Game Changer: New Rules for Dicamba Herbicides

Now that new herbicides for dicamba-tolerant crops are registered, growers and applicators need to learn and follow a whole new set of rules to apply them correctly and not damage nearby fields. Training is key.

By Marilyn Cummins

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Unfortunately, the 2016 crop season in the Midwest and Southeast is likely to be remembered for a long time as the summer of dicamba drift damage. Some fields of new dicamba-tolerant soybeans and cotton were seeded and then treated with older dicamba formulations not labeled for use on those new crops. That’s when growers learned the hard way that the herbicide often didn’t stay where it was sprayed.

“They were shocked by how far it went,” says Larry Steckel, Extension weed scientist with the University of Tennessee. He personally looked at 30,000 acres of mostly soybeans, some cotton, damaged by off-target movement of dicamba. He says there were likely close to 70,000 damaged acres in his state, some of which were hit two or three times with dicamba drift.

Weed Specialist Kevin Bradley

Weed Specialist Kevin Bradley

In Missouri, State Extension Weed Specialist Kevin Bradley was walking thousands of acres of crops damaged in June and July—estimated at 100,000 acres of soybeans plus many acres of specialty and orchard crops. He and Steckel talked every week about what they were learning about the causes and researching how to avoid them.

Now, it’s the mission of Steckel, Bradley and their peers in other states, along with the manufacturers of the new traits and companion chemicals, to educate anyone planning to apply the new auxin herbicides in 2017 of the new requirements for safe application.

“They are so different,” Bradley says of the new formulations. “Unlike anything we’ve had before. Farmers we’ve talked to are pretty surprised, even kind of shocked by what is required.” Steckel agrees: “It’s just a game-changer.” How little of the chemical can damage a sensitive broadleaf crop “is not on their radar screen. Just a little dab will get you.”

One good thing to come out of the experience? “We have a really teachable moment here in Tennessee,” Steckel says. “That is the bright spot.” As he conducts training almost daily, “We have a very attentive audience.”

New Formulations

At the time this article went to press, the new products registered by the EPA for in-crop use for dicamba-tolerant soybeans and cotton (pending in-state approvals) were XtendiMax™ herbicide with VaporGrip™ Technology from Monsanto, Engenia™ herbicide from BASF and FeXapan™ herbicide plus VaporGrip Technology from DuPont. Be sure to check the company websites to determine if these products have been approved for use in a particular state. They are formulated to greatly reduce the volatility of dicamba. No other dicamba herbicides can be sprayed on crops with these traits. They have been developed to tackle the growing list of broadleaf weeds no longer controlled by glyphosate, especially Palmer amaranth, waterhemp and marestail. The big issue is that what is required to apply the new products properly is nothing like spraying glyphosate.

The companies offer stewardship and application training on their websites, and both Steckel and Bradley urge applicators to get into training events, whether from the companies or state Extension specialists, and to continue checking the online label information before selecting and applying the products. Some states are requiring training and/or recertification before applicators can apply the new-formulation auxin herbicides (dicamba and 2,4-D).

Damaging Drift

Both specialists emphasize how inherently sensitive soybean is to extremely low concentrations of dicamba. Bradley’s research shows that even 1/20,000th of the 1X use rate (or 0.000025 pound of active ingredient per acre) of dicamba resulted in visible damage to soybeans at both V3 and R2 stages. Even 8 fluid ounces of dicamba solution (whether new or old) in a 1,200-gallon spray tank would result in significant foliar injury to non-dicamba-tolerant soybeans; a gallon in the same-size tank would result in significant yield loss.

Growers learned the hard way that the herbicide often didn’t stay where it was sprayed.

Growers learned the hard way that the herbicide often didn’t stay where it was sprayed.

That’s why when old formulations were applied last year without special precautions (and off-label), the damage was so widespread when even small amounts of dicamba moved off-target through physical drift, volatilization and temperature inversions. And it’s why the requirements for the new products, even with low-volatility formulations, are so many and so important.

They are also quite different from standard application practices, especially for glyphosate; hence, the need for new training and exact adherence to label directions.

Be Good Stewards

To sum up, reading herbicide labels and getting training is more important than ever before in working with these new products. As everyone tries to understand how the chemistry will work in 2017, Bradley says to stay away from late-afternoon and evening spraying, and certainly don’t spray at night. Steckel advises that, in addition to getting trained, it can help to keep one’s eyes open and talk with neighbors.

“If you see somebody with a nurse truck in the middle of July with boxes of generic dicamba sitting on the back of it, you might want to talk to them,” he says. “Change may come from peer pressure better than anything else.”

Step By Step

According to weed scientists Steckel and Bradley, the following are critical factors to learn in herbicide stewardship training for the new dicamba products this spring and summer. The No. 1 goal is minimizing drift of all types, and the online product label is the official guide in all of these categories.

What’s growing where. Talk to neighboring growers, look for flags denoting herbicide technology in fields, and check maps for sensitive specialty crops. Dicamba-tolerant crops may not be a good fit in some fields.

Right crop and product, in right place. Choose and use only the labeled product for the crop planted. To help ensure the correct products are used, Steckel notes that manufacturers of the new formulations offer rebates that make up the cost difference between them and old-formulation dicamba.

Tankmix/additives. Check the label carefully, including online updates, because nothing can be added unless approved on the label, Steckel says. In general, plan on no tankmixes, and for sure no AMS (ammonium sulfate). “Be careful not to ruin the formulation,” he says.

Nozzle choice. Check online product labels for approved nozzles and how they must be used. At press time, the air-induction TTI 11004 from TeeJet® was approved for all three of the new formulations, as were nozzles from multiple manufacturers for XtendiMax. Follow label directions precisely for operating pressures and other requirements.

Boom height and sprayer speed. Low and slow. No more than 24 inches above the target, traveling around 10 mph to minimize drift.

Timing. Steckel says that to kill pigweed (like Palmer amaranth or waterhemp), spray when the weed is about 4 inches in height. He has documented the weed going from germination to 8 inches tall in 12 days, so the window is small unless pre-emergent herbicides and/or cover crops are used to delay emergence and reduce the number of plants. And the spray window may be even smaller depending on the environmental factors that follow.

Wind speed and direction. Check wind speed and direction at the level of the boom, not the cab. Spray only when wind is between 3 mph and 10 mph, and be conscious of susceptible plants downwind, maintaining a 110-foot downwind buffer between spray area and adjacent areas with sensitive plants.

Avoid applying in temperature inversion. Bradley says this was a huge factor in the drift damage in Missouri in 2016. When the volatile old dicamba products were applied during a temperature inversion (when air temperature at ground is lower than that of air above it) with wind speeds less than 3mph, fine droplets of dicamba became suspended at ground height in the cool air and then were transported horizontally for miles sometimes before dropping on sensitive targets. (See more about recognizing the signs of temperature inversions online at

Keeping records. Both experts say keeping detailed records will reduce mistakes and possibly protect an applicator from legal action. Record environmental conditions (wind speed and direction, temperature), nozzles used, sprayer speed, product formulation and other details. For any crop protection treatment, “the applicator is responsible for anything that goes wrong,” Bradley says. “Follow the label, and write down what you did.” In another first for this year, he says, applicators need to go by the online labels, which are updated frequently with new information.

Photo: Univ. of Wisconsin Extension