens in the field, and a consideration of the distribution,
previous occurrence, and cropping history, you probably will have suspected that the disease in
question is one of several that, from previous reading, you know occurs on the crop under
consideration. You know that the disease may be caused by a virus, mycoplasma, fimgus, bacterium,
nematode, or change or variation in climatic or cultural condition of the host. How do you determine
which of these, or possibly a combination of these causes is involved?

13

If you cannot track down the answer in reference books or from local authorities, submit a
specimen(s) to the Plant Disease Clinic at Montana State University. Please use a Specimen
Identification Form that you can get from your county agent. Specimens will be checked with a
microscope for the following:

>' Is there evidence of mycelium or spores on the surface of the lesions?

>- Is it in the phloem (suggestive of virus diseases) or xylem (suggestive of ftingus diseases)?

>- If the vascular tissue is discolored, is there evidence of mycelium?

>* If possible the organism will be cultured, portions of tissue will be plated out on appropriate
agar media and the organism isolated in pure culture.

>- To prove absolutely beyond a doubt the relationship of the organism with the disease,
inoculation must be made into healthy plants, again reproducing the symptoms initially
observed. The final step is to recover the same organism from the inoculated plants that were
first obtained from the diseased plants. This sequence is referred to as Koch's postulates of
pathogenicity.

If a virus is suspected, tests may be made in the greenhouse using various host plants that will aid
in identification of the virus. It will be necessary here to demonstrate transmissibility by mechanical
inoculation, budding, or grafting. For positive identification, it may be even necessary to make tests
of the physical properties of the virus and to determine the vector, probably an insect, and
demonstrate virus transmission by the vector. Accurate, rapid diagnosis is important for initiating
effective control. The above questions indicate what information is important in this diagnosis.

14

PROTECTIVE CHEMICALS

■ Introduction

Chemicals used for the control of plant diseases are specific to the type of microorganism causing
the disease. Fungicides control fiingal pathogens, bactericides control bacteria, antibiotics control
mycoplasmas, and nematicides control nematodes. There are no chemical controls for viral diseases
or physiological disease. Correct diagnosis of the disease organism is critical prior to the use of any
protective chemical.

■ Fungicides

A fungicide is a chemical that kills or inhibits fungal growth. Fungicides are widely used to protect
plant seeds, foliage, fruit, and roots against disease-causing fungi, as well as to preserve wood
against decay. Wood preservatives are not covered in this manual. No single fungicide is suitable
for all purposes or is effective agamst all fungi.

^- Protective fungicides are applied to seed, foHage, flowers, fruits, or soil as sprays, dusts, or
granules to keep disease-causing fungi from entering plants. These materials provide external
protection, but do not kill ftmgi established within a growing plant or seed. An exception is the
case of powdery mildew and sooty mold fungi, which are superficial and can be killed by surface
dusts or sprays after infection has occurred without injuring the host plant. They also do not
protect against disease-causing organisms entering through the roots, such as root rots, wilts, and
clubroot. They do not control bacterial diseases, protect against viruses or MLOs, or control
nematodes.

Most fiangicides in use today possess protective qualities. Those that are only protective include
zineb, thiram, ferbam, ziram, sulfur, iprodione, chlorothalonil, captan, dithane, inorganic copper
materials (copper sulfate), and some others. These chemicals must be applied before an infection
starts. They require frequent applications at seven to fourteen day intervals, depending on the
weather conditions. During rainy weather, sprays need to be applied at shorter intervals.

Practically all dust and granule formulations function as protective fungicides and should be used
accordingly. Dusts should be applied when the air is calm and foliage is lightly covered with
moisture. Early mornings or evenings are ideal times.

^^ Protective-con ta ct fungicides are used the same as protective fungicides, however, another
dimension of effectiveness is that of destroying established infections. A commonly used term
is "kickback" which means that an infection may be stopped after becoming established. For
example, dodine will still provide control if applied 72 hours after apple scab infection has
occurred. Thus, it has a 72 hour kickback for apple scab. In other words, dodine can prevent
infection, and it also has good contact toxicity to fiongus growth. "Contact toxicity" means that
the fungicide may either kill or merely inhibit further growth. Protective-contact fungicides
include benomyl, difolatan, folpet, dodine, limesulfur, thiabendazole or TBZ, maneb and zinc
iron.

15

^ Systemic fungicides, or chemotherapentants . are chemicals that are absorbed and distributed
within the plant, destroying established infections and hence controlling certain diseases for
several weeks or months. Very few chemicals now available work in this way. Examples would
include chloroneb (Demosan), carboxin (Vitavax), difenoconazote (Dividend), thiophanate
(Topsin) and terrazole (Koban). To be effective, a systemic fungicide must be taken up by the
seed, foliage, roots, or stem(s) of the plant and be transported in an active state to where disease
infection occurs.

■ Bactericides

Bactericides are used primarily for the control of bacteria. Some may have limited activity on fungi
as well. A bacteriostat prevents growth or multiplication of bacteria, but does not necessarily kill
them. There are very few active ingredients that are effective against bacteria.

Copper compounds, such as Bordeaux (copper sulfate + hydrated lime), copper ammonium
carbonate, copper sulfate, and copper oxides, are important and effective dormant season disease
control products. Bordeaux mixture is generally useful under rainy conditions.

Streptomycin and oxytetracycline are antibiotics that are typically systemic when applied to foliage.
They can be absorbed by leaf tissue to inhibit bacterial infection, but do not move systemically from
leaf to leaf

Plant protectant chemicals that have both bacterial and fungicidal properties include the copper
compounds listed above, soil fiimigants (chloropicnn and methyl bromide), and bleach.

■ Use Precautions And Application Efficiency

Read and follow all label recommendations when using any plant protectant chemical. To get the
best operation from any application equipment, observe and follow the guidelines below. Also refer
to the equipment section in the Basic Pesticide Manual.

♦ Use the appropriate equipment for the area to be treated. Smaller areas may require the use
of a backpack sprayer or hand duster, while large areas may require a field sprayer.

♦ Use the manufacturer recommended nozzle size.

♦ Check both nozzles and the pump for wear on a regular schedule.

# Check engine and pump speeds.

# Make sure all belts to the fan and pumps are under the proper tension.

# Keep all moving parts of equipment lubricated with the manufacturer's recommended
lubricant.

♦ Wash the equipment with clean water after completing spray applications.

♦ Drain all water from equipment before cold weather.

16

♦ Refer to the label for product compatibility before mixing any sprays.

♦ Use only recommended label rates.

♦ Time all applications according to label directions.

17

Plant Disease Review Questions

1 . Plant diseases are the result of the right
combination of:

a. susceptible host plants

b. virulent pathogen

c. suitable climate conditions

d. all of the above

6. Viral diseases can be controlled by the
following chemicals:

a. Captan and copper sulfate.

b. Benomyl, dodine, and folpet.

c. There are no chemical controls.

d. Vitavax and Dividend.

2. Fungal pathogens can spread spores and
mycelium through:

a. erosion

b. water

c. animals

d. b and c

3. Bacteria are:

a. complex macro-molecules
composed of ribonucleic acid.

b. one-celled microorganisms.

c. microscopic, unsegmented
roundworms.

d. none of the above.

4. What are the five fundamental principles
of plant disease control?

a. Biological, protection, IPM,
chemical, and exclusion.

b. Host resistance, eradication,
exclusion, biological, and
protection.

c. Exclusion, elimination, resistant
varieties, IPM, and protection

d. Exclusion, eradication,
protection, host resistance, and
elimination.

5. The crop history and the distribution of
the disease must be considered when
investigating a disease in the field.

a. True

b. False

7. Crop rotation, seed and soil treatment,
and destruction of overwintering hosts all
describe biological control for plant disease.

a. True

b. False

8. Creation of an unfavorable environment
for the pathogen during:

a. growth, storage, and shipment is
an effective means of protection.

b. germination, shipment, and death
is an effective means of
protection.

c. growth, shipment, and regrowth
is an effective means of
protection.

d. none of the above.

9. Non-parasitic or physiological diseases
include:

a. air pollution and pesticide injury

b. nutrient deficiencies

c. mycoplasmas

d. a and b

10. The disease triangle includes the
following principles:

a. Pathogen, host, eradication and
the environment.

b. The environment, time, habitat,
and the pathogen.

c. Host, pathogen, environment and
time.

d. Time, habitat, eradication and
precipitation.

18

WEEDS - PART II

INTRODUCTION

A weed can be defined as:

^ a plant growing where it is not wanted;

^ a plant out of place; or

^ a plant that is more harmful than beneficial.

Any plant can be a weed in a given circumstance. Kentucky bluegrass that spreads into a flower bed
is a weed; volunteer wheat in a sugar beet field is a weed. A plant is a weed only in terms of its
impact on human activities.

Plants commonly referred to as weeds have characteristics that give them the ability to spread and
compete well with many cultivated and rangeland plants. Most major v/eeds have at least several
of the following characteristics:

>- Continuous seed production for as long as growing conditions permit;

>■ Unique ways of dispersing and spreading, including vegetative propagation and seed
production;

>■ Ability of seeds to remain dormant in soil for long periods of time;

>- Ability to grow under adverse conditions;

>■ Adaptation to a wide variety of soil and climatic conditions;

>- Compete well for soil moisture, nutrients and sunlight; and

>- Genetic adaptability, with a wide gene base for competition with beneficial plants.

Economic losses caused by weeds occur every year in Montana. Weeds cause losses to agricultural
production by:

♦ Decreasing crop yields by removal of water and nutrients from the soil. Many weeds
need more water to produce one pound of dry matter than do most of the cereal
grains.

♦ Weed seed contamination in grains reduce the value of these products.

♦ Dairy animals that eat certain weeds may produce milk with an unpleasant odor or
off-flavor.

♦ Weed control may require extra tillage operations in preparing soil for planting.

♦ hrigation costs are increased by weeds growing in and along irrigation ditches. This
often results in decreased water flow and added weed control costs.

♦ Weed infestations may serve as a source of plant diseases and insect pests. Weeds
may also act as alternate hosts for diseases and insect vectors.

♦ Some weeds are poisonous to humans and livestock.

To produce crops efficiently, it is necessary to reduce the effect of competition by weeds. Although
weeds cannot be entirely eliminated, they can be reduced to manageable levels.

19

SOURCES OF WEED INFESTA TIONS

♦

Humans are the most effective agent in the dissemination of weeds. Most exotic weeds found in the
United States are here because of the movement of people and their products. Weed seeds are
moved in hay and seed products; by machinery and vehicles; and in common carriers, railroads
and trucks hauling cargoes of grain, hay, livestock, and other farm commodities. Movement
along travel corridors scatter seeds along rights-of-way and highways, which become sources of
infestation to adjoining fields.

Wind spreads seeds over great distances. Many weed seeds
have structural features which aid their distribution by wind
(Figure 11- 1 ). Some seeds have wings, like those of maple
trees, or they may have long, silky hairs or parachutes
attached to them. Tumbleweeds (such as Russian thistle)
are especially adapted for seed dispersal when blown along
the ground.

Figure II-2

Water also effectively spreads seeds. Most weed seeds will float if
they fall on the surface of streams, lakes or irrigation canals (Fig-
ure II-2). Flood waters, running streams, and irrigation water all
contribute to spreading weed seeds. Irrigation canals, when first
filled, often carry heavy loads of weed seeds downstream where
they may be washed ashore or deposited in silt along the way.

curly dock
seed has
bladder-like
floats

gureII-1.

common milk-
weed seed is
readily carried
by the wind.

♦♦♦ Wild and domestic animals also aid in the dispersal of seed.
The viability of most weed seeds is unaffected by passage through the digestive
tracts of animals. Many weeds, such as cocklebur, sandbur, and beggar-ticks, have
awns or hooks on the seeds that attach to the hair (Figure 11-3).

**** Planting contaminated small grain, legumes, or grass seed
is another way to spread weeds (Figure II-4). Farmers then plant weeds
with the crop seed, often giving the seed a competitive advantage. The
planting of certified seed may help prevent the spread of weeds. Mechani-
cal seed cleaning can also remove weed seeds fi-om grain prior to planting.

Figure II-3.

common
cocklebur
clings to
clothing and
animal fur.

V Farm machinery spreads weed seeds, especially in wet weather when seeds stick to
muddy implements and vehicles. Plows and cultivators drag roots, rhizomes, tubers or
seeds to another area. Combines and hay balers spread weeds fi"om field to field. All farm
machinery should be cleaned before moving it from one area to another.

Figure II-4. bent awn on the
lemma of wild oat seed twists with
changes in moisture to bury the
seed in the soil.

20

Infestations of perennial weeds are aided by different types of rooting systems. Identifying the root
system of a weed is beneficial when selecting a control method. The following are some of the common
types of root systems of perennial weeds.

BULBS

Examples: wild garlic,
bulbous bluegrass, and
wild onion.

Examples: Saltgrass, sweet pea, and
oxeye daisy.

Examples: Bermudagrass and
strawberries.

CREEPING ROOTS ^^^i

Examples: Canada thistle and
leafy spurge.

Example: Creeping bellflower
21

CLASSIFICATION OF WEEDS

Weeds can be classified by life cycle or plant structure. Identification and control practices are
determined in part by understanding these classifications.

■ Life Cycle

The life cycle (or growth habit) of each weed species describes how long each plant lives and
timing of development.

DEATH

Annuals complete their life cycle from seed to mature plant in less than one year. Summer annual
plants germinate in the spring, flower, produce seed in mid- to late-summer, and die in the fall.
Winter annuals germinate from late summer to early spring, flower, and produce seed in mid- to
late-spring and die in the summer. Plant growth as a winter or summer annual often depends on
geography and climate.

SUMMER ANNUAL

SPRING

WINTER ANNUAL #^

— FALL

FALL

SUMMER

Kochia, lambsquarters, redroot and prostrate pigweed, Russian thistle, green and yellow foxtail,
and crabgrass are all examples of summer annuals. Winter annuals include common chickweed,
downy brome, field pennycress and many other mustards.

22

Biennials live for two growing seasons. Seeds germinate in the spring, summer, or fall of the first
year and plants overwinter as a basal rosette of leaves with a thick storage root. Plants flower and
produce seed the summer of the second year and die in the fall. Common biermials include com-
mon mullein, burdock, wild carrot, bull thistle, and musk thistle. Effective control of biennial
plants is very similar to control for annuals. Early spring or fall spraying of the rosette is an
effective time for control.

BIENNIAL ^Y

SPRING >

FALL

SPRING ,

^- FALL

Perennials produce vegetative structures, allowing them to live for more than two years. They
reproduce by seed in addition to spreading vegetatively. Simple perennials overwinter by means of
a vegetative structure, such as a perennial root with a "crown," but they reproduce almost entirely
by seed. Dandelion, curly dock, and spotted knapweed are common examples of simple perenni-

QIC

SIMPLE PERENNIAL

First Year

Year after Year

Creeping perennials overwinter and produce new, independent plants from vegetative reproduc-
tive structures. These structures include rhizomes, tubers, bulbs, stolons, and creeping roots. Most
creeping perennials can also reproduce and spread from seeds. Quackgrass, Canada thistle, leafy
spurge, and field bindweed are creeping perennials.

CREEPING PERENNIAL

eedling

4 weeks

6 weeks

1 year

Every Year

23

Weed Control for Annual, Biennial, and Perennial Weeds

Control
is most

Ueed Control - Annuals/Biennials

of annual and biennial weeds must be accomplished before the plant produces seed. This
effective when the plant is in the seedling stage. Weeds are small and succulent and less

energy is required for control at this stage.
Control during the vegetative stage is
possible but more difficult since the plant
is putting energy into the production of
stems, leaves and roots. Chemical control
of annuals during the flowering stage is
not feasible because most of the plant's
energy is going into seed production.
Often flowering annual plants will set
viable seed even after control. Maturity
and seed set completes the annual plant
life cycle. Control is not effective at this
stage.

"1 1 '' — I '' — r

Seedliag Vegetative Flowering Mature

Growing Stages

Perennial weed control must be aimed at either the seedling or the regrowth stages of development.

Chemical control during the vegetative growth stage is generally less effective. Control is more

effective at the bud stage than the

flowering stage. Control at maturity

is not feasible since the above ground

portions of the plant die back at this

time. Fall treatment of regrowth is

most effective because the plant is

translocating nutrients to the root

system and will also translocate

herbicide to kill the roots. To achieve

effective control of perennials,

underground plant parts must be

killed. Long-term management is

essential for effective control.

Meed Control - Perennials

100

Vegetative Early Flower Mature
Seedling Bud Full Flower Regrowth

Crowing Jtagej

24

■ Plant Structure

Differences in plant structure or morphology are important to recognize.
For weed control purposes plants are divided into three main categories-
grass, broadleaf and woody.

Grass plants have one seed leaf (monocot). They typically have parallel leaf
venation (Figure II-5a), narrow, upright leaves and flower parts in threes or
multiples of threes (Figure II-5b). Examples include quackgrass, green
foxtail and dovray brome.

Broadleaf plants have two seed leaves (dicots). They generally have
broad, net-veined leaves (Figure II-6a) and flower parts in four, five or
multiples thereof (Figure II-6b). Examples include kochia, sunflower, and
Canada thistle.

Figure II-5a

Figure II-5b

Figure II-6b

Figure II-6a

Woody plants persists from year to year with woody aerial stems
and include brush, shrubs, and trees. Brush and shrubs have
several stems and are generally less than ten feet tall. Trees have a
single stem and are over ten feet tall. Multiflora rosa, sagebrush
and salt cedar are examples of woody weed plants (Figure II-7).

25

Figure II-7

METHODS OF CONTROLLING WEEDS

For a weed control program to be successful, weeds or undesirable plants must be destroyed without
damaging crops or desirable plants. Good farming and land management practices should be first
in any weed control program. Causes of weed problems should be identified and corrected by
implementation of an integrated weed management program, including all effective control methods.

The most effective or economical method or combination of methods for weed control depends upon
an accurate assessment of the situation.

■ Prevention

Prevention is the most practical and economical method of controlling weeds. Once weeds are
established they are difficult and costly to control and may persist for many years as dormant seeds
in the soil.

Preventative control measures should be adopted whenever practical. They include: a) the use of
clean, certified seed; b) cleaning all implements, vehicles, and harvesting equipment before moving
it fi^om infested areas: c) keeping irrigation ditches, fence rows, roadsides and other non-crop areas
free fi^om weeds; d) not bringing infested soil, hay, straw, or manure into clean areas; e) spot treating
small infestations or isolated individual plants; and f) not allowing new weeds to set seed or
reproduce.

■ Cultural and Mechanical Control

Cultural and mechanical control includes cultivation, mowing, mulching, crop competition, and crop
rotation.

Cultivation stimulates the germination of weed seeds by bringing them to the soil surface. These
weed seedlings are then easily controlled with a second tillage operation. Tillage is most effective
on annual weeds. Repeated tillage operations (every two to three weeks throughout several growing
seasons) may control some perennial weeds, such as Canada thistle. Other perennials, such as field
bindweed, are spread rather than controlled by cultivation. Handhoeing can be effective in
ornamental settings and some high value crops.

Mowing can be an effective weed control practice under certain conditions. It should be part of an
overall crop management program. Mowing controls weeds by preventing seed production,
depleting underground food reserves, and by favoring growth of more competitive plants. Plants
must have a relatively tall growth habit to prevent seed production. Mowing must be done prior to
pollination and fertilization. Since most plants regenerate, repeated mowing is required for adequate
weed control. It is important to remember that repeated mowing may change upright, single
stemmed plants into prostrate, several stemmed plants that can still set seed.

Mulches control weeds by excluding light. They are most effective on small areas with high value
crops that are already established, such as tomato transplants or flower plants. Mulching material
should be thick enough to exclude light, relatively cheap, and easy to work with. Straw, sawdust,

26

wood chips, bark chips, grass chppings, heavy plastic and paper cHppings are all good mulches.
Perennial weeds are difficult to control with mulches due to the persistent nature of their vegetative
growth.

Crop competition can be an effective tool. Early spring seeding can allow cereal grains to germinate
earlier than weeds. If the crop is established before the weeds germinate, it will often crowd out the
weeds. Crops need to grow rapidly and establish early, taking the nutrients and water the weed
would normally use.

"Smother" crops may be valuable in a weed control program. They compete with weeds for water,
light, and nutrients. The main competitive crops valued in weed control are crested wheatgrass,
sweet clover, sunflower, rape, barley, rye, soybeans, alfalfa, and silage com. These crops grow
quickly, produce an abundance of shade, and can be harvested early enough to permit fall cultivation.

Crop rotation is another method for weed control. Certain crops have their own characteristic
weeds, and these weeds tend to accumulate when the same crop is repeated year after year. These
repeated plantings favor disease and insect problems resulting in weak, patchy stands which are
easily invaded by weeds. Crop rotation allows use of alternative control methods, including a wider
variety of herbicides, to control weeds.

■ Biological Control

Biological weed control is the use of a living organism to control weeds, hisects are the most
commonly used agent but fish, nematodes, snails, and plant pathogens (fungi, bacteria) offer
additional means of controlling plants.

Biological controls can be useful for suppression of unwanted plants, generally in a non-crop
situation. Development of a biocontrol agent is long-term and expensive. Research is needed to find
host specific agents and anywhere fi-om 5 to 10 different agents are needed to give economic control
of a single weed species. Biological control is generally not recommended in cropland situations
because of a lack of adequate economic threshold data for weeds. Biological control insect agents
are generally too slow acting to be effective in cropland situations. Plant pathogens show more
promise in this area and some are registered pesticide products (examples - Mycostop for fiangi on
field crops and Noyall for Agrobacterium on nursery stock).

There are several excellent examples of weed control by insects. The most outstanding is prickly
pear cactus control in Australia. Over 60 million acres of infested land were reclaimed using a moth
assisted by a scale insect. Another example is found in California and the Pacific Northwest where
St. Johnswart (or goatweed) has been reduced on millions of acres to about 1% of its former range
by a leaf feeding beetle.

Some results in Montana using biocontrol agents include:
^ The St. Johnswart beetle, Chrysolina hyperici, was first introduced to Montana in 1948, with
supplemental releases made over the years. The beetle is cyclical in areas where it is
established and has not shown the same dramatic results in Montana as was found in

27

California. This may be because the insect is hmited to only one generation per year in the
colder Montana climate.

^ A weevil, Rhinocylliis conicus, is well established on musk thistle in Montana. It is effective
at reducing seed production of this biennial species.

^ A biological control program on spotted knapweed in Montana includes the release of several
gallfly species {Urophora affinis and U. quadrifasciata), a root boring moth (Agapeta
zoegana), and a root boring weevil {Cyphocleonus achates). Research continues on several
other root and seed head insects.

p*- Dalmatian toadflax has two insects established on it, a foliage eating moth {Calophasia
lunula) and a seed head beetle {Brachypterolius pulicarius). Several root boring moths and
seed head weevils were cleared for release in 1996 and research continues on these insects.
Some work is also being done on common toadflax biological control agents.

^^ A wide range of biological control agents have been introduced on leafy spurge. The most
effective to date have been a complex of flea beetles, Aphthona species. Research is also
targeting plant pathogens that could be used in combination with insect agents.

^ Research on plant pathogens for several weeds continues. The fungus, Sclerotinia
sclerotiorium, attacks a broad host range of weed species, including Canada thistle, and
spotted knapweed.

^ Sheep and goats can be used to suppress growth and prevent seed production of leafy spurge
in environmentally sensitive areas.

■ Chemical Control

Herbicides are an important weed control tool in Montana. Research over the past few decades has
produced increased knowledge and new, safer chemicals for use in weed control. Herbicides will
continue to play an important role in weed control in Montana. The Chemical Weed Control chapter
(page 30) further discusses weed control with chemicals.

■ Integrated Weed Management

Integrated weed management (IWM) is an ecological approach to managing unwanted plants. It is
a systems approach to weed management that uses all suitable methods in a compatible manner to
reduce weed populations to levels below those causing acceptable economic or ecological
consequences.

Factors to consider pn'or to making a management decision include:
^ Weed species present and size of infestation.

^- Environmental conditions: non-target vegetation, soil types, climatic conditions, and water
resources.
p^ Site restrictions.

28

^ Understand the overall management objectives for the area: different land managers and
agencies have different goals and restrictions on their activities.

^ Consider the many different control techniques and combinations available when developing
a management plan.

All weed management tools must be used to effectively control weed infestations. Annual, biennial,
and perennial weeds have certain growth habits that influence the type of control method or methods
implemented. Soil type, weather conditions, recreational activity, wildlife or domestic grazing and
future use of the land will influence your choice of weed control methods. Consider all information
known about the weed and the site as you develop a long term management plan for control of a
weed infestation.

29

CHEMICAL WEED CONTROL

Herbicides are effective tools when used properly. Since the early 1950's, thousands of chemicals
have been evaluated for effectiveness as weed killers. Safe and effective herbicides are available for
controlling many weeds growing in various environments including cropland, rangeland, gardens,
lawns, ditchbanks, non-crop areas, and in irrigation, drainage, navigable, and drinking waters.
Because of the many factors and principles involved in research on herbicides, information about
chemical weed control is rapidly increasing. New recommendations are continually replacing old
ones. Be sure to read and follow all label directions from a current product label.

■ Selective Herbicides

Chemicals which can be used to remove certain plant species with little or no effect on other species
are referred to as selective herbicides. Selectivity depends on the amount of chemical used, the
application method, the degree of foliage wetting, soil moisture and texture, temperature, and
humidity. Since selectivity can be influenced by all of these factors, the same chemical may be
either selective or non-selective, depending on the amount used. For example, atrazine used at a
high rate is an effective soil sterilant (non-selective) and used at a lower rate is a selective herbicide
for weed control in com.

♦ Foliage applications are treatments made to the leaves of growing plants, usually as a spray or
mist.

□ Translocated herbicides move within the plant after the material is absorbed into the tissue.
The greatest amount of transport is through the vascular system of the plant (phloem and/or
xylem). Translocated herbicides may be effective in desfroying roots as well as top growth of
plants. Selectivity depends on physiological differences of plants. 2,4-D is a commonly used
selective, translocated herbicide in Montana.

□ Contact herbicides do not translocate or move in the plant. This group of herbicides kills
only the plants or portion of the plant actually contacted by the chemical. In order to obtain
effective control, adequate coverage of the foliage is essential. This may be accomplished by
using a high volume of carrier or diluent to apply the herbicide. Dinitrophenols and certain
petroleum oils are used as selective, contact herbicides.

♦ Soil apphcations are herbicide treatments applied to the soil. To be effective, the chemical must
be carried into the soil by moisture or mechanical incorporation. Selectivity depends on the plant
tolerance, soil texture, location of the herbicide m the soil, and difference in growth habit of the
crop and the weed. These herbicides are generally translocated in the xylem.

♦ Selectivity can also be determined by timing of applications:

D Preplant treatments are made to the soil before the crop is planted. Typical preplant
treatments are applied after seed bed preparation but directly before planting the crop. This type
of treatment is considered pre-emergence with respect to weeds if applied prior to weed
germination.

30

□ Pre-emergence treatments are made to the soil after the crop is planted but before emergence
of the crop or the weeds.

□ Post-emergence herbicides are applied to the soil after the crop or weeds have germinated and
started to grow. Other post-emergence treatments may include:

* Pre-harvest herbicide treatment applied before crop harvest to remove weed growth that
could interfere with the harvesting operation.

•* Post-harvest herbicides applied to kill weeds present after harvest as part of the weed
control program for the next season.

■ Non-Selective Herbicides

Herbicides which are toxic to all plants may be used to control a wide variety of vegetation in an
area. These chemicals can be used to control vegetation in non-cropped areas such as along fence
rows, around electrical power lines and substations, right-of-ways, and storage areas.

♦ Foliage applications are applied to the leaves of growing plants as sprays or mists.

□ Translocated herbicides move fi-om the foliage to the roots, resulting in control of a wide
variety of plant species. There are few herbicides that can be classified as translocated, non-
selective. Glyphosate (Roundup) is one good example.

□ Contact sprays kill vegetation at the point of contact. One treatment is usually sufficient to
control annual weeds. Perennial plants are not effectively controlled with contact herbicides.
Acrolein and paraquat are examples of non-selective contact herbicides.

♦ Soil applications include a wide variety of soil fumigants and soil sterilants that are applied
directly to the soil. These are used where it is necessary to remove all plant growth.

□ Soil fumigants are non-selective chemicals that are most often used to kill all plant growth,
as well as other soil organisms, before planting a desirable species. They function as a vapor
or gas which diffiases through the soil and has a short life in the soil. The treated area may be
replanted, usually within a month or less. Methyl bromide is a commonly used soil fumigant.

□ Soil sterilants are chemicals that kill all green plants for a period of up to two or more years.
They are classified as:

* Temporary sterilants which kill plant life for four months or less.

* Semi-permanent sterilants which kill all plant life for four months to two years.

* Permanent sterilants which persist in the soil for longer than two years.

31

The length of time the herbicide residue remains depends on the herbicide used, the rate of
apphcation, and the soil moisture and texture.

H Basics of Herbicide Selectivity

It is important to understand how herbicides kill plants, why a herbicide is phytotoxic to one species
and not another, and how herbicides can be used to best accomplish the results desired. Selectivity
is relative.

The most important factors that affect herbicide selectivity are: 1) structural differences in plants, 2)
differences in absorption, 3) differences in translocation, 4) physiological differences, and 5) herbi-
cide concentration. Combinations of these factors can be used to improve herbicide selectivity.

♦ Structural differences among plants permit selective applications. The narrow, upright
leaves of a cereal plant lack the exposed leaf surfaces of a broadleaf plant. Water droplets
can stick only to a small portion of an upright leaf surface. On the other hand, a broadleaf
plant has a wide leaf surface which extends parallel to the ground and will hold more spray
and therefore be affected more by the herbicide. Another important structural difference is
the location of the growing point of the plant. The growing point of many grasses is pro-
tected because it is located at the base of the plant. Contact sprays may injure the leaves of
the grass plant but not contact the growing point. Broadleaf plants have exposed growing
point at the tips of the shoots and in the leaf axils. The growing point is therefore more
accessible to the herbicide.

Waxiness, hairiness or pubescence of a plant may prevent spray droplets from adhering to
the leaf. If the chemical droplet adheres to the leaf hairs without contacting the leaf surface,
it will not be absorbed. On the other hand, hairs may collect and hold greater amounts of
droplets, preventing the spray from running off the leaf surface. Waxy leaves may require
use of an additive with the herbicide to dissolve the waxy layer and allow contact with the
leaf surface.

♦ Absorption is the movement of a material into the plant from an external source. Some
plant surfaces absorb herbicides quickly; other surfaces may absorb the chemical slowly, if at
all. Parts of the plant leaf surface, the cuticle and the stomate, account for differences in
absorption.

♦ The cuticle is a waxy layer or thin film on the leaf
surface (Figure II-8) which retards the movement of
water and gases (oxygen and carbon dioxide) into and
out of the leaf The cuticle varies in thickness in differ-
ent plants and can vary within the same plant exposed
to different environmental conditions. Shaded plants
often have thinner cuticles than plants grown in the
sun, and young leaves usually have thinner cuticles than
older leaves. A herbicide must penetrate the cuticle
layer and cell wall. High temperature and low humid-
ity usually result in poor cuticle penetration.

Cuticle
Epiderrr

Leaf
cross
section.

■^^tomate

32

♦ A plant leaf is perforated by small openings or pores called stomates; these open
into the intercellular spaces within the leaf (Figure II-8 Pg. 32). The number and
distribution of the stomates varies from plant to plant. The stomatal opening can be
an effective port of entry for the herbicide if they are open at the time of application.
This is why some foliar applied sprays are more effective when applied in the early
morning or late evening when there is less sunlight and the stomates are more likely
to be open. Stomatal penetration carmot occur unless the surface tension of the
spray solution is significantly reduced by the use of wetting agents.

♦ After the herbicide is absorbed, it must be translocated within the plant to the site of
action. There are two tissue systems in which a herbicide may move in the plant: the
phloem, which conducts food from the plant leaf to the stem and roots; and \h.exylem, which
conducts water and nutrients from the roots to the stem and leaves. Herbicides move through
these conducting tissues to other parts of the plant.

Figure II-9

Phloem trans-
port pathways of
sugars to and
from storage in

the roots
(solid line).

*> Phloem tissues are composed of living cells. It is important,
therefore, not to kill the stem and leaf tissues too quickly. Rapid
foliage kill will result in poor transport and poor root kill. Movement
in phloem will be toward the roots during maturation of the plant and
near budding (Figure II-9). This indicates the importance of proper
timing of a herbicide application, especially for the control of peren-
nial weeds. It is necessary to apply a translocated herbicide when a
perennial is storing up root reserves. Most growth regulators, in-
cluding 2,4-D, as well as dicamba (Banvel), and glyphosate (Roundup),
move readily in phloem tissue.

**** Xylem tissue of a plant is made up of non-living cells. It is the water conducting,
transpiration system in the plant and movement is only from the roots upward to leaf
and shoot tips (Figure II-9). Any chemicals applied either to the roots or foliage will
only be translocated toward the leaf tip. Atrazine, metribuzin, and diuron are ex-
amples of xylem conducting herbicides.

♦ The physiological differences between plants also affect herbicidal tox-
icity. Differences in enzyme systems, responses to pH changes, cell metabo-
lism, cell permeability, variations in chemical constituents and polarities may
all influence the selectivity of a herbicide to plants. Any herbicide that stimu-
lates or blocks certain biochemical processes in a plant can affect the plant's
growth and cause herbicidal action.

Xylem transport
pathways of water
conducting from
the roots upward to
the leaves
(dashed line).

♦ Enzyme reactions may be blocked in one plant species, but
not in another, by the same chemical. Activation of chemical into
an active compound, such as 2,4-DB converted to 2,4-D by cer-
tain plants, is an example. Degradation of a herbicide to a harm-
less compound is another example; com has enzymes that can de-
grade triazine herbicides into harmless compounds.

33

♦ The rate of application or concentration may determine whether a herbicide inhibits or
stimulates plant growth. Under low concentrations 2,4-D can act as a growth hormone and
increase the rate of respiration and cell division, resulting in stimulated plant growth. At
higher rates, growth is excessive and results in death of the plant. The concentration of a
herbicide at certain sites in the plant may determine the herbicide effectiveness.

H Herbicide Formulations

Almost all herbicides must be combined with a liquid or solid carrier to uniformly distribute them
during application. The formulation of a chemical is the manner in which the active ingredient and
the carrier are mixed. Proper formulation of agricultural chemicals increases their effectiveness.
Inert ingredients make the herbicide easier to handle, less likely to settle out or degrade during
storage, and may minimize the hazard of handling the chemical. The way the herbicide is formulated
may change its chemical characteristics, including solubility, volatility, and toxicity to plants.

Common types of formulations are classified as follows:

♦ Liquid Formulations

n Emulsifiable concentrates (EC) are nonpolar (oily) liquids containing emulsifiers, a
substance promoting the suspension of one liquid in another. The active ingredient is not
soluble in water, but is dispersed in water to form emulsions (droplets of oil surrounded by
water). Agitation is usually required to prevent separation.

□ Solution(s) are herbicides (liquid or powder) that are directly and rapidly soluble in the
carrier liquid. These require no agitation once dissolved in solution. Often they need a
surfactant for maximum activity.

n A suspension consists of a finely ground wettable powder (WP) dispersed in a liquid.
Wettable powders are used if a solid concentrate is preferable to a liquid or if the solubility of
a herbicide is so limited that it is impossible to formulate an economical solution or emulsi-
fiable concentrate. These herbicides are nearly insoluble in water or oil but may be dispersed
in them by forming a slurry. Adding it to the carrier and using constant agitation.

n Water dispersible liquids and granules are often referred to as flowables (F) or dry
flowables (DF). These formulations readily disperse in the herbicide carrier. They require a
moderate amount of agitation. Both liquids and granules can be added to water without first
making a slurry. Water dispersible granules poor cleanly fi-om the container, giving them
handling advantages over dispersible liquids and wettable powders.

♦ Dry Formulations

□ Granule formulations have been impregnated into coarsely ground carriers, such as clay
or vermiculite, and formed into small pellets, generally less than 10 mm in size. These
chemicals are used directly fi-om the bag but require special application equipment, and
usually require soil incorporation to be effective.

D Pellets are discrete particles usually larger than 10 mm. They are fi"equently used for

spot treatments.

34

□ Dusts are finely ground chemicals that may or may not be mixed with diluents. Their use
is limited because of the hazard of drift and the high cost of the herbicide.

H Spray Additives

Adjuvants or spray additives are often used to enhance herbicidal performance or handling. They
include surfactants, anti-foaming agents, compatibility agents, crop oils, crop oil concentrates, and
drift control agents.

♦ Surfactants (surface-active agents) bind two or more incompatible phases, such at water
and oil, in more intimate contact by modifying forces between them. A surfactant is any
material that affects the surface properties of spray solutions and includes wetting agents,
emulsifiers, dispersing agents, detergents, and stickers.

□ Wetting agents are materials used
to increase a liquid's ability to moisten
a solid. They lower the surface ten-
sion, bringing the liquid into closer
contact with the solid (Figure 11-10).
Wetting agents increase or decrease the
effectiveness of herbicide sprays; they
may also reduce selectivity, especially
if selectivity depends on selective wet-
ting or selective absorption.

Figure 11-10 a water soluble herbicide over tiie plant surface:
(A) without wetting agent, (B) with wetting agent.

n An emulsifier is a material used to disperse one liquid in another. An emulsion is one
liquid dispersed in another, each maintaining its original identity.

n Dispersing agents reduce cohesion between particles. They are materials used to dis-
perse the particles of a solid in a liquid. Some dispersing agents also act as wetting agents,
but others have little or no effect on surface tension. Some wetting agents and dispersing
agents are not compatible and interfere with each other if used together.

□ Detergents are used to remove dirt or grime. They are usually wetting agents and
surface active. Many common detergents have been used with herbicides as wetting agents
and emulsifiers. Anti-foaming agents can be used to reduce foaming in a sprayer system so
pumps and nozzles can operate properly.

□ A sticker is designed to hold the active ingredient on the sprayed surface.

□ A penetration agent is any substance that assists plant absorption of a herbicide. Such
substances may dissolve the waxy cuticle or fatty portion of the cell wall or membrane of the
plant to allow more rapid penetration.

□ Anti-caking agents are used to prevent solid herbicide formulations from forming

aggregates.

35

Surfactants are classified as ionic and nonionic, depending on their disassociation in water.
Nonionic agents have no particle charge, while ionic agents have either a positive or negative
charge.

Nonionic surfactants are classed as nonelectrolytes and are usually chemically inactive in the
presence of usual salts. They can be mixed with most herbicides and still remain chemically
inactive. Ionic surfactants ionize in an aqueous medium. These agents can be used to unite oil
or water soluble properties of a molecule and allow alignment in water to reduce water surface
tension.

♦ Compatibility agents aid suspension of herbicides when they are combined in tank mixes with
other pesticides, herbicides or fertilizers. They are used frequently when a liquid fertilizer is the
carrier solution.

♦ Crop oil and crop oil concentrates are non-phytotoxic light oils that also contain surfactants to
allow mixing with water. They are added to water solutions to enhance herbicide foliar activity.

♦ Drift control agents reduce the fine particles in a spray pattern that are primarily responsible
for herbicide drift and nontarget injury.

All adjuvants should be used in accordance with label directions and chosen only from those proven
effective for herbicide applications. Refer to the manufacturer's recommendations and herbicide
label recommendations.

■ Mixtures of Herbicides with Other Pesticides or Fertilizers

The use of herbicides mixed with other pesticides or with fertilizers is not new but it is growing in
popularity. The biggest advantage to farmers is the savings in time and labor and number of trips
across fields. Yields can be as good with combination applications as with split applications.
Research has confirmed that herbicides applied with some fertilizers can perform as well as with
single applications.

Most herbicides are specific and their activity is not the same toward all weeds. For example,
trifluralin does not control nightshade species in beans and alachlor is weak on kochia. Because of
these and other limitations of single herbicides, interest in mixing herbicides to control a broader
spectrum of weeds and provide more consistent control over a wide range of climatic conditions has
increased. Combinations can also lower the rates of application necessary and thus decrease crop
injury and soil persistence.

There is a possibility of synergistic (additive) effects resulting in increased herbicidal activity beyond
that of either single chemical. There can also be an antagonistic effect in which injury to the weeds
may be less than with either chemicals alone. There are limitations and concerns about mixing
chemicals without research data. Herbicides should not be mixed with other herbicides or fertilizers
unless the combination has been thoroughly researched and is registered for use.

36

The following factors should be considered before mixing herbicides with any pesticide or fertilizer:

♦ Pesticides vary greatly in their physical and chemical compatibility with each other and with
fertilizers. In many cases there can be a physical inactivation when two formulations precipitate
out of solution. There can also be a chemical reaction and inactivation between two incompatible
products. A small scale test for physical compatibility is recommended if the applicator has no
previous experience with the mixture. Mix proper concentrations of the chemicals to be tested
with the proper amount of carrier in a wide-mouth one quart jar. Agitate well and let stand over
night. Check for precipitate in the bottom of the jar. This will only indicate physical compatibility
- not possible chemical incompatibility, or synergistic or antagonistic effects.

♦ Agitation (keeping a herbicide uniformly dispersed in a mixture) is also important. It is a
general rule to never add a wettable powder to the surface of a full or nearly full tank of liquid.
Slurry the powder before adding it to the tank.

♦ Optimum placement of each product may rule out a combination application. Some fertilizers
are incorporated fairly deep, while many herbicides need shallow incorporation or are left on the
soil surface. Some fertilizers are broadcast while others should be soil incorporated. Each
herbicide must be considered separately. Correct placement of the herbicide should have
preference.

♦ The applicator must determine if the timing of the application, placement, and distribution of
each component of the mixture is similar enough to be applied as a mixture.

Often the application time is different for herbicides and fertilizers. Optimum time for herbicide
application is usually just before planting, during planting, or soon after planting. Fertilizers are
often applied in the fall or early spring. Again, correct timing should have preference.

■ Herbicide Application

Ideal application techniques provide uniform distribution of the herbicide on plant foliage or in the
soil. Chemical formulation will usually dictate what type of equipment should be used for
application.

♦ Spraying is the most common method of application. A spray may be defined as liquid
discharged so that it subdivides into particles that scatter and fall as dispersed droplets. Spraying
permits reasonably uniform application and allows accurate direction of the herbicide to a given
area (such as foliage or soil). Sprays may be applied from sprinkler cans, hand pumps, and
compressed air and power sprayers. Most available herbicides can be sprayed using a water
carrier. Water acidity or alkalinity can chemically affect a herbicide and inactivate it. If this is a
concern water pH should be tested.

♦ Granules are spread by hand or with special mechanical spreaders designed specifically for such
use. Applicators may broadcast the granules evenly over the entire spreader width or in bands over
the crop row. These applicators are generally refined fertilizer applicators or seeders and may

37

include equipment for soil incorporation. Granular herbicides have the advantage of being less
bulky since they are premixed and eliminate the need to handle water. The equipment is also less
complex. The major disadvantages include lack of uniform herbicide distribution and lack of
versatility of equipment. Granulars are often more expensive than sprays.

♦ Ftimigants are injected into the soil by both hand and power-operated equipment. The utility
of this equipment is obviously limited and cost of application is generally very high. Fumigants
demand caution in handling since they are highly volatile and extremely toxic. Usually airtight
covers must be laid down over treated areas to prevent escape of vapors. Fumigants will give
increased control for soil insects, nematodes, and some plant diseases, as well as weeds.

For more complete information on sprayer calibration and spray equipment maintenance, please
refer to the Montana Department of Agriculture Basic Pesticide Manual.

38

CHEMICALS USED AS CROP AIDS

■ Defoliants and Desiccants

Materials generally referred to as harvest aid chemicals fall into two classes: 1) defoliants that
induce the plant to drop its leaves but do not kill the plant; and 2) desiccants that kill plant foliage.
These classifications often overlap, depending upon the amount of chemical apphed. Before the use
of chemicals to defoliate plants, root crops, such as potatoes, were defoliated mechanically with
rubber flails or chains. In many areas, contact chemical vine killers, have replaced machines, giving
growers a method of artificially hastening the maturity of the crop. Desiccation of seed alfalfa plants
is common in some areas and has replaced mowing and wind-rowing in harvesting alfalfa seed.
When weather conditions do not favor drying, bean fields can remain green until frost. Desiccation
and pre-harvest drying is beneficial in these cases. There is also considerable interest in the use of
desiccants to speed up drying of crops, such as soybeans, in the field rather than depending on heat
for drying after the crop is harvested.

Some of the commonly used defoliants or desiccants registered by the EPA are: paraquat and diquat,
DNEP, endothall, pentachlorophenol, sodium borate, and sodium chlorate.
>- Timing of the desiccant is the most important factor affecting efficient use of the chemical.
The crop must be sufficiently mature before growth is stopped. Often varying degrees of maturity
are found throughout a field and the applicator must judge the correct time to defoliate. It is also
important to know when harvesting can begin after treatment, as the crop will usually not stand
up to much wet weather after a desiccant is applied. This is especially important when using a
desiccant on an alfalfa seed crop or beans.

>- Additives can improve defoliation and desiccation, especially when there are conditions of
moisture stress or cool weather. Some harvest aid chemicals are formulated with additives.

■ Plant Growth Regulators

Plant growth regulators (PGRs) are used to regulate or modify the growth of plants. A plant is made
up of many cells with specialized functions. Plant growth regulators can change or regulate the
development of these cells. PGRs are used to thin apples, control the height of turf grass, control
the height of some floral potted plants, promote dense growth of omamentals, and stimulate rooting.
They are used in minute amounts to change, speed up, stop, retard, or in some way influence
vegetative or reproductive growth of a plant.

Maleic hydrazide is a plant growth regulator that restricts development of new growth by preventing
fiirther cell division. The older cells, although affected by the chemical, may continue to grow. In
other words, cell division, but not cell maturity, is prevented. Maleic hydrazide is also sometimes
used to control suckers.

Potted plants, such as chrysanthemums, Easter lilies, and poinsettias, may grow too tall. Plant height
can be regulated with growth regulators that are applied at the proper stage of growth. Plant grov^h
regulators are used to control vegetative growth and promote earlier flowering and development in
some species. Some are used to kill shoot tips, resulting in additional branching.

39

Plant growth regulators are used on apples and peaches to increase fruit color and may result in
earlier and more uniform ripening of fruit. They can also be used to thin the fruit, widen branch
angles, produce more flower buds, prevent fruit drop, increase fruit firmness, reduce fruit cracking,
reduce storage problems, and encourage more uniform fruit bearing.

Rooting hormones are used to increase the development of roots and speed up rooting of certain
plants. Gibberellic acid stimulates plant growth. This is sometimes used to initiate uniform
sprouting of seed potatoes and increase the size of sweet cherries.

40

ENVIRONMENTAL FACTORS INFLUENCING
HERBICIDE EFFICA CY

Rainfall, soil type and conditions, temperature, light and crop type all have a direct effect on
herbicide efficacy. Understanding these effects aids in proper herbicide use, improves weed control,
and reduces crop injury.

■ Rainfall

Time of germination of crop and weed seeds, their growth rate, and stage of growth at spraying time
are partially determined by the incidence and amount of rain. Rain a few days before spraying can
improve penetration of a herbicide into a plant by increasing the wettability of the leaf. Rain may
mechanically damage the wax structure of the leaf surface, making the plant more susceptible to
chemical absorption. The wax, cuticle and hair on the leaf surface, the angle of the leaf, and the
humidity of the air help to determine how much chemical is retained and absorbed.

Rain, during or closely following application of a herbicide, may wash the spray from the leaves and
reduce its effectiveness. The degree of leaf washing depends, not only on the quantity of rain and
its intensity, but also on the structure of the crop-weed stand. The leaf penetration of herbicides
ceases, or is reduced, a few hours after application when droplets have dried. Traces of rain, dew,
or fog after spraying increase penetration.

The relative humidity at the time of chemical application and for many days after application, will
effect the degree of weed kill. Moist air increases herbicide penetration, absorption, and
translocation within the weed. Crop density and stand height also effects the relative humidity in
the area.

■ Sml

Soil composition and moisture influences herbicide persistence. The length of time that a herbicide
remains active or persists in the soil influences the length of time weed control can be expected. It
also determines the length of time until a sensitive crop can be grown in a treated area. Persistence
is a desirable or undesirable characteristic depending on the crops to be grovra or the weeds to be
controlled.

>- Soil moisture, rainfall or irrigation is essential in a successful weed control program. Sufficient
moisture stimulates uniform germination of weed seeds and vigorous growth of the plant.
Chemical application under these conditions is more likely to succeed than when the soil is dry
prior to treatment.

Dry conditions cause uneven germination of the weeds and delay crop development. As a result,
proper timing of post-emergence herbicides is difficult. Weeds will be uneven in size and difficult
to kill and the crop may be at a stage where injury could occur.

Water stress can affect herbicide retention, penetration, and absorption. Leaves grown under water
stress have more cuticle per unit area and a lower wettability than leaves from plants not under
stress.

41

'>' Factors having the greatest effect on herbicide soil residues are leaching, fixation on soil
particles, chemical and microbial decomposition, and volatilization.

^ Leaching is the movement of a herbicide through the soil. The extent to which a chemical
is leached depends upon its solubility in water, the amount of water passed through the soil, and
the adsorptive relationship between the herbicide and the soil. In general, water soluble
herbicides and those not readily attached to soil particles are most readily leached.

^ Fixation, or adsorption, of herbicides on soil particles reduces the concentration that is
available in soil water. Soils heavy in organic matter or clay type soils tend to hold the herbicide
for a longer period of time, thus slowing the rate of chemical release and either prolonging or
lessening its effectiveness, depending on the rate of application.

^- Chemical decomposition, involving reactions such as oxidation, reduction, and hydrolysis,
destroys most herbicides and activates others. Very little is known about the effects of soil
chemistry on herbicides.

^^ Microorganisms in the soil are responsible for much herbicide decomposition. Algae, fiingi,
and bacteria need food for energy and growth. Organic compounds in the soil, including
herbicides, provide most of this food. Warm, moist, well-aerated, fertile soils are most favorable
to soil microbes and, under ideal conditions, will quickly decompose most organic herbicides.
The effect of herbicides on the microbe population is minor when used at normal field rates.

^- Volatilization causes herbicide loss to the atmosphere as a gas. All chemicals have a vapor
pressure and this usually increases as the temperature rises. The gases formed may be toxic to
plants and may drift to susceptible plants. Water will leach the herbicide into the soil and aid
soil adsorption. Once adsorbed, loss by volatilization is greatly reduced.

■ Temperature

Temperature conditions influence germination and growth rates of weeds and crops. Temperatures
at the time of spraying are important in determining the plant response to the herbicide. High
temperature generally increases the activity of herbicides. There is also an increase in translocation
at higher temperatures. In general, high temperatures before and after spraying appear to increase
weed susceptibility and mortality, but extremely high temperatures may reduce penetration by
causing wilting, closing of leaf openings, and evaporation of the spray drops. High temperature also
increase the incidence of herbicide drift or volatilization.

Temperature change produce metabolic differences in some plants which effect their susceptibility
to herbicides. A plant at a low temperature may not produce a particular metabolic substance which
is necessary to obtain a response to a herbicide. Tests indicate this occurs in plants such as big
sagebrush or rabbitbrush, which do not respond to 2,4-D at low temperatures and low moisture.
Temperature also has an effect on direction of movement in a plant.

42

Temperatures have important effects on the dissipation of herbicides from plant fohage or from soil.
Some esters of 2,4-D evaporate readily. When such herbicides are applied at high temperatures their
loss as vapors is quite rapid. These losses reduce herbicide effectiveness.

■ Light

Light is essential for optimum plant growth. Weed growth in a crop situation can be affected by
shading. Growth response to shading will vary among species;

The leaf surface may be affected by light intensity. Leaves have less cuticle, cutin, and wax when
grown in the shade. This might lead to differences in susceptibility of the leaf wax structure to
weathering and abrasion. The leaf wettability increases when plants are grown in the shade.

Light (sunlight and ultraviolet light) can cause decomposition of some herbicides also. It is difficult
to determine the relative importance of this phenomenon in the field where the herbicide may be lost
through other factors, but it can be demonstrated under laboratory conditions. Loss from
photodecomposition of such herbicides as the dinitroalinines when not soil incorporated can be
important in a field situation.

43

WEEDS AND HERBICIDES IN THE ENVIRONMENT

All weed control practices alter the environment whether it is hand pulling, hoeing, cultivating,
burning, chemical application, or use of biological control agents. Our concern is that the change
in the environment does not produce harmful side effects to non-target plants, soil, water, animals,
or man.

■ Drift and Volatility of Herbicides

Herbicides, if used correctly, can be usefiil tools in land management programs, but if used
incorrectly, they can create serious problems. With greater emphasis on a healthy environment, it
is important that herbicides be applied in a proper manner. People involved in application must
understand such things as spray drift and spray volatility and take precautions to prevent damage to
non-target organisms.

>■ Spray drift is the movement of spray particles out of an intended area. Drift is dependent
mainly on 1) droplet size; 2) wind velocity; and 3) height above the ground. A water droplet 5
microns in diameter can drift over three miles, falling 10 feet, when the wind velocity is 3 mph.
Certain atmospheric conditions associated with high temperatures can cause thermal updrafts-
lifting spray droplets in the air and depositing them a considerable distance away.

In the last few years, several methods of reducing drift have been attempted. The most advertised
method has been invert emulsions. Esters of 2,4-D make a milk-like "oil-in-water" emulsion that
sprays like water. If the emulsion is reversed (inverted) to a "water-in-oil" liquid, and with proper
spray equipment, the mixture can be sprayed in large droplets. Other methods for reducing drift
include using shields, placing more nozzles on the boom, reducing pressures, and use of drift
control additives.

>■ A considerable body of literature exists on the volatility of esters of 2,4-D and related
compounds. Volatilization is the tendency of a sprayed material to vaporize after it has hit the soil
or plant surface. Because of the small amount of material involved, volatility is usually a hazard
only when extremely sensitive crops are nearby. For example, cotton is sensitive to as little as
1/1000 pound per acre of 2,4-D. Tomatoes and some ornamentals are also sensitive to 2,4-D
damage.

Volatihty can be controlled only by reducing the tendency of the chemical to vaporize. The major
herbicide which causes economic crop damage due to volatility is 2,4-D. The crystals of 2,4-D
acid and amines of 2,4-D are not volatile, while ester formulations have varying degrees of
volatility depending on the type of alcohol used to make the ester. Butyl, ethyl, and propyl esters
of 2,4-D are very volatile and should not be used if sensitive crops are growing in the area. Iso-
octyl and propylene-glycol are examples of ester formulations which are classified as low volatile
and do not vaporize easily. These esters are about 1 0 to 20 times less volatile. However, all forms
of amines are less volatile than any of the ester forms. In the last few years, attempts to reduce
volatility have resulted in the formulation of 2,4-D acid in oil mixtures and more recently, in oil
soluble amine formulations. To spray an amine with oil will usually increase its effectiveness to
equal that of an ester formulation.

44

■ Protection of Non-Target Plants

By far the greatest hazard associated with herbicides is the phytotoxic effect on non-target plants
caused by incorrect or inaccurate apphcation.

Examples of hazards that should be avoided are:

a Spray drift, in either particle or vapor form, deposited on plant foliage;

O Soil contamination resulting in root uptake by non-target plants;

D Excessive soil persistence causing injury to subsequent crops; or

O Sprayer contamination.
Because of the effects that herbicides produce on plants, their presence can be readily detected in
terms of characteristic symptoms or death.

Spray drift of certain soil applied or persistent non-crop herbicides can injure susceptible non-target
plants (beans, sugar beets) even when the drift occurs before seeding the crop.

Plant growth regulating (hormone-like) herbicides present the greatest visible hazard to non-target
broadleaf plants. Conversion to a vapor associated with temperatures of about 90 degrees and higher
can be a hazard with low volatile ester forms of 2,4-D and related herbicides. High volatile 2,4-D
esters present an extreme vapor hazard and their use should be confmed to areas where sensitive
crops are not in close proximity.

All of the herbicides listed below are plant growth regulators and can promote abnormal plant
growth when found in trace amounts. Once these herbicides are used, adequate decontamination of
sprayers poses a problem, especially if the sprayer is multipurpose and must be used for application
of other pesticides. Emulsifiable (oil-soluble) forms such as esters and oil soluble amines are more
difficult to clean from spray equipment than the water soluble metallic and amine salts.

Herbicides that May Present a Drift or Equipment Contamination Problem

There are several suggested decontamination
procedures (see MDA, Basic Pesticide
Manual). Using the right procedure and with
enough effort, decontamination can be
accomplished. When using sprayers for
multiple use applications, extreme care
should be exercised.

Remember that all herbicides are subject to drift under certain conditions. Good judgment should
be used when applying any herbicide.

2,4-D

2,4,5-T

MCPA

picloram

MCPB

dicamba

silvex

fenac

45

TOXICITY OF HERBICIDES

Any herbicide, in large enough doses, can pose a health hazard. However, at recommended rates,
most herbicides are relatively non-toxic to humans and the environment. Herbicides, as with all
pesticides, should be used only according to label directions. The information provided on the label
is for the safety of the applicator as well as for anyone in the area and label directions, including use
of safety equipment, should be carefully followed.

■ T.D.Q Values

Toxicity is the capacity of a substance to produce injury. The toxic action of greatest concern is the
lethal dosage (LD) or the amount that will kill. Toxicity of a given substance varies with species,
age, sex, and nutritional status of the test animal as well as with the route of administration (internal
or dermal).

The basis used to express acute toxicity of a pesticide is LDjg, which is the average lethal dosage
(LD) per unit of body weight required to kill one-half (50%) of a population of test animals. The
usual test animals are white rats, but may be mice, rabbits, and sometimes dogs. The most common
LD50 is the acute oral toxicity, that is, the single internal dosage necessary to kill half of the test
animals.

The acute oral toxicity has limitations because it represents only the immediate toxicity of an intemal
dosage and not the chronic and cumulative effects or any skin absorption or irritation. Few
herbicides are absorbed rapidly through the skin and most herbicides do not accumulate in the body
to a toxic level. However, some do cause skin irritation. LD50 values are expressed in terms of
milUgrams of chemical per kilogram of body weight (mg/kg). Some conversion factors to convert
to common terms are:

1 ounce = 28.38 grams = 28,380 milligrams

1 kilogram = 1,000 grams = 2.2 pounds

Therefore, an LD50 of 1,000 mg/kg would be 3 ounces of material per 180 pounds of body weight,
while LD50 values of 100 would be 0.30 ounces per 180 pounds. Since toxicities depend on body
weight, it would take only one-third of this amount to kill a 60-pound child and five times as much
to kill a 900-pound animal.

LD50 values are expressed on active ingredient. If a material is only 50 percent active ingredient, it
would take two parts of the material to make one part of the active ingredient. In some cases,
adjuvants mixed with the active ingredient for formulating a pesticide may cause toxicity to differ
from that of the active ingredient alone. For example, the LDjq of 2,4-D acid is 320 mg/kg, while
that of the ester formulation is 500 to 600 mg/kg.

The acute oral LD5Q values for the active ingredient of some common herbicides are given in the
table below. Remember, the lower the LDjq value, the greater the toxicity. A common standard for
comparison might be aspirin, which has an LD50 value of 1,200 mg/kg.

46

Herbicides (common name)

Acute Oral Toxicity ■1

LD,o (mg/kg)

Test animal

Acrolein

46

rat

Endothall (acid)

51

rat

(sodium salt)

190

rat

(amine salt)

206

rat

Dicamba (acid)

2900

rat

Dinoseb (DNBP)

58

rat

Paraquat

120

rat

Picloram (Trodon)

8200

rat

2,4-D (various fonriulations)

300-1000

rat, guinea pig

Glyphosate (Roundup)

>5000

rat

■ Toxicity Classification

All pesticides are classified according to their toxicity to man. The following table indicates the
relative toxicity of most herbicides to man. To find the common names of herbicides associated with
the list, refer to the family classification in Appendix C.

SIGNAL WORD

TOXICITY CA TEGORY

LD,„

LD^ is the amount of pesticide, measured in milligrams per kilogram (mg/Kg) of body weight,
thai will kill one-half of the exposed population

Oral

common measuring unit

Dermal

DANGER -POISON

I

high toxicity

0 - 50

. taste to 1 tsp.

0 - 200

WARNING

II

moderate toxicity

50 - 500

tsp to Tbsp

200 - 2,000

CAUTION

III

low toxicity

500 - 5,000

1 oz to 1 pt

2,000 - 20,000

IV

relatively nontoxic

over 5,000

more than 1 pt

over 20,000

47

Chemical Toxicity

Chemical Family

., Toxicity Class

I

II

III

IV

acetanilides

/:-\'-

•

aliphatic carboxylic acid

V

^^-•.;

amino acids

•

benzoic acids

•

•

benzonitriles

•

•

bipyridiliums

V

V

carbanilates

•

dinitroanilines

•

diphenyl ethers

.•?;,;

inorganic compounds

•

organic arsenicals

•

■ \^!\:'

phenols

:\^yy.

phenoxy compounds (acetic)

V

••■■ ;':

(butyric)

•

(propionic)

•

•

(phthalic acids)

:*<:-/

•

pyridines

^v^^'"

pyridazinones

/•-,■

thiocarbamates

•

s-triazines

•

•

as-triazines

•

tnazoles

•

•

uracils

•

•

ureas

•

48

Weeds Review Questions

1 . A weed can be defined as:

a. a plant growing where it is not
wanted.

b. a plant out of place.

c. a plant that is more harmful than
beneficial.

d. all the above.

2. Sources of weed infestations include:

a. humans, wind, and water.

b. wild and domestic animals,
planting contamination, farm
machinery.

c. a and b

d. none of the above

3. Perennial weeds may have the following
types of root systems:

a. rhizomes and stolons

b. creeping roots

c. bulbs and tubers

d. all of the above

4. What growing stage is the best time for
controlling annual weeds?

a. flowering

b. seedling

c. vegetative

d. mature

7. Pre-emergence treatments are:

a. applied to the soil after the crop
or weeds have germinated and
started to grow.

made to the soil after the crop is
. planted, but before emergence of
the crop or the weeds,
applied after the harvest of the
crop.

applied to the stack of hay or
straw bales.

b.

c.

d.

8. Rain a few days before spraying can
improve penetration of a herbicide into a
plant by increasing the wettability of the
leaf

a. True

b. False

9. Microorganisms in the soil are an
important component of herbicide
decomposition.

a. True

b. False

1 0. Spray drift is dependent only on droplet
size.

a. True

b. False

5. Perennial weed control is most effective
in which growth stages?

a. seedling or regrowth

b. vegetative or regrowth

c. full flower or mature plant

d. bud or mature plant

6. Methods of controlling weeds include:

a. biological

b. chemical

c. mechanical

d. all the above

11 . A surfactant is any material that affects
the surface properties of spray solutions and
includes:

a. granules

b. stickers

c. emulsifiable concentrates

d. water dispersible liquids

12. The cuticle is a waxy layer or thin film
on the leaf surface which retards the
movement of water and gases out of or mto
the leaf

a. True

b. False

49

AGRICULTURAL INSECT PESTS - PART III

ARTHROPOD RELATIVES OF INSECTS

A universal system has been developed to categorize all organisms into groups and subgroups. The
animal kingdom for example, is first divided into a number of phyla. Each phylum is then divided
into a number of orders, which in turn are divided into families followed by divisions into genera
and species. Thus, the classification of the alfalfa weevil, an important economic pest, is as follows:

Kingdom ■•■*

Animal

Phyli

urn ■-* Arthropoda

Class

-* Insecta
Order -♦ Coleoptera

Family ■-* Curculionidae

Genus

■->■ Hypera
Species ■-»

pQstica

Insects belong to the class insecla, which is in the phylum, Arthropoda. The Arthropoda is the
largest group of animals which make up the animal kingdom. The following are important phyla
of animals. The first nine are invertebrates (without a backbone). Only the Chordata are vertebrate
animals (with a backbone).

□ Protozoa (amoeba and other single-celled animals)
D Porifera (sponges)

□ Coelenterata (jellyfishes, corals)

□ Platyhelminthes (flatworms, flukes, tape worms)

□ Aschelminthes (roundworms, trichina)
O Mollusca (snails, slugs, clams)

□ Echinodermata (starfish, sea cucumbers)

□ Annelida (segmented worms, earthworms)

□ Arthropoda (insects, spiders, crayfish, millipedes)

□ Chordata (fishes, amphibians, reptiles, birds, mammals)

Insects and their relatives which make up the phylum, Arthropoda, are characterized by having the
following features in common: a chitinous exoskeleton and segmented bodies with appendages (legs,
antennae). Five important types (classes) of arthropods include the Insecta, the Crustacea (crayfish,
sowbugs or pillbugs, and fairy shrimp), Arachnida (spiders, daddy longlegs, ticks, mites and
scorpions), Diplopoda (millipedes or thousand leggers), and Chilopoda (centipedes or hundred
leggers). In terms of sheer numbers, insects make up nearly 7/8 of all arthropods. Included in this
class are bugs, beetles, butterflies, bees, etc. All insects have 3 body parts (head, thorax and
abdomen), three pairs of jointed thoracic legs and one pair of segmented antennae. This is the only
class that has members which can fly, many having two pair of functional wings.

50

INSECT CLASSIFICA TION

There are vast numbers of different types of animals in the world. Common names of insects often
vary for one species from one locale to another. To avoid much of this confusion, a systematic and
standardized arrangement of scientific names exists. The name of each insect consists of the Order,
Family and Genus which are capitalized, followed by the Species and Sub-species (when applicable).
The name of the person who described the species appears last. The genus and species name are
underlined or written in italics. A shortened form of the complete scientific name consists of the
genus and species.

Examples:

Pea aphid - Full scientific name: Acrthosiphon pismn (Harris) (Homoptera: Aphididae)

Short scientific name: Acrthosiphon pi sum

Explanation:

Order «»*■ Homoptera

Family "*■ Aphididae

Genus •'"*■ Acrthosiphon
Species "*■ pi sum

Cereal Leaf Beetle - fiill scientific name: Oulema melanopus (L)

Short scientific name: Oulema melanopus

Explanation:

Order ""*■ Coleoptera (beetle)

Family ""*■ Chrysomelidae (leaf beetle)

Sub-Family »"»• Criocerinae (shining leaf beetle)
Genus ""*■ Oulema

Species ""*• melanopus

There are approximately 26 orders of insects. This manual will deal only with those orders
containing species considered injurious to plants, animals, humans or the beneficial types that aid
in their control. Twelve such orders are described as follows in Table 1 .

51

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53

Another method of insect recognition involves the examination of damage done by the pest. Pest
identification can often be made based on the nature of the feeding damage as indicated below:

Damage From Chewing Insects

Defoliators- Those pests which chew portions of leaves or stems, stripping or chewing the
foliage of plants. Examples: leafbeetles, caterpillars, cutworms, grasshoppers, flea beetles.

Borers- Those pests with chewing mouthparts which bore into stems, tubers, fruit trees, etc.
Examples: com borer, white grub - potatoes, granary weevil - grains, codling moth - apple.

Leaf Miners- Pests which bore into and then tuimel beneath surface layers of the leaf.
Examples: leaf miners.

Damage From Piercing and Sucking Insects

Distorting plant growth- Those pests that cause leaves, fruits or stems to wilt, curl or become
distorted. Examples: aphid injury, cat facing of peaches from lygus bugs, cone gall on
spruce.

Causing stippling effect to leaves- Pests which may cause small, discolored spots on the
leaves which eventually turn yellow. Example: thrips

Causing burn on leaves- Pests which secrete toxic substance in the host tissue, causing
foliage to appear burned. Examples: leafhopper injury, greenbug (aphid) injury.

54

INSECT STRUCTURE

There are a great variety of shapes and forms in the external structure of different insect species. For
example, the mosquito which sucks blood has piercing-sucking mouthparts adapted for this purpose.
The plum curculio has chewing mouthparts which enable it to chew its way into an apple. Through
study it becomes apparent that structures have evolved which play an important role in the insect's
development and survival. This chapter will provide an introduction to the variation and complexity
of the external anatomy of insects, which is basic to fiirther study.

■ The Body Wall or Cuticle

The cuticle makes up the major structural portion of the outer body wall (known as the exoskeleton)
and is a protective covering which regulates the passage of liquids and gases. Chitin is soft and
pliable but very strong. The exoskeleton has 3 major functions:

•" Protection and support of delicate internal muscles, nerves and other tissues from

weather, desiccation, enemies and disease.
^ To enable communication between the outside and the inside of the insect. Some sites

on the exoskeleton are modified for sensory purposes (seeing, hearing, feeling, etc.).
• Movement.

■ Structures of the Exoskeleton

Segmentation is a process by which the insect body becomes divided into a series of parts or
segments. It allows greater flexibility for the insect. Numbers of segments will fuse together into
body regions such as the head, thorax or abdomen.

The following characteristics distinguish insects from other animals:

♦ Three body regions - head, thorax and abdomen
♦> Three pair of jointed legs on the thorax

♦ One or two pair of wings (some have none)

♦ Onepair of segmented antennae

♦ Compound eyes and/or

♦ Simple eyes

♦ The Head

General Structure: The insect head is a hard capsule whose form and position are generally
dependent on the mouthparts and type of food ingested (eaten) by the particular insect. An
understanding of the mouthparts and feeding habits of insects can be helpftil in selecting control
measures. Mouthparts are of two general types, chewing or sucking.

bisects with chewing type mouthparts move their mandibles or jaws in a sideways motion. These
types of insects include adult beetles, ants, wasps, dragon and damsel flies, grasshoppers, and
crickets. Immature insects such as caterpillars, maggots, and beetle larvae also have chewing
mouthparts.

55

Sucking type mouthparts are highly modified. Insects with these mouthparts cannot chew their
food. Sucking mouthparts are in the form of a somewhat elongated beak through which food is
sucked. This type of structure may be further modified to be:

♦> Piercing-sucking as in the mosquitoes, true bugs, and aphids

♦ Lapping-sponging as in the housefly

♦ Rasping-sucking as in the thrips

<• Tube-like as in the moths and butterflies

Insects with sucking mouthparts include the adult sucking lice, flies, mosquitoes, true bugs, aphids,
scale insects, leafhoppers, moths and butterflies, fleas, and thrips.

♦ The Thorax

The thorax controls the insects' locomotion. This is the middle region of the insect body and is
divided into three segments. One pair of legs is attached to each of these segments. When present,
paired wings are also attached to the thorax. Characteristics of the wings and legs are often useful
in insect identification.

♦ The Abdomen

The abdomen, generally composed of 10 or 11 segments, is usually very flexible, facilitating such
possible functions as copulation, oviposition, and stinging. On each of the first eight segments of
many adult insects are found a pair of spiracles (small openings to breathing tubes) with the last
several segments modified for various structures, the most important being reproductive in nature.

Stemming from the eighth and ninth abdominal segments is the female egg-laying mechanism, used
to place eggs in protected sites. This is called the ovipositor and is most often an extended tube.

Antenna

INSECT DEVELOPMENT

All insects develop from eggs, most after the eggs have been laid. A few insects develop from eggs
within the body of the female and are bom alive. Insect eggs vary widely in size and shape. They are
usually laid in protected locations that afford the young good conditions for survival.

After hatching, insects develop by passing through a series of growth stages. The size of an insect is
restricted by its hard outer exoskeleton. Each new growth stage involves shedding of the old exosk-
eleton and forming a new one. This shedding process is called molting. The insect stage between
molts is call the instar.

.^

As young insects progress toward adulthood, they may change not only in size, but
also in form. Metamorphosis describes the process of changing from egg to adult.
Most insects have either hemimetabolous (incomplete) or holometabolous (com-
plete) metamorphosis.

Hemimetabolous insects resemble the adult form in the immature stages in many
ways, but are not reproductively mature and do not have ftmctional wings. How-
ever, these immature stages often live in the same environment and feed on the

same food as the adults. The term "nymph" is given to the immature stage of this

group.

<Mj

Holometabolous development characteristically includes a pupal instar in which
great changes in form and structure occur and larvae most often live in different
environments and feed on different food than the adults. The immature is
called a "larva" and never possesses wings and are sexually immature. Al-
though there is much transformation occurring during the pupal stage, it is
also a resting stage as far as eating, reproduction and locomotion are con-
cerned. As a result, the pupa are immobile and in need of protection. Some
insect types remain in a protective skin from their last molt called a pu-
parium while others spin cocoons using silk glands. A third type find refiige in hard-to-reach places
such as spaces underneath bark or debris.

(Hemimetabolous
metamorphosis

Eggs

Holometabolous metamorphosis j

Larva

Adult

Pupa
57

IMMATURE STAGES OF INSECTS

The immature stages of insects are of particular importance in pest management because these are
the stages when insects do most of their feeding, and in most cases cause the most damage. These
stages are highly variable. Immature insects are commonly classified into types based on their
appearance and common characteristics. Insects are generally broken down into two major types,
NYMPHS which have hemimetabolous metamorphosis, and LARVAE, those with holometabolous
metamorphosis.

The NYMPH, aside from having hemimetabolous metamorphosis, looks like the adult. It has six
legs on the thorax. The nymph does not have fully developed wings, but usually has wing pads.

The LARVA, which has holometabolous metamorphosis never look like the adult in appearance.
Legs on the thorax may be absent or present. Wing pads are never present. Among larvae there are
several distinct types as follows:

Vermiform (Figure III-l) larvae are cylindrical, elongate and wormlike without legs. These

include bees and wasps (Hymenoptera), some beetles, (Coleoptera)

and flies (Diptera). In the case of Diptera, the larva is called a maggot

and is characterized by the absence of a distinct head, presence of mouth

hooks, and spiracles on the anal end of the body. Figure III-l

igureIII-4

The eruciform (Figure III-2) larva is cylindrical. It has six legs on the thorax and also fleshy

prolegs on the abdomen. The head is distinct and well-formed. These larvae are commonly

called caterpillars. Caterpillars may be found in two economic orders. Those that become

moths or butterflies (Lepidoptera) have five or fewer pairs of pro-

^^>^^^^iy^gEis^^^^ legs on the abdomen. Those that become sawflies (Hymenoptera)

"^^^ 3 ^^^^7J -^ have more than five pairs of abdominal prolegs.

Figure III-2 Figure III-3

The carabiform (Figure III-3) larva is the common form found
among ground beetle larva and leaf beetle larvae.

Scarabaeiform (Figure III-4) larvae are commonly called grubs after the larvae of
May and June Beetles. They are typically C-shaped with a well-developed head
and usually have six thoracic legs, but no abdominal prolegs. This form is also
found in several other groups of beetles.

The elateriform (Figure III-5) larva is cylindrical, smooth and "hard shelled" in
appearance. It has short thoracic legs, but no abdominal prolegs. The destructive
wireworm larva of the click beetle is elateriform.

Figure III-5

58

THE INSECT PEST

A PEST may be any organism which competes with mankind for a hmited resource, or is threatening
to human health or comfort and possessions. It has been estimated that there are a milhon species
of insects which have been identified and named, of which ten thousand are considered economic
pests. This number is only one percent, or one in each 100 species. This may seem low, but a single
species can be devastating. Insects have been known to cause crop failures, induce plagues and
spread epidemics producing enormous suffering from famine or disease, or both.

Ecologically, there are no pests, only consumers. However, when an organism begins to take what
mankind wants, that organism becomes a pest. The insects categorized as pests are everywhere, they
even attack us and our pets.

Variables such as temperature, moisture, soil fertility and natural controls interact to complicate the
assessment of insect damage and the prediction of loss. An insect population is dynamic (constantly
fluctuating), and influenced by its surrounding environment. Certain pests become problems when
such factors as the lack of sanitation (in the case of house flies or stable flies), or the flooding of land
(in the case of mosquitoes), create an optimal habitat for the insect. The impact of many crop pests
may be intensified when the crop is affected by disease pathogens, or is in competition with weeds.
These variables, or a combination thereof, along with other physical and biological factors predicate
the loss that will occur. Thus, damage from an insect pest will vary from year to year, from area to
area, and from crop to crop.

■ When Do Insects Become Pests?

Insects generally reach pest status in one of the following ways:

>- By being introduced into, invading or otherwise entering an area previously uncolonized
by the species. This movement may be iritracontinetital where an insect moves from one
area to another. It may also be intercontinental (between continents). Either case often
results in serious pest situations. In this movement from area to area, natural enemies are
often left behind, climate may be more suitable for reproduction and development, and food
sources more available.

>■ A great and lasting increase in numbers of a species takes place. Such numbers can
generally be categorized as resulting from either:

♦ A lasting or permanent increase in a favorable resource (in contrast to year to year
fluctuations) such as food, oviposition sites, or other requirement, or

♦ A lasting decrease in a repressive factor such as inclement weather, natural enemies
or sanitation. In some cases, both of the above conditions may play a role in allowing
an insect population to fully utilize resources.

>■ There may be a change (usually genetic) in an insect population which results in a
characteristic which now causes insect-crop interactions which did not occur before the
characteristic change. The European com borer, which changed from one generation per

59

year to two or three generations per year, is an example. This change brings the destructive
larval stage in contact with many more crops than only a single generation.

>" Changes in the activities and habits of people may occur in such a way that they become
sensitive to insect activities to which they were previously indifferent. Prior to the time it
was realized that apple maggots might be kept out of the orchard, the apple maggot was not
considered a pest. Likewise, aphids dropping honeydew on an old 1 967 Oldsmobile parked
under a tree could be disregarded, but the same aphids in the same tree become pests when
the same person's new Oldsmobile is involved.

Seldom can a pest situation be attributed to only one of these causes. Often, all may play a role to
varying degrees. However, it is the great and lasting increases in number that we think about most
often when we label an insect a "pest".

■ The Causes of Insect Outbreaks in Crops

The ways insects become pests and the causes of insect outbreaks are related. Some of the causes
of crop-pest problems follow:

^ Large scale single crop culture provides mass quantities of a specific food that may be
desirable to a certain species of insect. This greatly reduces the constraints on the species,
thus allowing large pest populations to build-up.

^ Indiscriminate use of pesticides reduce the species diversity. The application of an
insecticide not only reduces the population of a pest, but also its competitors. Should an
insect pest acquire resistance to an insecticide through genetic selection, the lack of
competition from other feeders for the food resource can lead to serious outbreaks of the
insecticide resistant pest.

^ The sensitive balance of insects and their natural enemies may be disrupted. This may
be the result of cropping systems which establish breeding grounds for particular insect
species while making conditions unfavorable for their parasites and predators. It may also
result from attempted pest control procedures which destroys the pest's natural enemies
without effectively controlling the pest itself

• Favorable weather conditions may contribute to increased insect pest populations. Many
aphids, such as the pea aphid, develop huge populations when there is a cool spring with
temperatures of 15 to 18 degrees C (59 to 64 degrees F) predominating. The cool
temperatures are favorable for the aphid, but unfavorable for the development of its natural
enemies.

■ The Kinds of Damage Insects Cause

Insects that attack and damage agricultural commodities are classified as either direct or indirect
pests.

60

Direct Pests are those organisms which attack the marketable part of the crop, such as the apple
maggot which feeds on and destroys the fruit.

Indirect Pests are those which cause loss by attacking the non-marketable part of the crop, such as
the western com rootworm which attacks the com root system and causes plants to lodge.

The damage insects cause can be broadly categorized as either quantitative or qualitative.

Quantitative Damage is the actual destmction of plant tissue, intermption of metabolism, or
commodity injury which results in less yield or marketable product than would occur in the absence
of harmful insects. This may occur when the leaf is consumed and there is a subsequent reduction
in the photosynthetic capability of the plant. Product destmction by direct insect feeding, such as
tomato homworm on tomato fruit, or by secondary plant pathogens entering wounds caused by
insects (soft rot of carrots or potato) is also quantitative in nature. Types of quantitative damage
include:

>- Loss in yield: The reduction in harvestable yield is usually the first consideration of loss
from insect infestation. Thus, most economic thresholds are based on the population size
of an insect pest that will reduce yield sufficiently to make control of the pest profitable.

>' Lower plant tolerance: Stress from insect infestation may hinder recovery following
harvest, reduce stand, and consequently reduce the yield of later harvests. It can be
shown that an alfalfa weevil infestation on the first-cutting alfalfa crop, not only
decreases the growth of the first cutting, but also the second or third cuttings. Yield, rate
of recovery and stand can be reduced for the entire growing season.

^ Transmit disease to plant: Insects which may not cause serious economic damage from
feeding alone, may cause serious losses by transmitting disease pathogens. Viral
diseases, many of which are transmitted by insects, generally reduce yield from 0 to
20%. The green peach aphid is known to feed on plants of 30 different families
(transmitting, in course, more than 100 vims diseases) including such important crops
as potatoes, beans, peppers, tomatoes, sugar beets and tobacco.

Qualitative Damage affects the physical shape, size, appearance, or nutritive composition of a
product and is often difficult to evaluate. In addition, the presence of insects or insect fragments in
a marketable commodity also affects the quality of the product. Although no health hazard may be
involved, the public has come to believe that insect contamination is generally unacceptable in its
food products.

%/ Loss in marketability of commodities: Qualitative losses which affect the marketability
of a commodity may involve such things as aphids on lettuce or broccoli (for which there
are federal standards specifying how many may be present), or flea beetle damage to
potatoes. If a crop is graded and those items of lesser grade removed, this becomes actual
quantitative loss. Often, however, lower prices may be available for those products of lesser
grade. Cooking or juice apples may bring as little as one-sixth the price of dessert apples
because of insect damage.

61

%/ Alter nutritional components of the plant: In some cases feeding by insects can influence
the physiology of the plant to the extent that nutritional quality is affected. For example, a
serious loss in protein occurs when the potato leafliopper feeds on alfalfa, causing the plant
to produce less protein and more sugars. This loss, results in significant reduction in
nutritional value of alfalfa as a livestock feed.

62

PRINCIPLES OF INTEGRA TED PEST
MANAGEMENT

To a large extent, the value of entomology is based on applied insect control. To an even greater
extent, the support given to this branch of science by the public is in direct proportion to the
efficiency of measures for insect control which have been developed by entomologists. While the
lessening of insect damage or the control of insect outbreaks is far from the only aim of insect study,
it is the most important. Insect control includes all those factors, natural and applied, which make
life difficult for insects, that regulate their rates of increase, and that make it laborious for them to
spread about the world. This chapter outlines the many ways in which insect control can be
accomplished and establishes a framework in which these techniques can be organized into systems
of applied ecology, that is integrated pest management (IPM) of insects.

Integrated pest management is simply the ecologic approach to insect control. It is a system in which
all available techniques are evaluated and consolidated into a unified program to regulate insect
populations so that economic damage is avoided and environmental disturbances are minimized
(National Academy of Sciences, 1969). Rabb (1970) defined IPM as the intelligent selection and
use of pest-control actions that will ensure favorable economic, ecological and sociological
consequences. Thus, IPM is philosophically related to the more familiar concepts of fisheries, forest,
and game management.

There are four basic principles of integrated pest management. IPM must:

O be a part of the total crop production program.

© be economical.

© recognize that pest control actions can result in undesirable effects such as water
pollution and the destruction of non-target species.

0 refer to all pests including weeds, pathogens, insects, nematodes and vertebrate animals,
such as moles, ground squirrels, and pocket gophers.

■ Requirements for a Pest Management Decision

In order to make intelligent decisions regarding pest control, integrated pest management requires:

^ Identification of the pest.

► An accurate measurement of the pest population. This is accomplished by scouting the
field and sampling.

An understanding of the pest's habits and seasonal development.

The assessment of damage levels. The producer saves money by not taking action until
action is required. Many times the economic threshold, or acfion threshold is not reached
and it is not necessary to apply a control.

63

►

^ An assessment of potential ecological or environmental hazards that may occur with a
proposed control methodology.

■ Background for Integrated Pest Management

Following World War II, growers achieved crop production with unprecedented quality and yield
by indiscriminately using many of the new "miracle" chemicals that became available. This is
understandable because of the tremendous economic benefits realized from higher yields and the
high premiums obtained because of the "cosmetic" effect of insect-free produce at the market.
Pesticides were inexpensive when weighed against the consequences of non-use. Consequently, the
grower became almost totally dependent upon chemical pest control for almost 30 years. The
intensive use of these chemicals frequently violated basic ecological principles. Consequently,
serious problems developed as follows:

^ Pests developed strains which were resistant to chemicals.

► It became necessary to increase levels and frequency of pesticide applications to kill
insects as they became more and more resistant. This in turn increased the cost of insect
confrol.

^ Certain pesticides tended to persist in the environment.

► Some pesticide residues became biomagnified in the environment.

^ Non-target organisms were adversely affected.

► Finally, the public was disturbed by reports of extensive amounts of pesticides which
were not biodegradable released into the environment.

These problems led to the reassessment of biological and ecological principles and the development
of modem integrated pest management systems.

■ The Economics of Pest Management

The use of prophylactic or "insurance" treatments against possible infestation and loss of a crop is
against fimdamental pest management principles. However, in a practical sense, such freatments can
not be avoided unless the consequences can be accurately predicted. To do this, it is necessary to
understand the insect population level that will cause loss and how to sample to determine when
there is a potentially damaging population infesting a crop.

64

■ Economic Injury Level

A basic concept underlying all pest management decisions is the economic injury level. It has been
defined in various ways as...

"the lowest pest population density that will cause economic damage"
(Stemetal. 1959).

"the loss caused by the pest equals in value the cost of available
control measures" (National Academy of Science, 1969).

"the pest population that produces incremental damage equal to
the cost of preventing the damage" (Headley, 1972).

Regardless of how the economic injury level is defined, it essentially depends on whether or not
treatment will make money for the producer. Thus, the term economic injury level (EIL). For

example, if the value of crop damage prevented by a pesticide application is $12 per acre and the
cost associated with treatment (pesticide materials, application equipment costs and labor) is greater
than $12, the pesticide application is not economical. In this instance, the pest population has not
exceeded the economic injury level.

■ Economic Threshold (ET)

The economic threshold (ET) is the "pest density at which control measures should be applied to
prevent an increasing pest population from reaching the economic injury level." Therefore, the ET
generally represents a pest density lower than that of the EIL and is the guideline for the initiation
of applied control measures. When the density of a pest population reaches the economic injury
level, the crop has already sustained damage and loss in yield. In many cases, this is a "tolerable
loss" and that control would be uneconomical. However, when the density of the pest population
increases through time it becomes desirable to implement control procedures in those instances when
pest populations will ultimately exceed the economic injury level.

The economic injury level is always tied, in some way, to the pest population. Pest population
density, like the population density of all organisms on earth, fluctuates over time. When this
fluctuation is averaged over a period of time it is termed the equilibrium position.

Changes in population numbers below the equilibrium position can be caused by environmental
factors (i.e. rainfall, adverse temperatures), natural enemies (i.e. parasites, predators, diseases), or
competition between members of the population for food or space. Those populations that remain
close to their equilibrium position are termed stable populations, while those that fluctuate widely
are termed unstable populations. Pest populations are frequently divided into groups according to
the relationship of the equilibrium position and the economic injury level.

65

■ Economic Classes of Insects

Many insect species feed on crops, but never reach densities high enough to cause economic injury.
These insects are non-pests and treatment is never required.

Some insect species have very unstable populations and under favorable environmental conditions,
their numbers grow rapidly and exceed the economic injury level. These insects are termed
occasional pests. Many insects fit into this category and include com rootworm beetles, Diabrotica
spjL, that feed on com silks; the green clovenvorm, Plathypena scahra (Fab.), on soybeans or the fall
webworm, Hyphantria cimea (Drury), on trees.

A number of insects have populations that nearly always exceed the economic injury level and are
termed perennial pests. The Colorado potato beetle, Leptinotarsa decemlineata, is an example of
a perennial insect pest.

The final group of insects are severe pests. Severe pests have an equilibrium position above the
economic injury level and always require control intervention to prevent economic loss. Common
examples are the com earworm, Heliothis zea, on sweet com; the codling moth, Laspeyresia
pomonella, on apples; and the house fly, Musca domestica, in dairy bams.

■ Basis of the Economic Injury Level

The economic injury level is frequently based on a direct measure of the pest population. For
example, insects per stem, or "grubs" per cow. However, many economic injury levels are based on
indirect measures which are often easier to obtain than actual pest population counts. These indirect
measures fall into two general categories;

>- The damage that is of interest is measured and includes a sampling for the percentage of
leaf defoliation, or the number of fruit with oviposition scars, etc.

>- The measure of a factor that is not in itself damaging to the plant which indicates the
presence of a pest population that will create damage later. Leaf feeding by early instar
com borer larvae, Ostrinia nubilalis, on com leaves is such an indicator.

It is important to consider plant damage in association with an estimate of the insect population. It
is possible that unfavorable environmental conditions might reduce the pest population below
damage thresholds. This would eliminate the need for a control action even though early leaf
feeding exceeded the economic threshold indicated by the damage index. Indirect indices of pest
damage can be very useful for determination of economic injury levels. However, their limitations
should be considered when making control decisions.

■ Factors Influencing the Economic Injury Level

Economic injury levels are dynamic values. The value for any pest is influenced by a number of
factors including value of commodity, cost of control, host plant tolerance, interaction of pest
species, and environmental stress on the crop. In general, as the cost of control measures and the
tolerance of the crop to the pest increase the economic injury level also increases. This means that

66

as the cost of an insecticide treatment increases from $10 to $15 per acre a producer would need a
more damaging pest population before the yield savings would pay for the additional pesticide cost.
Also, if tolerant varieties were used, larger pest populations would be required to justify treatment.
Thus, the economic injury level goes up.

As the value of the commodity increases, the economic injury level goes down. Fewer soybean pests
are needed to pay for the cost of treatment when soybeans sell for $8 per bushel than when they sell
for $6 per bushel. In general, seed producers of any crop have lower economic injury levels than
commercial growers. This is primarily because of the greater value of a unit of the crop. In addition,
the plants used to produce seed might also be less tolerant than commercial varieties, thus reducing
the economic injury level.

It is difficult to say that environmental stress and interaction of pests always affect the economic
injury level in the same direction. As a general rule, however, increased stress on the plant, whether
from the environment or other pests tends to decrease the economic injury level. Treatment may be
economically justified at lower pest levels when the plant is under moisture stress than when
adequate moisture is available. The important point is that many factors influence the economic
injury level and it may change from area to area, year to year, and even from field to field.

■ Zero Damage Concept

A concept that is essential to a discussion of the economic injury level is what has been called the
zero damage level. For every pest there exists a population level that will not have an impact on the
yield or quahty of the plant. When the pest population is at or below this level, it no longer has pest
status. Thus, considerations regarding changes in the economic injury level are no longer relevant.
Unfortunately, many farmers have unnecessary production costs because they have become
accustomed to killing pests, regardless of demonstrated need. Furthermore, there is increasing
evidence that populations at or below the zero-damage level may produce a positive yield response
as shown with alfalfa and the alfalfa weevil. Research at Laconia, Indiana show that low populations
of alfalfa weevil larvae feeding on the plant stimulated alfalfa to produce more growth. This appears
to continue until the weevil population gets so large the plant cannot tolerate it and loss occurs.

■ The Sporadic Nature of Certain Pests

Many pests are not only sporadic through time, but also occur sporadically throughout a field. The
desirable approach would be to spot-treat those areas where the pest infestation exceeds the
economic injury level. However, when spot treatment is not feasible the pest manager must decide
whether the potential losses from areas of the field economically infested would pay for the cost of
freating the entire field. Generally, in these situations a farmer must leam to tolerate some damage
in small areas in order to make money.

In the same way, the sporadic natirre of certain pests over years must also be considered. It doesn't
make economic sense to freat in "insurance fashion" a field that faces a low level loss in 1 year of
6 when the cost of the treatment over the years exceeds the value of the crop saved. An alternative
would be to attempt to control the pest in those years when it appears. However, in some situations
a small probability of high crop damage from pests exists. Such damage could seriously impair the
financial stability of a farm operation. In this instance the application of insecticides, even though

67

the added cost is higher than the potential gain, is the safe approach in terms of the total farm
operation. It is important to consider the relevance of the nature of the pest population over the years
in making a pest control decision.

The economic injury level is the basis of most pest management decisions. Farmers are in business
to make money and the use of urmeeded pest control chemicals is a production cost that comes
straight out of the profit column on the balance ledger.

■ Categories of Insect Control

There are two broad classifications of insect control »"•■ natural and applied.

Natural control occurs when the forces of nature reduce insect populations and they include:
>- Physical factors (i.e. temperature, moisture)
>- Biological factors (i.e. natural enemies)
>- Topographical factors (i.e. mountains and lakes)

(The above may serve as barriers to insect migration or movement.)
>' Climatic factors. Certain insects such as the potato leafhopper do not become pests early
in the season in the north because they cannot survive the winter. Consequently, they have
to migrate fi'om the south each year and their arrival is later in the season.

Applied control involves any methods used by farmers to suppress insect populations to non-
damaging levels. Applied methods may be:

•* Legislative - The state or federal legislature may place a quarantine on a pest prohibiting
the movement of commodities the pest infests from infested areas to non-infested areas. By
law, the commodity cannot be shipped out of the infested area without inspection or
treatment.

i/ Physical control involves the use of physical factors such as temperature, moisture, light
and sound. People use physical control where they can, but in most cases utilization of
physical factors is difficult or impossible, except in controlled environments.

•" Mechanical control involves the use of a mechanical device such as a fly swatter or
mechanical barrier. Flaming alfalfa with an LP gas burner to control the alfalfa weevil and
shredding com stalks to control the European com borer were once used as mechanical
methods. In modem day pest management other control methods are usually more
economical or more effective.

^ Cultural control utilizes agricultural practices to alter the environment so that it is
unfavorable for a pest. Important cultural practices include: sanitation, tillage, crop rotation,
fertilization, harvesting, trap crops, crop site, etc.

•" Biological control technically includes any biological factor that suppresses insect
populations. In insect pest management, biological control implies the manipulation of
parasites, predators, and pathogens to manage the density of insect populations.

68

• Host resistance is categorized into three types:

♦ Antibiosis is an inherited characteristic in a plant which has an adverse effect on the
biology of an insect which causes any or all of the following: mortality, reduced
reproductive potential, reduced size or weight, inability to store food reserves or other
physiological abnormalities. This may be caused by a chemical in the plant which
interferes with normal physiological functions of the pest, or it may be from a
characteristic, such as the presence of hairs, spines, etc. that make it unsuitable.

♦ Antixenosis is a term synonymous with "non-preference." It means that the insect
finds the plant unattractive, or has inherited avoidance behavior towards it.

♦ Tolerance is the ability of a plant to sustain injury or recover through increased
growth and produce a crop in spite of insect attack.

• Chemical control is presently the only practical pest management method when insect
populations approach or are at the economic threshold. Chemicals must be used whenever
other measures have failed and when emergency intervention is necessary. With some pests
there is no alternative to the use of insecticides. Response to them is quick, producing
curative action and preventing economic damage. Chemicals are usually classified according
to their mode of action.

O Stomach poisons kill when ingested (eaten).
D Contact poisons kill by absorption through the body wall.

□ Fumigants, which are in a gaseous state, kill by penetrating the insect through the
trachea.

• Attractants comprise a relatively new and imaginative approach to insect pest
management. This methodology utilizes the instinctive behavior of the pest insect itself to
regulate the pest's population. Chemicals are used to attract insects at sites where they are
destroyed; to divert insects in their search for mates; or to divert the insect's orientation.

♦ Pheromones are chemicals which insects emit and respond. Sex pheromones attract
the opposite sex of the same species. In some cases pheromones trigger aggressive or
flight responses and others may mark a path to a food source.

♦ Allelochemicals, unlike pheromones stimulate insects of another species rather than
those of the species producing the chemical. Allomones are allelochemicals which are
defense secretions (i.e. toxins in the larvae of the monarch butterfly make them
unpalatable to birds; the irritant produced by bombardier beetles).

♦ Kairomones include plant substances that emit odors which warn insects of toxicity
or attract them to the right source of food (e.g. coumarin in sweetclover attracts flying
sweetclover weevils to their food plant).

^ Repellents are chemicals that are applied to prevent damage by rendering the commodity,
animal or person unattractive, unpalatable, or offensive.

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• Growth regulators which have been used extensively against weeds are now available for
insect control. An example is "Altosid" which is registered for use against mosquitoes.

Hormone chemicals which interrupt normal processes associated with growth have not been found
to be toxic or hazardous to higher animals. However, the possible adverse effects on a wide variety
of beneficial insects and non-target species is not yet fully understood.

Sterile release of males into the environment is another way of controlling insects. The sterile male
mates with females, which produce inviable offspring. Examples: screworms and medflies.

70

THE ECOLOGICAL BASIS FOR INTEGRA TED
PEST MAN A GEMENT

Integrated insect pest management must be based on an understanding of the ecological factors
which regulate insect populations. Ecology is the study of the interrelationships between organisms
and their environment. There are many environmental factors (water, oxygen, predators, parasites,
food, sound, reproduction, gravity, light, heat, etc.) in addition to the process of development and
the physiological status of the insect that affect growth, reproduction, and behavior. It is in this
setting that man's variety of management practices must fit to compliment those factors which
naturally regulate the pest population. In the definition of ecology given above organisms are
referred to as:

>- Single individuals or one unit.

>- A population which is comprised of a number of individuals of the same species.

>- A community which is comprised of a number of individuals of more than one species
living together in a habitat or environment.

The space and conditions surrounding an organism is termed the habitat. The habitat can vary
tremendously. It may be so small that it comprises only a thin layer of air around an individual, or
it may be large enough to encompass a field, an island, a continent, or the entire world.

Interrelationships refer to the way organisms are affected by numerous physical and abiotic factors
in the environment which is comprised of the species in question and all the factors of this habitat.
The following brief summary of the ecological factors which affect insect populations will help to
give a background for pest management concepts and the integration of various agricultural
management practices.

■ Natural Abiotic Control

The abiotic potential of a species is its maximum possible growth rate if no regulating or control
factors are acting against it.

If such a trouble-free environment did indeed exist, an insect would be able to produce an enormous
number of offspring; and although the abiotic potential in reality is never realized, the concept is
nonetheless usefiil in helping to identify the "effectiveness" of each regulating factor. Each species
has its own abiotic potential owing to the particular growth and reproductive characteristics of that
species, such as sex ratio, fecundity, fertility, number of generations per year, length of each life
cycle, etc.

A natural abiotic control is any condition of the environment that inhibits the growth of insect
populations and cannot be altered by human actions. Examples are as follows:

♦ Weather- temperature is the most important component of the weather. The insect's body
temperature is dependent on the air or soil temperature, thus warmer weather conditions
increase its metabolic rate, while cooler temperatures slow it. The insect's activity also
generally parallels temperature levels, the result being that in many species the individual

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may consume greater amounts of food, reproduce more and may experience more
generations in a given warm season. In addition, the insect's ability to fly may
sometimes be diminished by lower temperatures; consequently, the distribution of the
species is reduced, as are the opportunities to find both food sources and mates.
Sometimes, extremely low temperatures may fi-eeze and kill insects. However, most
species have the ability to lower the fi-eezing point of their bodies well below the fi-eezing
point of water.

Other weather conditions can also be controlling factors. One of these is moisture. Dry
weather may desiccate an insect, reducing its metabolic activity or rendering it
susceptible to disease or affect its behavior. On the other hand, excessive moisture may
also act as an indirect controlling factor by providing conditions favorable to the increase
of harmfiil microorganisms.

Another major weather factor is directive air movement. Winds may affect populations
either by helping them to move to new food sources and breeding areas, or by driving
them away. In addition, winds increase the evaporation rate and may be a significant
contributor to insect desiccation.

♦ Sunlight intensity and duration constitute the next major controlling factor. For many
species there exists a specific cutoff day length under which the insect may experience the
onset of diapause (a slowdown of metabolism and development). Other light-related
reactions include lower fecundity (or reproductive potential) and certain aspects of behavior
such as egg laying.

■ Biotic Control Factors

The living components which affect the survival of insects in the environment are called biotic.
These include food, competitors and natural enemies. Other areas of behavioral changes include
some species' ability to regulate their oviposition as well as the percentages of each caste produced
in the colony (i.e. honey bees and termites). Insects may also select favorable habitats such as
protected burrows within trees. Examples of biotic factors include:

Food- Plant feeding insects in the community are called phytophagous, whereas those
species that feed on other insects are called entomophagous. In general phytophagous insects
are considered injurious and entomophagous insects, beneficial. Insects may be further
classified by their feeding habits.

Competition is a major regulating biotic factor. It occurs between individuals of the same
species as well as between species. Competition between individuals for food can become
very intense as the available food supply diminishes. This adds stress to the community as
a whole. For example, a given food supply may be sufficient to support a populafion of
insects to complete their development. An increase in the population may exhaust the food
supply and the population will be destroyed before any individuals reach maturity. However,
the latter rarely occurs because of biological variability between individuals which allows

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some to feed faster, or develop faster and survive at the expense of the slower individuals.
This intraspecific competition brings about the selection of better adapted individuals. There
can also be competition for mates, space and habitat, all of which can limit the development
of insect populations.

When different species compete {interspecific, competition) with each other for food and
space, a small species which needs less food to complete its development, usually has an
advantage over a larger species. Likewise, a species which completes its development in a
short time usually will have an advantage over a monophagous species because it may be
able to move to a different food source.

Occasionally, even favorable environmental conditions may, in a sense, act as a regulating
factor by allowing the vigor of the overall population to decrease. Such favorable conditions
allow weaker individuals to survive, and if continued for several generations, may render the
population too weak to reproduce. As a result, the population may suddenly be depleted by
adverse conditions that normally would not be considered severe.

Natural enemies- Other insects, animals, and pathogens which are natural enemies of an
insect species contribute to the regulation of its numbers. However, through natural selection
a balance has usually been developed. Predators do not always get their prey, nor do
parasites find the last host. It has been found that the reaction time of many predators and
their prey is about the same, so that about half the time the predator gets its prey or the prey
escapes. Likewise, a parasite population may kill most of its host in a short time, but as host
numbers diminish, the parasite has difficulty locating the last few host individuals. It may
itself be reduced to low numbers through starvation. Thus, host species are able to rebuild
their populations. This preserves both predator and prey species, and is important if a
biological control program is to have lasting effectiveness. Extreme efficiency on the part
of predators and parasites, eliminating all prey and hosts would eventually cause the
predators, parasites, and pathogens to perish, too.

■ The Pest and The Agroecosystem

Pest populations live in agricultural habitats which are man-made ecosystems or agroecosystems.
In order to obtain economic production of a crop the farmer has disturbed the habitat by tilling the
soil and resorting to many practices which increase production, but also change the ecological
balance. A crop field is a habitat which supports a community of insects and other organisms in
what may be called an agroecosystem. The crop grown creates an environment which either
favorably, or unfavorably may affect the species in the community.

The crop produces a stand of vegetation which establishes the physical conditions of the habitat.
First, light within the crop canopy is reduced since this vegetation prevents some light irom reaching
the ground. In turn, this shade limits the extent to which the soil temperature rises and is directly
related to the density and height of plants, and to the size of the leaves. Vegetation can greatly
moderate the soil temperature. When the canopy is open, or vegetation is removed, soil temperature
can be raised to a level higher than soil insects can tolerate if living close to the surface.

73

Dense crop vegetation also reduces evaporation from both ground and plant surfaces because of a
reduction in wind penetration. This results in greater retention of moisture in soil and vegetation and
also tends to minimize the heat loss usually associated with evaporation. On the other hand, plants
also use a great deal of moisture and can hasten the drying out of the soil, or deplete it of moisture
under conditions of drought.

Tilling the soil may clear the soil surface and deprive insects of their food plants. Clean cultivation
of weeds is effective in reducing stink bug and tarnished plant bug infestations in soybeans and flea
beetles and billbugs in com. Likewise, the application of both inorganic and organic fertilizers or
irrigation can favor some insects and have adverse effects on others.

This section illustrates the importance of having an understanding of the crop ecosystem and the
consequences either an agronomic or a pest management decision will have. The decisions the
grower makes including the sequence of crops he grows, the cultural practices he uses, the timing
of farm operations, and the apphcation of chemicals largely determine the severity of pest problems
he/she will encounter. The risk/benefit ratio of all farm operations has to be weighed for economic
crop production.

74

BIOLOGICAL CONTROL OF INSECTS

Biological control involves the use of living organisms to destroy, suppress or regulate pest species.
In the natural environment insect populations are regulated or kept in check by various
environmental factors. Some of these are living organisms which are called natural hiological
control agents because they can not be readily manipulated to control a pest.

■ Natural Biological Control Agents

Natural biological controlling factors have a great effect in limiting insect populations. These
include:

/ predators,

/ parasites,

*^ pathogens,

/ natural resistance of plants or animals to attack by insects, and

y competition between the same or different species for a given food supply.

There are many vertebrates that feed on insects including birds, some mammals, amphibians, and
some reptiles. Although vertebrates consume great quantities of insects, the most abundant predators
of insects are other insects. Ladybird beetles are considered by some as the most valuable family
of predacious insects, but there are many others.

■ Applied Biological Control Agents

One of the oldest and most successful methods of controlling insects and related pests is by using
their natural enemies - parasites, parasitoids, predators, and disease organisms to attack and destroy
them. The first noteworthy demonstration of biological control occurred in California in 1888.
Entomologists discovered that many pests that became established in new environments often did
so unaccompanied by their natural enemies that attacked and often controlled their populations at
the place of origin.

At that time, the California citrus industry was seriously threatened by the cottony-cushion scale,
which was introduced from Australia or New Zealand. The ladybird beetle known as Vedalia, was
found to attack the scale. The beetles were imported and within a year the scale were no longer a
serious threat. Vedalia beetles continue to this day as an important pest control for the citrus
industry.

When serious pest situations are found to exist, the most appropriate strategies for controlling them
must be determined. Biological controls usually are not effective alone, but are important as a part
of a broader strategy that includes other controls.

The mode of life adopted by parasites or parasitoids has greatly limited their freedom of action; they
have become highly adapted to certain niches. The host and parasite or parasitoid must be in an
identical microhabitat when both are in the appropriate stages of development. The ability to find
hosts varies widely among parasites and parasitoids. Some species often possess a high reproductive
potential and are able to expand their numbers rapidly when there is an abundance of hosts. Such
species are able to overcome and may suppress pest populations of outbreak proportions.

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■ The Use of Parasites^ Parasitoids and Predators

The introduction of exotic species is the primary procedure or technique involved in the use of
parasites, parasitoids or predators as biological control agents. This requires the moving of the
organism from a place where it has been established to a place not yet occupied by that particular
species. In order for this procedure to be effective, there must be an unoccupied niche in the life
cycle of the pest which can be filled by the introduced parasite or predator, or a niche must be
inhabited by an inefficient regulating organism which could be displaced by a more aggressive and
efficient species.

Some protective measures for conservation of natural enemies of a pest are:

»• Protection against pesticides.

►• Development of resistance against pesticides.

►• Preservation of the inactive stages.

►• Avoidance of harmful cultural practices.

►■ Maintenance of diversity.

►■ Use of alternate hosts.

►■ Use of artificial food and shelter.

By adding mass reared or collected individuals to an existing population, the total effectiveness of
the regulating organism can be increased.

Insect Pathogens

Pathogens, or disease causing organisms, may be introduced into an insect pest population as a
control factor. While repeated applications are often necessary for temporary control, a single
application may be all that is needed to permanently introduce the microorganism into the population
as a mortality factor. These pathogens include viruses, bacteria and fungi and are usually applied
by means of spraying or dusting for ingestion by the insect.

Pathogens are not as popular as insecticides for a number of reasons. Compared to insecticides,
pathogens require an incubation period before infection causes death to the insect. This may require
anywhere from several hours up to two weeks, as opposed to insecticides which may take only
minutes to cause death. Also, because of the relative host-specificity of pathogens, companies are
reluctant to invest millions of dollars for their development. Another problem is the susceptibility
of some pathogens to weather conditions unfavorable to their growth. Fungi, for example, seem to
be sensitive to direct sunlight and dependent upon high humidity for their survival. Means of
encapsulation with various products are being developed to deal with this weakness.

However, this is not to say that pathogens are of no use. In particular, bacteria have proved to be
effective when introduced against specific hosts. The most well-known of these bacteria is the
crystal forming Bacillus thuringiensis (Bt), which infects the larvae of many species of Lepidoptera.

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■ Biological Control Information Needed For Pest Management Use

>- Chronological life history of the pest and its natural enemies.

>- Gross description of the physical environment.

>- Factors regulating the pest (to determine the most vulnerable stage).

Advantages of Biological Control

>■ Persistence or permanence.
> Safety.
>- Economy.

Disadvantages of Biological Control

>■ Length of time to become effective.

>■ Cannot prevent all damage.

>- Effect of weather and other ecological factors on the controlling agent.

>■ Specifically may be a problem where more than one pest must be controlled on a single

crop.
>- Difficulty in producing some microorganisms in reasonably large quantity.

77

GENETIC APPROACHES TO
INSECT PEST MAN A GEMENT

The utilization of genetic principles in dealing with insect populations is a relatively recent
occurrence, with the exception of host plant resistance. In a number of beneficial species, genetic
manipulation through selective cross-breeding can yield favorable results. Hybridization of
particular strains of honeybees has resulted in greater resistance to disease, greater cold-hardiness,
and increased honey production. In addition, valuable parasitic and predacious species of insects
may be made more resistant to normally lethal insecticides.

■ Genetic Manipulation

Increasing interest in genetic manipulation to control insect populations has produced a great number
of studies. Studies on the Hessian fly have shown that the prevalent strain of fly from Kansas cannot
survive on any of the resistant soft red winter wheats of the eastern United States. Furthermore, it
was found that when crosses were made between the Kansas race and all other known races of
Hessian fly, the inability to survive was genetically dominant to the ability to survive on resistant
wheats.

One of the most successful utilizations of genetic control has been the sterile insect release method
or SIRM for short. In this method, mass reared males are sterilized by irradiation, and then released
into the population to mate, and so reduce the fertility of the entire population. This procedure can
be utilized only when the females mate once or twice (i.e. Diptera and Lepidoptera); otherwise the
sterile male will not limit the fertile female's mating activity. Although introduced in the 1950's,
SIRM has already been shown to be effective; it has been responsible for the eradication of the
destructive screwworm from Florida and Georgia.

An altemative method to the release of sterile, mass-cultured insects is the use of chemosterilants.
Applied to bait, these chemicals cause sterilization in the wild population by interfering with cell
division. Although less expensive to implement, this method has some serious drawbacks, including
the chemosterilant's non-specificity, its harmful action on beneficial insects, wildlife and people, and
their frequent carcinogenic activity.

■ Host-plant Resistance

Another effective method of pest control is the introduction of increased resistance in plants through
selection and breeding. This inbred resistance can take the form of chemical changes within the
plant, or actual changes in plant structure. Entomologists have demonsfrated three mechanisms of
resistance to insects in plants; antixenosis, antibiosis and tolerance.

Antixenosis is a condition in a plant which makes it unattractive to the insect for food, oviposition,
shelter, or for combinations of all three. This type of resistance in a crop to insect attack is many
times due to the condition of the crop at the time of infestation.

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Antibiosis is a condition in a plant which is unfavorable for the development or survival of the
insect. It may affect the insect by reducing fecundity, decreasing size, or causing mortality.

Tolerance is a condition in a plant which makes it possible to support a pest population and continue
to grow, repair injury and reproduce itself under infestations that would destroy a susceptible plant.

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INSECT CONTROL WITH CHEMICALS

Insecticides are pesticides used to control or manage pest insect populations. As a chemical group,
pesticides are unique because they are designed to disrupt the physiology and/or behavior of target
organisms, hisecticides have traditionally been classified according to their mode of entry into the
insect as stomach poisons which kill when ingested, contact poisons which kill when absorbed
through the body wall, andfumigants which kill when entering through the trachea.

The introduction of the synthetic organic compounds has made it difficult to classify modem day
insecticides in the above categories since many of these materials may enter the insect's body in
more than one way. Thus, insecticides are more commonly referred to as inorganic or organic
compounds. In the discussion that follows, the organic compounds will include botanicals, synthetic
organic compounds, microbial compounds and growth regulators.

■ How Pesticide Toxicity Is Determined

An understanding of the basic principles of toxicity is essential. In the early stages of developing
a pesticide for further experiments and exploration, toxicity data are collected on the pure toxicant,
as required by EPA. These tests are conducted on test animals that are easy to work with and whose
physiology, in some instances, is like that of humans; for example, white mice, white rats, white
rabbits, guinea pigs, and beagle dogs. For instance, intravenous tests are determined usually on mice
and rats, whereas dermal tests are conducted on shaved rabbits and guinea pigs. Acute oral toxicity
determinations are most commonly made in rats and dogs, with the test substance being introduced
directly into the stomach by tube.

These procedures and others determine the overall toxic properties of the compound to various
animals. From this information, toxicity to humans can generally be extrapolated, and eventually
some micro-level portion of the pesticide may be permitted in food as residue, which is expressed
in ppm (parts per million). Simple animal toxicity tests are used to rank pesticides according to their
toxicity. Long before pesticides are registered with the EPA and eventually released for public use,
the manufacturer must declare the toxicity of their pesticide to the white rat under laboratory
conditions. This toxicity is defined by the "LDjq", expressed as milligrams (mg) of toxicant per
kilogram (kg) of body weight, the dose that kills 50 percent of the test animals to which it is given
under experimental conditions.

The LD50 is measured in terms of oral (fed or placed directly in the stomachs of rats), dermal
(applied to the skin of rats and rabbits), and respiratory toxicity (inhaled). The size of the dose is
the most important single item in determining the safety of a given chemical.

■ Inorganic Chemical Compounds

With the development of the synthetic organic compounds following World War II the inorganic
insecticides have largely been replaced by more efficient toxicants. Most of the inorganic
compounds are stomach poisons. Some that are occasionally used include:

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Lead arsenate- used for foliage feeders in orchards and forests.

Sodium fluosilicate- used in baits for cockroaches, ants and grasshoppers.

Cryolite- used on truck crops which are generally sensitive to chemical injury.

■ Botanical Compounds

Plant derivatives have a long history of use in insect control. Although their major use has been as
insect toxicants they have had other uses in insect control. For example, eugenol and geraniol as
attractants, citronella and oil of cedar as repellents, and walnut shell flour and cottonseed oil as
solvents or extenders have practical uses. Of the insect toxicants, pyrethrum, rotenone and nicotine
are the most important.

Pyrethrum is produced from the ground flowers of the daisy. Chrysanthemum cinerariaefolium, by
extracting the active materials with solvents and formulating the extracts into sprays and dusts.
Pyrethrum acts almost entirely as a contact poison, working on the nerve axon causing a quick
"knockdown". Many times it knocks down insects which recover later. Because it is relatively
harmless to mammals and plants, it is advantageous for many uses. It has two major disadvantages,
it lacks persistence because of breakdown by sunlight and is relatively expensive. Pyrethrum is
commonly formulated with a synergist such as piperonyl butoxide to increase toxicity and reduce
the amount of pyrethrum necessary for a satisfactory kill.

Rotenone is extracted from the roots of two species of Denis grown in the Amazon Valley of South
America. Rotenone is a selective insecticide acting as both a stomach and contact poison. It is
believed that it kills insects by inhibiting the utilization of oxygen by the body cells. Rotenone is
harmless to plants and most mammals with the exception of swine which are highly susceptible to
rotenone poisoning. It is highly toxic to fish and is used to clean trash fish from farm ponds.
Rotenone is widely used, particularly in the home garden and on livestock because of its advantage
of safety. However, its low toxicity, slow action, and tendency to breakdown in storage are major
disadvantages.

Nicotine is extracted from the leaves of tobacco. It is not only highly toxic to many insects, but has
a very high mammalian toxicity. It is toxic if ingested, absorbed through the body wall, or taken in
through the tracheae. It acts on the nervous system and has very low phytotoxicity.

■ wSynthetic Organic Chemical Compounds

Chlorinated hydrocarbon insecticides The rediscovery of DDT with its miraculous killing powers
during World War II opened the door to the development of the synthetic organic insecticide
industry and the chemical control era of the 40's, 50's and 60's. Never before had the world
experienced such spectacular insect control. Although DDT has been largely banned or phased out
(by world-wide authorities) because of undesirable characteristics, (primarily its persistence in the
environment and its accumulation in the fat tissue of animals), it has been humans' most significant
insecticide discovery. Even though it was found that organisms in the food chain accumulate DDT
and pass it on through the food chain with increasing concentration (through a process called
biomagnification), it has done more to relieve human suffering and death than any other chemical.
It led to extensive research not only on the chemistry and biological activity of DDT, but in the
development of newer materials which are less hazardous in their persistence.

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To realize the impact of DDT one needs only to look at the tremendous human mortality in World
War I caused by typhus. It was estimated that 25% of the Serbian army died and the Russians lost
several million people. In 1944, during World War II, a typhus epidemic broke out in Naples. A
mass delousing program was initiated with the new insecticide and within three weeks the outbreak
was under control. This was the first time that an epidemic of typhus during wartime had been
halted before it had taken its toll of thousands of lives. The results obtained in bringing malaria
under control on a world-wide basis through the use of DDT are equally impressive.

Chlorinated hydrocarbon insecticides are made up of molecules composed of chlorine, hydrogen,
carbon and occasionally oxygen or sulfur. Many of these materials, particularly the chemically
related cyclodienes (aldrin, dieldrin, chlordane, heptachlor, endrin, and endosulfan) have been
banned by the EPA or are being phased out of use because of their persistence and tendency to
produce carcinogenicity and possible mutagenicity in test animals.

Methoxychlor is possibly the most widely used chlorinated hydrocarbon in the U.S. today. It is
closely related to DDT without the latter's disadvantages. It accumulates less in fatty tissue and is
secreted less into milk. It is not only effective against many of the same pests as DDT, but is of
particular value where environmental contamination is concerned.

Organophosphorous insecticides: Organophosphorous compounds are made up of organic
molecules containing phosphorous. All appear to have a common mode of action as irreversible
inhibitors of en2ymes of the nervous system.

Organophosphorous insecticides were first developed in Germany during World War II. Intensive
research since then has led to the discovery of thousands of chemicals with various insecticidal
properties. Some of these compounds are contact poisons; some are stomach poisons with limited
contact activity. Others act systemically; they are absorbed by the plant either through the foliage
of root system, making the plant sap toxic to insects, or they may be taken in by animals, rendering
the blood toxic. Examples of insecticides which have been developed from this research and that
have different insecticidal properties include:

►• Tepp, parathion and mevinphos-short residual activity, broad-spectrum insecticides with
very high mammalian toxicity.

►■ Diazinon and azinphosmethyl-prolonged activity, broad spectrum insecticides.

► Malathion-broad-spectrum insecticide with low mammalian toxicity and short residual
activity.

►■ Demeton, dimethoate and phorate-systemic insecticides.

Carbamate Insecticides Carbamates resemble organophosphorus insecticides in use and activity.
Some have low mammalian toxicity while others are very toxic. They have the advantage of being
rapidly detoxified and eliminated from animal tissues and are not accumulative in fats or milk. Also,

82

toxic effects to the nervous system are reversible. These compounds break down readily, leave no
harmful residues and are unstable in alkaline solutions.

►• Carbaryl is very well knovm and useful in commercial and home gardens because of its
low mammalian toxicity and broad spectrum of activity.

►• Carbofuran is an example of a highly toxic carbamate which has particularly effective
agricultural use against the alfalfa weevil and has also been registered to control com
rootworms.

*■ Propoxpur is a moderately toxic carbamate with some agricultural use, but has been
developed for the control of household insects and is used extensively by pest control
operators.

► Aldicarb is an extremely toxic carbamate which is known for its wide spectrum of
effectiveness against not only insects, but also mites and nematodes. It acts only
systemically as an insecticide.

Synthetic Pyrethroids Synthetic pyrethroids are related to natural pyrethrins, but are synthesized
from petroleum-based chemicals. In recent years, this class of insecticides has grown tremendously
and new pyrethroids are being registered constantly. This class of compounds has a long and
successful history. The newest types require only one-tenth of the active ingredient of the older
pyrethroids. Among these are cypemiethrin, fenpropathrin, flucythrinate, and fluvalinate. All of
these are photostable and provide long residual effectiveness in the field.

► Allethrin has the characteristics of quick knockdown, high toxicity to insects and low
toxicity to warm blooded animals that are similar to the pyrethrins. It is commonly used
by pest control operators to flush cockroaches when determining the extent of an
infestation.

>■ Resmethrin has greater residual activity then the pyrethrins and is more toxic to insects
and less toxic to mammals. It does not need to be synergized. It is commonly used
against insects in households, greenhouses and industrial buildings, and in mosquito
control.

►

Permethrin is a broad-spectrum insecticide with greatest activity against lepidopterous
insects. Fenvelerate also has broad spectrum activity. It is registered on more than 20
crops. These materials are effective at very low rates, but also have been highly toxic to
some insect parasites and predators.

Microbial Compounds Considerable research is underway to develop commercially produced
insecticides from naturally occurring diseases of insects.

►• Bacillus thiiringiensis commonly called "Bt" is the most widely used microbial agent and
a bacteria. It is most effective against lepidopterous leaf-eating caterpillars, but its
toxicity varies tremendously among species. One disadvantage of 5/ is that it has very
little residual activity and must be present at the time the caterpillar is actively feeding.

83

»• Bacillus popilliae is an obligate bacterial pathogen that causes a milky disease in the
larvae of the Japanese beetle and other scarab beetles. It is often used in grub control in
turf.

Several species of protozoans are effective insect pathogens. Nosema locustae is registered for the
control of grasshoppers, and Nosema pyraustae for the European com borer.

Immature insects are often attacked by naturally occurring viral pathogens which generally are
remarkably host specific. Despite the large number of insect viruses, their use as microbial
insecticides has been limited because they must be produced from live hosts. Viruses of the alfalfa
caterpillar and the codling moth have been used commercially. Viral pathogens of the gypsy moth,
tussock moth and the pine sawfly have been used by the U.S. Forest Service.

Insects are known to be attacked by a variety of disease-producing microorganisms, and more than
80 species of bacteria, 250 protozoans, 460 fiangi, and 450 viruses have been identified as insect
pathogens. Under favorable conditions, some of these pathogens may become epidemic and cause
destructive epidemics in natural insect populations, but many others produce only chronic effects.
Insect pathogens are used in pest management in three different ways by:

>- Maximizing the extent of naturally occurring diseases.

>- Introducing insect pathogens into insect pest populations as permanent mortality factors.
>- The application of insect pathogens as microbial insecticides using suspensions of
spores, toxins, or viruses.

Advantages of microbial insecticides:

>- Their specificity of attack on insects and their safety to humans, domestic animals and

wildhfe.
>■ Their specificity is insect pest species so that beneficial insects are not affected.
>- The safety of their application to crops just before harvest because they leave no toxic

residues.
>- Their compatibility with almost all other elements of insect suppression used in IPM.

Disadvantages of microbial insecticides:

>- Their lack of persistence and their susceptibility to destruction by desiccation, sunlight

and heat so that proper timing of applications is essential.
>- The extreme specificity to insect pests, which limits general applications for pest control,

resulting in high development costs of most products.

Growth Regulator Compounds

These are also known as insect growth regulators (IGRs). They are low in toxicity with acute, oral
LDjqS that range from roughly 5,000 mg/kg to 35,000 mg/kg. They are non-irritating to the skin, low
in odor, and represent one of the safest pesticide groups available. Most IGRs mimic insect juvenile
hormones. If these hormones are present when they should not be, pupation or adult development
becomes abnormal. The disruption of this development process results in long term control of the
insect population.

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♦ Kinoprene (sold under the trade name, Enstar) is an insect growth regulator that is
registered for control of whiteflies and aphids on ornamental plants in greenhouses. It
produces morphological, ovicidal and sterilizing effects which result in a gradual
reduction of insect populations to below damaging levels.

♦ Methoprene (Altosid, Precor) is a relatively nonpersistent chemical which exhibits
morphologically toxic activity. It is fed to cattle to control horn flies and is also used for
mosquito control. The acute oral LD50 is greater than 34,600.

♦ Diflubenzuron (Dimilin) kills insects by preventing the formation of cuticle. It controls
a wide range of leaf feeding and certain other insects in forests. It must be fed upon to
be effective. Its use is restricted to uninhabited areas until its possible carcinogenic
nature can be determined.

Factors Which Affect Insect Toxicity of an Insecticide

^ Bioavailability - An insecticide must be in a form and applied in a manner that will get
to the insect when it is used. It must be able to penetrate the cuticle, or be fed on by the
insect.

^ Residual life.

^ Sunlight or photo-decomposition is a significant factor in the breakdown of a chemical.

^ Rainfall soon after application may wash the pesticide off the leaves. It may also cause
the pesticide to leach through the soil. On the other hand, it may bring the insecticide
into contact with the insect.

t^ Humidity is not a significant factor unless it is very low when concentrate sprays are
being applied. In this case, it may have an unfavorable drying effect on the fine mists
being applied.

^ Soil moisture is beneficial in moderate quantity for the efficacy of most pesticides. Wet
soil is unfavorable since it may prevent the insecticide fi"om reaching and contacting soil
particles.

^ Soil type plays an important role, especially in the control of soil insects. Sandy soils
have course particles and consequently have less surface area. Lower rates of insecticide
can usually be used on them to control soil insects. Silts and clays consist of fine
particles which have the most surface area. Chemicals can be physically fied up in clays
and may require higher rates of insecticide to accomplish control. Organic soils require
higher rates of insecticides to control insects because these soils tend to bind, or absorb
the chemicals, limiting pesticide activity.

85

^ Sorption refers to the adsorption of a material on a surface. For example, some plants
have waxy leaves from which spray materials tend to run off and drip to the ground. A
wetting agent (spreader-sticker) may be necessary to prevent this from happening. The
type of surface, whether shck or rough, has considerable effect on whether a pesticide
adheres or doesn't.

^ Temperature affects the rate at which an insecticide is absorbed into the insect cuticle and
the rate at which the insecticide is detoxified by the insect. Thus, theoretically, the most
successful control is usually obtained when temperatures are high at the time of
application to get the insecticide into the insect's body, followed by low temperatures to
slow the rate of detoxification. However, this may not always be true. A comparison of
the effectiveness of malathion and methoxychlor, each applied at the rate of one pound
of toxicant per acre at two temperatures to control the alfalfa weevil, is shown in Table
2. These data are part of a series of tests conducted at Vincennes, Indiana. Meth-
oxychlor consistently gave better control at low temperatures, while malathion was
consistently more effective at higher temperatures.

Table 2. Effect of Temperature on Insecticide Efficacy (Armbrust and Wilson, 1970)

TREATMENT

PERCENT FOLIAGE CONSUMED*

.60° : .:

-.85V ,,-

.....Jii

Methoxychlor

11.0

14.0

Malathion

19.0

10.3

Untreated Check

45.0

45.0

* Alfalfa weevil damage measured 2 weeks after treatment. Differences between the insecticides were
statistically significant.

^ High temperatures may also be unfavorable causing some soil pesticides to evaporate
rapidly.

^ Wind governs air currents which are particularly important since they may evaporate fme
spray mists before they reach their target or carry spray and dust particles away from the
target causing uneven distribution of the material or uneven deposits. Wind may also
erode spray materials from the treated surface.

^ Growth rate of the crop plant is significant. A rapidly growing plant such as com may
grow 6 to 10 inches in a few days. When this happens, new growth quickly generates
plant surface area that has no toxicant, giving conditions for pest resurgence.

^ Conversion by microorganisms cause insecticide residues to be converted to other
materials and are detoxified in the process. This is an important environmental safety
factor, but also reduces the length of the period of residual activity for the pesticide.

86

Stability of the chemical is affected by its volatility or vapor pressure. Will it disappear
as a gas? How long will it take before the pesticide will change degrades to something
else? Some materials break down relatively quickly compared to those with greater
residual lives.

Resistance is playing an ever increasing role in insects evolving genetically through
natural selection to the environmental stress of insecticides.

87

PESTICIDES AND POLLINA TORS

Bees are used to pollinate many different crops, including fruit trees and seed crops. The honeybee
is the most widely used pollinator although leafcutting bees are used in Montana exclusively for
alfalfa seed production. For almost 1 00 years, the pollination industry has sustained serious losses
from agricultural pesticide applications. Chemical pest control in forests, recreational and residential
areas and on rangeland inflict even fiirther damage to pollinators. It is believed that chemical
poisoning overshadows all other bee problems, including bee diseases.

The most important factor in preventing bee poisoning is good communication between all parties
involved: grower, applicator, dealer, field consultant, and beekeeper. In addition, there are a number
of specific practices that can help prevent bee poisoning. Herbicides and fungicides do not greatly
affect pollinating insects directly, however, they do affect them indirectly. The acfion of added
carriers or surfactants may either cause harm to the insects themselves or render the food supply
undesirable. Many wild pollinators rely heavily upon weedy plants, such as sweetclover, dandelion,
knapweed, and mustard as a source of food. The use of herbicides in weed control may seriously
reduce food supplies in some areas resulting in decline of pollinator numbers.

No insecticide is so species specific that nontarget insects are not at risk. Application of pesticides
will always result in the killing of beneficial pollinators, both domestic and wild. However, the
adverse effects of pesticide applications can be greatly minimized.

What the Grower Can Do

y Remove blooming weeds from the treatment and border area prior to the application.
This may be accomplished by mowing, discing or applying an appropriate herbicide.

y Avoid pesticide applications when pollinators are present. If possible, use either a pre-
or post-bloom spray.

y Notify nearby beekeepers if you must treat your crop during bloom, so they can attempt
to minimize the impact on their bees.

What the Applicator Can Do

♦ Follow the pesticide label for bee protection. Most labels prohibit application and/or
drift onto blooming plants.

♦ If possible, use the pesficide formulations which are the least hazardous to bees. The
formulations which are the most hazardous to bees are microencapsulated compounds,
dusts, and wettable powders.

♦ If possible, use pesficides with a short residual hazard and apply them in late evening or
early morning when bees are not actively foraging. Evening applications are generally
the least hazardous to bees, but if a hazardous residue persists for a day or more this
technique will not prevent poisoning.

88

• Let nearby beekeepers know when the apphcation will be made, so they can attempt to
minimize the impact on their bees.

What the Dealer and Field Consultant Can Do

>■ Recommend products that are low in hazard to pollinators when blooming plants are
present adjacent to or in the treatment area. If bloom is present, pollinators will be
present.

>■ Inform the applicator of label and rule restrictions for bee protection.

>■ Get to know who the beekeepers are in your area so you can help your growers know
who to contact before their crop is treated.

i'VJtat the Beekeeper Can Do to Protect Colonies

• Ensure that your hives are clearly marked and you have the landowner's permission prior
to placing them in a location.

• If possible, place your hives in a location which is several miles from any pesticide
application. If you cannot use an isolated location, then select a site which is normally
upwind from the crop to be treated and try to have an untreated buffer between the hives
and the crop.

• Get to know the landowners and pesticide use pattern in the area.

• Be prepared to move or protect your bees if necessary.

There are three basic ways to reduce pesticide damage to pollinators - the use of consideration,
common sense and cooperation.

"^ Consideration involves realizing that the beekeeping industry is an important part of
agriculture because of the vital pollination service it provides and that any pesticide damage to bee
colonies may have a severe economic affect upon individual beekeepers who rely upon beekeeping
for their livelihood. Reahzing these two points, efforts should be taken to prevent any pesticide
damages to honeybees and other pollinating insects.

^'^ Common sense involves selecting and applying damage prevention methods to each pesticide
application situation. For example, if two different insecticides are both effective in controlling a
pest insect, select the one which is least toxic to bees.

"S" Cooperation between pesticide applicator and beekeeper is perhaps the most important point
in reducing pesticide damage to bees. Discussion of tentative plans for pesticide application between
the applicator and the beekeeper will prevent most pesticide damages to honeybees. If a pesticide
applicator contacts these beekeepers in advance who may be affected by a certain application, the
beekeeper can remove his bees from the area and prevent serious damage from occurring.

89

Agricultural Insect Pest Review Questions

1 . All insects have three body parts which
include the following:

a. head, antennae, and legs

b. head, thorax, and abdomen

c. wings, antennae, and legs

d. none of the above

2. Coleoptera is the order of

which have chewing mouth parts.

a. flies

b. beetles

c. spiders

d. grasshoppers

3. The female egg-laying mechanism is
called the ovipositor.

a. True

b. False

4. Holometabolous metamorphosis is the
development in which great changes in form
and structure occur and larva most often live
in different environments and feed on
different food than the adults.

a. True

b. False

5. The nymph is a stage in the
holometabolous metamorphosis.

a. True

b. False

6. Quantitative insect damage includes:

a. Loss in yield

b. Lower plant tolerance

c. Transmit disease to plant

d. All the above

8. The zero damage level can be defined as
the population level that has the greatest
impact on the yield or quality of the plant.

a. True

b. False

9. Pheromones, allomones, and kairomones
are all attractants.

a. True

b. False

1 0. Organophosphorus insecticides all
appear to have a common mode of action as
irreversible inhibitors of enzymes of the
nervous system.

a. True

b. False

1 1 . Termites have chewing mouth parts and
are in which of the following order:

a. Hymenoptera

b. Orthoptera

c. Isoptera

d. Dermaptera

12. Pesticide applicators need to be aware
of pollinators and can help protect bees in
the following ways:

a. use the pesticide formulations
which are the least hazardous to
bees.

b. apply the pesticides in the day
when bees are most active.

c. let nearby beekeepers know
when the pesticide application
will be made.

d. a and c

7. To regulate insect populations so that
economic damage is avoided and environ-
mental disturbances are minimized is called:

a. chemical control program

b. integrated pest management

c. integrated insecticide program

d. biological control program

13. Most insect growth regulators (IGRs)
mimic insect juvenile hormones.

a. True

b. False

90

NOTE to Commercial mi Governmental
Vestidk Ayylicators

The following appendices (A - C) are additional reference material. The test wiU

NOT include information from these appendices. The information is only added

for your benefit to identify pests in the field or for reference in the future.

The availabUity of registered pesticides for pest control in agricultural crops

changes regularly as new pesticides are registered and older products are removed

from use. There may be state registrations available for a special local need (24 (c)

Registrations) or for a temporary use on a specific pest (Section 18 Emergency

Registrations). To determine the registration status of a pesticide in Montana or

the most current pesticide recommendations contact your local Montana State

University extension office or the Montana Depanment of Agriculture at (406)

444-5400.

91

APPENDIX A

Test Mana^mmt in Major Montam Crop

Qgicl Reference

1 Croo/Pest Soecies

Psee # 1

1

ALFALFA HAY

Alfalfa caterpillar

96

Alfalfa looper

96

Alfalfa weevil

96-97

Aphids - pea aphid and spotted alfalfa aphid

97-98

Armyworms - western yellow striped

armywonm and bertha armyworm

98

Blister beetles

98-99

Cutworms

99-100

Grasshoppers

100

Meadow spittlebug

101

Spider mites

101

ALFALFA SEED

Alfalfa weevil

102

Aphids

102

Armyworms SC cutworms

102

Grasshoppers

102

Lygus bugs

102

Seed chalcid

103

Spider mites

103

Thrips

103

92

Crop/Pest Species

Page#

CANOLA

Aphids

104

Cutworms

104

Diamondback moths

104

Flea beetles

104-105

Lygus sc plant bugs

105

CORN

Aphids

106

Corn earworm

106

Cutworms St armyworms

106

European com borer

107

Grasshoppers

107

Seed com maggot

107-108

Spider mites

108

Western com rootworm

108-109

Wireworms

109

CHERRIES

Black cherry aphid

111

Cutworms

111

Fruittree leafroller

111

Pacific flatheaded borer

111-112

Peach tree borer

112-113

Pear slug

113

Pear thrips

114

San ]ose scale

114

Shothole borer

115

Spider mites

115

Western cherry fruit fly

115-116

93

Crop/Pest Species

Page#

PEPPERMINT

Garden symphylan

117

Grasshoppers

117

Loopers

117

Mint flea beetle

117

Mint root borer

118

Strawberry root weevil

118-119

Two-spotted spider mite

119-120

Variegated cutworms

120

Wireworms

120

POTATOES

Blister beetle

121

Colorado potato beetle

121

Cutworms, armyworms sc loopers

121

Flea beetles

122

Green peach aphid

122

Potato leafhoppers

122

Western spotted cucumber beetle

122-123

Wireworms

123

' SMALL "GRAINS

Cereal leaf beetle

124

Grasshoppers

124

Cutworms and Armyworms

124

Russian wheat aphids

124-125

Thrips

125

Wheat stem maggot

126

Wheat stem sawfly

126

Wireworms

126

94

Crop/Pest Species

Page#

SUGARBEETS

Beet leafhopper

127

Cutworms

127

Flea beetles

127

Sugarbeet root maggot

127-128

Sugarbeet webworm

128

Sugarbeet root aphid

128

Wireworms

128

95

Alfalfa Hay

Alfalfa cakmlkr [colm
eiiJjtheme)

Life cycle: Mature caterpillars are about 1.5
inches long, green, with a white stripe along each
side of the body. Adult male butterflies are yel-
low with black wing margins and a wing span of
2 inches. Some females are white and lack the
back margins. However, both have orange col-
oring to the upper side of the wings.

Damage: Larvae feed on the leaves of alfalfa
plants. Infested fields show parts of the leaves
eaten out or entirely consumed by the larvae.

Habitat: Adults can be seen in open sunny
meadows, fields, and along road sides. The Lar-
vae are found feeding on plant material (alfalfa).

Control: Treat only when 10 or more
nonparasitized larvae are present per straight
sweep (90 degrees) with a net. They are nor-
mally controlled by natural enemies, but heavy
infestations may require an insecticide treatment.

Alfalfa caterpillar larva

mlipmic/i)

Life cycle: Mature larvae are about 1 inch
long, light to olive green with a palecolored head,
and stripes along its' side. These larvae only
have 3 prolegs giving them the characteristic
"looping motion" like an inch worm. Adults have
dark mottled gray forewings with a silvei^ white
spot in the center of the wing that is elongated

and angular and a wingspan of 1.5 inches. Al-
falfa loopers overwinter as pupae in the soil or
litter next to the base of the plant. Moths emerge
in May. The female deposites her eggs singular
on weed hosts. The eggs will hatch in 3 to 5
days. Moths appear early with 3 to 4 genera-
tions each year. Eggs are round, white to cream
in color, and are laid on the underside of leaves.

Alfalfa looper larva .^

Damage: The larvae

are general feeders that

cause damage to leaves

as they feed. Damage

is most noticeable in

June and July, then

again in September and October.

Habitat: Alfalfa loopers are found in crop
fields, waste lands, and open areas. The larvae
will feed on alfalfa, cereals, vegetables, garden
flowers, ornamentals shrubs, and orchard trees.

Control: The alfalfa looper is often reduced
by a virus and several natural enemies. Heavy
looper populations will require the use of insec-
ticides. To determine if treatment is needed,
sample the field using a standard sweep net. Take
at least 100 sweeps in groups of 10 in different
paits of the field and along the field margins. An
average of 10 loopers without signs of disease
can be used for a threshold. Bacillus
thuringiensis (Bt) is also successful at reducing
populations.

Alfalfa weevil [H^mt postic^i)

Life cycle: Alfalfa weevil adults are 4 to 5
mm long and vary from light to dark brown. They
have a broad, dark brown stripe extending from
the front of the head along the middle of the back
approximately two-thirds the length of the body.
The stripe tapers to a triangular shape on the

96

wing covers. The larvae are legless, 8 mm long,
and green with a dark brown to black head and a
white stripe down the middle of the back. The
first instar larvae are white.

Damage: The larvae feed within the buds at
the terminal and skeletonizing the leaves. Dam-
aged leaves dry rapidly and the field appears gray
or frosted. The larvae do the greatest damage
to the first crop of hay. There is only one gen-
eration per year. Adults also feed on the foliage.

Adult alfalfa weevil

Habitat: The alfalfa weevil is the major pest
on alfalfa in the United States. It also feeds on
clover and other legumes

Alfalfa weevil larvae
Control: Early

cutting of alfalfa
may reduce the
damage caused by
the larvae and ex-
pose large num-
bers to the sun
and natural en-
emies. The para-
sitic wasp, Bathyplectes curcidionis, may reduce
the population in some areas. Damage may jus-
tify treatment with insecticides when the larval
population reaches about 10 per straight sweep.
Severe damage may also be expected if 1.5 to
2.5 overwintering adults per square foot are
found early in the spring (April-May).

Avhids - Tea ajjkd [Acyrthosij/Iuvi j/isimh &
Sjjottei alfalfa ajkul [Thermj/hls mamkt/j\

Life cycle: Adult pea aphids are soft-bodied,
about 4 mm long, and range in color from light
green to yellow-green. Their legs and antennae
are long and slender. The nymphs closely re-
semble the adults except in size and are produced
at the rate of 1 - 14 per day asexually. During
the fall, sexual forms are produced, which mate,
and females lay overwintering eggs. The eggs
are glued to alfalfa stems and leaves. There are
6-8 generations per year.

Adult spotted alfalfa aphid

Spotted alfalfa

aphid are about

2 mm long, pale

yellow and

have 6 or more

rows of black

spots along the

back. Under

magnification, each spot will have a setae (bristle

or hair) projecting from it.

Damage: Adult aphids and nymphs suck plant
juices from alfalfa stems and leaves causing the
leaves to curl, turn yellow, and drop off the plant.
The pest injects a toxin while feeding, which may
quickly kill seedlings and stunt growth of older
plants. In Montana, these symptoms can easily
be confused with drought in dryland fields. The
aphid seems to affect dryland plants differently
than irrigated plants. For example, in dryland,
symptoms (yellow streaking and yellowing of
leaves) occur when populations are as low as 5
to 10 individuals per straight sweep. In irrigated
fields no symptoms may be evident at 50 or even
iOO aphids per sweep.

Habitat: In Montana, these aphids affect al-
falfa much differently than in other states west
of the continental divide. The spotted alfalfa

97

aphid feeds on clovers. The pea aphid also feeds
on clover, peas, lentils, and vetch.

Control : Rapid growth of alfalfa in the spring
helps reduce the possibility of pea aphid dam-
age. High temperature reduces pea aphid re-
production and plants tend to outgrow the dam-
age. Many natural enemies, such as lady beetles,
lacewings, syrphid larvae, and parasites help re-
duce the aphid population. However, popula-
tions of natural enemies may not adequately re-
duce high populations of aphids. The use of in-
secticides may be necessary if the pea aphid popu-
lation reaches about 300/sweep depending upon
the number of predators present. Insecticides
should be used only when necessary and accord-
ing to directions on the label to protect natural
enemies and pollinators.

Adult pea aphid

AWiywoWlS - mclmies western yellow striml

awiwonn [Sj^yloptcm jmie/icij) and Bertha

annwcnn [Miimestm mijhjiimbi)

Life cycle : Western yellow striped armywonn:
Mature larvae are about 1.5 - 2.0 inches long
and have velvety black stripes on top with two
prominent and several narrow, bright yellow
stripes on the sides. The key identification is an
inverted, white "Y" on the top of the head. Adult
moths are gray, mottled, and often referred to as
"millers".

Bertha armyworms: Mature larvae are about
30 mm long, dark on the top, have a yellow-

orange strip on each side and are mottled gray
or green on the bottom. These differ from the
western yellow striped armyworm by having no
"Y" on the head. The adults are brown in color
and are also known as "millers".

Damage: Typical damage includes irregular
holes with edges eaten out that gives plants a
ragged appearance. And at times the whole leaf
may be striped. When the food supply is ex-
hausted, armyworms will move in masses to ad-
jacent fields. Larvae feed on foliage during the
day and cause defoliation.

Habitat: Western yellow striped armyworms
feed on peas, beans, lentils, alfalfa, sugarbeets,
and potatoes. Bertha armywonns feed on rape,
legumes, sugarbeets, hops, cabbage, com, peas,
and beans. Young larvae may be found feeding
on the terminal leaves and buds during the day.
Older larvae tend to be found in trash (leaf and
plant matter) and on the soil surface.

Control: These pests rarely reach population
levels that require chemical treatments.

Western yellow striped armyworm

Bertha armyworm

^liskr Medics {Ej/icmda y^j/)

Life cycle: Adult blister beetles are 3/8 to 1
1/8 inches long. They have a broad head which
is usually wider than the prothorax (bulbous) that
is often neck-like. Adults emerge from the soil

98

in early summer and the females lay their eggs in
cluster of about lOOin the soil. These eggs hatch
in 10-21 days. The larvae burrow into the soil
looking for grasshopper eggs to feed on. The
larvae pupae within 2 weeks and overwinter in
the soil. There is one generation per year. All
species of bhster beetles contain a bhstering sub-
stance called cantharadin. And when the adults
are crushed, the will cause bhstering on the skin.

Damage: Blister beetles usually become a
problem where host crops are grown next to
rangeland or where grasshoppers breed. The
adults feed on plant foliage and flowers. Crops
include alfalfa, corn, potatoes, beans, peas, on-
ions, carrots, peppers, radishes, cereal, ornamen-
tals and weeds. In alfalfa the adults will feed on
new crown growth in late spring and summer.
The larvae feed on grasshopper eggs deposited
in the soil and are considered beneficial. One
larva can destroy 30 or more eggs.

Habitat: Adult beetles tend to appear in years
of grasshopper outbreaks since the larvae are
parasitic on grasshopper eggs. Problems have
occurred where numbers of beetles are contained
in hay bales and fed to horses resulting in sick-
ness and death. Blister beetles can be found in
fields, pastures, and crop lands.

Control: Early cutting will avoid most prob-
lems with blister beetles. They usually do not
build up until the alfalfa is in full bloom to feed
on the flowers. If swarms are noted in the field
and the hay crop is to be fed to horses, an insec-
ticide treatment should be justified.

Adult blister beetle

Cutworms

Life cycle: Adults emerge in the spring after
overwintering as larvae or pupae. The female
moths deposit several hundred eggs in grassy
areas and weedy fields. The eggs hatch in about
one week. The larvae feed on young plants by
cutting them just above or below the soil sur-
face. Mature larvae also feed on the foliage of
older plants. The mature larvae burrows into
the soil and form a cell and pupates. Nearly all
species of cutworms overwinter as larvae or
pupae in the soil. There is usually one genera-
tion per year.

Cutworm larvae

Cutworm larvae are usually

soft, fat, dull gray, brown, or

black in color and may be

striped or spotted. They will

often curl up into a "C"

shape when disturbed. The larvae are typically

38 - 58 mm long. The adults are usually silvery

gray, with spots or bands. They are active at

night and are often attracted to lights.

Damage: The larvae usually feed at night and
cut off young plants or feed on the foliage of
older plants. If alfalfa fields do not "green up"
in the spring it may indicate the presence of cut-
worms.

Adult cutworm moth

Habitat :

Cutworms are
primarily a
pest of alfalfa
and clover, but
will attack
other legumes.

Control: Examine the soil around plants to
locate the larvae. They will spend the day "rest-
ing" just under the soil surface. Treat when 5 or
more larvae per square foot are present. Irrigat-
ing the field before treating helps bring the lar-

99

vae to the surface. Late evening applications
are most effective when they are beginning to
feed. Weed control is important along field
edges. Cutworms move from edges to the field
as weeds dry up.

Grasslwvjie

Life cycle: There are over 100 species of
grasshoppers in Montana, but only a few ever
reach economically important levels. These in-
clude the migratory grasshopper, twostriped
grasshopper, redlegged grasshopper,
clearwinged grasshopper and the bigheaded
grasshopper These species overwinter in the
egg stage in the soil. The eggs are laid in pods in
the soil during late summer and fall and the
nymphs begin emerging in April, May, and June.
Nymphs feed on vegetation for 40 to 60 days
before molting into the adult stage. Adults dis-
perse to suitable hosts during the summer and
lay the overwintering eggs. Some species have
well defined breeding and egg laying areas. In
most areas, eggs are laid in waste areas, along
roadsides, and around field margins.

Adult grasshopper

Damage: Damage to crops occur when hop-
pers migrate from rangeland adjacent to fields
as the vegetation drys. The green crops are a
very appealing site to these hoppers. Grasshop-
per adults and nymphs cause defoliation as they
feed. They will feed on all of the above ground
parts of a plant. In large numbers grasshoppers
can totally eat whole fields of crops.

Habitat: Grasshoppers are found in range-
lands, roadsides, and croplands.

Control: Temperature and moisture are im-
portant factors in reducing grasshopper popula-
tions. Heavy mortality occurs in the spring when
warm weather causes premature hatching of
eggs. In late spring, short periods of hot weather
increases the incidence of fungus (Entomophaga
grylli. Figure 1 ) and bacterial diseases. Grass-
hopper control should be initiated when the
population reaches about 10 per square yard and
are in the nymphal stage (see Table 1).

Figure 1 . Life cycle of Entomophsgj gry/// fungus

Infected grasshopper

climbs to final clinging y- ^MB^ Grasshopper's cadaver

place, and dies ,t^C-x^ ^^^^^^ disintegrates

Inside the insect the tungus
feeds on organs and eventually

Resting
spore
falls

Conidium gets stuck on the body

of a foraging grasshopper,

germinates there, and penetrates

the hopper's cuticle.

and remains on
under soil

Spore germinates the same or

following year, and forms a

sticky conidium which it ejects

into surrounding area

Table 1 . Grasshopper nymph and adult infestation
ratings based on numbers per square yard.

Rating

Nymphs

Adults

Margin Field

Margin Field

per square

yard -__--.

Light

25-35 15-23

10-20 3-7

Threatening

50-75 30-45

21-40 8-14

Severe

100-150 60-90

41-80 15-28

Very severe

200+ 120

80 28 +

100

Syikr Mites [Tetmujchus Sfy/)

Life cycle: Spider mites are not insects. They
belong to the arachnids (spiders). They differ
from spiders in that their oval to elongated bod-
ies are not divided into two parts.

Adult two spotted spider mite

""" Adult mites are 0.3 to
0.8 mm long. They
are pale yellow to
green in color with
two very distinct
black spots on the
rear of their bodies
(two spotted spider
mite). They are also covered with black bristles
on their bodies and legs. Spider mites overwin-
ter as pregnant females beneath debris and in
cracks in the soil. Female mites emerge in the
spring, disperse, and begin laying eggs on the
alfalfa leaves. The eggs hatch into larvae in four
to five days. The newly hatched larvae have 6
legs and after the first molt gain 2 more legs and
are called nymphs. A complete life cycle takes
one to three weeks.

Other Alfalfa Hay Pest

Wiiah'^ Sy\iM}Vi^ [phikemis
sf/ummu^

Contact your local Montana State University
(MSU) Extension Agent or the Montana Depart-
ment of Agriculture formore information.

'*''^r^.

■4^*^

V-'

Nymph meadow spittlebug

NOTES ^

Damage: Spider mites cause leaf yellowing,
and if abundant, defoliation of alfalfa from leaves
dropping because of the sucking of plant juices
(desiccation). Spider mites of this family often
introduce diseases through feeding or by weak-
ening the plants. Look for webbing on the un-
derside of the leaves.

Habitat: Spider mites attack many crops in-
cluding: alfalfa, beans, peas, sugarbeets, pota-
toes, ornamentals, fruit trees, cereal, and corn.

Control: Treatment may be justified when 25%
of the leaves show damage in early summer and
50% in midsummer. However, control is ques-
tionable with 75-100% leaf damage after Au-
gust 15.

101

Alfalfa Seed

Most, if not all pesticides registered for use on alfalfa lack legal tolerances established for residues
that may be present on the seed. Therefore, in the case of screenings or products of harvest, Mon-
tana seed producers have declared through an agreement with the Montana Department of Agricul-
ture that alfalfa produced for seed is a non-food crop. This declaration means that none of the seed,
screenings or products resulting from harvest will be available for human or animal consumption.

Alfalfa Weevil [H^em Postic^

See previous section (alfalfa hay, pages 96-97)
for description.

See previous section (alfalfa hay, pages 97-98)
for description.

Awiywoms and Cutwowis

See previous section (alfalfa hay, pages 98, 99
andlOO)for description.

Grasslwmrs [Mekno/Jiis sj/j;)

See previous section (alfalfa hay, page 100) for
description.

Life cycle: Adults are 3/16 of an inch long
and have a "V" on the back. The adults mate
soon after emerging and immediately begin lay-
ing eggs in plant tissues. The eggs hatch in 1 - 4
weeks, depending on the temperature and the
young pass through 5 nymphal instars requiring
about 3 weeks. Adult females begin egg laying
in about 10 days. Three or four generations per
season may occur depending on climatic condi-
tions.

Damage: Lygus bugs suck juices from the
productive portions of the plant causing blos-
soms to drop and shriveled seed.

Habitat: They overwinter in plant debris and
weeds, becoming active on the first warm days
of spring.

Control: First application — if lygus numbers
approach 5 to 6 per 1 80 degree sweep prior to
the introduction of pollinators, treatment can be
made with a greater number of insecticide op-
tions. It is critical that a safe interval is main-
tained between the insecticide application and
the introduction of pollinators.

Second application — during bloom, usually
when the lygus (adults plus nymphs) approaches
5 or 6 per sweep, but before the nymphs reach
the third instar stage (1/2 grown), an economic
threshold is reached. With certain new, "bee safe"
pyrethroids, it is possible to apply an insecticide
after bee flight has ceased in the evening. This
enables the chemical to dry overnight with little
if any noticeable effect on bees the following

Adult lygus bug

102

Seei chalcii (Bruchoj^hajjiis roMi) Svikr bAiks - Tetrmchis svy.

Life cycle: The adult is a small, shiny, black,
wasp-like insect 2 mm long. The larvae are white
and about 1 mm long when mature. All stages
of development are completed in the seed. The
chalcids overwinter as mature larvae within seeds
on the ground, on unharvested plants, along field
margins, and in stored seed. The adults gener-
ally emerge from the seed in July. There are 2 to
3 generations per season. The larvae from the
last generation remain within the seed to over-
winter, and a mature larva can remain in a seed
for two or more years when conditions are ex-
cessively dry before pupating.

Seed chalcid damage
Damage: The larvae
feed within the seed and
destroy it.

Habitat: Infested al-
falfa seed may be found in
volunteer plants, along
roadsides, in surrounding alfalfa fields, in chaff
stacks, or scattered on the ground in alfalfa fields.

Control: Cultivating in the fall with a
springtooth harrow to a depth of at least 1 inch
to bury infested seed followed by irrigation, aids
in reducing chalcid numbers. Cutfing and re-
moval of hay during May will delay and reduce
populations. Destroy or bum chaff stacks and
screenings by the first of April and remove vol-
unteer and waste area alfalfa plants to also re-
duce populafions.

There are several spe-
cies of Chalcidoidea
that are natural para-
sites of the alfalfa seed
chalcid that attack the
larvae and pupae.

Adult seed chalcid

~^^

^^ /

\J

wL/^

^ i!

1

/

w ^

/

X

See previous section (alfalfa hay, page 101) for
description.

ikriys - Yrankliniella spj).

Life cycle: Thrips are small, slender, quick-
moving insects less than 2 mm long.

Damage: The adults and nymphs feed by rasp-
ing flower and leaf surfaces and sucking up the
exuding juices. This injury can distort flower
racemes and potentially damaging the seeds.

Habitat: Thrips are found in all crop environ-
ments including greenhouses.

Control: Almost all pro-
grams involving the use of
insecticides to control
other injurious insects will
reduce thrip populations.
Therefore, chemical con-
trol is not recommended
when applied solely for
thrips.

Adult thrips

103

Canola

From emergence, canola crops are subject to attack by a number of insect pests. Fields should be
examined daily during the seedling stage and regularly thereafter. By recognizing which insects
found in the crop are capable of causing major losses and which are of no economic importance, you
will avoid unnecessary and costly treatments. If there is a suspected problem, consult with your
county agent or production agronomist.

Aj)kds - Bmicorjnc, Hjdjihs, md
Myzus syj).

See previous section (alfalfa hay, pages 97-98)
for description.

Habitat: These small moths move to canola in
late spring or early summer from volunteer
canola, rapeseed, and other mustard hosts. The
migration of the moth may be from local popu-
lations or populations that have developed in
more southern areas.

CM{y^or)\is - (family Noduidac)

See previous section (alfalfa hay, pages 99- J 00)
for description.

Diamon^adc moth - pktelk

Xjlostelk

Life cycle: The eggs are laid on the underside
of lower leaves. The young larvae hatch and
first mine the leaves, eventually eating holes in
them. They may move up the plant to feed on
the growing tip. The next generation lays eggs
higher on the plant. These larvae, as they ma-
ture, move over to the buds, flowers and seed-
pods to feed.

Control: Cool, wet weather during and after
egg laying will reduce populations below eco-
nomic levels. Usually damage is considered se-
vere enough to treat when populations reach 28
per square foot or 10 per plant, and the plants
are under drought or other stress.

Adult diamondback moth

^0^^^;

Diamondback moth larva

Damage: The small (up to 1/3 inch long),
greenish larvae make tiny irregular holes in the
leaves. Larger larvae feed on buds, flowers, and
developing seedpods. Seedpod damage can lead
to the development of undersized, poor quality
seed. Foliar damage by the larvae may look bad,
but significant yield losses are not common. The
damage is much worse when the plants are
drought or heat stressed. Pod damage is likely
to occur if lower foliage is damaged by drought
or other insects.

¥lca Beetles - vhyllotrcta svy.

Life cycle: The shiny, black beetles (1/10 inch)
move into fields just as seedlings are emerging.
Eggs are laid in the soil and hatch into larvae
that feed on the roots of the canola plant. The
larvae feed for 3 to 4 weeks, pupate, and emerge
as adults during July or early August. Emerging
adults feed on any green plant tissue and then
move to protected areas surrounding the field to
overwinter.

104

Damage: Adult feeding in the spring on the
cotyledons, can lead to seedling death and sig-
nificant stand loss. Cotyledons can withstand
up to 50% defoliation without yield loss. Dam-
age becomes more severe when plants are
stressed, particularly during periods of drought.

Habitat: Flea beetles overwinter as adults and
fly to volunteer rapeseed, canola, or wild mus-
tards when the temperature reaches 68 ° F.

Control: Treat when 25% of
the cotyledons show severe pit-
ting or tissue loss. Normally,
plants are not treated once past
the first true leaf stage.

Adult flea beetle

ivgui mAvUni h^s - (fajnily
Miridae)

See previous section (seed alfalfa, page 102) for
description.

NOTES

105

Corn

Aj^huis - (several syecies)

See previous section (alfalfa hay, pages 97-98)
for description.

Com eawowi - Heliotksiea

Life cycle: The larvae are brownish to green-
ish, striped worms, which are about 2 inches long
when fully grown.

Com earworm larvae

Damage: This is the most
destructive and hard-to-control
pest of sweet com in the United
States. First generation larvae
may feed as "budworms" dam-
aging leaf whorls and newly
forming ears. Corn attacked by
the com earworm will show the
ears with masses of frass (insect feces) at the tip
of the ear, and may be eaten down to the cob.

Habitat: The time of planting will have a
marked effect on injury by this pest, but will not
always be the same in different years; i.e., in some
years early-planted corn will be injured, while in
most years the latest corn suffers the worst dam-
age. The moths prefer to lay their eggs on fresh
corn silks, so com which silks before or after the
greatest abundance of moths will largely escape
infestation. Fall plowing, to disturb the over-
wintering pupal stage, may be of importance.
Resistant varieties of corn will greatly reduce
damage from corn earworm.

Control: The com earworm is best monitored
with pheromone traps. Pheromone trapping is
an easy method of monitoring male moth activ-
ity and gives an indication of the female egg-
laying activity and of subsequent caterpillar dam-
age. Spraying the silks when they first appear
with a registered insecticide gives effective con-

trol in commercial plantings if pheromone traps
indicate a need to do so. As a rough mle, a cu-
mulative catch of 0 - 50 moths from first tassel
to first silk indicates that no pesticide applica-
tions are needed; in processed com, catches of
50-150 moths indicate a possible need for con-
trol, and catches of over 150 moths indicate a
likely need for control.

CJifwon?f5 ml Annwonm -

Various syy.

See previous section (alfalfa hay, pages 98-99)
for description of life cycle, damage, and habi-
tat.

Control: One of the best methods of avoiding
damage by cunvorms is to rotate the crops in
such a manner that corn is not planted on sod
ground unless sod has been broken early in the
fall or during late summer. Cutworms are para-
sitized by tachinid flies, by braconid and ichneu-
mons wasps and are also readily fed on by many
types of birds.

The armyworm is preyed on by a number of in-
sects, especially the tachinid fly, Winthemia
quadripustulata, which lays its eggs on the backs
of armyworm larvae. They are also preyed on
by several ground beetles and certain parasitic
wasps. Perhaps the most efficient insect enemy
of the armyworm is an extremely small, black
wasp (scelionids) parasite which deposits its eggs
inside the eggs of the armyworm. Braconid
wasps attack the armyworm larvae when they
are partly to nearly fully grown and they prevent
an excessive increase in the next generation, but
they do not kill the larvae until after most of their
feeding has been done. The egg parasite, on the
other hand, by preventing the eggs from hatch-
ing stops all damage by these insects.

106

Eurowm com hrcr - Ostrink
mikklls

Life cycle: The European corn borer over-
winters as mature larvae in debris in the fields.
These larvae pupate in the spring for about 2
weeks. The adults then emerge in late June. The
female lays her eggs on the under side of corn
leaves. There is usually an incomplete second
generation in Montana. Ninety percent of corn
in Montana is grown as silage (feed corn). Be-
cause of this most overwintering larvae are de-
stroyed in the silage process. The larvae in sweet
corn fields probably survive.

The adult female moths are yellowish-brownish
in color with a distinguishing white zig-zag mark-
ings on the wings. The males are smaller and
darker in color. The moths are nocturnal. The
larvae at first are pale yellow with several rows
of black to brown spots and a black head. They
are about I inch when mature and gray to light
brown or even pink in color, and faintly spotted.

Damage: The first generation larvae will
greatly affect corn yields. They attack the early
stages of corn where they begin feeding in the
whorls on the leaf surface of the plants. Later
they bore into the stalk. This boring causes dam-
age by weakening the plant and causing the ears
not to properly develop or not develop at all.
The second generation larvae cause less dam-
age, but can further weaken the plant and cause
ears to drop. This also opens the plant up to
infections of corn rot.

European corn borer larva

Habitat: European corn borers are found in
fields of corn and weedy areas near these fields.

Control: Thresholds vary depending on crop
stage. The earlier the stage of growth, the lower
number of larvae percent to cause economic
damage. Check at least 100 plants in 4 to 5 lo-
cadons in the field. Count the number of plants
with "shotholes". When more than 75% show
whorl feeding, insecticide control would be war-
ranted.

It is best to use a granular insecticide with distri-
bution aimed at the whorls where larvae are feed-
ing. One of the newest technologies being de-
veloped and used that show the best promise of
control is genetically generated hybrid corn us-
ing Bt. The hybrid plants are used as a trap crop
to attack the early flying moths by planting the
Bt hybrids early. As the first generation larvae
feed on the leaves they ingest the Bt which stops
development to adulthood.

Grasskoj^vers - (many species)

See previous section (alfalfa hay, page J 00) for
description.

Seed com nm^ot - Delia j/ktiim

Life cycle: The maggots pass the winter in
the soil, and are found inside of dark-brown cap-
sule-like pupariums about 1/5 inch long. The
adult flies are grayish brown in color and about
1 /5 inch long. They deposit their eggs in the soil
where there is an abundance of decaying veg-
etable matter, on the seed, or on small plants.
The eggs will readily hatch at temperatures as
low as 50° F and the larvae and pupae may de-
velop at any temperature from 52° to 92° F. The
maggots burrow in the seed, often destroying
the germ. When full-grown, they are of a yel-

107

lowish-white color, about 1/4 inch long, sharply
pointed at the head end, legless, and very tough-
skinned. They pupate inside the brown puparium
in the soil and emerge as adults in 1 2 to 15 days.
The insect can complete a life cycle in 3 weeks
making 3 generations per year a possibility in
Montana.

Seed corn maggot larvae
Damage: Seed at-
tacked by the seed com
maggot usually fails to
sprout, or if it does
sprout, the plant is weak and sickly. The mag-
gots will be found burrowing in the seed and in-
jury is usually most severe in wet, cold seasons
and on land rich in organic matter.

Habitat: Seed com maggots are found in fields
where corn is planted and volunteer com grows.
These insects can also be found where the fields
contain a high amount of organic material.

Control: Shallow planting of corn in a well-
prepared seedbed, sufficiently late to get a quick
germination of the seed, is probably the best
means of preventing injury. Land that is heavily
manured, or where a cover crop is turned under,
should be plowed early in the fall if possible, so
it will be less attractive to the egg-laying females
the following spring. Prompt resetting or re-
planting of the damaged crops will usually give
a stand. This insect is particularly susceptible to
control by insecticidal seed treatments.

Western com rootiwm - Dkhotica

Life cycle: There are 3 species of corn root-
worms in the USA. Only the western com root-
worm is know to infest corn in Montana. The
adult beetles are about 1/4 inch long, yellow or
greenish-yellow in color with 3 dark stripes on
its back. Com rootworm larvae are thread-like,
wrinkled, white worms about 1/2 inch long with
yellowish-brown heads.

Corn rootworm adults emerge in late summer
and are present until the first frost. The female
beetles deposit eggs about 2 weeks after emerg-
ing. The eggs are laid in the soil around the base
of the corn plant. The eggs overwinter there
until the next spring when they hatch.

Damage: Infestations of corn rootworms
cause slow growth of plants which is most no-
ticeable about the time tassels appear. Plants
will become undersized and frequently fall over
(lodging) after heavy rains, making harvesting
difficult. Adult beetles feed on newly formed
com silks and may be so numerous as to clip off
the silks before pollination, producing ears with
few kernels (scatter com). The larvae causes
the most sever damage to the corn.

Western corn rootworm larva (left) and adult

Sy'xkx \A\[es - [jeixmdm syy)

See previous section (alfalfa hay, page 101) for
description.

Habitat: Rootworms are found in fields of com
and where volunteer com stands are found.

Control: Observance of an economic thresh-
old based on the number of adult beetles per com
plant in the late summer prior to egg laying is a
reliable way to determine the need for control.
If the beetle population is averaging 5 or more
per plant as silking begins, control may be nec-

108

essary. If beetles average 3 or more per 4 ears
on any one scouting day during July and Au-
gust, then a soil insecticide application should
be considered for the following season. Notice-
able damage will occur when populations reach
2 adults per ear.

WirCWOWlS - (many sj)ccks of ik orkr
Colcoyicm, family Ektcridac)

Life cycle: The wireworm larvae are usually
hard, dark brown, smooth, and wire-like. The
larvae vary from 1/2 to 1 1/2 inches in length as
mature larvae. The adults are know as click
beetles. They have an elongated body and are
light brown to black in color. They can arch
their backs when up-side down and "click" them-
selves right-side up making a clicking noise.

Mature larvae pupate in the soil in the late sum-
mer, the adults overwinter. In the spring the
adults emerge and the females lay eggs in the
soil or plant roots. The larvae then hatch in a
few weeks to begin feeding.

Damage: They are very destructive and wide-
spread pests of com. Crops often fail to germi-
nate since the insects eat the germ of the seeds
or hollow them out completely leaving only the
seed coat. The crop may not come up well, or it
may start well and become thin and patchy be-
cause the larvae bore into the underground part
of the stem causing the small plant to wither and
die, though they do not cut it off completely.
Their injuries are usually most severe to crops
planted on sod ground or the second year from
sod.

Wireworm larvae

Habitat :

Wireworms are
common in gar-
dens and fields.
They are most
common where
the soil is high in
organic mate-
rial.

Control: Crop rotation is an important long-
term control method for wireworms. A 2 to 3
year rotation of alfalfa significantly reduces wire-
worm populations in most infested fields in Mon-
tana.

NOTES ^

109

The 3 best times to scout for corn insects

Grasshopper

Western corn
rootworm

Corn
Earworm

Spider
mite

Seed corn
maggot

Com rootworm

May & June

June & July

July 8c August

110

Cherries

bUA cherry avM - Mjziiscerasi

See previous section (alfalfa hay, pages 97-98)
for description.

Cutwonns - (many species)

See previous section (alfalfa hay, pages 99-100)
for description.

Fmittree leafroller - Archifs

Life cycle: The adult moth has a wingspan of
3/4 to 1 inch in length and is brown with vari-
able lighter markings on the fore wings. The
slender, pale green larva reaches a length of 3/4
inch. It has a black head and a black spot on the
thorax just behind of the head. Eggs are laid in
gray, compact oval masses on the bark of twigs
and branches, each mass contains up to 100 or
more eggs. They are coated with a secretion
from the moth which hardens and serves to pro-
tect the eggs.

This insect overwinters in the egg stage and
hatching occurs when the buds begin to open.
The larvae feed on the buds, blossoms, leaves,
and fruit, becoming fully grown in June and pu-
pate inside rolled or folded leaves. The larvae
when disturbed will wriggle and drop from the
leaf on a silk thread. In about 2 weeks the moths
begin emerging and shortly afterwards lay their
eggs and die. Only 1 generation develops annu-
ally.

Damage: Early larval feeding on blossom buds
may prevent setting of fruits. Most damage from
larvae is done in the spring. Serious damage re-
sults where the leaves are held against the cher-
ries with silk, the larvae feed within. Foliar in-

Fruittree leafroller larva

jury is of less consequence although it may also
be severe. Damage to the fruit opens it up to
decay organisms.

Habitat: Fruittree leaf rollers attack cherry,
apple, and pear trees.

Control: Fruittree leaf rollers are rarely a ma-
jor pest. There are several natural enemies that
help to keep it below the economic threshold.
Trichogramma a small parasitic wasp, lays its
eggs in the leaf rollers eggs. There are also sev-
eral predators that feed on leafroller larvae. They
include lacewings and lady bird beetle larvae.

Facific flatiieaM hrer -
chfjsokthris malis

Life cycle: The beetles are flat, bronzy-black
and nearly 1/2 inch in length. The larvae are
white, legless, and about 1 inch long when fully
grown, with the forepart of the body is broad
and flattened. The adults are more prominent in
sunny locations. Eggs are laid beneath scales of
bark and hatching larvae burrow under the bark.
Development is usually completed within 1 year
although 2 years are sometimes required. Partly
grown larvae winter in tunnels. In the spring
before pupation they tunnel a cavity almost at a
right angle to the bark surface. Adults may be-
gin emerging in May and this continues until
midsummer.

111

Pacific

flatheaded
borer larva

Damage: This borer is one of the worst en-
emies of deciduous trees and shrubs in western
North America. They are especially destructive
during the first 2 to 3 years after the trees are
planted, in very dry seasons, or where parts of
trees that have been shaded are exposed to the
sun by pruning. Damage is caused by tunnelling
under the bark in the larval stage and feeding on
the foliage as adults. The feeding of the larvae
may cause parts of the bark to die, or girdle and
kill young trees.

Habitat: The Pacific flatheaded borer attack
most deciduous trees. Among the fruittrees that
it attacks in Montana are apple, cherry, peach,
and pear.

Control: Maintenanceof tree vigor is consid-
ered of utmost importance. Shading the trunks
of newly set trees by wrapping with paper or
burlap impregnated with a residual pesticide in-
hibits egg deposition and kills newly hatched lar-
vae. Applying external white latex paint to the
trunks of young trees before borer eggs are laid
prevents sunburn and reduces borer attacks.
Removing and destroying infested wood and
prunning during winter are recommended prac-
tises.

Teach Tree Bora - Sdwiimmien
e^itiosa

Life cycle: The adult is a clearwinged moth,
steel blue with yellow or orange markings; both
pairs of wings of the male are transparent, and

there are several narrow yellow bands on the
abdomen; the female's forewings are covered
with metallic blue scales, and there is a broad
orange band on the abdomen. The female is
about 1 inch in length, the male is slightly smaller.
The moths are day fliers and may easily be mis-
taken for wasps. Fully grown larvae may ex-
ceed a length of 1 inch and are white with brown
heads. There is only 1 generation each year.

Various larval stages of the peach tree borer over-
winter in burrows under the bark at or near
ground level. The larvae resume their feeding
and complete their development in the spring and
early summer. They pupate within a cocoon that
is constructed in an upright position just beneath
the soil at or near the trunk. After 3 to 4 weeks
the adults emerge leaving the empty pupal case
protruding from the cocoon. The females mate
and begin laying eggs on the day of emergence.
Each female will average 400 eggs within a few
days that are laid on the trunks of trees, weeds,
and on the soil around the base of the tree. The
eggs hatch in about 10 days and the larvae enter
the tree through cracks or wounds in the bark
near the soil. The larvae feed and develop in the
cambium layer until winter.

Peach tree borer larva

Damage: The larvae are the damaging stage.
They feed in the inner bark and cambium tissue
of the trees within a few inches to below ground
level. Feeding may also occur on large roots
near the soil surface. Evidence of infestation is
frass and fine wood borings mixed with gum at
the base of the trees. Young trees may be com-
pletely girdled in a single season resulting in

112

death. Older infested trees are less vigorous and
productive and will often succumb to other in-
sect diseases or winter injury before girdling kills
them.

Habitat: The peach tree borer is found in cher-
ries, plums, and related species.

Control: Control of the peach tree borer is
like many orchard crops and is depended on a
good monitoring program. Using pheromone
traps to attract male moths at emergence is good
for determining when egg laying is beginning.
Experience has shown that populations seldom
need treatment when trap catches peak at less
than 10 moths/trap/week.

Also determine the average number of cocoons
and empty pupal cases in the soil or near the base
of trees. In trees up to 3 years of age, if any
evidence is shown, treatment is warranted. In
older orchards, an average of one cocoon and/
or empty pupal case per tree would warrant treat-
ment.

Maintaining healthy trees is very important. Only
previously damaged trees will become infested.
Pruning at the proper time of the season will help
to lower populations. Chemical treatments tar-
geted at the larval stage should be applied with a
hand gun directed at all the wounds on the base
of the trunk. Thoroughly wet the top few inches
of the soil.

Pear slug - Qilirod cerm

Life cycle: The larvae of the pear slug appear
as shinny, black, and slug-like. They reach 1/3
of an inch in length. When larvae first hatch,
they are white with a brown head. They soon
secrete a dark coat of slime which gives the larva
its slug-like appearance. The head end is some
what wider than the rest of the body. The larvae

have 7 pairs of prolegs that separate them from
lapidoptera larvae (caterpillars), but these are
covered by the slime. The full grown larvae turn
yellow-orange in color. The adults are black with
4 transparent wings about 1/5 of an inch long.
The adults are known as sawflies (Hymenoptera)
and are often mistaken for bees or wasps.

Pupae overwinter in the soil. The adults emerge
in the spring and the females begin to oviposite
(lay eggs) on the leaves. The females usually
reproduce parthenogenetically (asexually). The
eggs are inserted into small slits in the leaves
and hatch shortly (1 week). The larvae com-
plete their development in 2 to 3 weeks and drop
to the soil and pupate within cocoons about 4
inches deep in the soil. There are usually 2 gen-
erations per year.

Pear slug larva

Damage: The pear _^^iBte^-.^

slug is a widely distrib-
uted chewing insect
which skeletonizes the upper surface of the leaves
of cherry trees. Such injury may be extensive
especially the second generation. If the injury is
severe, tree growth may be reduced in the fol-
lowing year.

Habitat: Host trees include cherry, pear, apple,
and plums. They also occur on shrubs, trees,
and willows.

Control: Observe skeletonizing injury in mid
to late summer. There are no thresholds and
minor injury does not warrant treatment. Insec-
ticidal soap may be effective in controlling the
pear slug. Dislodging the larvae with a strong
blast of water is usually all that is needed to con-
trol this insect.

113

Tear tJirip - Taeniotlirij^s
inconse^iuem

See previous section (alfalfa seed, page 103) for
description.

San lose Scale - Quadraspidiotii^
j^emicwsiis

Life cycle: Winter is passed in the partly grown
nymphal stage under the scale coverings on the
host plants. Development continues in the spring,
and maturity is reached usually in May or June
when very small, 2-winged adult males appear,
which mate with the females and die soon after-
wards. The female produces young which crawl
from under the edge of her covering. Newly bom
lemon-yellow nymphs resemble mites, but they
can be distinguished by the presence of 3 pairs
of legs and a pair of antennae. The nymphs are
called "crawlers" and migrate over the host for
a few hours before inserting their mouthparts into
the bark, leaves, or fruit to feed. After the first
molt the legs and antennae are shed; these are
incorporated in the scalelike covering that in-
creases in size as the nymphs continue to grow.
Underneath these scale-like coverings may be
found the yellow, nearly circular sack-like bod-
ies of the insects. Growth is completed in about
6 weeks and 2 or more overlapping generations
are produced each season.

Damage: Tree vigor is reduced and fruits are
blemished by the nymphs and the adults remove
sap and part of the plant, but especially the wood.
Diagnosis can be easily made by the encrusted
scales on the branches and the tiny red circles
with white centers. Unchecked, heavy infesta-
tion may kill the trees.

B

^

^Pl

|S

1

1

■^ _»--''"^^^^ ^i

1

^rf«2

^t

^

Adult San ]ose scale

Habitat: The San Jose scale attacks most cul-
tivated fruits and a large number of ornamental
shrubs and trees. Included are apple, pear, plum,
cherry, peach, currant, and gooseberry.

Control: If twigs look unhealthy or are dead,
examine them closely for the crusty scales. Also
examine twigs for scale during pruning. Look
for the scales or their feeding blemishes on the
skin of the fruit at harvest; if they are found, be
prepared to initiate control the following spring.
The adult males can be monitored by using phero-
mone traps. The traps should be hung in the
trees during the early pink bud stage. The males
usually will begin to fly at bloom or petal-fall.

Once there is an infestation detected it is more
than likely it will get worse and not better as
time goes on if no action is taken. The first step
in control is to apply a dormant oil in the spring
before growth starts. This should be followed
by a foliar insecticide directed at the crawler
stage. If after 10 days there are still many crawl-
ers, a second application should be applied.

114

shotMe hm - Scolytus m^ulosiis Syikx mites - (tAcmmd mite, jwosjiotted

Life cycle: The adult beetle is 1/4 inch or less
in length, brown-black with brown legs, and a
short, stubby snout. The larva is a small, white,
footless grub, slightly larger at its anterior end
and about 1/8 inch in length. The adults emerge
in the spring and early summer. They burrow
into the bark until they reach the sap wood. A
long, narrow, longitudinal gallery about 1/2 inch
is excavated and is called the "maternal gallery".
This is where the female lays up to 50 eggs. The
eggs soon hatch and the young larvae tunnel
outwards from the maternal gallery between the
bark and sap wood. When mature, the larvae
dig a deeper cell in which they pupate. The new
adults emerge and bore out through the bark and
cause the familiar "shot-hole" like holes. There
are 2 generations per year and the larvae of the
second generation overwinters.

Damage: The shothole borer holes are about
the diameter of small lead shot and are often filled
with gummy exudates. They are not serious en-
emies of healthy trees, but occasionally they may
be found infesting broken, dead or dying
branches. A weakened tree with a serious infes-
tation may die.

Habitat: These beetles are common and widely
distributed. They attack apple, cherry, plum, and
other fruit trees.

Control: Healthy, vigorous, well-cared-for
trees are less subject to be attacked by shothole
borers. Removal and burning of infested or dis-
eased branches or trees during the winter period
destroy the insects while still in their burrows.
This helps prevent the increase of beetles to the
point where they might attack healthy wood.

Sj)ider mite, Ewroyem Ke^ mite, anti others)

See previous section (alfalfa hay, page 101) for
description.

westmi cherry Ymit pfy -
Rha^oletis imiiferens

Life cycle: The winter is passed in a brown,
capsule-like puparia in the soil. The adult cherry
fruit flies emerge from the soil about the middle
of May to the middle of July and are active 3 to
4 weeks. They fly to cherry trees exuding juices
where the females feed on the leaves and fruits.
Mating then takes place and eggs will be depos-
ited over a period of about 25 days during which
she lays 50 to 200 eggs These are inserted
through small slits cut with the ovipositor into
the flesh of the fruit. The adult is a little smaller
than the housefly and is a general black color
with white bands on the abdomen. The wings
are transparent with distinct dark bands. It can
be distinguished from other fruit flies by this pat-
tern. Eggs will hatch in 5 to 8 days after they
are deposited. The young larvae burrow directly
into the surface of the cherry seed. They pass
through 3 instars over 10 to 12 days. The last
instar, forms one or two breathing holes to the
surface of the fruit and about 3 days later emerges
and drops to the ground where it seeks a pupa-
tion site in the upper 3 inches of the soil. About
1% of the flies may emerge in August or Sep-
tember as a second generation, but the remain-
der overwinter as the pupa.

Damage: The maggots will cause cherries to
become somewhat misshaped and undersized;
they may turn red ahead of the main crop, often
with one side of the fruit partly decayed and
shrunken or wrinkled and closely attached to the
pit.

115

Habitat: The cherry fruit fly attacks all variet-
ies of cultivated and wild cherries.

Control: The western cherry fruit fly may be
controlled by spraying the fruit at the time the
first adults are captured in pheromone traps. A
single adult catch is the threshold. Two or three
applications of insecticide is usually required at
10-day intervals starting just after the blossom
buds open. These applications protect the fruit
by killing the adult flies. Cull cherries around
canneries and picking stands should be destroyed
by heat or buried.

The cherry fruit fly is attacked by several para-
sitic wasps. Parasitism may reach 50% of the
flies breeding in the native wild cherries, but is
less than 3% in cultivated cherries where the lar-
vae are much better protected.

A post-harvest control should be considered for
late emerging flies from the cherries left on the
trees. These should be treated to prevent the
flies from completing their life cycle and reduce
problems for next season.

NOTES ^

Adult western cherry fruit fly

116

Peppermint

Garden symfihylm - Scutl^erelk
iMMmikk

Life cycle: Symphylans are not insects. Ma-
ture symphylan are 3 to 6 mm long, white, with
prominent antennae, 12 pair of legs, and 15 body
segments. This pest spends its entire life cycle
in the soil. Symphylans can be distinguished from
centipedes by their rapid movement, vibrating
antennae, and a pair of spinnerets on the poste-
rior end of its body. Symphylans are long lived
and some have survived up to 5 years.

Symphylans reproduce from eggs which are de-
posited in clusters in the soil. The newly hatched
nymphs have 6 pairs of legs. They shortly molt
into a second instar with 7 pair of legs. An addi-
tional pair of legs is added with each new molt
until all the legs are added ( 12 pair). Symphylans
continue to molt their entire live (up to 52 times).
Eggs, nymphs, and adults can be found at any
time of the year. The majority of the eggs are
found in early spring and fall. The nymphs and
adults become active in the spring within the
upper 6 inches of the soil. In the fall and winter
they dig deeper into the soil. It takes 3 months
to develop from egg to adult. There is at least
one generation per year that overlaps with other
generations.

Damage: Symphylans are general feeders that
attack germinating seeds, plant roots, and the
above ground plant parts in contact with the soil.
Surviving plants are stunted and produce poorly
in yield and quality.

Habitat: Symphylans are found in high or-
ganic soils. They attack all field crops and are
found in home gardens.

Control: The best time of the year to sample
for symphylans is from March through Septem-
ber. However, to properly control them with an
insecticide, you must apply it prior to spring re-
growth. Take a shovel full of soil to a depth of
10 inches from different sites in the field (one
site per 1 1/2 acres). Count the number of
symphylans per sample and calculate an average
number per sample. If an average of 4 to 5
symphylans are found per sample, control may
be required depending on the vigor of the stand.

If chemical treatment is justified, the material
should be incorporated into the soil by irriga-
tion. If possible, identify areas in the field where
the population is concentrated and treat only
those areas. Symphylans prefer heavier soils to
sandy soils and often infest ridges or high areas
avoiding low spots where water concentrates.
Soil fumigation may be needed in extreme cases.
Soil tillage helps to reduce numbers by disrupt-
ing symphlar activity.

Grassomrs

See previous section (alfalfa hay, page 100) for
description.

looj)crs - Auto^mj^hn califomica

See previous section (alfalfa hay, page 96) for
description.

Mint flea kdlc - Loiujitnrm
imterhousei

See previous section (canola, pages 104-105)
for description.

Adult garden symphylan

117

Mint wot hrer - Fumlktysjiimalis

Life cycle: Mint root borers overwinter as a
mature larvae in an earthen cell in the soil. In
early spring, the mature larvae pupate and adults
emerge in June and July. This emergence con-
tinues throughout the summer until early August.
The female moths deposit their eggs that look
like small scales on the leaf veins on both sides
of the leaf. The female moths can lay from 100
to 200 eggs each. The eggs will hatch in 5 to 10
days when the newly hatched larvae feed on the
leaf surface for 1 to 2 days. These larvae then
drop to the soil and tunnel into the rhizomes at
the bases of buds. The larvae will feed for 70 to
80 days until early October. The larvae then
emerge from the rhizomes and construct an
earthen cell where they overwinter. There is one
generation per year.

Damage: Mint root borer larvae cause dam-
age by feeding inside peppermint and spearmint
rhizomes during the summer months. Feeding
damage weakens mint stands which overwinter
poorly and regrow slowly in the spring. Adults
will be active in the summer. When disturbed,
adults fly a few feet and land on the underside of
a mint leaf.

Mint root borer larva

Habitat: The mint root borer is a pest of pep-
permint and spearmint fields.

Control: To monitor for mint root borer adults,
pheromone traps should be placed at 2 traps per
field. For larvae sampling, one square foot per
every 2 to 3 acres should be done. Collect moths
by sweeping foliage, then shaking net contents
to the bottom and slapping lightly against a hard

surface. Empty net contents onto a light back-
ground. The presence of adults in a field should
serve as a signal to take postharvest soil samples
for larvae in the fall. Treatment is justified if an
average of 2 to 3 larvae are found per square
foot sample. Chemical control should be applied
after harvest. Only soil treatments are effective
and must be irrigated into the soil. This requires
at least 1 inch of water. Treat only the acreage
that can be irrigated immediately. Chemigation
of an insecticide as a postharvest application is
also effective. A minimum of 1/4 inch of water
to pre- wet the soil surface prior to chemigation
is recommended.

Tillage, after harvest, has been shown to signifi-
cantly reduce mint root borer populations. In
sprinkler-irrigated fields, plowing and double
discing mint fields in late October, early Novem-
ber or in the spring may provide 80% or more
control. Tillage may spread verticillium wilt;
growers should use this practice only in fields
with a low incidence of verticillium wilt.

A parasitic nematode, Steinemema carpocapsae,
is also approved for use on mint to control mint
root borer larvae.

Stray^hrry root }um\ -
Otiorhyftchis ovdi^s

Life cycle: The larvae are white with tan col-
ored heads and have no legs. The adults are black
weevils about 1/4 to 1/2 inch in length and have
a long snout with its mouth parts at the end. The
strawberry root weevil mainly overwinters in the
soil as larvae, but a few adults will also overwin-
ter in protected areas along the field margins.
These overwintering adult females will start de-
positing eggs soon after emerging in the fields.
The overwintering larvae will pupate in the spring
(April/May) in the soil. The new adults emerge
in mid-Mav to earlv June. All of these adults are

118

Strawberry root weevil larva (top) and adult

female. They begin to depost their eggs in about
2 weeks around the bases of the plants. There is
one generation per year.

Damage: The larval stage of this insect causes
damage to mint by feeding on the roots.

Habitat: The strawberry root weevil feeds on
many different crop roots including mint, straw-
berry, blueberry, and others.

Control: Sampling for this pest is generally
done in late August and September or the fol-
lowing spring in March, April, or early May.
Take at least 25 soil samples from different ar-
eas of the field (one site per 2 1/2 acres), screen
the soil, count the number of larvae and calcu-
late the average number per sample. If the aver-
age number of root weevil larvae exceeds 2 per
sample, treatment of adults is recommended.

When sampling for adults, one should use a
sweep net in the evening a couple of hours after
sunset. Still, warm and dry evenings are the best.
Windy, cool and/or rainy periods produce fewer
weevils per sweep, giving the impression of a
smaller field population than is actually present.
Take 10 sweep samples in at least 5 different sites
in fields up to 30 acres. Add one additional
sample site for each additional 10 acres.

There is not a treatment threshold for adult
weevils, but once an infestation becomes estab-
lished in a field, it can be difficult to control. An
evening insecticide application against adults may
be justified even if the population is at a rela-
tively low level. Ideally, this measure is timed
after 90 to 100 percent of the adults have
emerged and prior to egg laying in June or early
July. Weevils will not have mature eggs in their
bodies until about 2 weeks after emergence. If
one sprays too late, egg laying will have already
occurred. Two applications may be necessary in
some cases.

A parasitic nematode is labeled for control of
strawberry root weevil larvae in mint. For best
results, applications should be injected through
sprinkler irrigation after harvest in the evening
or at night at a rate of 3.0 billion juvenile nema-
todes per acre. This application can control both
strawberry root weevil larvae and mint root borer
larvae.

Two-sptid sviiler mite - Tetmnchus
urticae

Life cycle: See previous section (alfalfa hay,
page 101) for description.

Damage: Feeding from these mites may cause
a speckled appearance on the mint leaves. The
leaves may turn brown or bronze and drop from
the plant mid to late season. The undersurface
of such leaves look as though they had been very
lightly dusted with fine white powder. When
examined under a lens, the fine white specks are
empty wrinkled skins and minute spherical eggs
and are suspended on almost invisible strands of
silk. On the strands of silk, and beneath it on the
surface of the leaf, mites of several sizes, up to
about 0.4 mm long can be found. These mites

119

live on the sap of the plant, which is drawn by
piercing the leaf with two sharp slender lances
attached to the mouth. Feeding injury caused
by densities greater than five mites per leaf in-
creases water stress, reduces photosynthesis, and
alters plant metabolism to negatively influence
mint oil quality. Spider mite populations can in-
crease rapidly during hot, dry weather and even
after an insecticide application. Fields should be
inspected twice weekly during these times.

Habitat: See previous section (alfalfa hay,
page 10 J ) for description.

Variegated cubwnn - Pen/Imim
saucia

See previous section (alfalfa hay, pages 99-100)
for description.

Wireworjfis - limonius syy.

See previous section (corn, page 109) for
descrpition.

Control: Correct sampling procedures for
spider mites involve close observation of leaf
samples taken from different areas in a field. The
use of a 1 5 power hand lens will enable growers
to distinguish between spider mites and preda-
tor mites. By walking in a "Z" or "M" pattern in
the field, randomly collect stems and inspect the
leaves from the bottom, middle, and top of the
stems for mites (count adults, nymphs, and eggs).
Classify the leaves as "infested" if the mites
(adults and nymphs) number five or more.

^OTES ^

For each 30 acres, 1 5 individual field sites should
be monitored for mites by examining a total of
45 leaves (15 leaves each from the bottom,
middle, and top) from 15 randomly selected mint
stems per site. It also is important to count the
number of predator mites on each leaf. These
natural predator mites help reduce spider mite
populations below economic levels through har-
vest. If predator mites are present, the field may
not require immediate treatment and should be
rechecked at a later date. Treatment of spider
mites is justified if there are no predator mites
and if 18 or more of the leaves in the 45-leaf
sample taken at each site are infested with 5 or
more spider mites. It is also important to esti-
mate the number of spider mite eggs on the
leaves, because their numbers will help predict
an emerging infestation.

120

Potatoes

Blister kdks - Eficmdasf'^,

See previous section (alfalfa hay, pages 98-99)
for description.

Colomkptato ketle - Leptinokrsa
decemlmeak

Life cycle: Adult Colorado potato beetles are
oval, strongly convex beetles with hard wing
covers marked with black and yellow stripes run-
ning lengthwise along their back. They are about
12 mm long and 6 mm wide. The larvae are
dark red when young, but become orange as they
near maturity. They have two conspicuous rows
of black spots along the sides of the body and
are about the same size as the adults. The Colo-
rado potato beetle overwinters as an adult in the
soil (25 to 30 cm deep) and emerges in late April
and May to lay eggs. Adults lay orange-yellow
eggs in masses of 10 to 30 on the underside of
the leaves. Eggs hatch in 7 to 10 days and the
larvae begin feeding on the underside of the
leaves. Larvae mature in 2 to 3 weeks, drop to
the soil and enter cracks to pupate. Adults
emerge in 5 to 10 days, mate, and deposit eggs
as before. In Montana, the beetle usually has
one generation per year. On some occasions,
especially if the first generation develops on vol-
unteer potatoes, two generations may occur.

Adult Colorado potato beetle with eggs

Damage: The Colorado potato beetle is one
of the most widespread and destructive potato
insects in the United States. Adults and larvae
feed on the foliage and will consume nearly all
the leaves in heavy infes-
tations. This pest also
spreads several potato
diseases, including brown
rot, spindle tuber, and

bacterial ring rot.

Colorado potato
beetle larvae

Habitat: Colorado potato beetles are found
in and around potato fields and where volunteer
potatoes are found. The Colorado potato beetle
can also be found feeding on tomatoes and egg
plants. They can also be found in mountain
meadows feeding on wild members of the night
shade family.

Control: Most insecticides used to control
other potato pests feeding on the foliage may
also control the Colorado potato beetle. Insec-
ticides applied early in the spring will reduce
damage caused by larvae of the first generation.
If properly timed, treatment will substantially re-
duce the likelihood of a heavy infestation during
a second generation. Observations of other
solanaceous plants, such as black nightshade may
be useful to detect larvae and adults in the field
or around the field margins.

Infestations should be treated at about 10% de-
foliation. Potatoes can tolerate about 20 - 25%
defoliation before yields will be affected. The
pest has developed resistance to all classes of
insecticides and control may be difficult. There
is one native species of tachinid fly and at least 3
kinds of predacious bugs that attack adults or
prey on the larvae.

CVib^oviws, armwonns, anA. looms

See previous sections (alfalfa hay, pages 96, 98,
99, and 100) for description.

121

¥lm hetles - (mcklm^ tuhcrflca ketlc

Ej^itriX tukrismA wskmyoMoUci kdle

EXj^ltriX siikriuiitij)

See previous section (canolo, pages 104-105}
for description.

Green veach ayhid - Mjubyersicae,

Yoi^ovz ayhitl - Acyiilwsij'kvi sduii, ?oiaio
ayhid - Mncmsij'Imm mj/Jwrkae

See previous section (alfalfa hay. pages 97-98)
for description. The green peach aphid is the
major vector of potato leaf roll virus (PLRV).

Votato leajkoyvers - Emj^onsca
Jikmenk

Life cycle: The potato leatliopper is not com-
monly reported in Montana, but is found annu-
ally in North Dakota. Certain weather condi-
tions could conceivably blow it into Montana.
The adults and nymphs are both green in color.
There are a series of 6 white spots on the
pronotum. Potato leafhoppers are very active.
The nymphs will quickly run sideways to the
other side of the leaf if disturbed.

Adult potato leafhopper

Damage: Both the adults and the numphs feed
on the underside of the potato leaves causing a
stippling or speckling of the leaf surface called
"hopper bum". The edges of the leaves curl
down ward, first turning lighter green, then yel-
low, and finally brown and necrotic.

Habitat: Host plants for the potato leafhop-
per include potatoes, tomatoes, apple, and mem-
bers of the night shade family.

Control: The economic threshold for potato
leafhoppers is 1 or more adults per sweep and
10 or more nymphs per 100 leaves.

y^esiem spotted cucumher heetle -
Dkkoticn ufidecwpmclata

Life cycle: Adult western spotted cucumber
beetles are 6 mm long, yellowish-green and have
12 distinct black spots on 1/4 inch long wing
covers. This is a subspecies of the southern corn
rootworm which is a serious pest of corn in the
central United States. Mature larvae of the beetle
are 14 to 17 mm long. They are yellowish, ex-
cept the head and last abdominal segment, which
are brown. This beetle overwinters as a fertil-
ized female. Adults are active during mild peri-
ods in the winter, but do not lay eggs until early
spring. Eggs are deposited in the soil around
the bases of potato plants. The eggs hatch in 7
to 10 days and larvae feed in roots for about
three weeks before pupating in the soil. Adults
emerge in

two
and
feeding

weeks

begin

on

pollen. There
is one genera-
tion per year
in Montana.

Adult western spotted
cucumber bettle

122

Damage: The larvae of this pest feed on the
roots of com, beans, potatoes, immature cole
crops, and some other vegetable crops. Adults
feed on com silk, pollen, bean blossoms, and
pollen of cucurbits.

Habitat: The spotted cucumber beetle is found
in meadows, wastelands, field crops, and gar-
dens. They feed on a wide variety of crops in-
cluding cucumbers, melons, com, potatoes, and
beans.

Control: Elimination of weedy areas around
the field can help reduce the number of over-
wintering sites for adults, although adults can
readily disperse into adjoining fields in the spring.
Insecdcides are the most common method of
preventing damage by this pest.

Wirewomis - incMin^ lUnoniiL^ syy.

See previous section (com, page 109) for de-
scription.

blOTES ^

123

Small Grains

Cereal leafhetle- Oidema miknoj/ns

Life cycle: The adult cereal leaf beetle over-
winters in small grain stubble and becomes ac-
tive by April to mid-May. The females oviposit
singly, 12 to 50 very small (1 mm) eggs near the
midrib on the inner side of winter wheat and late
spring grains. The eggs will hatch in 10 to 13
days to form wrinkled, hairy, humped back, yel-
lowish larvae with dark brown legs and head that
are usually covered with a glob of excrement (fe-
cal matter). In about 2 weeks, larvae pupate in
earthen cells in the top 2 inches of soil and emerge
after 17 to 25 days as metallic, blue-black beetles
about 1/6 inch long with a red thorax and red
legs. This entire life cycle takes 45 to 47 days
and the newly emerged beetles feed on grasses
for a few days and enter summer diapause until
fall when they hibernate under crop refuse in
September and October. There is one genera-
tion per year.

Cereal leaf beetle adult (left) and larva

Damage: Adults and larvae feed on young
leaves of grain crops, the adults feed primarily
on shoots causing small slits and the larvae feed
on tissue between the leaf veins causing a
windowing affect. Barley, oats, wheat, rye, com,
timothy, and other grasses are preferred in that
order. In severe infestations, 20 to 50% of the
crop is destroyed.

Habitat: The cereal leaf beetle can be found
in small grain fields or grassy field margins.

Control: Monitor the eggs and larvae to de-
termine the thresholds. Examine 10 plants per
location with one location for every 10 acres.
Count the number of eggs and larvae per plant
and determine the average. There are different
thresholds based on the growth stage of the plant.
For smaller plants (pre-boot) 3 eggs and/or lar-
vae is the threshold. One larva per flag leaf in
larger plants is the threshold.

There are several biocontrol agents currently
used to help reduce the cereal leaf beetle popu-
lation. Anaphes flavipes is a small wasp which
is an egg parasite and lays its eggs in the cereal
leaf beetle eggs. Tetrastichus julis attacks the
larvae of the cereal leaf beetle by laying its eggs
directly into the cereal leaf beetle larvae. Both
these parasites are available in Montana.

Grassliom

ers

See previous section (alfalfa hay, page 100) for
description.

Cutwowis and ann

iwonns

See previous section (alfalfa hay, pages 98, 99,
and 100) for description.

Life cycle: The Russian wheat aphid is light
green, elongated and spindle-shaped and the an-
tennae are very short. It has a wart-like projec-
tion above the tail that gives it a two-tailed ap-
pearance (see Figure A- 1 , page 121). The dor-
sal tubes (cornicles) are present, but they are very
short and not obvious. The aphids appear on

124

plants in the spring in colonies. As the crops
mature aphid populations increase. In June, colo-
nies consist of adult parthenogenetic, wingless
females that live from 12 to 16 days. There are
several generations per year.

Damage: Russian wheat aphid damage to grain
is easy to recognize. The aphids secrete a toxin
that causes leaf rolling and white (warm weather)
or purple (cool weather) streaking on the leaves.
Heavily infested plants are severely stunted and
sometimes flattened. Heads of infested plants
may become twisted and distorted and sometimes
fail to emerge properly. Sometimes a large
colony inside the flat leaf sheath can kill the head
while leaving the rest of the tiller green. Dam-
age in the field will first appear as patches of
stunted or discolored plants which resemble
drought-stressed areas. Whole fields can be lost
if infestations are not detected and controlled
early. The Russian wheat aphid is a vector of
barley yellow dwarf virous.

Figure A-1

Russian Wheat Aphid

Supracaudal process

Cauda
Cornicle
Antenna

Other Grain Aphid

Habitat: Barley and wheat are the most im-
portant host of the Russian wheat aphid. It is
also found on oats, rice, com, sorghum, brome,
wheat grass and other native grasses.

Control: Early detection is difficult because
the pest tends to hide in the plant. Colonies are
most often found in tightly rolled leaves near the
base of the leaf, in leaf whorls or concealed on
the stem inside the flag leaf sheath. The easiest
way to detect Russian wheat aphids is to look
for the characteristic damage. Plants from sev-
eral areas of the field should be thoroughly in-
spected for symptoms of aphid infestation.
Mixed colonies of Russian wheat aphids and
other species are common. ^ ,
The presence of detectable f
infestations varies from .4 '
year to year and at differ- f \
ent times. There are sev-
eral natural enemies that are
reared for release including
lady bird beetles, preda- '
clous flies and parasitic
wasps.

Adult Russian
wheat aphid

iknys - (incMin^ Limothri^s
denticoml^

See previous section (alfalfa seed, page 103} for
description.

Cauda

125

what stem ma^ot - Mermiyza
miericmta

This insect is not a major pest in small grains in
Montana. In most years a very small percent-
age of stems will be
infested. Heads of the
infested plants turn
white "white top " and
are easily pulled out
of the terns. Crop ro-
tation and removal of
volunteer grain is
helpful in lowering
the population of the
wheat stem maggot.

Wheat stem maggot larva

forming a chamber in which the larvae overwin-
ter. Late in May of the following year, pupation
occurs, and adults begin emerging about June
10 and are present until about July 15. Egg-
laying in the stems begin during this period with
hatching taking place a few days after. This in-
sect spends most of the year in the larval stage.
Only one generation occurs annually.

Damage: The damage most distinct is the cut-
ting of the wheat stem by the adult sawfly laying
her eggs. This causes the lodging and loss of
grain in the wheat fields. The feeding of the lar-
vae also causes damage to the conductive tis-
sues of the plant by their feeding inside the stem.

Habitat: The wheat stem sawfly is found in
wheat fields and where volunteer wheat is found.
They are also found in grasses that serve as al-
ternative hosts.

what stem sawfly - Cej/his cindib'

Life cycle: The adult insect is a small, slen-
der-bodied sawfly of black and yellow color. The
larva is a slender, yellowish, almost legless cat-
erpillar-like worm that tunnels up and down in-
side the stems. This weakens the stem enough
to reduce the yield of grain or cause loss by stalk
breakage. Fully grown larvae attain a length of
10 mm. By late July, the
larvae move to the base
of the stems and gnaw
a ring around each from
the inside, weakening
the straw which easily
breaks off at ground
level. Each infested
stub is then plugged at
the top with frass (in-
sect feces) and lined
with silk-like material

Adult wheat stem sawfly

Control: Control may be obtained by plowing
under the stubble in the fall and working the soil
to prevent escape of the adults. Grasses that
serve as alternate hosts should be destroyed
where feasible. These include Elymus
condensatus, Elymus canadensis, species of
Agropyron. Bromus inermis. and timothy. Ro-
tation of crops should also be of some value in
checking the insect. Parasites that reduce the
sawfly populations are Bracon cephi, Bracon
lissogaster, and Eupelmus allynii. Planting the
resistant spring wheat varieties Rescue and Chi-
nook has resulted in economical production in
spite of this pest. Other resistant varieties are
Golden Ball and Stewart.

wirewo]ins

See previous section (corn, page 109) for de-
scription.

126

Su^arbeets

3cd Icafkomr - Circulifer tenellus

Life cycle: The beet leafhopper is gray-green
in color and about 3 mm long. They are also
know by the common name of "white fly". This
leafhopper will travel several hundred miles in
the winds.

Damage: The direct feeding of the beet leaf-
hopper is not of economic importance, but it is
the vector of curly top virus in beans and
sugarbeets. A single highly infected leafhopper
can transmit the disease.

Habitat: The beet leafhopper overwinters on
Russian thistle and other plants in weedy areas
and rangeland. Host plants include, in addition
to Russian thisde, tomato, lambsquarter, beans,
melons, mustards, nightshade, and squash.

Adult beet leafhopper

Control: The best control for the beet leaf-
hopper is cultural. There are several resistant
varieties and planting as early as possible will
help to withstand curly top virus. During hot,
dry weather, frequent irrigation will help to keep
high humidity in the plant canopy which repels
the leafhoppers. Since the leafhoppers prefer the
edges of the field, a perimeter application of an
insecticide may work best. When scouting the
field, the threshold to determine if an applica-
tion is needed is 5 hoppers/10 sweeps. The beet
leatTiopper can become a problem in Montana
after a prolonged period of hot, dry weather.
Most years it is not a problem pest.

Cutworm - Peridmna smck mi

See previous section (alfalfa hay, page 99) for
description of life cycle, damage, and habitat.

Control: Control of cutworms is advised when
there is a 4 to 5% cutting of seedling beets.

Flea kdles

See previous section (canola, pages 104-105)
for description.

Sugarkd root ma^ot - Teknoj^s
myoj^aefomis

Life cycle: The adult fly is about 6 mm long.
It has a glossy, black body with clear wings that
have a smoky color to the margins. The adult
female has a very distinct ovipositor. The adults
emerge from the soil in early June to early July
and start laying eggs shortly thereafter. The fe-
male lays her eggs singly or in clusters of up to
40 eggs just below the soil surface in cracks close
to the beet seedlings. The eggs hatch within 3
days and the larvae move down into the soil to
feed on the taproot. The mature larvae (or mag-
gots) are yellow-white and about 12 mm long.
The body of the larvae tapper towards the head
end. After feeding for about 2 months the ma-
ture larvae begin to burrow deeper into the soil
where they overwinter. Then in the spring when
temperatures increase the larvae move up to-
wards the surface
(about 7 cm below)
and pupate. There
is usually one gen-
eration per year,
but two are not un-
common. . . ,, . ,

Adult sugarbeet root maggot

127

Damage: Wilted plants in June and July are a
sign of root maggot damage. The sugarbeet root
maggot may cause severe injury in some parts
of individual fields, particularly in dry sandy soils.
The maggots feed on the taproot of sugarbeets,
sometimes cutting it off, resulting in death of the
plant. Plants that survive produce small stubby
roots with low sugar content.

Habitat: Where ever sugarbeets are grown
throughout western United States and Canada.

Control: Where possible, irrigation may be
used to keep the soil-moisture content up in or-
der to force maggots to feed high enough to pre-
vent injury to the taproot. The number of in-
sects which justifies treatment is poorly defined.
Seeding beets early in the spring when the dan-
ger of frost is over to obtain a strong stand, helps
to combat this pest.

Su^arheet wchwom - LoMege
stidimlis

Life cycle: The sugarbeet webworm over-
winters as larvae in the soil and then pupates in
the spring. The adults first appear in late May
and early June. These adults are smoky colored,
about 12 mm long, and are nocturnal. During
the day these moths hide in the beet foliage and
are readily observed when the foliage is disturbed.
The larvae are olive green, 25 mm long, with a
black strip down the middle of its back and wavy
white lines on each side and black and white tu-
bercles. There are two generations per year. The
first is in June and the second generation is in
August.

Damage: The webworm larvae feed on the
beet foliage, skeletonizing the leaves and are
protected by the webbing that they spin. In heavy
infestations total sugarbeet defoliation can oc-
cur. Hot weather will increase the larvae's food
intake and can contribute to a rapid rise in web-
worm populations.

Habitat: Host plants include sugarbeets, car-
rots, cabbage, beans, and potatoes.

Control: If 50% of the leaves have eggs on
them or if 1 or 2 larvae are found, an insecticide
application is warranted. This insect is not usu-
ally a major pest in Montana.

Other Sugarbeet Pests

Sugarbeet root ajihid

Contact your local Montana State University
(MSU) Extension Agent or the Montana Depart-
ment of Agriculture for more information.

Wircwoms

See previous section (corn, page 109) for de-
scription.

Sugarbeet webworm larva

128

APPENDIX B

NoXious Weeis in Montana

Control of perennial noxious weeds should be of concern to every landowner and land
manager in Montana. An integrated weed management approach of good farming and ranch
management practices; cultivation, mechanical, and cultural methods; biological control
when available; and herbicides wiU continue to aid the control of noxious weeds. The pages
that f oUow give a brief description of the most serious noxious weeds threatening Montana
agriculture. For specific control information on all weeds refer to current Cooperative
Extension pubhcations. For color plates and a more complete description of these weeds
refer to publications found in the References section of this manual. Noxious weeds are
defined by rule in the County Noxious Control Act. The three categories in weed
classification are defined as follows:

Montana County Noxious IVeed Classification
Category 1

Category 1 noxious weeds are weeds that are currently established and generally widespread
in many counties of the state. Management criteria includes awareness and education,
containment and suppression of existing infestations and prevention of new infestations.
These weeds are capable of rapid spread and render land imf it or greatly Hmit beneficial uses.

Category 2

Category 2 noxious weeds have recently been introduced into the state or are rapidly
spreading from their current infestation sites. These weeds are capable of rapid spread and
invasion of lands, rendering lands unfit for beneficial uses. Management criteria includes
awareness and education, monitoring and containment of known infestations and
eradication where possible.

Category 3

Category 3 noxious weeds have not been detected in the state or may be found only in small,
scattered, localized infestations. Management criteria includes awareness and education,
early detection and immediate action to eradicate infestations. These weeds are know pests
in nearby states and are capable of rapid spread and render land unfit for beneficial uses.

129

SUNFLOWER FAMILY (Astcracm)
Diffuse Kmjjwd (cmtaurca Mm) - Category 1 Noxious Weed

Diffuse knapweed is a biennial or short-lived perennial forb that grows to a height of 1 to
3 feet. It has a taproot and only one or very few stalks. The tip of each branch has a single
flower head. The flowers are most commonly white with the upper portion of the bract
narrowing to a distinct spine. Often the outer most flowers are sterile. The bracts are
yellowish green with a light brown margin. Seeds are achenes, dark brown, 1 inch long,
with faint pale brown or ivory lines.

Diffuse knapweed grows well in dry sites and is found on waste grounds, fields, and along
roadways in many areas of western Montana. The most serious infestation is located near
East Helena.

Diffuse Knapweed

A. Plant Habit

B. Young Rosette

C. Leaf

D. Flower Head

E. Flower

F. Achenes

Helpful identification tip: Bracts
under the flower have yellow spines
with teeth appearing as a comb
along the spine margins.

130

sjjottd Kmywd (centmrea nmculosa) - Category 1 Noxious Weed

Spotted knapweed is a short-lived perennial reproducing primarily by seed. The stems
are erect with slender, wiry branches, rough and hairy, and approximately 1 to 3 feet tall.
Leaves are alternate with deep, narrow divisions and a rough, hairy surface. Flower
heads are clustered and numerous at the top of the stems. Flowers range from pink to
purple and the outer bracts are tipped with black, comb-like margins. Heads are 1/2 to 1
inch in diameter. The seed is an achene, brownish with one side notched near the base.
There is a short tuft of bristles at the tip end and the seeds are approximately 2 mm long.

Spotted knapweed is introduced and naturalized from Europe. It is often found in dry
gravelly or sandy pastures, old fields, and along roadsides. It readily invades pastures
and can take over nearby range and pasture. Spotted knapweed is found in every county
in Montana but the heaviest infestations are in the western part of the state.

Spotted Knapweed

A. Plant Habit

B. Enlarged Leaf

C. Flower Head

D. Disk Flower

E. Achenes

Helpful identification tip: Bracts
under the flowers have dark spots
tipped with fringe.

i tJ.^^64J.ti

131

Russim KMjJwed (cmtaurca rcycm) - Category I Noxious Weed

Russian knapweed is a bushy, branched perennial plant reproducing by seed and
underground rhizomes. The roots are characteristically black in color and have a scaly
appearance. The stems are erect, 2 to 3 feet tall, branched at the base, ridged and have a
dense gray hair-like covering. The basal leaves are hairy and the upper leaves are small
and linear with smooth edges. The intermediate leaves have slightly toothed margins.
The flowers are 1/2 inch wide, rose to purple composite heads and solitary on the ends of
leafy branches. The seeds are grajdsh to yellow, smooth, flattened, oval, and about 1/8 of
an inch long. The flowers generally bloom from June to August.

Russian knapweed was introduced from southern Russia and Asia. It grows in pastures,
grain fields, cultivated fields, meadows, waste places, roadsides, and irrigation ditches. It
is found throughout Montana. Once established it will completely crowd out other
vegetation.

fi^'^hi

Russian PCnapweed

A. Plant Habit

B. Head

C. Bracts

D. Flower

E. Achene

Helpful identification tip: Bracts
under the flower are rounded with
pointed papery tips.

|,,,|,..l.,.l...'li..lmliuluil

132

Yellow starthistk (centmrea solstitmlis) - Category 3 Noxious Weed

Yellow starthistle is commonly a winter annual but it can germinate and grow to maturity
in one season. The plant is gray green in color with cottony hair on the leaves and stems.
It reaches a height of 1 to 3 feet, is branched, and has a yellow flower on the end of each
branch. The leaves are narrow with the base of the leaf extending along the stem, giving
them a winged or ridged appearance. The flower is bright yellow and has long sharp rigid
spines as bracts below each flower. Two types of seeds are produced; light colored with
bristly awns and dark with no bristles.

Yellow starthistle is found in cultivated and fallow fields, pastures, rangelands and waste
places. It can invade range and pasture and competes well with existing vegetation. It
crowds out existing grasses where moisture is limited and grasses are weakened from
overgrazing. It produces a toxic chemical that can cause death in horses and the spines
can cause serious injury to grazing animals. It has been reported in Montana in RavalU,
Lake, Gallatin, and Liberty counties. It is a serious problem in Idaho and Washington. It
should be eradicated when found in Montana.

.^?^S

Yellow Starthistle

A. Plant Habit

B. Involucre

C. Flower

D. Achenes

Helpful identification tip:

Yellow spines up to 3/4 inch long
extend from the involucre or seed
case.

133

Rush skldonwcd (dwnirilk jmcea) - Category 3 Noxious Weed

Rush skeletonweed is a taprooted herbaceous perennial plant that overwinters as a
compact rosette resembling an immature dandelion. The plant bolts in early spring and
the flower stalk is 1 to 4 feet, nearly leafless with spreading side branches. Stem leaves
are narrow and linear. The flowers are yellow, 3/4 of an inch in diameter, and composed
of 7 to 15 individual florets. An individual plant may produce up to 20,000 seeds. Each
seed is attached to a light pappus, similar to the dandelion. Seeds have no dormancy and
remain viable for only 18 months under normal environmental conditions. Taproots may
extend to soil depths of 7 feet and produce lateral roots which give rise to satellite plants.
Cut plant surfaces exude a milky white latex sap.

Rush skeletonweed generally inhabits well-drained, light soils along roadsides, in
rangelands, grain fields and pastures. Soil disturbance aids establishment. It presently
infests several million acres of rangeland in Idaho, Oregon, Washington, and California.
It can potentially become a problem in cropland areas with light textured soils. It has
caused an estimated $30 million loss in Australian wheat producing areas. It is not
currently found in Montana and detection and eradication programs should be initiated
for the state. Cooperative detection programs have been developed for the Pacific
Northwest.

Helpful identification tip: Yellow
flowerheads, less than one inch wide,
have strap-shaped petals that are flat
across the end with distinct lobes or
teeth.

134

camk Thistle (clrsium amnse) - Category I Noxious Weed

Canada thistle is a perennial plant reproducing by creeping horizontal roots and by seed.
The extensive roots are fleshy and send up frequent new shoots. The stems are erect,
hollow, smooth or slightly hairy, up to 4 feet high and branched at the top. The plants are
leafy but no wings or spines occur on the stem. The wavy leaves are oblong to lance shaped
and vary from irregular and deeply cut, to spiny toothed on the margins, to almost smooth
with few or no spines. The color is usually bright green but the upper surface varies from
dark to light and the leaves are sometimes very light green and slightly hairy on the
underside. The flowers are numerous, small, compact, and vary from light lavender or
white to rose-purple. There are many flower heads clustered together on the ends of
branches. Canada thistle flower heads often appear much smaller than most other
thistles. The bract on the heads are not spiny. The plant is dioecious, with male and
female flowers produced on separate plants. Seeds are oblong, flattened, curved, smooth,
dark brown, and approximately 1/8 inch long.

Canada thistle is an introduced species from Eurasia and grows throughout the northern
half of the United States and north into Canada from British Columbia to Quebec. It
grows in all crops, pastures, meadows, and waste places in rich, heavy soils. Canada
thistle is a serious threat to grain crops in Montana. Wheat 5delds have been reduced from
15 to 60% in infested areas.

Canada Thistle

A. Plant Habit

B. Head

C. Flower

D. Achenes

Helpful identification tip:

Bracts under the flowers are
spineless.

135

common cmyim icmfim mil^ms) - Category 3 Noxious Weed

Common crupina is a winter annual that reproduces by seed. It is closely related to the
knapweed species. The cotyledon leaves are large, thick and dark green. They generally
germinate in the fall when moisture is adequate and from a basal rosette. The true leaves
are finely divided. A dense, fibrous root system develops quickly once the seedling is
established. The plants overwinter as compact rosettes. In the spring the plant bolts and
has a main flower stem from 1 to 4 feet tall. Leaves are alternate the length of the stem
and are finely divided, lace-like leaflets. Stiff hairs on the leaf surface give them a sticky
feel. Flowers are lavender to purple and are 1/2 inch long. Plants produce 5 to more than
100 flower heads. Each head produces 1 to 5 seeds. Seeds (achenes) are large, cylindrical,
tapering slightly to a blunt end. They have a dark, stiff pappus at the basal end. Dense,
fine hairs cover the seed, giving it a black to silver color.

Common crupina is generally found on well-drained, rocky to silt loam soil in pasture or
rangeland. Infestations start in disturbed areas or sites with sparse vegetation. It is a
recent introduction and is currently found on the federal noxious weed list. Current
infestations are found only in Idaho and Washington. An effort must be made to keep this
weed out of Montana.

Helpful identification tip: Flower
heads are narrow, cylindric and topped
with pink, lavender or purple flowers.

136

Tdfisj Ra^ort (scnecio jacohea) - Category 2 Noxious Weed

Tansy ragwort is a biennial or short-lived perennial plant. Most seeds germinate in the
fall, form a rosette the following year and flower and set seed the next year. If the plant
is cut, pulled or broken the second year this damage results in regrowth and blossoming
during the third year. Tansy ragwort has daisy-like golden flowers with a long blossoming
period. The rosettes have irregular, lobed leaves with a visible blade region near the tip.
The stems are 1 to 6 feet high. The leaves, 5 to 9 inches long, are attached directly to the
main stalk. Leaf color may vary from light to dark green. The plant spreads principally
by seeds, and individual plants may have as many as 150,000 seeds.

Tansy ragwort is a native of Europe. It grows well in pastures and disturbed areas on a
wide range of soil types. It can survive under most soil moisture conditions and does well
through the Northwest area. Hot dry summer and very low (-20 degrees) winter
temperatures do not adversely affect this plant. The plant is toxic to both cattle and
horses, and to some extent sheep. Alkaloids found in all parts of the plant cause
irreversible liver damage. This plant is currently one of the most serious weed problems
in Oregon and is also found in Northern California, western Washington and British
Columbia. It is found in limited areas of western Montana and detection and eradication
programs are important to keep it from spreading.

Helpful identification tip: Rosettes
have leaves that are deeply lobed and
the compound leaflets are also lobed.

Tansy Ragwort

A. Plant Habit

B. Flower Head

C. Ray Flower

D. Disk Flower

E. Achenes (ray flower)

F. Achenes (disk flower)

137

Meadow Hawhfccd Comyki (Hieracium j^mtcme, H, fiorihindum, H. viloschiks)
Category 2 Noxious Weed

Meadow hawkweeds are perennial weeds with shallow, fibrous roots. Leaves are hairy,
up to 6 inches long, spatula shaped, and almost exclusively basal. Stolons are extensive,
creating a dense mat of hawkweed plants that practically eliminates other vegetation.
Stems are bristly and usually leafless, although occasionally a small leaf appears near
the midpoint. Stems can reach a height of 3 feet and bear up to thirty, 1/2 inch, flower
heads near the top. Flowers are yellow and appear in late May or June. Stems and
leaves exude milky juice when broken. Seeds are black, tiny, and plumed.

Meadow hawkweed was introduced into the United States from Europe. Spread is aided
by contaminated grass seed. It is an extremely agressive weed that invades and domi-
nates hay fields, meadows, pastures, riparian areas, rights-of-way and similar sites. It is
found widely in northwestern Montana.

Native hawkweeds differ from introduced hawkweeds because they lack stolons and have
numerous upper stem leaves and a branched, open, flower arrangement.

Helpful identification tip:

Narrow, spatula-shaped leaves
are 4 to 6 inches long, dark
green above, and light green
beneath.

138

omnff Rawhfcd (Hicmcium mmntmcum) - Category 2 Noxious Weed

Orange hawkweed is a perennial weed with shallow, fibrous roots. Leaves are hairy,
spatula shaped, up to 5 inches long, and almost exclusively basal. Extensive stolons
create a dense mat of hawkweed plants that practically eUminates other vegetation. Stems
are usually leafless, although occasionally a small leaf appears near the midpoint. Stems
may reach a height of 1 foot and bear up to thirty, 1/2 inch, flower heads near the top.
Flowers are red to orange and appear in late May or June. Stems and leaves exude a
milky latex when cut or broken. Seeds are tiny and plumed.

Orange hawkweed is native to Europe. It is common in the eastern United States, where
it has become a troublesome weed. It invades meadows, pastures, roadsides, tree planta-
tions, riparian areas, and urban sites. Orange hawkweed is widely distributed in north-
western Montana.

Native hawkweeds differ from introduced hawkweeds because they lack stolons and have
numerous upper stem leaves and a branched, open, flower arrangement.

Helpful identification tip: Shorter
than meadow hawkweed, red to orange
flowers, and spreads less rapidly than
meadow hawkweed.

\J^^

139

WOSESTRIYE FAMILY (lythaccfic)

?urj)le Loosestrife (lytkmm salicam, i. vir^atiim, and my hhid crosses there ofi
Category 2 Noxious Weed

Purple loosestrife is an exotic perennial plant that infests wetlands. The seed germi-
nates in the spring and summer, although seedlings do not typically flower in their first
season. In autumn, the stems die back and the plant remains dormant through the
winter. The following spring, new stems form from root buds. Flowering starts in late
June and continues into September. Rose-purple flowers with spike-like panicles are
borne on upright 3- to 5-inch stalks. Single plants continue increasing in size with each
subsequent year of growth. New shoots form at the base of the plant, resulting in dense
stands. These dense clumps of semi-woody stalks resist decay, and overtime, debris
becomes trapped between roots and stems, resulting in the elevation of the ground level.
This eliminates water-dependent species such as cattail, rushes and sedges. The tall
stalks create shade that is detrimental to the growth of wildlife foods such as pond weeds.
In addition, the vigorous growth and extensive seed dispersal give purple loosestrife a
significant competitive advantage over most native species.

Purple loosestrife, a native of Europe and Asia, was introduced into North America in the
early 1800s. It has been found in flood plains, along drainage ditches and on marsh
edges in several places in Montana. The most severe infestations are often found in
areas where the natural vegetation has been distixrbed or eliminated. This plant is a
serious threat to wetlands.

Helpful identification tip:

Lance-shaped leaves with smooth
margins are arranged in whorls or
may be opposite on the stem.

140

MORNINGGLORY FAMILY (Convolwkceac)
¥ieU 3inhcd (convolvulus arvmis) - Category! Noxious Weed

Field bindweed is a veiny, weak-stemmed, persistent perennial weed. It reproduces from
an extensive root stock, rhizomes, and abundantly produced seeds. The plant forms a mat
on the soil surface with prostrate stems 2 to 7 feet long that can climb short distances. The
roots may extend 20 to 30 feet into the soil. The leaves are dull green and vary in size and
shape, depending on soil fertihty and moisture. Characteristically, they are ovate oblong
with acute spreading basal lobes. The leaves have short leafstalks that alternate on the
stem. The plants flower from May to August and the flowers are white to Hght pink in
color, funnel-shaped and borne on slender 1 to 2 inch stalks in the leaf axis. A pair of
narrow, pointed leaflike structures (bracts) are found on the flower stalks 1/2 to 1 inch
below the flower. The seed pod is round, pointed, light brown, and contains four seeds.
The seeds are dark-brown with a roughened surface, three-angled, and 1/8 to 1/5 inch
long.

This plant was introduced from Eurasia and is now found throughout the United States
except in the extreme Southeast and a few areas in the Southwest. It grows well under
most cultivated conditions as well as in all uncultivated and waste places. It is extremely
difficult to eradicate due to it's low growth and widespread, deeply penetrating root
system. It is a serious problem in cropland in Montana.

Field Bindweed

A. Plant Habit

B. Rootstock

C. Leaf Variation

D. Flower

E. Capsule

F. Seeds

Helpful identification tip:

Leaves of field bindweed are
shaped like arrowheads.

141

MUSTARD FAMILY (Bmsmccae)

whMoj) (carkria iraha) - Category I Noxious Weed

Whitetop (hoary cress) is a perennial reproducing by seed and rhizomes. It has numerous
erect stems 1 to 2 feet high that are branched at the top. An extensive root system spreads
both horizontally and vertically with frequent shoots arising from the root stock. The
plant seems to be gray green due to many fine hairs on the leaves. The leaves are simple,
alternate, oblong, toothed and the upper leaves have a broad clasping base. The flowers
are white, four parted, about 1/8 inch wide and borne in flat-topped clusters. Seed pods
are slightly flattened, two-valved, heart-shaped with a prominent persisting style. The
seeds are oval, slightly flattened, granular with reddish-brown seed coats.

Whitetop is naturalized from Europe and found throughout the United States except in
the Southcentral area. It is found in pastures, cultivated fields, hay fields, meadows,
waste places, and roadsides. It is most common in western and central Montana.

Helpful identificaiton tip:

Many white flowers with four
petals develop into bladder-like
seed capsules in mid-summer.

Whitetop

A. Plant Habit

B. Flower

C. Silicle

D. Seeds

i..i.„....i...i.iii...i..a

142

Djcrs wod (mils tindom) - Category 2 Noxious Weed

Dyers woad is a perennial, biennial or annual forb reproducing by seeds and from roots.
The plants may grow from 1 to 3 feet tall and have a smooth, bluish-green color. The lower
leaves clasp the stem with ear-like projections. The yellow flowers are very small and
form a flat-topped inflorescence. The seed pods are about 1/2 inch long, winged like a
maple seed and turn black when mature.

Dyers woad is native to Europe. It's name comes from Germany where dye was extracted
from the purplish black seed pods. It is a serious weed problem in both Utah and Idaho
and can be found in several locations in Montana. It spreads readily by seed from
roadsides to rangeland and crops. Detection and eradication is imperative for Montana.

Helpful identification tip:

Purplish-brown seed pods containing a
single seed appear near mid-summer,
giving this weed a totoally differnt
appearance.

Dvers Woad

A. Plant Habit

B. Flower Head

C. Fruit

143

ROSE FAMILY (ROSmdc)
Sulfur cinfcfoil (?otentilk recta) - Category 2 Noxious Weed

Sulfur cinquefoil is a long-lived perennial forb that begins growth early in the spring. It
reproduces by seed and can produce 1,650 seeds per year. Although it does not reproduce
vegetatively, as old roots die in the center, new shoots grow from the edges and can form
a ring-shaped clump of individual plants. Plants 20 to 30 years old have been reported in
Michigan.

Sulfur cinquefoil produces one to several erect stems which vary from 12 to 28 inches in
height. The compound leaves have five to seven leaflets arranged in a palmate pattern.
Numerous leaves are attached along the length of the stem, but few of them grow from
the base of the plant. The leaflets decrease in size, and the length of the leafstalks get
shorter near the top of the stem. Uppermost leaves are attached directly to the stem.
Stems and leafstalks are hairy.

This noxious weed is adapted to a wide range of environmental conditions. It grows in
open grasslands, shrubby areas and open forest and logged areas, often in association
with spotted knapweed. Disturbed sites such as roadsides, waste areas, logged areas and
abandoned fields are easily invaded by sulfur cinquefoil. It is widely distributed in Mon-
tana.

Helpful identification tips: Long,
right angled hairs on stem; many stem
leaves, few basal leaves; net-like (re-
ticulated) seed coat; and pale yellow
flowers.

144

SPURGE FAMILY {Euykorkdcm)
icafj sywfff (Euvkorha csuk) - Category I Noxious Weed

Leafy spurge is a perennial, reproducing by seed as well as an extensive underground
rhizome system. The heavy running roots are woody, persistent and widespread and give
rise to dense colonies of the plant. Pink buds on creeping rhizomes give rise to roots and
shoots every few inches. The stems are erect, smooth, and branched at the top. The entire
plant is a dull green color with milky juice and grows about 2 feet tall. The leaves are
alternate and irregularly spaced along the stem. There is a whorl of lance-shaped leaves
at the base of the umbel. The flowers are inconspicuous and are formed above pairs of
rounded floral bracts on repeated forking stems arranged in a flat-topped umbel. When
in full bloom the entire umbel, including the bract, turns a bright greenish yellow. The
seed pods are on a short stalk from the cup-like base and are three angled. There are three
ovoid, smooth, light gray to brownish seeds in each pod.

Leafy spurge is an introduced plant from Europe. It is found in most of the northern
United States and Canada. It grows readily in waste areas, pastures, roadsides,
cultivated fields and sandy banks. It can be toxic to cattle, but sheep do well eating it.
Leafy spurge is one of the most persistent noxious weeds in Montana. It is found
throughout the state and has a wide habitat suitability, prolific reproduction capabilities,
strong competitive abihty and is difficult to control.

Leafv Spurge

A. Plant Habit

B. Flower Cluster

C. Capsule

D. Seeds

Helpful identification tip: Heart-
shaped yellow bracts surround the
3-celled seed capsule, each cell
containing a single seed.

145

ST, JOHNSWORT FAMILY {Wjycrmcm)
St. johmorl (Hy ncum ftrjomtim) - Category 1 Noxious Weed

St. Johnswort (goatweed) is a perennial forb reproducing by seed and from rootstock.
Stems are smooth, branched, about 3 feet tall and woody at the base. The opposite leaves
are elliptic to oblong and have small, glandular dots. The orange-yellow flowers are about
3/4 inch in diameter and five-petaled. The three-parted seed pods are round, pointed, and
contain many seeds.

St. Johnswort is common in dry pastures, rangelands, and neglected fields and along
roadsides in western Montana. It is not readily grazed by livestock and causes
photosensitization in light skinned animals. It should be regarded as a poisonous plant.
It is difficult to control.

Helpful identification tip: Leaves
are oval in shape with prominent
veins. Tiny transparent dots are
visible when leaves are held up to a
light source.

D

St. Johnswort

%

A. Plant Habit

/>/

B. Enlarged Leaves

\(C

C. Flower and Bud

D. Capsule

E. Seeds

146

SNAPDRAGON FAMILY [scToyMmmac)
Dalmatm TodfiaX (limm Mmatica) - Category 1 Noxious Weed

Dalmatian toadflax is a perennial, reproducing by seeds and creeping rootstocks. The
plants are erect, about 2 feet tall, pale green and have showy, yellow flowers. The spurred
flowers are tinged with orange and are about 1 inch long. The leaves are broad, heart-
shaped, and clasp the stem.

Dalmatian toadflax is a native of the Mediterranean region. It is found scattered
throughout the northern and western United States. It is an escaped ornamental found
along roadsides and near dwellings, spreading to valleys and sagebrush flats. Large
infe

Helpful identification tip: Early
spring growth of this prolific peren-
nial has waxy leaves with a blue-
green color.

Dalmation Toadflax

A. Plant Habit

B. Flower

C. Capsule

D. Seeds

147

APVENDIX C

classification of Rerkciks Ij chemical Tmilies mi

Mok of Action

I. ckmcdfmiY

Common Nmc

Trakmmc

, MdicofAdim

acetanilides

alachlor

Lasso

Growth Inhibitors

bensulide

Betasan, Prefar

diphenamid

Dymid, Enide

pronamide

Kerb

propachlor

Ramrod

prynachlor

Basamaize

alphatic carboxylic

dalapon

Dowpon, Basfapon

Metabohc Inhibitors

acids

TCA

vanous

benzoic acids

chloramben

Amiben

Growth Regulators

dicamba

Banvel

2,3,6-TBA

Trysben, Benzac

benzonitriles

dichlobenil

Casoron

Photosynthetic Inhb.

bromoxynil

Brominil, Buctril

bipyridiliums

diquat

Ortho Diquat

Contact Herbicides

paraquat

Ortho Paraquat

carbanilates

chloropropham

Chloro-IPC, Furloe

Growth Inhibitors

barban

Carbyne

phenmedipham

Betanal

dinitroanilines

benefin

Balan

Mitotic Poisons

dinitramine

Cobex

fluchloralin

Basalin

nitralin

Planavin

proflurain

Tolban

trifliralin

Treflan

diphenyl ethers

bifenox

Modown

Contact Herbicides

148

II

cJimicdTmili

Common Name

Trak Name

Mok of Action

imidazolinones

imazapyr

Arsenal

Acetolactate synthase

imazathapyr

Pursuit

(ALS) Inhibitors

inorganic compounds

AMS

Ammate

Contact Herbicides

boron

Borax, Borascue

coppersulfate

Bluestone, Cutrine

sodium chlorate

Atlacide, others

organic arsenicals

DSMA

various

Unclear 11

MAA

various

MSMA

various

phenols

dinoseb

Premerge, Sinox

Contact Herbicides

phenoxy compunds

Growth Regulators

acetic

2,4-D

various

MCPA

Methoxone,
Weedar,

2.4,5-T

Weedone
various

butyric

2,4-DB

MCPB

Butoxone, Butyrac
Thistrol, Can-Trol

propionic

2(2,4-DP)

2(MCPP)

Weedone

silvex (2,4,5-TP)

several
Kuron

phthalic acids

DCPA

Dacthal

Metabolic Inhibitors

endothall

Aquathol, Hydrathol

naptalam

Alanap

pyridines

picloram

Tordon

Growth Regulators

pyridazinones

pyrazon

Pyramin

Photosynthetic
Inhibitors

substituted amino acids

glyphosate

Roundup
Rodeo

Metabolic Inhibitors

sulfonylureas

chlorsulfuron

Glean, Telar

Acetolactate synthase

metasulfuron methyl

Ally, Escort

(ALS) Inhibitors

149

chmicdNamc

Common Nme

Tvdk Nme

MokofAcUon

thiocarbamates

butyl ate

CDEC

cycloate

diallate

EPTC

EPTC + antidote

pebulate

triallate

vemolate

Sutan

Vegedex

Ro-Neet

Avadex

Eptam

Eradicane

Tillam

Fargo

Vemam ■

Growth Inhibitors

s-triazines

ametryn

Evik

Photosynthetic

atrazine

AAtrex

Inhibitors

cyanazine

Bladex

cyprazine

Outfox

prometon

Pramitol

simazme

Princep

terbutryn

Igran

as-triazines

metribuzin

Sencor, Lexone

Photosynthetic

(asymmetrical)

Inhibitors

triazoles

amitrole

Weedazol,

Amino-triazole,

Prob

Chlorphyll
Inhibitors

uracils

bromacil

Hyvar

Photosynthetic

terbacil

Sinbar

Inhibitors

ureas

chloroxuron

Tenoran, Norex

Photosynthetic

diuron

Karmex

Inhibitors

fenuron

Dybar

linuron

Lorox

monuron

Telvar

siduron

Tupersan

150

GLOSSARY

Abdomen - the third major division of the
insect body, consisting primitively of eleven
segments, but normally with 9 or 10
apparent segments and bearing no functional
legs in the adult stage.

Abiotic - non-living; devoid of life.

Allelopathy - the release into the
environment by an organism of a chemical
substance that acts as a germination or
growth inhibitor to another organism (see
antibiosis).

humans. Examples - potato ring rot,
bacterial wilt in alfalfa, bacterial canker.

Bacteriostat - prevents the growth of
bacteria without killing them.

Basidium (basidia) - a club-shaped fimgal
structure or stalk bearing the sporidia.

Biennial weed - a weed that completes its
life cycle from seed to mature plant in two
growing seasons. Examples: burdock,
common mullein, musk thistle.

Annual weed - a weed that completes its
life cycle from seed to mature plant in less
than one year. Examples: cheat grass,
kochia, field pennycress.

Antibiosis - the release of a chemical
substance by an organism which is
unfavorable for the development or survival
of another organism. Examples: plants
inhibiting insect development; fungi
inhibiting bacteria (see allelopathy).

Antixenosis - a condition in a plant which
makes it unatfractive to the insect for food,
oviposition, shelter, or for combinations of
all three.

Axil - the angle between a leaf and stem.

Biotic - relating to living organisms.

Bt - Bacillus thuringiensis, a bacteria used
as a microbial insect confrol agent.

Cambium layer - a layer of plant cells lying
between the xylem and phloem.

Catalyst - used to accelerate a chemical or
biochemical reaction. The catalyst is not
affected by the overall reaction. Enzymes
are naturally occurring catalysts.

Cell membrane - the sheet-like membrane
that encloses and delimits the contents of a
cell. A living structure that is selectively
permeable, allowing free water passage but
controlling other molecules.

Bacilliform - the shape or form of a
bacteria.

Bacteria - one-celled microorganisms found
in all types of air, soil, and water and are
common on or in all plants, animals, and

Cell wall - a strong, rigid extra protoplasmic
layer in plants whose growth is directed
from within the cell.

151

Chemosterilants - chemicals that cause
steriUzation in the wild population of
organisms by interfering with cell division.

Chitin - cuticle being insoluble in water,
alcohol, ether and other solvents and
resistant to acids and alkalis.

Chitinous - composed of chitin or like it in
structure.

and suitable climatic conditions experienced
during the growing season.

Disintegration - to break or decompose into
constituent elements, parts, or small
particles.

DNA - deoxyribonucleic acid; nucleic acid
providing the genetic template of
chromosomes.

Chlorophyll - the green photosynthetic
substance in plants which allows them to
capture solar energy.

Chromosome - a DNA - protein thread
usually associated with RNA, occurring in
the nucleus of the cell; best seen during cell
division.

Cotyledons - the first leaf (or pair of leaves)
of seed plants.

Cucurbit - a plant of the gourd family.

Cuticle - superficial non-cellular layer
covering a plant or animal; secreted by the
epidermis. In plants it retards the movement
of water and gases into and out of the leaf

Economic Threshold - the pest density at
which control measures should be applied to
prevent an increasing pest population fi^om
reaching the economic injury level.

Economic Injury Level - the lowest pest
density that will cause economic damage; or
the pest density that causes damage equal to
the cost of preventing the damage.

Elytra - the leathery forewings of beetles,
serving as a covering for the hind wings.

Entomophagous - consuming chiefly
insects or their parts.

Enzymes - naturally occurring organic
catalyst, being usually a protein.

Desiccate - to dry; to dry up.

Diapause - in insects, a period of suspended
development or growth, accompanied by
greatly decreased metabolism; often
correlated with seasons (i.e. hibernation).

Dicot - a flowering plant with two seed
leaves or cotyledons.

Diploid - having a double set of
chromosomes per cell.

Epidermis - outermost layer of cells of a
plant or animal. In plants one cell-layer
thick, covered in aerial parts by a non-
cellular protective cuticle.

Equilibrium position - the population
density of insects when fluctuation is
averaged over a period of time.

Eradication - the elimination of a disease-
causing agent, pathogen, weed, or insect pest
after it has become established.

Disease triangle - the right combination of
susceptible host plants, a virulent pathogen.

152

Exclusion - the prevention of disease-
causing organisms from entering and
becoming established where susceptible
plants are growing.

Excretion - the act of getting rid of products
of metabolism by storing them in an
insoluble form or by removing them from
the body.

Exoskeleton - the external skeleton
consisting of hard cuticle, to the inner side
of which muscles are attached.

Exuding - to cause to ooze or spread out in
all directions.

Foliage - the aggregate of leaves of a plant.

Frass - plant fragments made by wood-
boring insects, usually mixed with
excrement.

Fungi - simple microorganisms that lack
chlorophyll and are unable to manufacture
their own food. Examples - stem rust, leaf
rust, smut diseases, potato late and early
blight, alfalfa leaf spot, powdery mildew.

Girdle - in insects, a silk band used to
support the pupa, fri plants, cutting
transversely across the phloem in a stem so
that downward transport of substances is
stopped.

Grafting - to transfer part of an organism
from its normal position to another on the
same or a similar organism.

Halteres - modified hind wings, which are
sense organs concerned with the
maintenance of stability in flight.

Head - the first region of the insect body,
articulated at its base to the thorax, bearing
the mouth structures and antennae.

Hemelytra - anterior wing, the basal portion
of which is thickened.

Hemimetabolous insects - insect that
resemble the adult form in the immature
stages in many ways, but are not
reproductively mature and do not have
functional wings.

Holometabolous insects - insects which
have 4 general stages in metamorphosis -
egg, larva, pupa, and adult - each entirely
different from the others.

Hypha - a thread-like filament that is the
structural unit of a fungus mycelium.

Inoculation - the introduction of a pathogen
into a living organism to stimulate the
producfion of antibodies.

Inoculum - that portion of a pathogen which
is transferred to a host; usually consists of
spores, bacteria, mycelial fragments,
nematode cysts, or virus particles.

Instal - the stage between molts in the
nymph or larva, numbered to designate the
various stages.

Kairomones - plant substances that emit
odors which warn insects of toxicity or
attracts them to the right source of food.

Larva - a young insect which quits the egg
in an early stage of morphological
development and differs ftmdamentally in
form from the adult.

Haploid - having a single complete set of
chromosomes.

153

Mandibles - the first pair of jaws in insects,
being stout and jawlike in chewing insects,
or needle - or sward-shaped in piercing-
sucking insects.

MDA - Montana Department of Agriculture.

Mesosomes - a complex infolding of the
plasma membrane in prokaryotic cells.
Contains respiratory enzymes and appears to
play a role in cell division.

Metamorphosis - the series of changes
through which an insect passes in its growth
fi'om the egg to the adult stage.

Nematodes - microscopic, unsegmented
roundworms. Examples - root-knot
nematode and sugar beet nematode.

Nocturnal - active at night.

Nucleoid - one of a number of names given
to the area of a prokaryotic cell that contains
the chromosomal DNA.

Nymph - an immature stage of
hemimetabolous insects.

Ovipositor - in female insects, the organ by
which the eggs are deposited.

Molting - the shedding of the old
exoskeleton.

Monocot - a plant having a single cotyledon
or seed leaf Monocots, which include
grasses, usually have parallel leaf veins and
fibrous roots.

Monophagous - feeding upon only one kind
of food, e.g., one species of plant.

Morphology - the study of form and
structure (anatomy).

MSU - Montana State University.

Mycelium - the mass of interwoven threads
(hyphae) making up the vegetative body of
fungus.

Mycoplasma-Like Organisms (MLOs) -

microorganisms of an intermediate size
between viruses and bacteria, generally
without cell walls. Examples - witches
broom, hay wire, aster yellow disease.

Necrosis - the death of a circumscribed
piece of tissue.

Parasite - an organism that lives in or on
another (the host), from which it obtains
food, shelter, or other requirements.

Parthenogenesis - egg development without
fertilization.

Pathogen

disease.

an entity capable of producing

Perennial weed - a weed that produces
vegetative structures, allowing it to live for
more than two years. Examples: leafy
spurge, Canada thistle, quackgrass.

Pheromone - a chemical substance, usually
a glandular secretion, which is used in
communication within a species, such that
one individual releases the material as a
signal and another responds after sensing it.

Phloem - vascular tissue, composed of
living cells, which conducts food from the
plant leaf to the stem and roots.

Phyla - one of the major divisions of the
animal kingdom.

154

Phytophagous - feeding in or on plants.

Plasma membrane - see cell membrane.

Pleomorphic - the ability of an organism to
exist in different forms or shapes.

Predaceous - living by preying upon other
organisms.

Prokaryote - a type of organism which is
mainly unicellular and in which the cells
lack a true nucleus; now synonymous with
bacteria.

Prologs - any process or appendage that
serves the purpose of a leg.

Pronotum - the upper and dorsal part of the
pro thorax.

Propagation - to increase in numbers by
sexual or asexual reproduction.

Protein - a polymer that has a high relative
molecular mass of L-amino acids. Occupy a
central position in the architecture and
functioning of living matter.

Prothorax - the first thoracic ring or
segment, bearing the anterior legs but no
wings.

Pupa - the inactive stage in all
holometabolous insects, being the
intermediate stage between the larva and the
adult.

Puparium - the nymphal skin enveloping
the adult.

Rhizome - an underground, horizontal,
creeping stem which bears roots and leaves
and usually persists firom season to season.

Ribosomes - a sub-cellular granule
composed of RNA and protein, which is
found in cell types if cells and in some sub-
cellular organelles: The site of protein
synthesis.

RNA - ribonucleic acid, any of various
nucleic acids that contain ribose and uracil
as structural components and are associated
with the control of cellular chemical
activities.

Sclerotia - fungal resting bodies which are
resistant to unfavorable environmental
conditions and can remain dormant for long
periods of time.

Secreting- to release product by an animal
or plant.

Solanaceous - relating to the nightshade
family of plants.

Spinneret - small tubular appendage fi-om
which silk threads are exuded by spiders and
by many larval insects.

Spiracles - external opening of the tracheal
system.

Spiroplasmas - a genus of bacteria in which
the cells are variable in shape, but can form
helical filaments. The cells lack cell walls.

Spore - a microscopic structure which
functions in reproduction and dispersal. A
spore does not contain an embryo and is thus
distinct from a seed.

Sporidium (sporidia) - a small spore
produced by basidia.

Stolon - an aboveground, horizontal stem.

155

Stomates - the small openings on the plant
epidermis which allow transpiration to take
place.

Stylet - slender, tubular mouthparts in plant-
parasitic nematodes or aphids.

Viruses - complex macro-molecules
composed of ribonucleic acid with a
protective protein "overcoat". Examples -
wheat and barley streak mosaic, potato leaf
roll, alfalfa mosaic virus, little cherry, curly
top virus.

Tarsi - the leg segment attached to the apex
of the tibia, fourth segment of the leg.

Telispore - a thick-walled resting or
overwintering spore, produced by rust and
smut fiingi.

Terrestrial - living on the land.

Whorl - a ring of hairs, pestles, leaves etc.
set about in a joint or center like the spokes
of a wheel.

Xylem - vascular tissue, made up of non-
living cells, which conducts water and
mineral nutrients from the roots to the stem
and leaves.

Thoracic leg - the jointed appendage
attached to the thorax.

Thorax - the middle portion of the body
between the head and abdomen, consisting
of 3 segments, each of which usually bear a
pair of legs.

Translocation - the movement of food,
water, or mineral solutions from one part of
a plant to another.

Transpiration - the loss of water from plant
tissues in the form of vapor.

Tubercle - a small knoblike or rounded
body structure.

Tympanal organ - an organ sensitive to
vibrations, consisting of a thin area of
cuticle and an inner air sac.

Tympanum - tympanal organ.

Vector - an agent, such as an insect,
nematode, or fungus, that may transmit a
pathogen.

Zero Damage Level - when the pest
population is at or below the level that will
not have an impact on the yield or quality of
the plant, the insect no longer has pest
status.

Zoophagous - feeding on animals.

Zygote - a diploid cell resulting from the
union of two haploid cells.

156

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Flint, Mary Louise, 1990. Integrated Pest Management for small grains; University of
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159

ANSWERS

Plant Diseases - Part I

Weeds - Part II

Ag. Insect Pest - Part III

1. d.

1.

d.

• 1. b.

2. d.

2.

c.

2. b.

3. b.

3.

d.

3. a.

4. b.

4.

b.

4. a.

5. a.

5.

a.

5. b.

6. c.

6.

d.

6. d.

7. b.

7.

b.

7. b.

8. a.

8.

a.

8. b.

9. d.

9.

a.

9. a.

10. c.

10.

b.

10. a.

11.

b.

11. c.

12.

a.

12. d.

13. a.

160

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