Deep in Weeds

Dicamba Dominates Discussions During National Meeting

Pam Smith
By  Pam Smith , Crops Technology Editor
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Specific nozzles are just one of the several specific requirements growers must follow to comply with the federal labels when using new formulations of dicamba. (Photo by Pamela Smith)

TUCSON, Ariz. (DTN) -- The Arizona desert may not be a hot bed for row crop weeds, but it is the place to find weed scientists this week. The Weed Science Society of America (WSSA) is meeting to explore the latest in research on weeds and their impact on the environment. However, dominating the agronomic discussions has been how to manage herbicide-resistant weeds and new advances in weed control technologies.

Frustration was evident as weed scientists discussed how difficult it is to advise growers on the new label restrictions that the Environmental Protection Agency (EPA) has handed down on two dicamba herbicides recently approved for use in Roundup Ready 2 Xtend crops. Special sessions on understanding and reducing the impact of herbicide of off-site movement explored the challenges farmers, custom applicators and state regulatory officials face in interpreting a complex and sometimes contradictory federal label.

David Scott, Office of Indiana State Chemist, told the weed scientists in attendance that he's never seen a federal label quite like the one with XtendiMax with VaporGrip and Engenia, two recently approved dicamba formulations. "I've never seen a situation where it says if there are any differences between the supplemental label and the base label, ignore the base label," said Scott. He noted the differences in definitions on what constitutes a sensitive area, for example.

"I'll be honest with you, I've never spent this much time prior to a product being introduced in the market in my 30-plus years of doing regulation," he said. Scott emphasized that he wants the technology to succeed and wants farmers and retailers to have the tools to be successful, but explained that states can see regulatory programs consumed by complaints if the products are not shepherded wisely.

Representatives from the EPA explained the complicated backdrop of risk assessments and why many of the label restrictions have as much to do with protecting endangered species as they do with limiting drift. Meanwhile, several weed scientists noted that buffer zones stipulated on the Engenia and Xtend labels could actually become weed nurseries for resistant weeds. Weed scientists also voiced worries about whether spray applicators putting out the new dicamba products can keep boom heights to the required 24 inches and how the currently approved nozzle does not work with pulse width modulation sprayers, which are popular systems for drift control.

With BASF posting a few tank mix partners to their website this week, spray applicators are being advised to monitor the changing application picture. Adjuvants and drift control agents are the most likely tank mix partners to be approved and it is unknown whether additional herbicides will be available to add modes of action to the tank this season.

Scott noted Indiana had studied and watched the dicamba technology advance for five years, but has only had two short months to act after the products received registration. Indiana has initiated legislation to classify agricultural dicamba products as restricted use pesticides -- offering a way to record sales and hopefully limit older dicamba formulations from being used on the Xtend tolerant crops. However, Scott said it was unlikely the state would get restricted use language in place for 2017.

Scott also presented what people should do and not do. This is being distributed in Indiana and others. The information developed by the Illinois Fertilizer and Chemical Association is summarized here:


DO -- Only use lower volatility products approved for post-emergent use on Roundup Ready 2 Xtend soybeans (Engenia and XtendiMax)

DO -- Utilize a pre-emerge weed management program to help ensure effective early-season weed control.

DO -- Thoroughly read and follow all label directions for Engenia and XtendiMax, including weed height, wind speed restrictions, spray nozzle selection, boom height, required buffer zones, product use restrictions and scouting for sensitive crops. It is as equally important to know when not to apply these products to protect non-target, sensitive crops.

DO -- Consult FieldWatch ( and access their DriftWatch program to assist in identifying locations of sensitive crops in your area, such as vineyards, nurseries and vegetable crops. Make sure fields being sprayed are Xtend crops; non-Xtend soybeans are very sensitive to dicamba.


DO NOT -- Apply any other dicamba herbicides to Xtend soybeans. Doing so is a violation of law and misuse will be investigated and can lead to fines, civil litigation and threaten the continued availability of these products for agricultural use.

DO NOT -- Use Engenia and XtendiMax as a rescue treatment. They are not meant to be the only herbicides used to control weeds in soybeans.

DO NOT -- Tank mix Engenia or XtendiMax with any products such as ammonium sulfate, UAN, adjuvants or other herbicides without first consulting the product websites to determine if or when a tank mix is approved for these products. Go to or

DO NOT -- Violate the pesticide label.

While questions on how to implement certain application aspects of the dicamba herbicides continue to be hammered out, weed scientists were united in this point: Continued availability of this new post-emerge technology depends on good management decisions and complying with the pesticide label.

Watch for continued updates on dicamba application measures through the Dicamba Decisions series at DTN and The Progessive Farmer. See Dicamba Decisions - 1 at…; Dicamba Decisions - 2 at…and Dicamba Disaster Control at….

The Weed Science Society of America, a nonprofit scientific society, was founded in 1956 to encourage and promote the development of knowledge concerning weeds and their impact on the environment. The Society promotes research, education and extension outreach activities related to weeds, provides science-based information to the public and policy makers. For more information and more information on weed control and weed resistance, visit

Pamela Smith can be reached at

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Pam Smith