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Dicamba: removing a tool from the toolbox

The soybean growers in Nebraska and across the U.S. have just been thrown a curveball, as a federal court in Arizona vacated registration of dicamba formulations specific for use on dicamba tolerant soybeans (including Xtendimax, Engenia, and Tavium), finding that the Environmental Protection Agency (EPA) failed to meet regulatory requirements. Dicamba is still an effective weed control option, particularly when it comes to Palmer amaranth.

The ruling will put growers of the second largest crop in Nebraska, soybeans, at a management, if not a financial challenge. “It is taking a ‘tool out of the toolbox,’ as we (agronomists) like to say,” said Dr. Randy Lloyd, Nebraska Extension research facility coordinator at West Central Research, Education and Extension Center. “This will put growers in a bind, as most have purchased their soybean seed, which they can still use, but won’t be able to get the full benefits of the technology.”

Many growers favor genetically modified soybeans engineered to withstand glyphosate and/or glufosinate, and dicamba. This allows over the top dicamba use in soybeans and helps control Palmer amaranth since the weed can grow anytime throughout the summer and disperse thousands of seeds. “You can walk through a field in a fall, where a young two or three-inch Palmer is growing, and it will have a seed head with hundreds of seeds,” Lloyd said.

“It’s a tough time to make a decision this late in the game,” he said. “Growers can try to find other soybean seeds, but quantities will be limited.” A grower's ability to control weeds constantly challenges the farm economy. Weeds can easily cause a soybean yield to be reduced by 20 to 30 bushels or more, which is a huge yield and financial loss. They also drop hundreds of thousands of seed which could take many years for that field to regain what it lost.”

What implications does this hold for soybean producers in Nebraska? The answer remains uncertain for now. “We must await the response from the EPA and adjust our course accordingly,” Lloyd said, and he’s hopeful the EPA will appeal the ruling. If that doesn’t happen, it will put pressure on already limited alternative postemergence herbicide applications.

As growers move forward with purchasing seed, they should also prepare for alternative weed management strategies if the dicamba label remains vacated. “One viable option is implementing a preemergence program with extended residual activity. Such a program would effectively decrease weed pressure, facilitating suitable terrain for follow-up applications,” said Dr. Milos Zaric, Nebraska Extension assistant professor at West Central Research, Education and Extension Center. “When considering follow-up applications, it is crucial to ensure timely and precise execution, targeting small weeds (2-3 inches) and populations for postemergence treatment and utilizing increased spray volume.” 

Reliance, he said, may shift towards contact-type products available formulations based on glufosinate (essential to ensure the presence of the glufosinate-trait listed on the seed bag) or one of the PPO-inhibiting herbicides (acifluorfen, fomesafen, lactofen, or others classified under WSSA Group 14) for broadleaf weed control.

If a grower is unsure of a program selection, they can refer to the 2024 Guide for Weed, Disease, and Insect Management in Nebraska (EC-130) at Growers are also encouraged to contact their local University of Nebraska research and extension specialist for options and help in building alternative weed management plans.