• Crop Protection
  • Jun 19, 2019

Dicamba 101: Questions From the Field

Close up of four rows of growing soybeans
Low-volatility dicamba products have a new federal label and more specific state restrictions this season. Concerned farmers are wondering what that might mean for applications. Here are answers to some of the most common dicamba questions I’ve been hearing in the field.
What’s the difference between 2,4-D and dicamba?
Dicamba and 2,4-D are both Group 4 herbicides with the same mode of action. Both herbicides are growth regulators, but they cannot be used interchangeably in-season over crops. The technology that makes each crop tolerant to 2,4-D or dicamba is specific for each of those herbicides. Applying dicamba on 2,4-D tolerant crops will damage or kill them, and vice versa. Label requirements, including application rates and plant-back restrictions are also different for each herbicide. Always consult the label for the herbicide product you plan to use to be sure you’re following all requirements.
How can I differentiate between 2,4-D and dicamba damage in soybeans?
Dicamba and 2,4-D can both damage sensitive crops. Research shows that just 1/20,000 of a labeled rate of dicamba can cause cupping in non-tolerant soybeans. We’re still learning about 2,4-D sensitivity in soybeans, but it appears that soybeans are more sensitive to dicamba than 2,4-D. The extent of herbicide damage depends on a variety of factors, including the timing of application and the rate of herbicide applied. Yield loss is more likely if herbicide damage occurs during reproductive growth stages. In that case, pods could be aborted or damaged. Visual symptoms of dicamba damage include leaf cupping. 2,4-D damage in soybeans can result in leaf drooping, leaf strapping, elongated leaves, stem twisting and stem callouses.
What is a drift-reduction agent and is it necessary?
A majority of tank mix combinations of in-season dicamba require a drift-reduction agent (DRA). OnTarget® adjuvant is a specifically formulated DRA for ultra- and extra-coarse nozzles that are used in dicamba applications and can reduce driftable fine spray particles by up to 50 percent.1 It is designed to improve overall weed control by helping with droplet spreading and canopy deposition.
Is a DRA enough to adequately control dicamba drift?
Studies done at the WinField United Innovation Center indicate that adding specific adjuvants in addition to recommended DRAs can reduce the number of small droplets in a spray solution even more than by using a DRA alone. InterLock® adjuvant is a drift and deposition aid that can help further reduce the number of driftable fine droplets, and it improves spray deposition into the crop’s canopy. Adding InterLock with OnTarget in the spray tank, along with a water conditioner, can reduce driftable fines by 60 percent.1 The relative cost of using both products in the tank mix is much less than the cost of the dicamba herbicide, so it’s a good investment to ensure you’re getting the most from your herbicide application.
Why should I be concerned about the pH of my dicamba tank mix?
The new label for low-volatility dicamba products suggest that applicators test tank-mix pH to ensure it remains above 5.0. Research has shown that adding glyphosate with dicamba in a tank mix can lower the pH of the solution. That creates an acid, which can increase the risk of volatility when the spray is applied. We’ve found that adding MAX-IN® Boron plant nutrient to the dicamba tank mix raises the solution’s pH and can keep it within acceptable ranges to reduce the risk of volatility.
My dicamba-tolerant soybeans are going to be planted late. What does that mean for in-season dicamba applications?
Across the corn belt, planting is delayed. That has many farmers concerned about in-season dicamba applications. Several states have imposed restrictions on spraying dicamba after certain dates. For example, in Minnesota, dicamba can’t be sprayed over tolerant crops after June 20.
Some soybeans may not even be emerged by these dates, based on current planting progress. It’s critical for farmers to have a contingency plan for weed control on Roundup Ready 2 Xtend® soybean acres. Even before the planting delays caused additional challenges, the strict application restrictions impose logistical constraints that can make it difficult to get acres covered. It’s always good to have a Plan B if you’re intending to spray dicamba in-season.
A strong preemergence program that includes low-volatility dicamba plus a Group 14 or 15 soil-residual herbicide with metribuzin can help keep fields clean until you can get in with a postemergence application. There are no plant-back restrictions when low-volatility formulations of dicamba are applied as a burndown ahead of planting Roundup Ready 2 Xtend soybeans. Work with your local agronomist for postemergence herbicide options if you’re unable to apply dicamba in-season.
What label changes could affect me the most?
Whether you’re a farmer or an applicator, good record keeping will be the crucial this season. The updated federal label requires records to be completed within 72 hours of a dicamba application. Recording weather conditions and cleanout procedures are important in the event there are questions about dicamba applications in the future.
This year, the label mandates sprayer system cleanout before and after dicamba applications. Review specific label requirements for approved cleanout procedures. Another big change this year it that only certified applicators are permitted to apply low-volatility dicamba products, and they must be trained annually.
Get answers before you apply
As we’ve seen over the past couple of years, there are risks involved with spraying dicamba. Be sure you understand updated label restrictions and state-specific regulations before your dicamba is applied. Your locally owned and operated WinField United retailer can help with in-season dicamba recommendations.

1. Based on WinField United Innovation Center spray analysis data.
© 2019 WinField United. MAX-IN®, OnTarget®, InterLock® and WinField® are trademarks of WinField United.
Roundup Ready 2 Xtend® is a trademark used under license from Bayer CropScience.

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