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1983 Row Crop Weed Control Guide

IMPMiyolth*

JUL 1^1983

This guide is based on the results of research con- ducted by the University of Illinois Agricultural Experi- ment Station, other experiment stations, and the U.S. Department of Agriculture. Consideration has been given to the soils, crops, and weed problems of Illinois.

Rainfall, soil type, method of application, and formula- tion influence herbicide effectiveness. Under certain con- ditions some herbicides may damage crops to which they are applied. In some cases, herbicide residues in the soil may damage crops grown later.

When selecting a herbicide, consider both the risk in- volved in using the herbicide and the yield losses caused by weeds. If cultivation and good cultural practices are controlling weeds, herbicides may be unnecessary. You can reduce risks by taking these precautions :

• Apply herbicides only to those crops for which use has been approved.

• Clean tanks thoroughly when changing from corn to soybeans, especially when using a postemergence her- bicide.

• Use recommended rates. Applying too much herbi- cide is costly and in addition may damage crops and cause illegal residues. Using too little herbicide can result in poor weed control.

• Apply herbicides only at times specified on the label. Observe the recommended intervals between treatment and pasturing or harvesting of crops.

• Wear goggles, rubber gloves, and other protective clothing as suggested by the label.

• Guard against drift injury to nearby susceptible plants, such as soybeans, grapes, and tomatoes. Mist or vapors from 2,4-D, MCPA, and dicamba sprays may drift several hundred yards. Operate sprayers at low pressure with tips that deliver large droplets. Spray only on calm days or make sure air is not moving toward susceptible crop plants and ornamentals.

• Apply herbicides only when all animals and persons not directly involved in the application have been re- moved from the area. Avoid unnecessary exposure.

• Check label for proper method of container disposal. Triple rinse, puncture, and haul metal containers to an approved sanitary landfill. Haul paper containers to a sanitary landfill or burn them in an approved manner.

• Return unused herbicides to a safe storage place

promptly. Store them in original containers, away from unauthorized persons, particularly children.

• Since manufacturers' formulations and labels are sometimes changed and government regulations modi- fied, always refer to the most recent product label.

This guide has been developed to help you use herbi- cides as effectively and safely as possible. However, since no guide can remove all the risk involved, the University of Illinois and its employees assume no responsibility for results of using herbicides, even if they have been used according to the suggestions, recommendations, or direc- tions of the manufacturer or any governmental agency.

Cultural and Mechanical Control

Most weed control programs combine good cultural practices, mechanical weed control, and herbicide appli- cations. Good cultural practices to aid weed control in- clude preparation of a good seedbed, adequate fertiliza- tion, crop rotation, seeding on the proper date, use of the optimum row width, and seeding at the rate for optimum stands.

Planting in relatively warm soils helps crops compete better with weeds. Good weed control during the first 3 to 5 weeks is extremely important for both corn and soybeans. If weed control is adequate during that period, corn and soybeans will usually compete quite well with most of the weeds that begin growth later.

Narrow rows will shade the centers faster and help the crop compete better with the weeds. However, if herbi- cides alone cannot give adequate weed control, then keep rows wide enough to allow cultivation. Some of the newer herbicides are improving the chances of adequate control without cultivation.

If a preemergence or preplant herbicide does not ap- pear to be controlling weeds adequately, use the rotary hoe while weeds are still small enough to be controlled.

Use the rotary hoe after weed seeds have germinated but before most have emerged. Operate it at 8 to 12 miles per hour and weight it enough to stir the soil and kill the tiny weeds. Rotary hoeing also aids crop emergence if the soil is crusted.

Row cultivators also should be used while weeds are small. Throwing soil into the row can help smother small

Prepared by M. D. McGlamery, Professor of Weed Science, Ellery Knake, Professor of Weed Science, Dave Pike, Associate Agronomist, Allan Beuerman, Associate Agronomist, and F. W. Slife, Professor of Agronomy, all at the University of Illinois) with the assistance of George McKibben, Professor of Agronomy, Dixon Springs Agricultural Center, George Kapusta, Professor of Plant and Soil Science, Southern Illinois University, Carbondale, and Gordon Roskamp, Associate Professor of Agriculture, Western Illinois University. This guide is based in part upon research conducted by Loyd M. Wax, Agronomist, USDA, and Professor of Weed Science, and E. W. Stoller, Plant Physiologist, USDA, and Professor of Agronomy, both at the University of Illinois. Issued in furtherance of Cooperative Extension Work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agricul- ture. WILLIAM R. OSCHWALD, Director, Cooperative Extension Service, University of Illinois at Urbana-Champaign. The Illinois Cooperative Extension Service provides equal opportunities in programs and employment.

weeds. Cultivate shallow to prevent injury to crop roots. Avoid excessive ridging; it may hinder harvesting and encourage erosion.

Herbicides can provide a convenient and economical means of early weed control by allowing delayed and faster cultivation. Furthermore, unless the soil is crusted, it is usually not necessary to cultivate at all when herbi- cides are controlling weeds adequately.

Herbicide Incorporation

Soil-applied herbicides are incorporated to minimize surface loss, reduce dependence upon rainfall, and pro- vide appropriate placement of the herbicide. Sutan + and Eradicane are incorporated soon after application to minimize surface loss from volatization. Dinitroaniline herbicides such as Treflan and Prowl are incorporated within a few hours to minimize loss due to photode- composition and volatization. Triazine herbicides such as atrazine and Bladex and acetanilide herbicides such as Lasso and Dual may be incorporated to minimize de- pendence upon timely rainfall, but time of incorporation for them is less critical since they are not lost so quickly from the soil surface.

Incorporation should place the herbicide uniformly in the top 1 to 2 inches of soil for best control of small- seeded annual weeds that germinate from shallow depths. Slightly deeper placement may improve the control of certain weeds from deep-germinating seed under rela- tively dry conditions. The field cultivator and tandem disk place most of the herbicide one-half to two-thirds of the depth of operation. Thus for most herbicides the suggested depth of operation is 3 to 4 inches.

Thorough incorporation with ground-drive implements may require two passes. Single-pass incorporation tends to result in streaked weed control, especially in wet soils. Single-pass incorporation may be adequate with some equipment, especially if rotary hoeing and cultivation are used to improve weed control. If the herbicide is suffi- ciently covered to prevent surface loss with the first pass, the second pass can be delayed until immediately before planting. The addition of a coil-tine or spike-tooth drag harrow or rolling baskets behind the disk or field culti- vator can help provide uniform mixing.

The depth and thoroughness of incorporation depend upon the type of equipment, depth and speed of opera- tion, soil texture, and soil moisture. Field cultivators and tandem disks are common implements used for incorpo- ration. However, disk-chisels and other combination tools are being promoted and used in some areas.

Field Cultivators

Field cultivators are frequently used for herbicide in- corporation. They should have three or more rows of tool bars with an effective shank spacing of no more than 8 to 9 inches (a spacing of 24 to 27 inches on each of three tool bars) . The shanks can be equipped with points or sweeps. Sweeps usually give better incorporation, espe- cially when soil conditions are a little too wet or dry for

optimal soil flow and mixing. Sweeps for "C" shank culti- vators should be at least as wide as the effective shank spacing.

The recommended operating depth for the field culti- vator is 3 to 4 inches. It is usually necessary to operate only deep enough to remove tractor-tire depressions. The ground speed should be at least 6 mph. The field culti- vator must be operated in a level position so that the back shanks are not operating in untreated soil, which would result in streaked weed control. Two passes are recom- mended to obtain uniform weed control. If single-pass incorporation is preferred, the use of wider sweeps or narrower spacing will increase the probability of obtain- ing adequate weed control.

Tandem Disks

Tandem disk harrows invert the soil and usually place the herbicide deeper in the soil than most other incorpo- ration tools. Tandem disks used for herbicide incorpora- tion should have disk blade diameters of 22 inches or less and blade spacings of 7 to 9 inches. Larger disks are con- sidered primary tillage tools and should not be used for incorporating herbicides. Spherical disk blades give better herbicide mixing than conical disk blades.

Tandem disks usually place most of the herbicide in the top two-thirds of the depth of operation. For most herbicides, the suggested operating depth is from 3 to 4 inches. Recommended ground speeds are usually be- tween 4 and 6 mph. The speed should be sufficient to move the soil the full width of the blade spacing. Lower speeds can result in herbicide streaking.

Chemical Weed Control

Plan your chemical weed-control program to fit your soils, crops, weed problems, and farming operations. Herbicide performance depends on the weather and on wise selection and application. Your decisions on herbi- cide use should be based on the nature and seriousness of your weed problems.

Corn or soybeans occasionally may be injured by some of the herbicides registered for use on them. However, the benefits from weed control are usually much greater than the adverse effects. Crop tolerance ratings for var- ious herbicides are given in the table on the last page of this publication. Corn or soybeans under stress from soil crusting, depth of planting, or adverse weather are more subject to herbicide injury. Plants injured by a herbicide are likely to be more subject to disease.

Apply the herbicide at the time specified on the label. Select and apply herbicides at the correct rate in order to reduce crop injury. The application rates for most herbi- cides vary with soil texture and organic matter.

You must also consider the kinds of weeds likely to be present. The herbicide selectivity table at the end of this guide indicates the susceptibility of our most common weed species to herbicides.

Crop planting intentions for the next season must also be considered. Where high rates of atrazine or simazine

are used, you should not plant soybeans, small grains, alfalfa, or vegetables the following year. If you are con- sidering planting wheat after soybeans, be sure that the application of Treflan or similar herbicides for soybeans is uniform and sufficiently early to reduce the risk of injury to wheat or corn following soybeans. Refer to the herbicide label for cropping sequence information.

Names of Some Herbicides

Trade Common (generic)

AAtrex, Atrazine atrazine

Alanap naptalam

Amiben chloramben

Banvel dicamba

Basagran bentazon

Basalin fluchloralin

Bicep metolachlor + atrazine

Bladex cyanazine

Blazer acifluorfen

Bronco alachlor + glyphosate

Butoxone, Butyrac 2,4-DB

Dowpon M dalapon

Dual metolachlor

Dyanap naptalam plus dinoseb

Eradicane Extra EPTC

Evik ametryn

Furloe Chloro IPC chlorpropham

Fusilade fluazifop-butyl

Goal oxyfluorfen

Hoelon dichlofop

Laddok bentazon + atrazine

Lasso alachlor

Lorox linuron

Milogard propazine

Modown bif enox

Paraquat, Gramoxone paraquat

Poast sethoxydim

Princep, Simazine simazine

Prowl pendimethalin

Ramrod propachlor

Rescue naptalam plus 2,4-DB

Roundup glyphosate

Sencor, Lexone metribuzin

(several) 2,4-D

Surflan oryzalin

Sutan+ butylate

Sutazine butylate plus atrazine

Treflan trifluralin

Vernam vernolate

Vistar mefluidide

Some herbicides have different formulations and con- centrations under the same trade name. No endorsement of any trade name is implied, nor is discrimination against similar products intended.

Herbicide Combinations

Herbicides are often combined to control more weed species, reduce carryover, or reduce crop injury. Some combinations are sold as a "package mix," while others are tank mixed. Tank mixing allows you to adjust the ratio to fit local weed and soil conditions. If you use a tank mix, you must follow restrictions on all products used in the combination.

Problems sometimes occur when mixing emulsifiable concentrate (EC) formulations with wettable powder (WP), water dispersible liquid (WDL), or water dis- persible granule (WDG) formulations. These problems can sometimes be prevented by using proper mixing pro- cedures. Fill tanks at least one-third full with water or liquid fertilizer before adding herbicides. If using liquid fertilizers, check compatibility in a small lot before mix- ing a tankful. The addition of compatibility agents may be necessary. Wettable powders, WDGs, or WDLs should be added to the tank before ECs. Emulsify ECs by mixing with equal volumes of water before adding them to the tank. Empty and clean spray tanks often enough to pre- vent accumulation of material on the sides and the bottom of the tank.

Some of the herbicide combinations that have been registered are listed below. The herbicide listed first is the one that carries label or supplemental instructions on mixing. The label of the other herbicide (s) may also have mixing instructions.

Corn

Atrazine + Princep (PPI, Pre, NT/P, NT/R)1

Atrazine 4- propachlor (Pre, early Post)

Banvel + atrazine (Post)

Banvel + Lasso (Pre, early Post)

Banvel + 2,4-D (Post)

Basagran + atrazine (Post)

Bladex + atrazine (PPI, Pre, Post, NT/P)

Bladex + atrazine + Lasso (PPI, Pre)

Bladex + paraquat (NT)

Bladex + Sutan+ (PPI)

Dual + AAtrex (PPI, Pre, early Post, NT/P, NT/R)

Dual + Princep (PPI, Pre, NT/P, NT/R)

Dual + atrazine + Princep (PPI, Pre, NT/P, NT/R)

Dual 4- Banvel (Pre, early Post)

Dual + Bladex (PPI, Pre, NT/P)

Eradicane 4- atrazine or Bladex (PPI)

Eradicane + Bladex + atrazine (PPI)

Lasso 4- atrazine (PPI, Pre, early Post, NT/P, NT/R)

Lasso + Bladex (PPI, Pre, NT/R)

Lasso 4- Princep (NT/R)

Paraquat + atrazine (NT)

Prowl + atrazine (Pre, early Post)

Prowl + Banvel (Pre)

Prowl + Bladex (Pre, early Post)

Sencor 4- atrazine + Dual or Lasso (Pre)

Sencor 4- Bladex 4- Dual or Lasso (Pre)

Sutan4 — h atrazine (PPI)

Sutan4- 4- atrazine 4- Bladex (PPI)

Soybeans

Alanap + 2,4-DB (Post)

Amiben + Lasso (PPI, Pre)

Amiben + Lorox (Pre)

Amiben + Sencor (Pre)

Amiben + Surflan (Pre)

Amiben + Treflan or Basalin (PPI)

Amiben + Dual + Sencor or Lexone (PPI, Pre)

Amiben + Lasso + Sencor or Lexone (PPI, Pre)

Amiben + Treflan + Sencor or Lexone (PPI)

Basagran + 2,4-DB (Post)

Basalin + Sencor or Lexone (PPI)

Blazer + 2,4-DB (Post)

Dual + Amiben (PPI, Pre)

Dual + Dyanap (Pre, early Post)

Dual + Lorox (Pre, NT/P, NT/R)

Dual + Sencor or Lexone (PPI, Pre, NT/P, NT/R)

Dyanap 4- Lasso (Pre, early Post)

Furloe 4- Lasso (Pre)

Furloe 4- Treflan (PPI)

Furloe 4- Vernam (PPI)

Goal 4- Lasso (Pre, NT/P)

Lasso 4- Lorox (Pre, NT/P, NT/R)

Lasso 4- Lexone or Sencor (PPI, Pre, NT/P, NT/R)

Lorox 4- 2,4-DB (Post — directed)

Modown 4- Lasso (PPI, Pre)

Modown 4- Treflan (PPI)

Paraquat 4- Lorox (NT)

Paraquat 4- Sencor (NT)

Prowl 4- Amiben (PPI, Pre)

Prowl 4- Amiben 4- Sencor or Lexone (PPI, Pre)

Prowl 4- Lorox (Pre, NT/P)

Prowl 4- Sencor or Lexone (PPI, Pre, NT/P)

Sencor 4- Amiben (Pre)

Sencor 4- Dyanap (Pre)

Sencor 4- Lasso + Dyanap (Pre)

Sencor 4- 2,4-DB (Post — directed)

Sencore or Lexone 4- Treflan ( PPI )

Sencor 4- Treflan (PPI) 4- Sencor (Pre)

Surflan 4- Dyanap (Pre)

Surflan 4- Lorox (Pre, NT/P)

Surflan 4- Sencor or Lexone (Pre, NT/P)

Vernam 4- Treflan or Basalin ( PPI )

Vernam 4- Amiben (PPI)

1 PPI = preplant incorporated, Pre postemergence, NT = no-till, NT/P - NT/R = no-till with Roundup.

= preemergence, Post = no-till with Paraquat,

The user can apply two treatments of the same herbi- cide (split application), or he can use two different ones, provided such uses are registered. Applying two herbi- cides at different times is referred to as a sequential or overlay treatment. Sequential treatment can be done in a number of ways. For example, a preplant application might be followed by a preemergence application, or a soil-applied treatment might be followed by a postemer- gence treatment. One herbicide may be broadcast while the other is banded or directed.

Herbicide Rates

Herbicide rates vary according to the time of applica- tion, soil conditions, the Ullage system used, and the seriousness of the weed infestation. Sometimes lower rates are specified for preemergence application than for pre- plant incorporated application. Postemergence rates may be lower than preemergence rates if the herbicides can be applied at either time. Postemergence rates often vary depending on the size and species of the weeds and on whether an adjuvant is specified. Rates for combinations are usually lower than for herbicides used alone.

The rates for soil-applied herbicides usually vary de- pending on the texture of the soil and the amount of organic matter it contains. For instance, light-colored, medium-textured soils with little organic matter require relatively lower rates of most herbicides than do the dark- colored, fine-textured soils with medium to high organic matter. For sandy soils the herbicide label may specify "do not use," "use a reduced rate," or "use a postemer- gence rather than soil-applied herbicide," depending on the herbicide and its adaptation and on crop tolerance.

The rates given in this publication are, unless other- wise specified, broadcast rates for the amount of formu- lated product. If you plan to band or direct herbicides, adjust the amount per crop acre according to the per- centage of the area actually treated. Many herbicides have several formulations with different concentrations of active ingredient. Be sure to read the label and make the necessary adjustments when changing formulations.

Postemergence Herbicides

Postemergence herbicides applied to growing weeds generally have foliar rather than soil action. The rates and timing of applications are based on weed size and climatic conditions. Weeds can usually be controlled with a lower application rate when they are small and tender. Larger weeds often require a higher herbicide rate or the addition of a spray additive, especially if the weeds have developed under drouth conditions. Herbicide pene- tration and action are usually greater when the tempera- ture and relative humidity are high. Rainfall occurring too soon after application (1 to 8 hours, depending on the herbicide) can cause poor weed control.

Translocated (hormone) herbicides can be effective with partial foliar coverage, whereas contact herbicides require complete coverage. Foliar coverage increases as water volume and spray pressure are increased. Spray nozzles that produce small droplets also improve cover- age. For contact herbicides, 20 to 40 gallons of water per acre are often recommended for ground application and a minimum of 5 gallons per acre for aerial application. Spray pressures of 30 to 50 psi are often suggested with flat-fan or hollow-cone nozzles to produce small droplets and improve canopy penetration. Such small droplets are quite subject to drift.

The use of a surfactant or crop oil concentrate may be recommended to improve spray coverage. These spray

additives will usually improve weed control but may increase crop injury. Spray additives may be needed only under drouth conditions or on larger weeds.

Crop size limitations may be specified on the label to minimize crop injury and maximize weed control. If weeds are smaller than the crop, basal-directed sprays may minimize crop injury because they place more herbicide on the weeds than on the crop. If the weeds are taller than the crop, rope-wick applicators or recirculating sprayers can be used to place the herbicides on the top of the weeds and minimize contact with the crop. Follow the label directions and precautions for each herbicide.

Conservation Tillage and Weed Control

Efficient production with any tillage system is highly dependent upon effective weed control. Weed control problems have probably been the primary deterrent to widespread adoption of conservation tillage. However, the availability of a wide spectrum of effective herbicides has made acceptable weed control possible with conserva- tion tillage.

Conservation tillage protects the soil from erosion by leaving the soil surface rough and covered with crop residue. For effective erosion control it is essential that the soil surface be protected in the spring before and after corn or soybeans are planted.

Satisfactory weed control is more difficult with crop residue or clods on the soil surface because ( 1 ) the resi- due or clods may interfere with herbicide distribution or incorporation, (2) most weeds are not deeply buried, resulting in heavier weed infestations, and (3) the roots of perennial weeds are not disturbed as much.

Increased weed pressure coupled with decreased herbi- cide performance requires better herbicide management. You must exercise greater care in choosing herbicides and application rates. Preemergence herbicides require less secondary tillage than preplant-incorporated treatments, but they are more dependent upon timely rainfall. Soil- applied herbicides may require a higher application rate for satisfactory control with conservation tillage. In any case, do not use a higher rate than indicated on the label instructions. Effective postemergence herbicides may be a logical choice when available, as they depend upon foliar action rather than soil action.

No-Till and Double-Crop

Corn and soybeans are sometimes produced without seedbed preparation, either in last year's crop residue (no-till) or as a second crop after small grain harvest or forage removal (double-crop). The no-till concept of planting has greatly improved the probability of success of double-cropping by conserving soil, soil moisture, and time.

No-till herbicides must control both vegetation existing at planting and seedling weeds that germinate after planting. Existing vegetation may be a perennial grass sod, a legume or legume-grass sod, an annual cover crop,

or weeds that emerge in the previous years' crop stubble before planting. If a cutting of forages such as alfalfa or clover is removed before no-till planting, control of sod may be poor, especially if herbicides are applied before regrowth. Labeled applications of 2,4-D, Roundup, or Banvel can improve control of broadleaf perennials when used in registered crops, such as corn or sorghum.

Several precautions should be observed in no-till crop- ping systems. Crop seed should be planted to the proper depth and adequately covered to avoid possible contact from herbicide sprays. (Several herbicide labels give planting depths necessary to avoid possible injury.) Pre- emergence applications of the herbicide treatment may give better weed control than preplant applications since the planting process may expose untreated soil contain- ing viable weed seed. The total reliance on chemical weed control and large amounts of crop residue present under no-till cropping systems may require that the higher labeled herbicide rates be used to obtain accept- able weed control. Postemergence herbicides may be needed in no-till soybeans.

Paraquat or Gramoxone (1 or 2 pints per acre) plus a nonionic surfactant at 'A pint per 100 gallons of diluted spray is generally used to "knock down" existing foliage before crop emergence. Smartweed, giant ragweed, and fall panicum may not be controlled if they are over 10 to 12 inches high and if no rain occurs to "activate" the residual herbicides. A minimum of 40 gallons or more of spray per acre is suggested to insure adequate coverage of the foliage. Paraquat and Gramoxone are restricted-use pesticides.

Roundup (3 pints per acre) should be considered as an alternative treatment for control of the foliage prior to crop emergence in situations where fall panicum, smartweed, or certain perennial weeds are a problem. Roundup can translocate to the roots to give better con- trol of perennials. Use 20 to 30 gallons of spray volume per acre. Bronco is a formulated mixture of glyphosate (Roundup) plus alachlor (Lasso). Application rates are 4 to 5 quarts per acre. Do not apply in liquid fertilizers.

No-fill Corn

Herbicides registered with paraquat plus atrazine are Dual, Lasso, Princep, and Bladex. Dual plus Princep, atrazine plus Princep, and Bicep are also registered with paraquat. These combinations give better control of annual grasses than atrazine or Bladex plus paraquat.

Herbicides registered with Roundup plus atrazine or Princep are Dual and Lasso. Roundup is also registered with atrazine plus Princep, atrazine plus Princep plus Dual, Lasso plus Bladex, and Bicep for use in no-till corn. Bronco is registered for use with atrazine, Bladex, or Princep. The section entitled "Herbicides for Corn" pro- vides more information on these products.

No-iill or Double-Crop Soybeans

Preemergence herbicides registered in soybeans as tank mixes with paraquat (1 to 2 pints per acre) are Lorox,

Sencor, or Lexone alone or in combination with Lasso, Dual, Prowl, or Surflan. Goal plus Lasso is also cleared with paraquat. Registered tank mixes with Roundup are Lasso or Dual in combination with Lorox, Sencor, or Lexone. Bronco is registered with Lexone, Lorox, or Sencor. See the section entitled "Herbicides for Soy- beans" for more information on these products.

Herbicides for Corn

All herbicides mentioned in this section are registered for use on field corn and also on silage corn unless other- wise specified. Herbicide suggestions for sweet corn and popcorn may be found in Circular 907, 1983 Weed Man- agement Guide for Commercial Vegetable Growers. Growers producing hybrid seed corn should check with the contracting company or inbred producer about tol- erance of the parent lines.

Preplant Incorporation

Preplant application should be made anytime during the 1 or 2 weeks before planting. Incorporation should distribute the herbicide uniformly in about the top 2 inches of soil. Do not apply herbicides too early or in- corporate them too deeply.

Sutan-I- (butylate) or Eradicane (EPTC) may be

applied anytime during the 2 weeks prior to planting. It is best to incorporate them soon after application or preferably as they are being applied. Both herbicides are formulated with a crop safening agent to decrease the risk of corn injury. However, injury can still occur when growing conditions are unfavorable or when certain hy- brids are used.

Sutan+ and Eradicane control the seedlings of annual grasses, shattercane, and johnsongrass. Eradicane will suppress wild proso millet.

The suggested rate for these herbicides used alone or in combinations is 43/4 to 7Vi pints per acre. Use the higher amount on heavy infestations of wild cane or yellow nutsedge or to suppress rhizome johnsongrass (see section on specific weed problems). A lower rate may be used on sandy soils.

You can control broadleaf weeds by tank mixing with atrazine or Bladex or by sequencing with an appropriate postemergence herbicide. The rate for combinations of Sutan+ or Eradicane with atrazine is 114 to 2 pounds of atrazine 80 W (2 to 3 pints of 4L), while the rate for Bladex is VA to 33/4 pounds of Bladex 80 W (2 to 6 pints 4L) . A combination of atrazine plus Bladex with Sutan+ or Eradicane is also registered.

Eradicane Extra includes an extender (microbial in- hibitor) to lengthen weed control when Eradicane has been used the previous year. Herbicide combinations are the same as with Eradicane.

Sutazine+ is a prepacked combination of 4.8 pounds of Sutan+ and 1.2 pounds of atrazine per gallon. Sug- gested application rates are 7 to 10'/2 pints per acre.

Preplant or Preemergence Herbicides

Incorporation of the following herbicides is optional depending upon the weeds to be controlled and the likeli- hood of rainfall. Incorporation of these herbicides should be shallow but thorough.

AAtrex, Atrazine (atrazine), or Princep (simazine) can be applied anytime during the 2 weeks prior to planting, or soon after planting. Preplant incorporation of these herbicides controls weeds more effectively if rain- fall is limited. Corn tolerance of atrazine and simazine is good, but carryover to subsequent crops can occur.

Princep controls fall panicum and crabgrass better than atrazine but is less effective in controlling cocklebur, velvetleaf, and yellow nutsedge. Princep is less soluble, but just as persistent, as atrazine. Thus, Princep is usually preplant incorporated. Princep plus atrazine can be used in 1:1 or 2 : 1 combinations ; the total rate is the same as for atrazine used alone.

The rate for atrazine used alone is 2V2 to 3% pounds of atrazine 80W, 4 to 6 pints of 4L, or 2.2 to 3.3 pounds of AAtrex 90WDG. Atrazine controls annual broadleaf weeds better than it does grasses, and it is often used at reduced rates in tank mix combinations to improve broadleaf weed control. The rate for atrazine in combi- nations is l'/2 to 2 pounds of atrazine 80W, 2 to 3 pints of atrazine 4L, or 1.1 to 1.8 pounds of AAtrex 90WDG. These rates may not provide adequate control of cockle- bur, morningglory, and velvetleaf but can reduce the risk of carryover.

You can minimize carryover injury by mixing and applying the herbicides accurately, by applying them early, by using the lowest rates consistent with good weed control, and by tilling the soil thoroughly before planting susceptible crops. The risk of carryover is greater the year after a cool, dry growing season and on soils with pH over 7.3.

If you use atrazine at more than 3 pounds of active ingredient per acre or if you apply after June 10, plant only corn or sorghum the next year. If you use atrazine in the spring and must replant, then plant only corn or sorghum that year. Do not plant small grains, small seeded legumes, or vegetables in the fall or spring. Soy- beans planted the year after an application of atrazine can also be affected from carryover, especially if you use Sencor or Lexone.

Bladex (cyanazine) does not persist in the soil as long as atrazine, but atrazine does have the advantage of better corn tolerance. Bladex controls fall panicum and giant foxtail, but not broadleaf weeds, better than atra- zine. Bladex can be combined with atrazine at 3:1, 2:1, or 1: 1 ratios of Bladex to atrazine (see label for rates). The higher ratios will provide better grass control, while the 1 : 1 ratio will provide better broadleaf weed control.

Rates of Bladex must be selected accurately on the basis of soil texture and organic matter to reduce the possibility of corn injury. Rates are VA to 5 pounds of Bladex 80W, 1.2 to 4 quarts Bladex 4L, or 8 to 27 pounds

of Bladex 15G per acre. You can lessen the risk of corn injury by using reduced rates of Bladex in combinations.

Bladex can be tank mixed with Lasso, Dual, Ramrod, or Prowl to improve grass control. The Lasso or Dual combination can be applied immediately before planting or after planting. Do not incorporate the Prowl or Ram- rod combinations.

Three-way combinations of Bladex plus atrazine plus Lasso, Dual, Sutan+, or Eradicane are registered. The addition of a limited amount of atrazine should improve broadleaf control without increasing concern about carry- over.

Lasso (alachlor) or Dual (metolachlor) can be ap- plied preplant incorporated or at the preemergence stage. Preplant incorporation will improve control of yellow nutsedge and can lessen dependence upon rainfall. In- corporation should distribute the herbicide evenly in the top 2 inches of soil.

Lasso and Dual control annual grasses and help con- trol yellow nutsedge. You can improve broadleaf weed control by using atrazine or Bladex in preplant combina- tions or by using atrazine, Bladex, or Banvel in preemer- gence combinations.

Lasso can be applied anytime during the week before planting corn and incorporated evenly into the top 2 inches of soil, or it can be used immediately after plant- ing. The rate is 2 to 4 quarts of Lasso 4E or 16 to 26 pounds of Lasso 15G. Use the higher rate for the soil if you plan to incorporate Lasso.

Dual can be applied anytime during the 2 weeks prior to planting corn and incorporated into the top 2 inches of soil, or it can be used immediately after planting. The rates are IV2 to 3 pints of Dual 8E per acre.

Lasso or Dual plus atrazine can be applied preplant incorporated or after planting until corn is 5 inches tall and grass weeds are no larger than the two-leaf stage. Do not apply with liquid fertilizer after the crop emerges. The suggested rate is IV2 to 2'/2 quarts of Lasso or VA to 2Vi pints of Dual 8E plus IV2 to 2'/2 pounds of atrazine 80W, 1 to 2 quarts of atrazine 4L, or 1.1 to 2.2 pounds of AAtrex 90WDG. Dual is also cleared in a combina- tion with atrazine plus Princep.

Dual and Lasso are both formulated as packaged mixes with atrazine. Bicep contains 2'/2 pounds of metolachlor (Dual) and 2 pounds of atrazine per gallon. The rate is 2 to 4 quarts per acre. Lasso/atrazine (flowable) con- tains 2V2 pounds of alachlor (Lasso) and IV2 pounds of atrazine per gallon. The rate is 3V2 to 4'/2 quarts per acre.

Dual or Lasso plus Bladex can be applied prior to planting and incorporated, or they can be applied during the preemergence stage after planting. The rate is 2 to 2'/2 quarts of Lasso 4E or 1V4 to 2'/2 pints of Dual 8E plus 1 to 3 pounds of Bladex 80W or 1.6 to 4.8 pints of Bladex 4L. Adjust the rate carefully according to soil texture and organic matter.

Preemergence Herbicides

Banvel (dicamba) plus Lasso or Dual can be applied after planting until corn is 3 inches high, but before

grasses reach the two-leaf stage. The addition of Banvel improves control of broadleaf weeds without creating a risk of carryover injury. Banvel may injure corn, espe- cially if recommended rates are exceeded, applications are not accurate and uniform, or if corn is planted too shallow (less than IV2 inches). Do not use this treatment on coarse-textured soils or soils that are low in organic matter. The rate on soils with over 2'/2 percent organic matter is 1 pint of Banvel plus 2!/2 quarts of Lasso 4E, or 2 to 2V2 pints of Dual 8E per acre.

Ramrod (propachlor) can be applied alone or with atrazine after the corn is planted but before grasses reach the two-leaf stage. Granular formulations should be ap- plied before crop or weeds emerge. Ramrod performs well on soils with over 3 percent organic matter.

Ramrod is irritating to the skin and eyes, so observe label precautions. Corn tolerance is good. It controls annual grasses and pigweed. The rate is 4 to 6 quarts of Ramrod 4L or 20 to 30 pounds of 20G per acre.

Ramrod can be mixed with atrazine or Bladex to im- prove broadleaf weed control. The rate is either 2'/2 to 4 quarts of 4L plus 1 V2 to 2 pounds of atrazine 80W ( 1 .2 to 1.6 quarts of 4L) or l'/2 to 2!4 pounds of Bladex 80W ( 1.2 to 1.8 quarts of 4L) per acre.

Prowl (pendimethalin) is registered only for use on corn after planting. Incorporation of Prowl may result in serious corn injury. Use only where it is possible to cover seed adequately with soil. Prowl can control annual grasses and pigweed and provides some control of smart- weed and velvetleaf. You can improve broadleaf weed control by combining Prowl with atrazine, Bladex, or Banvel. Prowl plus atrazine or Bladex may be applied in the early postemergence period before grasses are in the two-leaf stage. These combinations may also help reduce the competition from wild proso millet. However, avoid postemergence application when corn is under stress from cool, wet weather; otherwise, corn injury may result. The rate for such combinations is 1 to 1 V2 quarts of Prowl 4E. Do not use Prowl plus Banvel on sandy soils or soils with less than 1 V2 percent organic matter.

Sencor (metribuzin) is registered for preemergence use in corn in three-way combinations. The rate is Vb pound of Sencor 50W, V2 pint of Sencor 4L, or Vi pound of Sencor 75DF per acre (!4 pound of active ingredient per acre) . Sencor can be used at this rate in combination with Lasso or Dual plus atrazine or Bladex. Applying Sencor at this rate with the atrazine or Bladex may im- prove velvetleaf control but may also increase the poten- tial for corn injury, especially with Bladex. Do not use this combination on coarse-textured soils, soils containing less than 2 percent organic matter, or soils with a pH of 7.0 or higher.

Postemergence Herbicides

Lasso, Dual, Ramrod, Prowl plus Bladex or atrazine, or Lasso or Dual plus Banvel can be used on corn be- tween the preemergence and very early postemergence stages (see preemergence section). To get satisfactory control apply before grasses reach the two-leaf stage.

Banvel plus atrazine can be applied up to 3 weeks after planting but before annual grasses are VA inches high. The rate is Vi pint of Banvel plus l'/2 to 2 pounds of atrazine 80W or 1 to 1 .6 quarts of atrazine 4L.

Atrazine can be applied before grass weeds are more than l'/2 inches high. Many annual broadleaf seedlings are more susceptible than grass weeds and may be treated until they are up to 4 inches tall.

The addition of oil-surfactant mixes or surfactants has generally increased the effectiveness of postemergence atrazine. Crop-oil concentrates (80 percent oil and 20 percent surfactant) are used at the rate of 1 quart per acre. Surfactants are usually added at 0.5 percent of the total spray volume or about 1 pint per acre. Results with the oil-surfactant mixes have generally been better than those with surfactants.

Applications of atrazine and oil sometimes damage corn that has been under stress from prolonged cold, wet weather, or other factors. Do not use more than 2Vz pounds of atrazine 80W or 2 quarts of atrazine 4L per acre if you mix with oil or oil concentrate. Do not add 2,4-D to the atrazine-oil treatment or severe injury may result. Mix the atrazine with water first and add the oil last. If atrazine is applied after June 10, do not plant any crop except corn or sorghum the next year.

Bladex (cyanazine) can be applied through the four- leaf stage of corn growth but before weeds exceed IV2 inches in height. The rate is IV2 to 2'/2 pounds of Bladex 80W per acre. Do not use Bladex 4L, as it contains oil and can increase the potential for injury. A mixture of Bladex plus atrazine is also registered for postemergence use. Injury to corn may occur under cold, adverse grow- ing conditions. The injury may only be temporary yellow- ing but can be more severe. Under drouthy conditions certain agricultural surfactants or vegetable oils may be added to Bladex 80W to improve weed control. Do not use petroleum crop oils or apply with liquid fertilizers for postemergence application. Do not apply Bladex post- emergence to corn under severe stress.

Banvel or Banvel II (dicamba) can be applied from emergence until corn is 36 inches tall. Banvel can be used at a rate of V2 to 1 pint per acre anytime after emergence until corn is 5 inches high. Banvel II is preferred at 1 pint per acre for applications on corn from 5 to 36 inches tall. The best time to apply is at the first flush of broad- leaf weeds and before the corn is 5 inches tall. Banvel should be used in a sequential treatment following a grass herbicide such as Lasso, Dual, or Sutan4~. Such timing allows for better crop tolerance than the pre- emergence treatments with Banvel, it permits application at a higher rate than the later postemergence treatment, and it diminishes the likelihood of significant injury to nearby soybeans.

Banvel should be applied before soybeans in the area are 10 inches high. Soybean yields are seldom reduced when slight injury occurs early. However, yields can be reduced if severe injury occurs when soybeans are bloom- ing or during pod fill. Banvel also can injure other sus-

ceptible plants, such as vegetables and ornamentals. Use extreme caution to avoid injury to desirable plants from either contaminated sprayers or drift of Banvel from treated areas.

Banvel II or Banvel may be applied until corn is 3 feet high or until 15 days before tasseling. When spraying near soybeans, do not spray corn after it is 2 feet high. If corn is more than 8 inches high, drop nozzles give better weed coverage, reduce drift, and lessen the chance of crop injury. If you direct the nozzles toward the row, adjust the spray concentration so that excessive amounts are not applied to the corn and risk of injury to corn is reduced. The broadcast rate is V2 pint per acre of Banvel or 1 pint per acre of Banvel II.

Do not use Banvel on sweet corn, popcorn, or seed corn. Do not graze or harvest corn for dairy feed before the ensilage (milk) stage.

A mixture of V2 pint of Banvel plus V2 pint of 2,4-D amine (4 pounds per gallon) per acre may present less risk of corn injury than 2,4-D alone. Use drop nozzles on corn more than 8 inches high when using the Banvel- plus-2,4-D mixture.

2,4-D is an economical and effective treatment for controlling many broadleaf weeds in corn. Use drop nozzles if corn is more than 8 inches high to decrease the possibility of injury. If you direct the nozzles toward the row, adjust the spray concentration so that excessive amounts are not applied to the com.

Do not apply 2,4-D to corn from tasseling to dough stage. After the hard dough to dent stage, you can apply 1 to 2 pints of certain 2,4-D's by air or high clearance equipment to control late-germinating broadleaf weeds that may interfere with harvest, or to suppress certain perennial weeds.

The suggested broadcast rate of acid equivalent per acre is Ve to 54 pound of ester formulations or V2 pound of amine. This would be Vs to V2 pint of ester or 1 pint of amine for formulations with 4 pounds of 2,4-D acid equivalent per gallon.

The ester forms of 2,4-D can vaporize and injure near- by susceptible plants. This vapor movement is more likely with high-volatile than with low-volatile esters. Spray particles of either the ester or the amine form can drift and cause injury.

Corn is often brittle for 7 to 10 days after application of 2,4-D and thus is susceptible to stalk breakage from high winds or cultivation. Other symptoms of 2,4-D in- jury are stalk bending or lodging, abnormal brace roots, and failure of leaves to unroll.

High temperature and high humidity will increase the potential for 2,4-D injury, especially if corn is growing rapidly. If it is necessary to spray under these conditions, it may be wise to reduce the rate by about 25 percent. Corn hybrids differ in their sensitivity, and the proba- bility of injury increases when corn is under stress.

Basagran (bentazon) is registered for postemergence use in corn in a manner similar to that for soybeans (see soybean section) . Since corn is quite tolerant of Basagran, the addition of a crop-oil concentrate is considered rela-

tively safe. Basagran is also cleared at the rate of 1 to \lh pints in combination with atrazine at 0.6 to 0.9 pound of 80W, 0.6 to 0.8 pound of 90WDG, or 1 to \lA pints of 4L per acre. Laddok is a formulated mixture of Basa- gran plus atrazine. The rate is 2.4 to 3.6 pints per acre. Oil concentrate is added at 1 quart per acre for control of annual broadleaf weeds only. The combination is more economical than Basagran alone and will reduce the carryover potential from atrazine alone.

Postemergence Soil-Applied Herbicides

Prowl, Treflan, and Lasso can be applied to the soil as postemergence treatments. It may be necessary to use drop nozzles to avoid interference from corn leaves and ensure uniform application to the soil.

Prowl (pendimethalin) or Treflan (triflurahn) maybe applied to the soil and incorporated after field corn is 4 (for Prowl) or 8 (for Treflan) inches high and up to the time of last cultivation. The field should be cultivated to control existing weeds and cover the roots at the base of the corn before application. The herbicide should then be thoroughly and uniformly incorporated into the top inch of soil. Prowl may not need incorporation if irriga- tion or rainfall occurs soon after application. Prowl can be combined with atrazine.

These treatments may help to control late-emerging grasses such as shattercane, wild proso millet, or fall panicum, which can still cause problems.

Lasso (alachlor) may be used as a soil-applied post- emergence treatment in corn grown for seed to help con- trol midseason annual grass weeds. Application should preferably be made after cultivation before weeds emerge and before the crop is 40 inches tall. Lasso plus atrazine is an alternative that can be used anytime from immediately after cultivation until weeds reach the two-leaf stage of growth and corn is 40 inches tall.

Directed Postemergence Herbicides

Directed sprays are sometimes needed for emergency situations, especially when grass weeds become too tall for control with cultivation. However, weeds are often too large for directed sprays to be effective. Directed sprays cannot be used on small corn because a height difference between corn and weeds is needed to keep the spray off the corn. Corn leaves that come into contact with the spray can be killed, and injury may affect yields.

Lorox (linuron) may be applied as a directed spray after corn is at least 15 inches high (free standing) but before weeds are 8 inches tall (preferably not more than 5 inches) . Lorox controls grass and broadleaf weeds.

The broadcast rate is VA to 3 pounds of Lorox 50 W per acre, depending on weed size and soil type. Add Sur- factant WK at the rate of 1 pint per 25 gallons of spray mixture. Cover the weeds with the spray, but keep it off the corn as much as possible. Consider this an emergency treatment.

Evik 80W (ametryn) is registered for directed use when corn is more than 12 inches tall and weeds are less than 6 inches tall. Evik should not be applied within 3

weeks of tasseling. The rate is 2 to 2'/2 pounds Evik 80W per acre (broadcast) plus 2 quarts of surfactant per 100 gallons of spray mixture. Extreme care is necessary to keep the spray from contacting the leaves. Consider this an emergency treatment.

Herbicides for Soybeans

Consider the kinds of weeds expected when you select a herbicide program for soybeans, especially when grow- ing soybeans in narrow rows. The herbicide selectivity table (see last page of this guide) lists herbicides and their relative weed control ratings for various weeds.

Soybeans may be injured by some herbicides. However, they usually outgrow early injury with little or no effect on yield if stands have not been significantly reduced. Significant yield decreases can result when injury occurs during the bloom to pod fill stages. Excessively shallow planting may increase the risk of injury from some herbi- cides. Accurate rate selection for soil type is especially essential for Lorox, Lexone, and Sencor. Do not apply Lorox, Lexone, Sencor, or Modown after soybeans have begun to emerge. Follow label instructions as to rates, timing, incorporation, and restrictions.

Preplant Herbicides

Incorporation is required for Basalin, Treflan, and Vernam. Incorporation is optional for Amiben, Dual, Lasso, Modown, and Prowl when used alone and in some combinations. Dyanap, Lorox, and Surflan should not be incorporated. Incorporation can improve performance if rainfall is limited and may increase the effectiveness of Dual or Lasso in controlling nutsedge. Incorporation should distribute the herbicide evenly in the top 1 to 3 inches of soil. Deep incorporation or very early applica- tion of the herbicide can cause significant reductions in weed control.

Dinitroaniline herbicides registered for weed control in soybeans are Basalin, Treflan, Prowl, and Surflan. Basalin and Treflan should be incorporated because of their low solubility and because of surface loss through vaporization and photodecomposition. Incorporation is optional with Prowl, but variable weed control and soy- bean injury may result from preemergence applications. Do not incorporate Surflan (see preemergence section).

Incorporation should distribute the herbicide evenly in the top 2 to 3 inches of soil (see label for implement set- tings). A deeper incorporation may improve shattercane and johnsongrass seedling control. Basalin, Prowl, or Treflan may be used for rhizome johnsongrass suppres- sion (see section on specific weed problems).

The dinitroaniline herbicides control annual grasses, pigweed, and lambsquarters and may provide some con- trol of smartweed and annual morningglory. Prowl and Surflan may also partially control velvetleaf. However, acceptable control of most other broadleaf weeds requires combinations or sequential treatments with other herbi- cides. The dinitroaniline herbicides provide similar weed control, soybean tolerance, and persistence when recom- mended rates are used.

Soybeans are sometimes injured by dinitroaniline herbi- cides. Plants that have been injured by incorporated treatments are stunted and develop swollen hypocotyls and shortened lateral roots. Such injuries are not usually serious. Plants injured by preemergence applications de- velop stem callouses at the soil surface, which can cause lodging and yield loss.

Crops of corn, sorghum, or small grains may be injured if they are grown subsequent to a soybean crop that has been treated with a dinitroaniline herbicide. The symp- toms are poor germination and stunted, purple plants with poor root systems. To avoid carryover use no more than the recommended rates. Also, be sure that applica- tion and incorporation are uniform. The likelihood of carryover increases with double cropping or late applica- tion and after a cool, dry season. Disking or chisel plow- ing provides for minimal dilution of herbicide residues.

Treflan (trifluralin) can be applied alone anytime in the spring. Combinations with Sencor or Lexone should be applied no more than 2 weeks prior to planting, while combinations with Amiben, Furloe, or Modown should be applied within a few days prior to planting. Incorpo- rate as soon as possible, but do not delay incorporation more than 24 hours (8 hours if soil is warm and moist) . The rate is 1 to 2 pints of Treflan 4E or 10 to 20 pounds of Treflan 5G per acre.

Basal in (fluchloralin) can be applied anytime during the 8 weeks (alone) or 1 to 2 weeks (with Sencor or Lexone) prior to planting. Incorporate within 8 hours of application. The rate is 1 to 3 pints Basalin 4E per acre. Basalin can be combined with Sencor or Lexone to im- prove broadleaf weed control.

Prowl (pendimethalin) can be applied within 60 days (alone) or 7 days (with Sencor or Lexone) prior to planting soybeans or applied after planting (see pre- emergence). Preplant treatments should be incorporated within 7 days of application. Mechanical incorporation may not be necessary if adequate rainfall occurs. Rates are 1 to 3 pints of Prowl 4E per acre, although rates for combinations with Sencor or Lexone are lower than when the herbicide is used alone.

Sencor or Lexone (metribuzin) plus Basalin, Prowl, or Treflan can be tank mixed and applied within 7 to 14 days of planting. Incorporate uniformly into the top 2 inches of soil. The rate of Sencor or Lexone in these combinations is lA to 1 pound of 50W, lA to 1 pint of 4L, or Vi to % pound of 75WDG. Use the normal rate, or slightly less, of the dinitroaniline herbicide (see labels).

A Sencor application can also be split, one part being incorporated with Treflan and the other part applied before emergence. This method requires two applications but can give better broadleaf control and less injury than incorporating the same total amount of Sencor with Treflan in a single application.

Amiben (chloramben) can be incorporated with Basa- lin, Treflan, or Prowl. The rate is 4 to 6 quarts of Amiben 2S per acre. Amiben can also be applied at the rate of 3

to 5 quarts per acre and incorporated with Treflan plus Sencor or Lexone as a three-way combination.

Vernam (vernolate) controls annual grasses and pig- weed. It sometimes provides fair control of annual morn- ingglory, velvetleaf, and yellow nutsedge. Some soybean injury may occur in the form of delayed emergence, stunting, and leaf crinkling. Vernam can be applied within 10 days prior to planting and should be incorpo- rated immediately. The broadcast rate is 2Vz to 3'/2 pints of Vernam 7E or 20 to 30 pounds of Vernam 10G per acre. Vernam plus Treflan is labeled at the rate of 1 pint of Treflan plus 2Vi to 3 pints of Vernam 7E per acre. The combination will reduce the risk of soybean injury, but it may also decrease control of velvetleaf and yellow nutsedge. Other labeled combinations include Vernam plus Amiben, Basalin, or Lasso.

Preplant or Preemergence Herbicides

Lasso (alachlor) or Dual (metolachlor) can be ap- plied to soybeans preplant incorporated or during the preemergence stage. If applied prior to planting, apply Dual anytime within the 2 weeks prior to planting and Lasso within 1 week of planting. If rainfall is limited, incorporation can improve performance and increase yellow nutsedge control. Soybeans are quite tolerant of Lasso or Dual. The first to second trifoliate leaves often appear crinkled with a drawstring effect on the middle leaflet, but these symptoms should not cause concern.

Lasso or Dual controls annual grasses plus pigweed and can help control nutsedge and black nightshade. These herbicides can be combined with Lexone, Sencor, or Amiben (incorporated or preemergence) and with Lorox or Dyanap (preemergence only) to improve broadleaf weed control.

The rate for Lasso is 2 to 4 quarts Lasso 4E or 16 to 26 pounds of Lasso II 15G per acre. The rate for Dual 8E is IV2 to 3 pints per acre. Use the higher amount for the soil when incorporating or when black nightshade or yellow nutsedge are to be controlled. The rate for combi- nations is about 75 percent of that for the herbicide used alone (see labels) .

Amiben (chloramben) can control annual grasses plus many broadleaf weeds in soybeans when used at the full rate. Do not expect control of cocklebur or annual morn- ingglory. Control of velvetleaf and jimsonweed is often erratic. Amiben occasionally injures soybeans, but dam- age is not usually severe. Injured plants may be stunted and have abnormal, shortened roots. If rain does not occur within 3 to 5 days of an Amiben preemergence application, you should rotary hoe. Amiben is best suited to soils with over 2.5 percent organic matter.

Amiben can be applied alone or with Dual, Lasso, or Prowl as a pieplant-incorporated or preemergence treat- ment. Amiben can also be mixed with Lasso or Dual plus Sencor as a preplant or preemergence treatment. Amiben can be applied as a preemergence treatment with Lorox, Lexone, and Sencor.

The Amiben broadcast rate alone is 20 to 30 pounds of 10G, 4 to 6 quarts of 2S, or 2.4 to 3.6 pounds of 75DS

10

per acre. The Amiben rate in combinations is 3 to 6 quarts of 2S (1.8 to 3.6 pounds of 75DS) per acre. Use the higher rate where black nightshade, velvetleaf, or common ragweed is a problem weed.

Sencor or Lexone (metribuzin) can be applied any- time during die 1 to 2 weeks prior to planting and in- corporated with Basalin, Dual, Lasso, Prowl, or Treflan. Incorporation should distribute the herbicide evenly in the top 2 inches of soil. It can be applied preemergence by itself or with Amiben, Dual, Lasso, Prowl, Surflan or Dyanap.

Sencor or Lexone can control many annual broadleaf weeds except annual morningglory. Control of giant rag- weed, jimsonweed, and cocklebur is marginal at the re- duced rates necessary to minimize soybean injury.

One symptom of soybean injury is yellowing (chlorosis) of the lower leaves at about the first trifoliate stage or later; it may be followed by browning of leaves and death of plants depending upon the severity of the injury. Seedling diseases, weather stress, and atrazine carryover may increase the possibility of soybean injury. Injury may be greater on soils with pH over 7.5. Accurate, uni- form application and incorporation are essential.

Adjust rates accurately according to soil conditions. Do not apply to very sandy soil. Combinations allow for reduced rates and thus reduce risk of soybean injury. The combinadon rate of Sencor or Lexone is Vi to 1 pound of 50W, Vz to 1 pint of 4L, or Vi to % pound of 75WDG. You can use the higher amount when you apply this treatment during the preemergence stage, either alone or sequentially after applications of a preplant herbicide. The higher amounts can improve broadleaf control but also increase the risk of soybean injury.

Modown (bifenox) can control pigweed, lambsquar- ters, and smartweed and provide some control of velvet- leaf. Combinations with Treflan or Lasso will improve grass control. Modown 4F rates are 3 to 4 pints per acre when used alone in a preemergence application or pre- plant incorporated with Lasso or Treflan. For preemer- gence applications with Lasso, the rate is 2lA to 3 pints per acre. For preplant incorporation, the application should be made within 2 to 3 days of planting, and in- corporation should place the herbicides evenly into the top 1 to 2 inches of soil. Do not apply Modown after soy- beans begin to emerge.

Soybeans may show stunting from Modown, especially from preemergence use followed by cold, wet soil condi- tions during early growth stages. Injury symptoms are cupping and crinkling of the first few leaves. Soybean injury is usually not reflected in yield.

Furloe Chloro IPC ( chlorpropham ) can be preplant incorporated with Treflan or Vernam; or it can be ap- plied preemergence by itself or with Lasso to improve smartweed control. Preplant application should be done within a few days of planting soybeans, and incorporation should distribute the herbicide uniformly in the top 1 to 2 inches of soil. The rate in sequential or tank mix combi- nations is 2 to 3 quarts of Furloe 4E per acre. Furloe 20G is used preemergence at 10 to 15 pounds per acre.

Preemergence Herbicides

Lorox (Iinuron) is best suited to silt loam soils that contain 1 to 3 percent organic matter. Do not apply to very sandy soils. Lorox controls broadleaf weeds better than grass weeds. It does not control annual morning- glory, and control of cocklebur and jimsonweed is vari- able. Accurate and uniform application, and proper rate selection are necessary to minimize the risk of crop injury. Tank-mix combinations allow the use of a reduced rate of Lorox to decrease the risk of soybean injury, but may also decrease the degree of weed control.

Lorox is registered in tank-mix combinations with Amiben, Lasso, Dual, Prowl, or Surflan to improve grass control. The rate of Lorox in these combinations is 1 to 1 Vi pounds of Lorox 50W or xh to % pint of Lorox 4L on silt loam soils with less than 3 percent organic matter.

Surflan (oryzalin) can control annual grasses, pig- weed, and lambsquarters if there is adequate rainfall. You should rotary hoe to control emerging weeds if ade- quate rain does not fall within 7 days after application. Do not use on soils of more than 5 percent organic mat- ter. The rate is 1 to 2 pounds per acre of Surflan 75W (3A to VA quarts 4L) used alone or % to Wi pounds of Surflan 75W in combinations. Surflan can be tank mixed with Amiben, Lorox, Lexone, Sencor, or Dyanap to im- prove broadleaf weed control. Surflan may cause stem callousing, which can lead to soybean lodging. Do not allow Surflan to contact the soybean seed.

Prowl can be applied preemergence in combination with Amiben, Lexone, Lorox, or Sencor. When applied to the soil surface, Prowl may cause stem callousing, which can lead to soybean lodging. (See preplant section for more information.)

Dyanap (dinoseb plus naptalam) can be applied to soybeans from the time they are planted until the uni- foliate leaves of the seedling unfold and expose the growing point. A tank mix of Dyanap plus Lasso, Dual, or Surflan is registered to improve grass control. Dyanap can also be tank mixed with Lasso plus Sencor. The Dyanap rate is 4 to 6 quarts per acre for preemergence application.

Goal (oxyfluorfen) is labeled for preemergence use in no-till soybeans with paraquat in a two-way combina- tion and with paraquat plus Lasso in a three-way combi- nation. Rates in these combinations are 1 quart of Goal, 1 pint of paraquat, and 2 quarts of Lasso per acre.

Postemergence Herbicides

In the past, most farmers have placed primary empha- sis on controlling weeds early with preplant or preemer- gence applications, and have considered postemergence applications as a backup measure when control from earlier treatments was not adequate. Research suggests, however, that soybean yields will probably not be reduced if weeds are controlled within 3 to 4 weeks after planting. The trend toward reduced tillage could encourage greater emphasis on postemergence treatments.

Postemergence herbicides are most effective when their

11

use is part of a planned program, and when they are applied while the weeds are young and tender. They should not be considered simply an emergency treatment. It is especially important to use timely treatments when using postemergence herbicides in narrow-row soybeans. Postemergence herbicides are often the best choice for controlling certain problem weeds such as cocklebur, annual morningglory, and volunteer corn.

Basagran (bentazon) can control many broadleaf weeds, such as cocklebur, jimsonweed, and velvetleaf. It is weak on pigweed, lambsquarters, and annual morning- glory. It can be used for control of yellow nutsedge and Canada thistle but not of annual grasses.

The suggested rate for Basagran is % to 1 quart per acre, depending on weed size and species. Application should be done when weeds are small (2-3 inches) and actively growing. These conditions usually exist when the soybeans are in the unifoliate to second trifoliate stage. Spraying during warm sunny weather can also improve performance. Do not spray if rain is expected within 8 hours. Use a minimum of 20 gallons of water per acre in order to get complete weed coverage. Adding a crop-oil concentrate to Basagran may increase performance, par- ticularly on yellow nutsedge, velvetleaf, and morning- glory, but may cause some soybean injury. Morningglory up to 10 inches long can be controlled with the addition of 2 fluid ounces of 2,4-DB with Basagran. Do not add crop oil when mixing with 2,4-DB.

Blazer (acifluorfen) can be used to control annual morningglory, pigweed, black nightshade, and jimson- weed. Under ideal conditions it may also help control small escaped annual grasses. The rate is 2 pints of Blazer 2S per acre when broadleaf weeds are at the 2- to 4-inch stage and actively growing. Cocklebur and morningglory control can be improved with the addition of 2 fluid ounces of 2,4-DB (Butyrac or Butoxone). Application should be made when cocklebur and morningglory are not more than 10 to 12 inches tall or long and soybeans have at least five trifoliate leaves.

Blazer is primarily a contact herbicide. Leaf burn often occurs, but the crop usually recovers within 2 to 3 weeks. Suggested spray volumes are 20 to 40 gallons of water per acre applied with a spray pressure of 40 psi. Surfactants or crop oil concentrates are not recommended with Blazer. Do not spray if rain is expected within 6 hours.

Dyanap (dinoseb plus naptalam) can be applied to soybeans after the second trifoliate leaf opens until beans become 20 inches tall. Two to 3 quarts per acre is recom- mended for control of cocklebur, jimsonweed, smartweed, and annual morningglory less than 3 inches tall and four quarts per acre if weeds are 3 to 6 inches tall. A split application of 2 quarts at the second trifoliate stage followed by 2 quarts 10 to 14 days later is recommended for severe weed infestations.

Best results are obtained by using high pressure (40 to 60 pounds per square inch) and 8 to 10 gallons of water per acre. Use 5 gallons of water for aerial applica- tion. Although leaf burn can occur, the crop usually re- covers within 2 to 3 weeks with little or no yield loss.

Do not apply Dyanap to wet soybean foliage or if rain is expected within 6 hours. Do not add a surfactant.

Amiben (chloramben) can be applied at 5 to 6 quarts per acre when soybeans are in the cracking to second trifoliate stage of growth. This treatment may control or suppress velvetleaf or smartweed that is less than 4 inches tall.

Alanap (naptalam) plus 2,4-DB can be used for emer- gency control of cocklebur and giant ragweed. Apply when soybeans are about 18 inches tall but before mid- bloom stage. Rates are 2 to 3 quarts of Alanap plus 3 to 4 fluid ounces of Butyrac 200 or Butoxone SB per acre. A nonionic surfactant should be added at the rate of 2 quarts per 100 gallons of water. Rescue is a formulated mixture of Alanap plus 2,4-DB for use at 2 to 3 quarts per acre. Expect some soybean injury from this treatment. Ground application should be at 10 to 20 gallons of spray volume per acre. Use hollow-cone nozzles positioned 18 to 24 inches above the soybeans or weeds. Maintain spray pressure at 40 to 50 psi.

Hoelon (dichlofop) can control volunteer corn and small annual grass weeds. Application should be made when volunteer corn has all emerged but is less than 10 inches tall. Annual grass weeds should be in the one- to four-leaf stage. The rate for volunteer corn is 2% to 3'/3 pints per acre and for annual grasses is 2 to 3Vs pints per acre. In most cases use Vi gallon of Hoelon per acre. Thorough spray coverage is important, so use a minimum of 20 gallons of water per acre and a minimum spray pressure of 30 psi. Do not tank mix Hoelon with other postemergence herbicides. Hoelon is a restricted use herbicide.

Poast (sethoxydim) is a selective postemergence her- bicide for grass control in soybeans. It was labeled for experimental use in 1982 and will probably be given full registration in 1983. If registered, Poast can be used at the rate of 1 pint per acre on annual grasses, volunteer corn, and shattercane. Oil concentrate should be used at the rate of 1 pint per acre for aerial application or 2 pints per acre for ground application. Use a minimum of 20 gallons of water per acre with 40 psi pressure for ground application and a minimum of 5 gallons of water for aerial application. Higher water volumes are sug- gested if grass foliage is dense. Poast may also be used for control of johnsongrass (see section on specific weed problems). Do not tank mix Poast with postemergence broadleaf herbicides as grass control will be reduced.

Fusilade (fluazif op-butyl) is a selective postemergence herbicide for grass control in soybeans. It was labeled for experimental use in 1982 and may be given full registration in 1983. Fusilade is used at the rate of V4 pint per acre on annual grasses up to 10 inches tall and at Vi pint per acre on volunteer corn up to 36 inches tall. Fusilade will also control johnsongrass (see section on specific weed problems). Oil concentrate should be used at the rate of 1 to 2 pints per acre for ground application and 1 gallon per 100 gallons of water for aerial applica- tion.

12

Vistar (mefluidide) may be used for postemergence control of johnsongrass in soybeans south of Highway 1-70 in Illinois. Vistar 2S is used at the rate of 1 pint per acre after the second trifoliate stage of soybeans, and when johnsongrass is less than 15 inches tall. A second application may be necessary 3 to 4 weeks after the first application but no later than 60 days prior to harvest. A nonionic surfactant should be used at the rate of 1 to 2 pints per 100 gallons of spray solution.

Johnsongrass is not immediately killed by Vistar, and usually about 10 days will elapse before the leaves turn brown. Maximum results will be seen in about 3 weeks. Soybeans may also show some injury from Vistar, as indi- cated by leaf crinkling or slight growth suppression.

Roundup (glyphosate) can be applied through several types of selective applicators — recirculating sprayers, wipers, or rope wicks. This application is particularly useful for control of volunteer corn, shattercane, and johnsongrass. Roundup may also suppress hemp dogbane and common milkweed. Weeds should be a minimum of 6 inches above the soybeans. Avoid contact with the crop. Equipment should be adjusted so that the lowest spray stream or wiper contact is at least 2 inches above the soy- beans. For calibration of equipment, refer to Round- up label. For recirculating sprayers and wipers, use the rates given on the label. For rope-wick applicators, mix 1 gallon of Roundup in 2 gallons of water.

Basal-Direcfed Postemergence Herbicides

Several herbicides have been approved for directed application to the bases of soybean plants for control of late-emerging weeds. The soybeans must be at least 8 inches tall and weeds less than 2 to 4 inches tall. Nozzles must be mounted in a fixed position and accurately adjusted to spray only the lower one-third to one-fourth of the soybean plant. Precise positioning of the spray is essential to prevent serious soybean injury. Special equip- ment such as oiling shoes or gauge wheels is usually specified. Read the label for correct rates and equipment and for precautions. Some of the herbicides cleared for basal-directed sprays are:

Lorox (linuron) alone or plus 2,4-DB or Premerge

Sencor (metribuzin) alone or plus 2,4-DB

Lexone (metribuzin)

Butoxone SB or Butyrac 200 (2,4-DB)

Paraquat

Premerge

Goal

Most of these herbicides call for application before bloom or the midbloom stage of soybeans. Some of these treatments can be applied a second time.

Basal-directed sprays are not very popular in Illinois because of the special equipment and degree of precision required for application. In Illinois the major weeds in soybeans usually begin growing at the same time and often at about the same rate as the soybeans. Thus it is often difficult to establish a suitable difference in height between the soybeans and weeds unless an early herbicide

treatment has been used. If the early treatment is effec- tive, a later directed treatment may not be needed.

Paraquat Harvest Aid

Paraquat and Gramoxone are registered for drying weeds in soybeans just before harvest. For indeterminate varieties (most Illinois varieties), apply when 65 percent of the seed pods have reached a mature brown color or when seed moisture is 30 percent or less. For determinate varieties, apply when at least one-half of the leaves have dropped and the rest of the leaves are turning yellow.

The rate is V2 to 1 pint of Paraquat or Gramoxone per acre. The higher rate is for cocklebur. The total spray volume per acre is 2 to 5 gallons for aerial application or 20 to 40 gallons for ground application. Add 1 quart of nonionic surfactant per 100 gallons of spray. Do not pasture livestock within 15 days of treatment, and remove livestock from treated fields at least 30 days before slaughter.

Herbicides for Sorghum

Atrazine may be used for weed control in sorghum (grain and forage types) or sorghum-sudan hybrids. Ap- plication may be made preemergence or postemergence. Plant seed at least 1 inch deep. Do not use preplant or preemergence on soils with less than 1 percent organic matter. Incorporated treatments may show injury if rain- fall occurs prior to or shortly after sorghum emergence.

Injury may occur when sorghum is under stress from unusual soil or weather conditions or when rates are too high. The rate of application for preplant and preemer- gence is 2 to 3 pounds of atrazine 80W per acre. The postemergence rate is 2SA to 3% pounds 80W per acre. Rotational crop recommendations and weed control are the same as for atrazine used in corn. Failure to control fall panicum has been a major problem.

Ramrod (propachlor) may be used alone or in com- bination with atrazine, Milogard, Bladex, or Modown for sorghum. Ramrod will improve grass control, but rates must not be skimpy, especially on soils relatively low in organic matter. For specific rates, consult the label.

Dual (metolachlor) or Dual plus atrazine (or Bicep) can be used on sorghum seed that has had the Concep- seed treatment. These herbicides will improve grass con- trol more than atrazine applied alone.

Milogard (propazine) has better sorghum tolerance than atrazine, but grass control is not as good. Only corn or sorghum may be planted in rotation within 12 months after treatment.

2,4-D may be applied postemergence for broadleaf control in 4- to 12-inch tall sorghum. Use drop nozzles if sorghum is more than 8 inches tall. Rates are similar to those for use in corn (see section on corn herbicides) .

Banvel can be applied postemergence until sorghum is 15 inches tall or 25 days after emergence. The rate is V2 pint per acre. Do not graze or feed treated forage or

13

silage prior to the mature grain stage. Sorghum may be injured by Banvel.

Specific Weed Problems

Yellow Nutsedge

Yellow nutsedge is a perennial sedge with a triangular stem. It reproduces mainly by tubers. Regardless of the soil depth at which the tuber germinates, a basal bulb develops 1 to 2 inches under the soil surface. A complex system of rhizomes (underground stems) and tubers de- velops from this basal bulb. Yellow nutsedge tubers begin sprouting about May 1 in central Illinois. For the most effective control, soil-applied herbicides should be incor- porated into the same soil layer in which this basal bulb is developing.

For soybeans, a delay in planting until late May allows time for two or three tillage operations to destroy many nutsedge sprouts. Tillage helps deplete food reserves in nutsedge tubers. Row cultivation is helpful. Preplant ap- plications of Lasso, Dual, or Vernan will also help.

Lasso (alachlor) applied preplant incorporated at 3 to 4 quarts per acre (V2 quart more than for surface- applied rates) often gives good control of nutsedge.

Dual (metolachlor) can be applied at 2 to 3 pints of 8E per acre to control nutsedge. Preplant treatment is preferred to treatment at the preemergence stage.

Vernam 7E (vernolate) applied preplant at 3 '/a pints per acre is also effective against yellow nutsedge. Imme- diate incorporation is necessary with Vernam.

Basagran (bentazon) is a postemergence treatment that can also help control nutsedge in soybeans. One quart per acre can be applied when nutsedge is 6 to 8 inches tall. A split application (two treatments) of Basa- gran has also been registered. Addition of a crop-oil con- centrate to Basagran may improve performance.

For corn, preplant tillage before nutsedge sprouts is of little help in control. Timely cultivation gives some con- trol, but a program of herbicides plus cultivation has provided the most effective control of nutsedge.

Several preplant treatments are available. Eradicane (EPTC) or Sutan+ (butylate) at 43/4 to IVi pints per acre are effective for control of yellow nutsedge in corn. They must be incorporated immediately. Lasso or Dual applied in corn as for soybeans can also be quite effective.

The combinations of Lasso, Dual, Sutan + , or Eradi- cane incorporated with atrazine may give better control of nutsedge while also controlling broadleaf weeds.

Atrazine or Bladex (cyanazine) is used as a postemer- gence spray to control emerged yellow nutsedge when it is small. Split applications of atrazine plus oil have been more effective than single applications. Basagran can be used in corn in a manner similar to that for soy- beans. Lorox (linuron) directed postemergence spray has also given some control.

Johnsongrass

Johnsongrass can reproduce both from seeds and by

rhizomes. Both chemical and cultural methods are needed to control johnsongrass rhizomes.

Much of the rhizome growth occurs after the johnson- grass head begins to appear. Mowing, grazing, or culti- vating to keep the grass less than 12 inches tall can reduce rhizome production significantly.

Control of johnsongrass can also be improved with tillage. Fall plowing and disking bring the rhizomes to the soil surface, where many of them are winter-killed. Disking also cuts the rhizomes into small pieces, making them more susceptible to chemical control.

Johnsongrass rhizomes can be controlled or suppressed using certain herbicides in various cropping programs. Several preplant-incorporated herbicides can provide control of johnsongrass seedlings in soybeans or corn (see the table at the end of this publication) .

Treflan (trifluralin), Prowl (pendimethalin), or Basa- lin (fluchloralin) used in a 3-year soybean program has been fairly successful in controlling rhizome johnson- grass. They are used at IV2 to 2 times the normal rate each year for 2 years, and then either at the normal rate, or another suitable herbicide is used the third year before resuming a regular cropping sequence. Thorough pre- plant tillage and incorporation are necessary for satis- factory control. Be certain not to plant such crops as corn or sorghum following application of these herbicides at the higher rates.

Fusilade (fluazif op-butyl) can control johnsongrass in soybeans. Apply Vi pint per acre when the weed is at most 36 inches tall. A split application of Vi pint plus V2 pint applied about 3 weeks apart may give better control.

Poast (sethoxydim) can control johnsongrass in soy- beans. Apply IV2 pints plus 1 quart crop oil concentrate per acre when the johnsongrass is 24 inches tall. A second application of 1 pint per acre may be required.

Eradicane (EPTC) or Sutan+ (butylate) will sup- press rhizome johnsongrass in corn when used at a rate of l¥i pints per acre as a preplant-incorporated treat- ment. However, this increase in rate also increases the risk of corn injury.

Dalapon can be used to treat emerged johnsongrass before planting corn or soybeans. Apply 5 to 7 pounds per acre after the grass is 8 to 12 inches tall. Plow or disk after 3 days and then delay planting corn or soybeans at least 1 week. See the label for specific intervals.

Dalapon can also be used to control johnsongrass after wheat that is not double cropped or undersown with a legume. A combination of mowing, timely dalapon ap- plication, and tillage has provided quite effective control.

Roundup (glyphosate) can be used as a spot treat- ment to control johnsongrass in corn, soybeans, or sor- ghum. Apply 2 to 3 quarts when johnsongrass has reached the boot to head stage and is actively growing. Use of Roundup in wick or recovery-type sprayers is effective for control of johnsongrass in soybeans. (See section on postemergence herbicides for soybeans.)

Roundup may be applied in small grain stubble when

14

johnsongrass is in the early head stage. Fall applications should be made before the first frost. At least 7 days should be allowed after treatment before tillage.

Quackgrass

Quackgrass is a perennial grass with shallow rhizomes. Most preemergence herbicides will not control it.

Atrazine is quite effective when used as a split appli- cation in corn. Apply 2Vz pounds of atrazine 80W per acre in the fall or spring and plow 1 to 3 weeks later. Another 2V2 pounds per acre should be applied as a pre- plant or preemergence treatment. Postemergence appli- cation is usually less effective. A single treatment with 3% to 5 pounds per acre can be applied either in the spring or fall 1 to 3 weeks before plowing, but the split application usually gives better control of annual weeds. If more than 3 pounds of atrazine is applied per acre, plant no crops other than corn or sorghum the next year.

Eradicane (EPTC) can be used to suppress quack- grass in corn where more flexibility in cropping sequence is desired. A rate of 4% pints per acre of Eradicane 6.7E can be used on light infestations, while IVs pints per acre is suggested for heavier infestations. There is some risk of corn injury, especially at the higher rate. A tank mix with atrazine should improve control.

Fusilade (fluazif op-butyl) is registered and will be labeled for quackgrass control in soybeans at % pint per acre. Apply when quackgrass is 6 to 8 inches high.

Poast (sethoxydim) can be applied in soybeans at the rate of 2'/2 pints plus 1 quart of crop oil concentrate per acre when quackgrass is 8 to 12 inches tall. A second application of IV2 pints per acre or a cultivation may be required for season-long control.

Dalapon can be applied to quackgrass 4 to 6 inches tall in the spring at a rate of 8 pounds per acre. Plow after 4 days and delay planting corn for 4 to 5 weeks. Up to 15 pounds of dalapon per acre may be used in the fall.

Roundup (glyphosate) can be used for controlling quackgrass before planting either corn or soybeans. Apply

2 to 3 quarts per acre when quackgrass is 8 inches tall and actively growing (fall or spring). Delay tillage for

3 or more days after application.

Canada Thistle

Canada thistle is a perennial weed that has large food reserves in its root system. There are several varieties of Canada thistle. They differ not only in appearance but also in their susceptibility to herbicides.

2,4-D may give fairly good control of some strains. Rates will depend on where the thistle is growing. For example, higher rates can be used in grass pastures or in noncrop areas than can be used in corn.

Banvel (dicamba) often is a little more effective than 2,4-D and may be used alone or in combination with 2,4-D. Banvel can be used as an after-harvest treatment in wheat, corn, or soybean fields at 2 quarts per acre.

Fall treatments should be applied before killing frosts. For best results thistles should be fully emerged and actively growing.

Atrazine and oil applied postemergence has been fairly effective in controlling Canada thistle in corn. Make the application before thistles are 6 inches tall.

Basagran (bentazon) can be used for control of Can- ada thistle in soybeans or corn when the thistles are 8 to 12 inches tall. Apply 3A to 1 quart per acre in a single application, or for better control make two applications of % to 1 quart per acre each, 7 to 10 days apart.

Roundup (glyphosate) can be used at 2 to 3 quarts per acre when Canada thistle is at or beyond the early bud stage. Fall treatments must be applied before frost for best results. Allow 3 or more days after application before tillage.

Amitrole or Amitrole-T effectively controls Canada thistle, but can be used only in noncrop areas. Tordon (picloram) gives good control of Canada thistle, but soybeans and most other broadleaf plants are extremely sensitive to it. Use only on noncropland.

Black Nightshade

Black nightshade is an annual weed that has become an increasing problem for Illinois soybean growers. The principal problem is caused by the berries, which are about the same size as soybeans at harvest. They contain a sticky juice that can gum up a combine.

Black nightshade does not present much of a problem in corn but should be controlled nonetheless to help re- duce production of the weed's seed. Herbicides such as atrazine, Bladex, Banvel, Lasso, and Dual are helpful for controlling this weed in corn.

It can be helpful to plant suspect fields to corn rather than soybeans. If soybeans must be planted, plant suspect fields last. This makes the full strength of the herbicide last longer to help control the midseason flush. Preemer- gence applications usually maintain control longer than those that are preplant incorporated.

For control in soybeans, Lasso, Dual, or Amiben at full rates or a combination of Amiben or Lorox with Lasso or Dual is helpful. Suspect fields should be monitored and a postemergence application of Blazer considered.

Harvest-aid sprays generally do not solve the problem because they do not make the berries fall before the soy- beans are harvested.

Additional Information

Not all herbicides and herbicide combinations avail- able are mentioned in this publication. Some are rela- tively new and are still being tested. Some are not con- sidered to be very well adapted to Illinois or are not used very extensively. For further information on field crop weed control, consult your county Extension adviser or write to the Department of Agronomy, N-305 Turner Hall, 1102 S. Goodwin Avenue, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801.

15

Relative Effectiveness of Herbicides on Major Weeds

This chart gives a general comparative rating. Under unfavorable conditions, some herbicides rated good or fair may give erratic or poor re- sults. Under very favorable conditions, control may be better than indicated. Type of soil is also a very important factor to consider when se- lecting herbicides. Rate of herbicide used also will influence results. G = good, F = fair or variable, and P = poor.

Grasses

Broadleaf Weed

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SOYBEANS

Preplan!

Treflan, Prowl, Basalin

F-G

G

G

G

G

G

G

F

P

F-P

P

P

G

P

G

P

P

P-F

P

Sencor, Lexone +

dinitroaniline

F

G

G

G

G

G

G

F

P

F

F

F-G

G

P

G

G

F

G

F-G

Vernam

F

G

G

G

G

G

G

F-P

F

F-P

P

P

F

P

G

P

P

P

F

Preplan! or Preemergence

Amiben

F-G

G

F-G

F-G

F-G

F

F

P

P

P

P

P-F

G

F-G

G

F-G

F

F-G

F

Lasso, Dual

G

G

G

G

G

P-F

P-F

P

F-G

P

P

P

F

F-G

G

P-F

P

P-F

P

Lasso or Dual +

Sencor or Lexone

F

G

G

G

G

P

P

P

F

P

F

F-G

G

F

G

F

F

G

F-G

Lasso or Dual +

Lorox1

F

G

G

G

G

P

P

P

P-F

P

F

F

G

F-G

G

G

F

G

F-G

Lorox1

F

F

F

F

F

P

P

P

P

P

F

F

G

F

G

G

F

G

F-G

Modown, Goal

F

F

F

F

F

P

P

P

P

F-P

P

F

G

F

G

F

P

G

F

Sencor, Lexone1

F

F

F

F

F

P

P

P

P-F

P

F

F-G

G

P

G

G

F

G

F-G

Postemergence

Basagran

F-G

P

P

P

P

P

P

P

F

P-F

G

G

F-P

P

P

F

F

G

F-G

Blazer

F

P-F

P

P-F

P

P

P

P

P

F-G

F

G

F-P

F-G

G

F

F

G

P

Dyanap

F

P

P

P

P

P

P

P

P

F-G

G

G

F-G

P-F

F-G

F

F

F

P

2,4-DB

P-F

P

P

P

P

P

P

P

P

F-G

G

P-F

F

P

F

F

F

P

P

Hoelon

G

G

G

F-P

F

P

P

G

P

P

P

P

P

P

P

P

P

P

P

Poast, Fusilade

G

G

G

G

G

G

G

G

P

P

P

P

P

P

P

P

P

P

P

CORN

Preplant

Sutan+, Eradicane

F-G

G

G

G

G

F-G

F-G

F-G

P

P

P

P-F

F

G

P

P

P

F

Sutan+ or Eradicane

+ atrazine, Bladex

F-G

G

G

G

G

F-G

F-G

F-G

F-G

F-G

G

G

G

G

G

F

G

F-G

Princep + atrazine

G

F-G

F-G

F

F

P

P-F

P

F-G

F-G

G

G

G

G

G

G

G

F

Preplant or Preemergence

Atrazine

G

F-G

F

P

P

P

P

F

G

F-G

G

G

G

G

G

G

G

F-G

Banvel + Lasso

or Dual

F-G

G

G

G

G

P

P

F

P-F

F

F-G

G

G

G

G

F

G

F

Bladex

F-G

F-G

F-G

F-G

G

P

P

P

F

F-G

G

G

G

F

G

F-G

G

F

Bladex + atrazine

F-G

F-G

F

F

F-G

P

P

P

F-G

F-G

G

G

G

G

G

F-G

G

F-G

Lasso, Dual

F-G

G

G

G

G

P-F

P-F

F-G

P

P

P

F

F

G

P-F

P

P-F

P

Lasso or Dual + atrazine

or Bladex

F-G

G

G

G

G

P

P

F-G

F-G

F

G

G

G

G

G

F

G

F

Prowl + atrazine

or Bladex1

F

G

G

G

G

F

F

P

F-G

F

G

G

G

G

G

F

G

F-G

Ramrod + atrazine

or Bladex1

G

G

G

F-G

F

P

P

P-F

F-G

F

G

G

G

G

G

F

G

F

Ramrod

G

G

F

F-G

F

P

P

P-F

P

P

P

F

P

G

P

P

P

P

Postemergence

Atrazine + oil

F-G

F-G

G

P

P

P

P

F

G

G

G

G

G

G

G

F

G

G

Banvel

F-G

P

P

P

P

P

P

P

G

G

G

G

G

G

G

G

G

F

Basagran

G

P

P

P

P

P

P

F

P-F

G

G

F-P

P

P

F

F

G

F-G

Bladex

F-G

G

G

F

F-G

P

P

F

F

F-G

G

F

G

F-G

G

F

G

F-G

2,4-D

F

P

P

P

P

P

P

P

G

G

F

G

F

G

G

G

P-F

F-G

1 Preemergence only

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