This publication is an important resource for UF/IFAS Extension agents. It provides specific information on herbicide options and application requirements on newer 2,4-D formulations to the appropriate stakeholders. The publication also provides information to the growers and pesticide applicators for safer use of newer low-volatility formulations of 2,4-D herbicide products on Enlist crops.
Enlist crops are a relatively new herbicide-resistant crop technology that allows the application of 2,4-D choline to Enlist Cotton, Enlist Corn, or Enlist E3 Soybean. Currently, Enlist One and Enlist Duo herbicide products are the only products with 2,4-D choline formulationthat are labeled on Enlist Crops because this formulation has very low volatility compared to the traditional 2,4-D formulations (such as amine, esters, etc.). Still, the concern with off-target injury to sensitive crops remains. Therefore, the herbicide label should be followed carefully. Proper precautions need to be in place to mitigateinjury to sensitive crops. Numerous crops grown in Florida (soybean, cotton, snap bean, peanut, watermelon, cantaloupe, tomato, pepper, blueberry, pecans, etc.) are sensitive to 2,4-D. Care should be taken during planning and herbicide application. Moreover, due to endangered species concerns and current label restrictions, Enlist Duo herbicide cannot be applied innumerous Florida counties (Brevard, Broward, Charlotte, Collier, DeSoto, Glades, Hardee, Hendry, Highlands, Hillsborough, Indian River, Jackson, Lee, Manatee, Martin, Miami-Dade, Okeechobee, Orange, Osceola, Palm Beach, Polk, Santa Rosa, Sarasota, and St. Lucie Counties). However, Enlist One herbicide can be applied tank-mixed with glyphosate product; the counties listed above cannot use the premix Enlist Duo.
Auxin herbicides have historically been associated with off-target injury potential. Therefore, the Enlist One and Enlist Duo labels provide details and important information for applying these products safely. This includes information on product selection, application rates, application timing, approved tank-mix partners, approved nozzles and pressure combinations, wind speed and spray application parameters, and sprayer cleanout procedures. Likewise, the Florida Department of Agriculture and Consumer Services (FDACS) Organo-Auxin Rule (“Organo-Auxin Herbicides: Restrictions and Prohibitions,” https://www.flrules.org/gateway/ruleno.asp?id=5E-2.033) outlines the guidelines for using auxin-type herbicide products. This rule must be followed while applying these herbicides. In addition, FDACS has made available the “Suggested Pesticide Recordkeeping Form for Organo-Auxin Herbicides” (https://forms.fdacs.gov/13328.pdf) for the pesticide applicators’ use.
Herbicide Product Selection and Application
Currently, there are two products containing 2,4-D choline that can be applied on 2,4-D-tolerant crops (Enlist Crops). Enlist One only contains 2,4-D choline, while Enlist Duo contains a premix of 2,4-D choline plus glyphosate. The product selection can be made according to the individual field situation and weed problems. Enlist One does not provide any level of grass weed control, while Enlist Duo does provide grass weed control because it contains glyphosate. Other products containing 2,4-D (2,4-D amine, LV4, 2,4-D ester, etc.) cannot be applied on 2,4-D-tolerant crops (Enlist Crops).
Table 1. Information on Enlist One and Enlist Duo herbicide rate and application timing on Enlist crops.
There are only certain herbicide or pesticide products that are compatible with Enlist One or Enlist Duo herbicides. Only products recommended in the Enlist One or Enlist Duo label can be safely tank-mixed. If incompatible products are tank-mixed, then it can result in a significant increase of 2,4-D volatility and off-target crop/plant injury. The list of recommended tank-mix products for Enlist One and Enlist Duo herbicides can be found below.
- Enlist One: https://www.enlist.com/en/herbicides/approved-tank-mix/enlist-one-tank-mix-products.html
- Enlist Duo: https://www.enlist.com/en/herbicides/approved-tank-mix/enlist-duo-tank-mix-products.html
Using Ammonium Sulfate
Ammonium sulfate (AMS) is a recommended product for Enlist One or Enlist Duo application. Appropriate AMS products can be used as water conditioning agents. Unlike 2,4-D choline products, AMS should never be used with XtendiMax, Engenia, or Tavium (which are newer dicamba formulation products).
A 30-feet downwind buffer to sensitive area/crops is required for Enlist One and Enlist Duo applications. Application swath cannot be initiated within 30 ft of any downwind sensitive areas. Even with the appropriate buffer distance in place, the safe practice to prevent off-target injury is not to spray when wind is blowing towards a sensitive crop.
Only qualified nozzles should be used with the corresponding pressure ranges for Enlist One or Enlist Duo herbicide applications. The use of unqualified nozzles can result in a higher percentage of driftable particles and cause significant off-target injury. Detailed information on Enlist One and Enlist Duo herbicide allowed nozzles and pressure combinations can be found below. Note that use of any nozzle not specifically approved and listed on these websites would be considered a misuse.
- Enlist One: https://www.enlist.com/en/herbicides/qualified-nozzles/enlist-one-tank-mix-products/enlist-one-allowable-nozzles.html
- Enlist Duo: https://www.enlist.com/en/herbicides/qualified-nozzles/enlist-duo-tank-mix-products/enlist-duo-allowable-nozzles.html
In the presence of wind, increased boom height increases the travel distance for a spray droplet. Higher boom height can increase the potential for drift. With appropriate boom height, the droplet is less likely to travel longer distances, thus reducing drift potential. A maximum boom height of 24 inches above the target weed/crop canopy is recommended for applying Enlist One or Enlist Duo herbicides.
Wind Speed and Direction
Even though the Enlist One and Enlist Duo herbicide labels include a maximum wind speed of 15 mph, it is essential to pay close attention to wind speed and direction requirements for the Florida Organo-Auxin Rule. The Florida Organo-Auxin Rule prohibits application of synthetic organo-auxin herbicides (such as 2,4-D, dicamba, etc.) if wind is blowing towards sensitive crops at the speed/gusts above 10 mph (FDACS 2021). At higher wind speed, spray droplets can move longer distances and increase drift potential.
Temperature Inversion Condition
Enlist One and Enlist Duo herbicides should never be sprayed if low-laying temperature inversion condition exists. Spraying during temperature inversion conditions poses significant risk for off-target herbicide movement and crop injury. Cool conditions near the ground, a low-laying layer of fog, or presence of dew represent temperature inversion conditions. The temperature inversion condition is usually common during early morning or the later part of the day but can also occur during the afternoon.
After applying Enlist One or Enlist Duo herbicide, the sprayer should be thoroughly cleaned following the triple-rinse procedure outlined in the label or the Enlist Product Use Guide. The entire sprayer, including tank, boom, hoses, connections, nozzles/screens, etc., should be cleaned properly to avoid spray contamination. If another tank-mixed product has a more stringent sprayer cleanout requirement, then follow that procedure. Do not let herbicide solution sit in the sprayer overnight or for extended hours.
According to the FDACS Organo-Auxin Rule, recordkeeping is mandatory for two years for synthetic organo-auxin herbicides if applied to more than five acres in a 24-hour window (this is a common scenario for crop field applications). The recordkeeping should contain the information outlined in the rule, which can be found below.
- FDACS Organo-Auxin Rule: https://www.flrules.org/gateway/ruleno.asp?id=5E-2.033
- FDACS Suggested Pesticide Recordkeeping Form for Organo-Auxin Herbicides: https://forms.fdacs.gov/13328.pdf
Corteva AgriScience. 2021. “EnlistTM Weed Control System – 2021 Product Use Guide.” Accessed June 23, 2022. https://www.enlist.com/content/dam/dpagco/enlist/na/us/en/files/fact-sheets/DOC-Enlist-PUG-NA-US.pdf
FDACS. 2021. "5E-2.033 Organo-Auxin Herbicides: Restrictions and Prohibitions." Florida Department of State Florida Administrative Code & Florida Administrative Register. Accessed June 23, 2022. https://www.flrules.org/gateway/ruleno.asp?id=5E-2.033