Weed Management in Transgenic, Herbicide-Resistant Cotton 1

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1 SS-AGR-13 Weed Management in Transgenic, Herbicide-Resistant Cotton 1 J. Tredaway Ducar, J.A. Ferrell, G.E. MacDonald, and B. J. Brecke 2 Transgenic or herbicide-resistant cotton allows the use of herbicides over-the-top of cotton that would injure conventional or non-transgenic varieties. These transgenic varieties are genetically altered to tolerate herbicides that would normally kill or severely injure conventional varieties. Although transgenic crops have become a controversial subject, the use of these varieties has enabled economical and efficient weed management. The transgenic cotton varieties which are commercially available include Liberty Link cotton and Roundup Ready cotton. Using transgenic varieties can expand weed management options while providing a more convenient and effective method of weed control because early post emergence directed applications can be avoided. It is important to be aware that will kill or severely injure Liberty Link cotton and glufosinate (Ignite) will kill or severely injure Roundup Ready cotton. Both herbicides will kill or severely injure non-transgenic conventional cotton. It is imperative that careful record keeping be implemented so that all varieties used can be identified and proper herbicide application can be ensured. Liberty Link Cotton Liberty Link cotton is a technology that allows the application of Ignite herbicide, glufosinate, over the top of green foliage. Glufosinate is considerably different from. Glufosinate inhibits glutamine synthase enzymes and toxic levels of ammonia quickly accumulate in plant tissues. Liberty Link technology results from a gene-insertion event. This gene produces a protein that attaches to glufosinate and deactivates the herbicide. Since these process are radically different from Roundup Ready technology - applications of Ignite to Roundup Ready Cotton will result in death of the crop. Likewise, can not be safely applied to Liberty Link cotton. 1. This document is SS-AGR-13, one of a series of the Agronomy Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Revised April Original written by J. Tredaway Ducar, revised by J.A. Ferrell and G. E. MacDonald. Please visit the EDIS Website at 2. J. Tredaway Ducar, former assistant professor, Agronomy Department; J.A. Ferrell, assistant professor, Agronomy Department; G. E. MacDonald, assistant professor, Agronomy Department; and B. J. Brecke, professor, Agronomy Department, West Florida Research and Education Center-Milton, FL; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition. Use herbicides safely. Read and follow directions on the manufacturer's label. All chemicals should be used in accordance with directions on the manufacturer's label. The Institute of Food and Agricultural Sciences (IFAS) is an Equal Employment Opportunity - Affirmative Action Employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / Larry R. Arrington, Interim Dean

2 Weed Management in Transgenic, Herbicide-Resistant Cotton 2 Application timing - The Liberty Link Cotton allows an effective broadleaf herbicide to be applied postemergence over-the-top of cotton. Ignite can be applied to Liberty Link cotton from emergence until early bloom. A spray volume of 15 gallons/a or more with an operating pressure of 40 psi or greater is recommended for use with flat fan nozzles with a 50 mesh screen. It may be applied postemergence without visible crop injury, yield reduction, or delay in maturity. No more than 80 oz/a can be made per growing season. Libery Link cotton can not legally be grown south of Tampa Florida (Route 60). Herbicide Program Ignite has no soil residual activity and will only control weeds that have emerged at time of application. A traditional preplant-incorporated or preemergence herbicide, such as Prowl, Treflan, Zorial or Cotoran may be desired to enhance the level of weed management. The suggested use rate for Ignite is oz/a depending on weed size and species. No more than 40 oz per application, or 80 oz per season, may be applied to cotton. See the label for weed size and rate information. Ignite may be applied from emergence to early bloom. Cultivation should be delayed 5 to 7 days following application. Ignite is rainfast in 4 hours. Therefore, if rain is eminent, applications of Ignite should be delayed. Ammonium sulfate at 3 lb/a has been shown to enhance the activity of Ignite (Table 1). Ignite fair to good grass activity; therefore, the addition of a herbicide for grass control may be desired. Postemergence grass control can be provided by Select. Select should be applied alone to avoid antanonism with Ignite. For other difficult to control weeds, such as pigweeds, Ignite may be tank-mixed with Staple. * NOTE - Liberty Link cotton use is limited to the area located north of Tampa (Florida Route 60). Also, Ignite will kill Roundup Ready Cotton, and vice versa. Rotation restrictions - Ignite requies a 120 day restriction for all rotational crops, except for wheat, barley, sorghum and other crops contained on the label. Roundup Ready Cotton Roundup Ready cotton has been genetically modified to tolerate (Glyphomax, Glyphomax Plus, Ultra Touchdown and Roundup Weathermax, etc.). There are several products containing, but all are not labelled for use on Roundup Ready cotton. Consult your county agent or the labels; use only those products that are labelled for use on Roundup Ready cotton. Glyphosate provides control of broadleaf weeds, grasses, and nutsedges. It must be applied at the proper timing to avoid crop injury (See application timing). Application timing - Proper application timing is essential to avoid injury in Roundup Ready cotton. Glyphosate can be applied overtop of Roundup Ready cotton anytime from cotton emergence until the fourth true-leaf stage. Applications of over the top of cotton are prohibited after the cotton exceeds the four-leaf stage, except in salvage situations. These late (after 4 leaf) overtop applications will result in bloom abortion and loss of yield. Roundup can be applied post-directed until layby. Consult the label for the suggested use rate. Glyphosate can be applied twice over the top of Roundup Ready cotton when the following criteria are met. The two applications must be at least 10 days apart, there must be two nodes of new growth between the applications, and the second application must be made before cotton exceeds the four-leaf stage. Directed application must minimize contact with the cotton plant when applied after the four-leaf stage. Glyphosate can be applied late season after 20% of the bolls have cracked. At least 7 days between application and harvest are necessary. Herbicide Program Preemergence - An advantage to the Roundup Ready system is the option to eliminate preemergence herbicides. Early season weed competition should be considered when determining the weed management program. This competition may be avoided by an early application,

3 Weed Management in Transgenic, Herbicide-Resistant Cotton 3 i.e. one leaf stage. If a preemergence herbicide is used, the application can be delayed until the three-or four-leaf stage. Consideration should be given to total cotton acreage, weed spectrum, and the acceptable risk level when weather delays postemergence applications. Preemergence herbicides are a type of insurance policy and often maintain a grower's peace of mind. If there is any doubt that two applications cannot be applied prior to the four-leaf stage, a soil-applied preemergence herbicide should be utilized in the program to provide early-season control of annual grasses and Florida pusley (Table 2). Tank Mixes Glyphosate does not provide any soil or residual activity. Therefore, tank mixtures can be utilized for broad spectrum weed control and/or residual activity. A tank mix of Staple and improves control of hemp sesbania, spreading dayflower, and morningglory species (all except tall). A premix of this combination is available under the trade name Staple Plus. Table 3 and Table 4 can be helpful in choosing the herbicide that is best suited for your particular situation.

4 Weed Management in Transgenic, Herbicide-Resistant Cotton 4 Table 1. Herbicide Program for Liberty Link Cotton. Trade Name and Broadcast Rate/Acre of Commercial Product Ignite (32-40 oz) Common Name and Broadcast Rate/Acre of Active Ingredient glufosinate Remarks Apply to Liberty Link varieties only. May be applied from cotton emergence to early bloom. Provides excellent control of morningglory, cocklebur and ragweed, but less effective on perennial weeds and grasses. Adequate spray coverage is essential for weed control. Do not apply more than 40 oz/a per application or 80 oz/a/yr. Not for use south of Tampa, FL (Route 60). Addition of ammonium sulfate (3 lb/a) often improves weed control. NOTE ROUNDUP READY COTTON WILL NOT TOLERATE IGNITE APPLICATIONS. Ignite Dual Magnum or Cinch (1.33 pt) glufosinate S-metolachlor Apply to Liberty Link varieties only. Do not apply Dual Magnum preemergence or severe injury will occur. Dual Magnum will provide residual control of grasses (except Texas panicum) and certain broadleaf weeds. Dual Magnum will only control weeds that have not emerged. Dual Magnum will provide good control of tropical spiderwort. Leaf burning may occur after application. Ignite Staple (0.6 oz) glufosinate pyrithiobac (0.032 lb) Apply only to Liberty Link varieties only. Staple provides additional broadleaf control (particularly pigweeds) as well as residual soil activity. Table 2. Herbicide Program for Roundup Ready Cotton. Trade Name and Broadcast Rate/ Acre of Commercial Product Glyphomax, Glyphmax Plus, Ultra Touchdown, Roundup Ultramax and others Common Name and Broadcast Rate/Acre of Active Ingredient ( lb) Remarks Apply only to Roundup Ready varieties. Avoid drift to non-roundup Ready cotton and other sensitive crops. Apply in 5-20 gallons of spray per acre over the top from crop emergence through four-leaf stage. Directed application is required if cotton has more than four leaves. May be applied overtop twice up to the fourth true-leaf stage; separate applications by at least 10 days and two nodes of new growth.

5 Weed Management in Transgenic, Herbicide-Resistant Cotton 5 Table 2. Herbicide Program for Roundup Ready Cotton. Trade Name and Broadcast Rate/ Acre of Commercial Product several Dual Magnum or Cinch (1.33 pt) Glyphosate Staple (0.6 oz) or Staple Plus (several) Direx 4F (1-1.5 pt) Common Name and Broadcast Rate/Acre of Active Ingredient (0.75 lb) S-metolachlor (0.75 lb) pyrithiobac (0.032 lb) ( lb) diuron ( lb) Remarks Apply only to Roundup Ready varieties. Do not apply Dual Magnum preemergence or severe injury will occur. Dual Magnum will provide residual control of grasses (except Texas panicum) and certain broadleaf weeds. Dual Magnum will only control weeds that have not emerged. Dual Magnum will provide good control of tropical spiderwort. Leaf burning may occur after application. Apply only to Roundup Ready varieties. See above comments. Apply over the top from one to four true leaves. Do not apply overtop after cotton exceeds four-leaf stage. Staple provides additional broadleaf control as well as residual soil activity. APPLY POST-DIRECTED TO ROUNDUP READY CULTIVARS ONLY. Use 1 pt of Direx on cotton 8 to 12 inches and 1.5 pt of Direx on cotton greater than 12 inches. Add surfactant according to label. Do not add other spray additives. Compared to alone, this combination controls larger morningglories and provides residual control of small-seeded broadleaf weeds, such as pigweed. However, the tank mix may give less grass control than alone. Do not reduce the rate of. Table 3. Estimated effectiveness of Recommended Herbicides on Common Weeds in Florida Cotton. 1 Weed Name Treflan or Prowl Cotoran or Meturon (Fluometuron) Karmex, Direx Command Zorial Time of Application PPI PRE PRE PRE PPI amaranth, Palmer F G F P F anoda, spurred P P P E G barnyardgrass E G F E E beggarweed, Florida P G G F-G G bermudagrass P P P P P burgherkin P F-G F P G carpetweed G G G G G citronmelon P F-G F P F cocklebur, common P G P F P copperleaf, hophornbeam P E E E E

6 Weed Management in Transgenic, Herbicide-Resistant Cotton 6 Table 3. Estimated effectiveness of Recommended Herbicides on Common Weeds in Florida Cotton. 1 Weed Name Treflan or Prowl Cotoran or Meturon (Fluometuron) Karmex, Direx Command Zorial Time of Application PPI PRE PRE PRE PPI cowpea P P - P P crabgrass E G G G E crotalaria, showy P G G - - croton, tropic P G - E G-E crowfootgrass E G G F G dayflower, spreading P P P - - eclipta P F F F F goosegrass E G G G G jimsonweed P G G-E G F johnsongrass (rhizome) P P P P P johnsongrass (seedling) G F F G G lambsquarters, common G E G G G morningglory, cypressvine P G - F-G F morningglory, entireleaf P G - F-G F morningglory, ivyleaf P G - F-G F morningglory, pitted P G - F-G F morningglory, purple P G - F-G F morningglory, smallflower P G - F-G F morningglory, tall P G - F-G F nutsedge, purple P P P P P-F nutsedge, yellow P P P P P-F panicum, fall E P P G G panicum, Texas E P P F F-P pigweed, redroot E E E P F-G pigweed, smooth E G-E G P F-G poinsettia, wild P p P F P purslane, common E F E G E pusley, Florida E G G G G-E ragweed, common P G G G G redweed P G G G G sandbur, field E G G F-G - senna, coffee P P P F P sesbania, hemp P F P F P sicklepod P G P P F sida, prickly P E F G E signalgrass, broadleaf E G G E G smartweed, Pennsylvania P P F E F spurge, spotted P P F P F starbur, bristly P G P P - velvetleaf P P F E F

7 Weed Management in Transgenic, Herbicide-Resistant Cotton 7 Table 3. Estimated effectiveness of Recommended Herbicides on Common Weeds in Florida Cotton. 1 Weed Name Treflan or Prowl Cotoran or Meturon (Fluometuron) Karmex, Direx Command Zorial Time of Application PPI PRE PRE PRE PPI 1 Estimated effectiveness based on rates recommended in this report. Effectiveness may vary depending on factors such as herbicide rate, size of weeds, time of application, soil type, and weather conditions. Weed Control Symbols: E = % control; G = 80-90% control; F = 60-80% control; P = less than 60% control. Time of Application Symbols: PPI = preplant incorporated; AC = cracking stage; EP = early postemergence; POT = postemergence over the top; PRE = preemergence; -- = insufficient observations. Herbicide recommendations in this report are contingent upon their registration by the Environmental Protection Agency. If a registration is canceled, the herbicide would no longer be recommended. Table 4. Estimated effectiveness of Recommended Herbicides on Common Weeds in Florida Cotton (continued). 1 Weed Name Staple Ignite 2 Glyphosate 3 Fluometuron MSMA Caporol MSMA Cobra MSMA Diuron Time of Application POST POST POST PDS PDS PDS PDS amaranth, Palmer G F E G E E E anoda, spurred E - G P P F - barnyardgrass P P-F F F G F G beggarweed, Florida G G G-F G G G E bermudagrass P P F-G P P P F burgherkin G G G P G G G-E carpetweed G - G G G G G-E citronmelon - G G-E P F-G G G cocklebur, common G G-E E G G G E copperleaf, P - G E E E G-E hophornbeam cowpea G - G-E G G G G crabgrass P G E G G G G crotalaria, showy P F-G G G G G G croton, tropic P G E G G G E crowfootgrass P G E G G F G dayflower, spreading G-E - F F F E - eclipta - - G F F F G goosegrass P F-G G-E G G G G jimsonweed E E G-E E G-E G-E E johnsongrass (rhizome) P P G-E P P F-G G johnsongrass (seedling) P P-F G-E G G G G lambsquarters, common P E G-E G G F G-E morningglory, G G-E F-G G-E G-E G-E G-E cypressvine morningglory, entireleaf G G-E F-G G-E G-E G-E G-E morningglory, ivyleaf G G-E F-G G-E G-E G-E G-E

8 Weed Management in Transgenic, Herbicide-Resistant Cotton 8 Table 4. Estimated effectiveness of Recommended Herbicides on Common Weeds in Florida Cotton (continued). 1 Weed Name Staple Ignite 2 Glyphosate 3 Fluometuron MSMA Caporol MSMA Cobra MSMA Diuron Time of Application POST POST POST PDS PDS PDS PDS morningglory, pitted G G-E F-G G-E G-E G-E G-E morningglory, purple G G-E F-G G-E G-E G-E G-E morningglory, smallflower G G-E F-G G-E G-E G-E G-E morningglory, tall G G-E F-G G-E G-E G-E G-E nutsedge, purple P P-F G P P-F P G nutsedge, yellow P P-F F P-F P-F P-F F panicum, fall P G-E E G G G panicum, Texas P G-E E G G G G pigweed, redroot E F E G E E E pigweed, smooth E F E G E E E poinsettia, wild F-G G G-E F P G F-G purslane, common F E E F G G E pusley, Florida P-F F-G F-G G G G F ragweed, common P E E G G G G redweed G P E G G G F sandbur, field P P E G G G F-G senna, coffee E G E P F P G sesbania, hemp E G-E P-F P F F G sicklepod P-F G E G G F-G G-E sida, prickly F G G F G G G-E signalgrass, broadleaf P G E G G G G smartweed, Pennsylvania E - G P P F E spurge, spotted F - G P P E E starbur, bristly G G G G G G G velvetleaf E G G F F G G-E 1 Estimated effectiveness based on rates recommended in this report. Effectiveness may vary depending on factors such as herbicide rate, size of weeds, time of application, soil type, and weather conditions. Weed Control Symbols: E = % control; G = 80-90% control; F = 60-80% control; P = less than 60% control. Time of Application Symbols: PPI = preplant incorporated; EP = early postemergence; POT = postemergence over the top; PRE = preemergence; -- = insufficient observations. 2 For use on Liberty Link varieties only. 3 For use on Roundup Ready varieties only. Herbicide recommendations in this report are contingent upon their registration by the Environmental Protection Agency. If a registration is canceled, the herbicide would no longer be recommended.