Historic, Archive Document Do not assume content reflects current scientific knowledge, policies, or practices. * 4 y * ‘ fe ‘ ‘ t" hy é« tee Fe i . t ih 2 a hil t = R1SA8e12Ce13 6HS11S2 \6 C (RRR } eRRS SF SeRebaSme eraer eeaeae r3 ete s toye nrireensfaetc ec eERr e reinse ae Sete R chia na : re. ee | a “ aN‘ | “ eaa e i :; : ao sae ACSeeReRe PUWnANM s T DR to SURG uesacseae et eed ATA ANTEATER ASS RATER A Cooperative Extension Publication, 1996™ NEW ENGLAND nen | AUG 3 | 199g GUIDE TO WEED CONFER IN CORN | Prepared by F. J. Himmelstein, University of Connecticut. Reviewed by S.C. Bosworth, University of Vermont, P.C. Bhowmik, University of Massachusetts, J.R. Mitchell, University of New Hampshire; J. Jemison, University of Maine; W.M. Sullivan, University of Rhode Island. HERBICIDE-RESISTANT WEED MANAGEMENT eo litedii n this bulletin.a re registered : There are a number of factors to consider when d for suggested uses according to developing a weed management program that fits your and state laws— a nd . farming operation. When choosing a herbicide program, decisions should be based on potential weed problems, (o rice: Tt‘ is unlawful to usea ny crop and herbicide rotation, injury potential, tillage system and available application equipment, soil texture and organic matter, potential environmental hazards and cost. One common problem farmers have noticed is that many of their old standard herbicide programs have been less effective in recent years. When herbicide rates were WARNING: Pecide: are poisonous. increased the weed problems remained. Most of these problems are due to herbicide resistance. Resistance follow the directions and safety . describes a condition whereby a plant's growth is not € = on labels. _ Handle carefully and affected by a herbicide application. The occurrence of herbicide-resistant weeds has been on the increase during the past decade. Herbicide resistance in weeds has containers. as”| required by your. ‘state - . reached a serious level in many agricultural areas around ions. Do not contaminate soil, forage, = the world. Presently at least 55 species of weeds have See telephone — LT Tops, or. water sources. * or location of your nearest. POISON : been documented with resistance to triazine 4x a TION CENTER. . herbicides. Aproximately 100 weed species have been reported to possess resistance to one family of herbicides or another. Increases in triazine resistant ns “using” ae e Use ee weeds in field corn in New England has increased ertified in conformity with standards - herbicide use on many farms. Practices that increased rt by” ‘state and Federal regulations. the probability of triazine resistant weeds in New SSO, DUAL, PRINCEP, BLADEX, England included: |. Fields were in continuous corn; 2. and GRAMOXONE EXTRA are All fields were continuously treated with atrazine year ; Restricted Use herbicides in all after year; 3. Use of postemergence herbicides were not herh erbicides may be Restricted lUs e common; 4. Cultivation was rare; and 5. Most of the com acreage is continuously used for silage and manure from com silage fed to cows was returned to the field. wa Cooperative Extension, these universities and the U.S.Department of _ Agriculture cooperating, offer education for everyone without regard to race, co or, national origin, sex, religion, age or handicap. Cooperative Extension is an equal opportunity employer. Issued in furtherance of Cooperative xtension work in agriculture and home economics, Acts of May 8 and June 4 30, 1914; the United States Department of Agriculture and the following _ Extension Services cooperating: KM. Kerr, Director, Cooperative Extension System, University of P.J. Home, Director, Cooperative Extension, University of Connecticut, Storrs New Hampshire, Durham _ V.H. Holyoke, Director, Cooperative Extension, University of RH. Miller, Director, Cooperative Extension, University of Rhode Island, Kingston _ Maine, Orono RG. Helgeson, Director, Cooperative Extension, University of L.K. Forcier, Director, Cooperative Extension System, University of :M assachusetts, Amherst Vermont, Burlington HERBICIDE-RESISTANT WEED MANAGEMENT - continued Management strategies to minimize further development than two consecutive applications of herbicides with the of herbicide-resistant weeds includes: same mode of action against the same weed may increase the probability of developing resistance unless SCOUTING: Scout fields regularly to identify problem other effective control practices are included in the weeds. Respond quickly to changes in weed populations management system. Combinations of herbicides that to restrict the spread of plants that may have developed include multiple modes of action will prevent an increase resistance. Fields should be scouted at least two times a in herbicide resistant weeds. year. Corn fields should be scouted when the corn is 3 to 4 inches tall in order to determine the need for With the recent registration of a number of new corn additional weed control such as cultivation or for use herbicides the use of both preemergence and of postemergence herbicides. Scouting at the end of the postemergence herbicides in rotation will reduce the season can help make decisions about future weed potential for development of herbicide-resistant weeds. control measures particularly if preemergence herbicides When using herbicide resistant and herbicide tolerant will be used the following year. Choose the right crops, more than two consecutive applications of management strategy for weed control before the season herbicides with the same mode of action should not be starts. If you know from past years which weeds need used against the same weed unless other effective control controlling and have scouted fields during the past practices are included in the management system. Refer growing season you should have enough information to to Table 5, Resistence Potential of Field Corn Herbicides select the best management strategy suited to the weed According to Mode of Action for assistance in forming problem. new weed management strategies. MECHANICAL CONTROL: Mechanical weed control TRIAZINE SPECIAL REVIEW can be an important component of many weed control programs. Cultivation cannot be substituted for chemical The triazines are one class of herbicides that has been controls, where reduced till and no-till cropping systems subjected to use restrictions within the past few years in are practiced. Where selective cultivation is possible, order to minimize potential adverse effects on ground however, the use of a rotary hoe, spring tine or rolling and surface water quality. The Environmental Protection — cultivator, shovel (sweep) cultivator or similar Agency (EPA) initiated a Special Review of the triazine — implements will aid in reducing the potential for herbicides that includes atrazine, cyanazine (BLADEX) development of herbicide resistant weeds. and simazine (PRINCEP). This process allows the EPA — to review additional evidence and reports associated with — \ If selective cultivation is used, it should be done early. the benefits and risks of this group of pesticides for Rotary hoes and spring tine cultivators are effective for which the agency has already granted a registration. controlling small weeds (less than 1 inch tall), and should be operated at a relatively high speed (7 to 10 DuPont Agricultural Products announced on August 2, | mph) on a fairly dry soil. For maximum effectiveness a 1995, that it was changing the label on cyanazine, to rotary hoe should be used when the weeds are just reduce the amount of active ingedient used per acre. | emerging from the soil. Cultivation with a shovel, sweep, DuPont also announced it will stop selling the herbicide or rolling cultivator is more effective on larger weeds in 1999 and that all use in the U.S. will stop at the end than a rotary hoe, and can also be effective when weeds of 2002. The company chose to phase out its herbicides, are very small. BLADEX and EXTRAZINE II, rather than risk the potential disruption to customers through changes in the CROP ROTATION: A key management stategy to use restrictions or a full cancellation. combat weeds is crop rotation. Certain weeds are commonly associated with certain crops. Rotating a crop Ciba Crop Protection, manufacturer of atrazine and can help reduce certain weeds that may become a simazine had decided to continue its commitments to problem under continuous cropping systems. these two products. The company indicated its _ confidence in the safety of these herbicides when applied |i HERBICIDE ROTATION: When crop rotation is not following the label restrictions currently in place. EPA feasible, a viable alternative for weed resistance expects to make a preliminary decision on atrazine and management would be to rotate herbicides from different simazine in 1996. A final decision is not expected until |f families with different modes of action. Making more 1997. POSTEMERGENCE HERBICIDES of annual grass and broadleaf weed species. Pursuit 2AS Postemergence weed control for corn in New England is applied at 4 fluid ounces per acre (1/4 pint) for all has been practiced very little due to both the lack of methods of application: early preplant, preplant materials available in past years, and the lack of incorporated, preemergence and _ postemergence knowledge and confidence by farmers concerning these (including minumum and no-till). Connecticut weed herbicides. The number of new postemergence herbicides control trials in 1994 and 1995 have shown excellent currently available has significantly increased. Use of control of large crabgrass, fall panicum, giant foxtail, postemergence herbicides presents the opportunity to common lambsquarter, redroot pigweed, and velvetleaf withhold preemergence treatments that are preventative was obtained with Pursuit applied either preemergence or in nature until weeds emerge, determine the weed species early postemergence. Good suppression of common present, and select the herbicide and rate required ragweed was also obtained with early postemergence _ according to the situation. These herbicides are not applications of Pursuit, however, a tank mix with either broadspectrum but are highly selective on certain weed Banvel or Clarity at 1/4 pint resulted in superior control | _ species. Therefore, when using postemergence herbicides, of common ragweed. Available premixes of Pursuit with appropriate scouting information for weeds is necessary. other herbicides include Contour, a combination of Such information will target the best time to control Pursuit and atrazine, and Resolve, a combination of weeds based on herbicide efficacy and the length of time Pursuit and dicamba. Commercial hybrids are available. eee key weeds can remain in the crop without causing _ economically important reductions in yields. Effective Sethoxydim resistant corn hybrids (SR-corn) have also | scouting enables optimization of the rate and timeliness been developed. Sethoxydim is the active ingredient in of the herbicide treatments. This concept offers Poast herbicide which is currently being evaluated alone _ significant advantages in herbicide savings but has not and in combination with other herbicides for weed loSneee, bmee n a widely adopted grower practice either due to time control with these new hybrids. Use of sethoxydim constraints from other farming operations, fear of not resistant corn hybrids will allow Poast to be used for _ being able to return to the field at the appropriate time of postemergence grass weed control in corn. Commercial | application due to unfavorable weather conditions, or the hybrids are expected to be available during the 1996 | need to change field planting patterns to avoid running growing season. Glufosinate-resistant or Liberty Link | over corn when applying postemergence treatments. com hybrids (GR-corn) are another new development. Glufosinate is the active ingredient in Liberty herbicide. Most of these herbicides also offer an environmental LibertyLink hybrids (GR-corn) may be available in 1997. advantage due to the low use rates. Furthermore, many Corn hybrids resistant to Roundup (glyphosate) and other are prepackaged and, thus, would greatly reduce the herbicides are being developed. likelihood of incorrect application rates and spills eeiae e ee | associated with mixing of materials. Use of these low INCREASING CORN PLANT POPULATIONS AND | dose compounds will substantially lower the total amount NARROW ROW PLANTINGS FOR WEED | of herbicide needed for weed control. Due to the large MANAGEMENT number of new postemergence herbicides now available Field corn competes with weeds for light, water, and it may be possible to use only postemergence products nutrients. Herbicides are needed to control weeds roenee f or weed control on many fields in the future. Farmers primarily during the period before the corn leaf canopy | going this route will need to closely manage their closes. The relative competitive ability of field corn can | program, particularly where grass weeds are present. be enhanced by increasing plant population. Faster canopy closure with higher plant populations will mean HERBICIDE RESISTANT FIELD CORN OPTIONS less herbicide than significantly recommended. Studies Herbicide manufacturers and seed companies have joined have shown that field corn planted in 15 inch rows had forces to commercialize corn hybrids that can be used greater silage and grain yields than corn planted in 30 with certain herbicides. This allows growers to have inch rows. In addition, field corn planted in 15 inch rows _another tool for weed management. With herbicide required significantly less herbicide for effective weed resistant corn comes more postemergence herbicides control than in the 30 inch rows. In one study herbicides options that allows more selectivity when problems were cut 75 percent on no-till cornfields without occur. The use of newer and safer chemistry without sacrificing yields when the number of corn plants were / concern for residual activity or groundwater doubled by narrowing the row spacing from 30 to 15 contamination is an important grower option. inches. Increasing plant populations in corn fields in IMI-corn refers to imidazolinone resistant (IR) or tolerant either 30 or 15 inch rows may enable a reduction in the (IT) corn. This allows the use of the imidazolinone rate of herbicide required for effective weed control but | herbicide, Pursuit, on corn. Pursuit controls a wide range may require changes to existing harvesting equipment. PROTECTING GROUND AND SURFACE WATER Nationwide studies continue to show the potential for Effective herbicide management depends upon weed size, groundwater contamination by herbicides may be greater weed species identification and soil moisture. Herbicide than was commonly believed a decade ago. Concerns selection and rate can be substantially adjusted as these involving herbicides in groundwater, have substantially parameters change. Significant rate reductions are heightened public awareness regarding the safety of the possible if a susceptible species predominates in a field water for drinking and other domestic uses. This problem and the correct herbicide is used to control the problem particularly raises public concern in the Northeast where weed. A high level of weeds producing seeds during the agricultural and suburban areas are situated in close growing season will likely lead to undesireable weed proximity to one another. Contamination may pose health levels in subsequent years. However, on many fields, risks to certain individuals. In such cases, alternate water weeds have decreased as a result of efficient weed sources must be found or filtration systems must be used. control and competive crops. As a consequence, the Property values will generally decline when domestic amount of herbicides can be reduced substantially. water sources are contaminated with pesticides. Alternative weed management practices which When manufacturers develop herbicide label rates, they significantly reduce the use of herbicides with high risk choose the rate possible that will control weeds under a potential for soil leaching or runoff in watershed areas variety of conditions. Little information has been will likely reduce the potential for future contamination previously available in New England on the use of of ground and surface waters. Use of herbicides with reduced herbicide rates to lower the impact of herbicides lower leaching potential, choosing the lowest dosage on production costs and environmental contamination. rates based on soil texture and organic matter content, Connecticut IPM weed control trials have shown that use of cultivation where possible, and increasing the significantly reduced rates work better under favorable adoption of new weed control technologies such as use weather conditions, but in the drought years, many of either postemergence herbicides on standard corn herbicides, particularly soil applied herbicides may not hybrids or herbicide tolerant hybrids will provide provide effective weed control even at labeled rates. effective, economical and environmentally sound weed That's not to say the herbicide labels are wrong. management alternatives in field corn. The effect of Herbicide labels provide optimum use rates for each soil herbicides on water quality will continue to be a major type under favorable growing conditions. Depending on public issue. the particular herbicide or weed problem, maximum labeled use rates may be needed. Custom applicators and USING IPM STRATEGIES FOR EFFECTIVE, dealers generally recommend combinations of herbicides ECONOMICAL, AND ENVIRONMENTALLY at listed labeled rates since they are responsible for SOUND WEED MANAGEMENT following up with that farmer and taking care of any There are a number of factors to consider when possible problems. It would be tough for the dealer to — developing a weed management program. Program carry the weight of reduced rate recommendations. They — decisions should be based on potential weed problems, are just safer sticking with the manufacturer's labeled crop and herbicide rotation, injury potential, tillage rate. system, available application equipment, soil texture and organic matter, potential environmental hazards and cost. The focus of the Connecticut IPM Field Corn Program Increases in the cost of herbicides coupled with the is to show growers that the same degree of weed control || environmental concerns regarding agricultural chemicals can be obtained with the lower use rates as the full — have placed additional burdens on production costs and labeded rates, particularly when more than one herbicide | agricultural viability. Financial hardships currently facing is necessary for broadspectrum weed control. Connecticut — many farmers have led to considerations that farm IPM weed trials have shown reduced herbicide rates are profitability might be increased by reducing the rate or effective under a wide variety of weed density and use of herbicides if effective, less costly alternatives were weather conditions. In many studies, half the labeled use available. Integrated Pest Management (IPM) strategies rates of a number of herbicide combinations for field can provide growers with effective weed control yet com provided the same degree of weed control as the — reduce the amount of herbicides required to provide this full use rates. Its not as simple as just using less. control. IPM plays an important role in protecting water Extensive research and experimentation is involved to — resources. Regular monitoring of crop conditions and provide reduced rate herbicide recommendations. For weed populations helps a producer make the most more information regarding effectiveness of reduced rate informed production decision. Herbicide applications combinations contact Dr. Frank Himmelstein, University | based on economic thresholds optimize grower profits of Connecticut Cooperative Extension System, 24 Hyde | while reducing environmental hazards. Avenue, Vernon, CT. 06066. (860) 875-3331. Table 1. Relative effectiveness of some common corn herbicides E E z ebe ss| b5e , : acn hee | ee So iaek OU = = ® sy o = = Sb erat o s lie mae e A f° 8 Bay fers 4 3 g = SP ee aa 3 ® a + a o 5 5 eae 5 & an ~ we fy =» OC 2 _ PREEMERGENCE | ATRAZINE P G/E N N C/E) RBE/GIEP/F P/PeorP F N F P - BLADEX N G/E N N G/E F G FIG F/G G P N P DUAL N N N F/G P N G/E G/E G G p N F FRONTIER N N N 56 eae N GE G/E -G GE. «Fr N F HARNESS N N F/G G/E F ly G/E > G/E goa GE, + Ger aPiFawaN F LASSOMT WN N F G P N GEXAG/E G G/E 2 N F _ SURPASS N N F/G *G/E* OF P GIESSG/E G/E G/E P/F N F _ PRINCEP P G/E N N GEE F/G G F/G G HG* =P P/F F j PROWL N r or = GTP G/E G GiE’ VG LG = Pern i% - BROADSTRIKE _ +DUAL N FIG FIG G F GE GE GE G G P/F N F .P OSTEMERGENCE ACCENT Per YP/Per te G/EPeP F G BiG 2aG/E" °G/E'™ E G/ET=P _ATRAZINE G G/EreorN N GE F/G F P P F N F F/G ~BANVEL Pa” 9G Gi GE? -G/E* —F /G. N N N N N N N ' BASAGRAN P G/E F/G F Eis a N N N N N N F/G ~ BEACON G GE elf/iG, ¢G/E E G iv E et ea Le en G P BLADEX N F/IG N N G/E, “F/Gee G HG + HG. EG. ..P iv P ~ BUCTRIL B/iGe »Gip wG/Eo* F F G N N N N N N N ree AGH MG EMG/E WE aGuaqP mR eer Po OPE P/F PPP : PERMIT F Wo eer Ge Se Gir YG/E®" N N N N N N G/E | RESOURCE F HG G/E G/fE F/G GE N N N N N N N _ STINGER N F/G. SP P E E N N N N N N N ~ TOUGH E b/GaeG/EesG/EeeP/Es, vwP /EracN N N N N N F/G ‘ 2,4-D E PiGaaGil G/E G/F. F/G aeN N N N N N N _ PREPLANT INCORPORATED | ERADICANE N E PE? UH/G P PF Pees .GE «= GE .G/E. _G P/F G/E | SUTAN N P P (Ce P/F G/E G/E G/fE G/F G N G/E TR=triazine resistant, N=no control, P=poor control, F=fair control, G=good control, E=excellent control. | The table above represents the relative effectiveness of herbicides on individual weeds. Effectiveness ratings are based on labeled application rates and correct weed size and stage of growth. Results may differ with variations in weed size, temperature, soil or water ph, or adverse rainfall and soil moisture conditions. Combinations of two herbicides are often necessary to improve the spectrum of weeds controlled. Connecticut weed control trials have shown below labeled rates of herbicides in tank mixtures may result in similar weed control as the labeled tank-mix rates. > SPECIFIC WEED PROBLEMS IN CORN WEED SITUATION PRODUCT AND RATE/ACRE ! I. CRABGRASS, FALL PANICUM, AND OTHER ANNUAL GRASSES DUAL 8E 1) 2" pis: FRONTIER 7.5EC 1 - 1.25 pts. HARNESS 7EC 1.75 - 2 pts. LASSO MT 4ME 3.5 - 4.0 pts. PROWL 3.3EC 3 - 3.6 pts. SURPASS 6.4EC 2-2 1/4 pts Comments and cautions: Dual, Frontier, Harness, Lasso, and Surpass will not control emerged weeds at time of planting. Prowl may be applied preemergence to early postemergence up to the 4-leaf stage of corn, and weeds are no more than 1 inch tall. Corn must be planted at least 1.5 inches deep to avoid Prowl injury. Do not incorporate Prowl. Il. ESCAPED ANNUAL GRASSES/ POSTEMERGENCE ANNUAL GRASS CONTROL OPTIONS ACCENT 75WDG ZI3%OZ BEACON 75WDG 0.76 oz Comments and cautions: For best results, apply Accent when annual grass weeds such as barnyardgrass, fall panicum, and foxtails are no more than 2-4 inches tall (1-5 leaves) prior to tillering. Accent has provided effective crabgrass control in Connecticut field trials when applied soon after emergence, (1-4 leaves) prior to tillering. Crabgrass control may be significantly reduced with Accent as the plant matures. Fall panicum is the only annual grass weed controlled with Beacon when applications are made to fall panicum less than 2 inches tall, 2-3 leaves. Accent or Beacon applications should include either a crop oil concentrate applied at 1 gallon per 100 gallons of spray solution or a nonionic surfactant (1 qt/100 gal). Accent or Beacon should be applied when the corn is 4-24 inches in height or with drop nozzles if corn is too tall. Read herbicide label regarding herbicide or insecticide combinations. I. TRIAZINE-RESISTANT LAMBSQUARTERS BROADSTRIKE+DUAL 7.67EC 1.75 - 2 pts. HARNESS 7EC 2 pts. PROWL 3.3EC 3 - 3.6 pts. SURPASS 6.4EC 2 1/4 pts. Comments and cautions: Broadstrike+Dual has displayed crop injury under cold wet conditions particularly on sandy-gravelly soils. Injury has also occurred in soils with pH <5.9 with high organic matter, high soil pH (>7.8), and when in-furrow insecticide applications are used. See comments for Prowl in Section I. IV. TRIAZINE-RESISTANT PIGWEEDS BROADSTRIKE+DUAL 7.67EC ja" ="2 pts: DUAL 8E 1.5 - 2 pts. HARNESS 7EC Lf SPD piss LASSO MT 4ME 3.5 - 4 pts. PROWL 3.3EC 3 - 3.6 pts. SURPASS 6.4EC 2-2 1/4 pts. Comments and cautions: See comments for Broadstrike+Dual in Section III. See Comments for Dual, Harness, Lasso, Prowl and Surpass in Section I. 1The application rates suggested in this section are based on average conditions for fine sandy loam soils (coarse) with over 3% organic matter. On fields with finer textured soils (medium and fine), higher rates of some herbicides may be needed. The application rates given for each herbicide are for a specific weed problem when applied alone. Combinations of two herbicides may be needed to achieve control of both grass and broadleaf weeds. The lower rates are generally suggested when tank mixtures are needed. Refer to the product for the appropriate rates. Some products listed may not be registered in all of the New England States. Only use products registered in your State. The following table gives only one formulation for each product listed. Some products may have more than one type of formulation. Choose the formulation that best fits your weed control program. Do not exceed the labeled rates for a given soil type, since crop injury may occur. 6