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Serving: IA

New rules for using dicamba

TAGS: Soybeans Weeds
Farm Progress Soybean field
DRIFT CONTROL: Approval of three dicamba herbicide products for soybeans also includes expanded measures to limit off-target damage.
EPA has approved new labels for dicamba herbicide products for five years.

The U.S. Environmental Protection Agency on Oct. 27 approved new label registrations for dicamba herbicide products used on dicamba-resistant soybean and cotton varieties. The labels include new restrictions to reduce off-target movement of the weed killer.

The registrations are for XtendiMax with VaporGrip Technology and for Engenia herbicide. A third dicamba product, Tavium Plus VaporGrip Technology, received an extension of its current registration. All of three of the newly registered product labels are scheduled to expire in 2025.

The decision to allow a five-year registration for use of these products in over-the-top applications on dicamba-resistant soybeans and cotton came after two of the three dicamba registrations were revoked by the U.S. Court of Appeals, due to concerns the existing labels didn’t go far enough to reduce the potential risk of drift. The court halted the use of dicamba this past June, and it was uncertain if the herbicide would be allowed for use in the 2021 growing season. Now EPA has given the go ahead.

New label requirements

“The new labels only describe the use on dicamba-resistant crops, therefore eliminating some of the confusion on earlier labels,” notes Bob Hartzler, Iowa State University Extension weed management specialist. He describes the following major changes in the labels and important requirements for farmers and all applicators to follow when using dicamba:

Use a volatility-reduction agent. You must use an approved volatility-reduction agent as an adjuvant added to the herbicide mix.

Follow revised cutoff dates. There are differences in wording among registered products. Apply XtendiMax before June 30 or up to R1 stage of soybean growth, whichever comes first. Apply Engenia before June 30. Apply Tavium before June 30 or up to the V4 stage, whichever comes first. The lack of the R1 growth stage restriction on Engenia label could allow for applications later in the season than with XtendiMax, particularly with early planting dates.

Always maintain a 240-foot buffer. Maintain this buffer between the last treated row and the downwind field edge. Roads, mowed grass and tolerant crops can be included in the buffer. The previous XtendiMax label required a 110-foot buffer at the 22-ounce application rate and a 220-foot buffer at the 44-ounce rate. The 44-ounce rate has been eliminated from the label.

General label restrictions

Other restrictions on the label specify you can only apply dicamba over the top beginning one hour after sunrise and then through the day until two hours before sunset. Apply when wind speed at boom height is between 3 and 10 mph. Don’t apply during temperature inversions.

Don’t apply the product if sensitive crops or certain plants are in an adjacent downwind field. Don’t apply if rain is expected in the next 48 hours that may result in runoff from the field. The maximum boom height is 24 inches above the ground and maximum ground speed is 15 mph.

Dicamba-specific training on the use of dicamba is still required of all applicators and users, as it has been in the past.

A buffer restriction to protect endangered species is still on the label for counties with endangered plant species. In Iowa, this buffer is required for the counties of Allamakee, Clayton, Delaware, Dubuque, Jackson, Iowa and Hardin. The labels direct users to an EPA website that provides up-to-date information on endangered species.

Weed control option

Iowa Soybean Association President Jeff Jorgenson says EPA’s Oct. 27 registration announcement came at an important time as farmers are making input decisions for the 2021 crop year. “Farmers needed this announcement — whichever way it was going to be — to make seed decisions for 2021,” says Jorgenson, farming near Sidney in southwest Iowa.

In June, when the U.S. 9th Circuit Court of Appeals announced its decision to vacate registrations on three dicamba products (XtendiMax, Engenia and Fexapan) it forced farmers to use existing stocks of dicamba sooner than they would have liked. “The window to spray was compressed as tight as it could be,” Jorgenson says. “For my operation, I sprayed sooner than I wanted, and we had some weeds escape because it rained after I sprayed, and we had more weeds.”

The rushed manner by which Jorgenson had to apply his existing dicamba supply caused a 5% to 10% yield reduction. The new five-year registration of dicamba products is welcomed, though he wonders how he might be affected by the new restrictions on use. For example, EPA has set a calendar cutoff date of June 30 for over-the-top application on soybeans according to the new labels.

“The number of days suitable for dicamba application are limited due to weather factors,” he points out. “In some years and situations, applying later may be better to get the needed weed control.”

Jorgenson is evaluating all options for his 2021 crop, including using dicamba products. He already uses cover crops in his crop production system to help suppress weeds. “Farmers have to figure out the best options and opportunities for their farm,” he says. “A one-size-fits-all approach doesn’t apply. Weed control programs are different for everyone.”

Controlling toughest weeds

Farmers planted an estimated 64 million acres of dicamba-tolerant soybeans and cotton in the U.S. in 2020, according to EPA. About 40% of all soybean acres were planted with dicamba-resistant seed. The technology helps control difficult weeds such as waterhemp and Palmer amaranth populations that have developed resistance to multiple herbicides.

Dicamba herbicide manufacturers say they will enhance their training sessions for farmers and commercial applicators heading into the 2021 growing season to make sure applicators are aware of the new dicamba label requirements.

ISU’s Hartzler says the effectiveness of the new volatility reduction adjuvants that applicators need to add to their dicamba spray mixture will be important to monitor in 2021. “These additives look good in small-scale trials the universities have looked at,” he says. “But small-scale trials are a different situation compared to spraying a product over large fields. I’m not totally convinced these additives will do the job. We’ll just have to wait and see.”

XtendiMax herbicide is a Bayer product. Engenia is from BASF and Tavium is a Syngenta product. When EPA vacated the registrations of three dicamba products on June 3, — the three were XtendiMax, Engenia and Fexapan. Bayer is also the registrant for the dicamba formulation that Corteva Agriscience had previously marketed as DuPont Fexapan herbicide with VaporGrip Technology. Now that EPA has registered Bayer’s dicamba formulation, Corteva will be able to apply for federal registration of Fexapan, Corteva officials say.

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More drift complaints in 2020

Complaints about pesticide drift involving dicamba reached record levels this year. The Iowa Department of Agriculture received 329 pesticide misuse complaints involving dicamba drift. Iowa State University Extension weed specialist Bob Hartzler says a variety of factors are involved.

“Some of it is the volatility of dicamba when used on soybeans, as you apply it later in the growing season when temperatures are warmer,” he explains. “This year, we saw a lot more movement out of cornfields than is typical. Dicamba use in corn has increased to control the spread of herbicide-resistant weeds.”

Hartzler says phasing out the higher-volatility dicamba products should be considered. “I think we ought to look at requiring all of those products to be lower volatility, because it’s not just volatility of dicamba applied on soybean fields that’s causing problems.”

Farmers are doing their best to follow directions when applying dicamba, but drift continues to cause damage. “It’s frustrating when they do everything right, and they still have issues,” Hartzler says. “The No. 1 criteria to preventing problems is to evaluate individual fields to determine the risk of off-target injury.”


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