Application requirements for dicamba in 2018 have the potential to leave farmers with a very small application window.
As the growing season begins, it’s important to have a plan in place to be prepared if dicamba application isn’t an option.
For farmers with herbicide-resistant weeds
The biggest challenge comes to those who specifically choose dicamba-tolerant soybeans to fight off Palmer amaranth and waterhemp that are resistant to multiple herbicide sites of action.
“If a grower chooses to plant dicamba-tolerant soybeans and these weeds are allowed to emerge, there is virtually no other treatment options besides dicamba,” says Kevin Bradley, Ph.D., weed scientist at the University of Missouri. “If the conditions aren’t right, the farmer could be faced with a large problem that could potentially affect yields.”
The solution, Bradley says, is to manage those types of resistant weeds from the beginning. This ensures they won’t become a problem later in the season when it could be too late.
“You need to rely on residual herbicides as your first line of defense and never give pigweed a chance to germinate, rather than count on dicamba to kill it all,” Bradley says.
Bradley recommends applying residual herbicides at planting and then coming in with another application later in the season to implement a “layered residual” approach.
“If you stay on the ball and make timely applications, you’ll prevent most or hopefully all of those weeds from emerging. If some do come through, you can eliminate the rest with a timely dicamba plus glyphosate application if the conditions are right,” says Bradley. “But that’s the big if; the pigweeds cannot be too big and the weather conditions all have to be on-label.”
For farmers not struggling with herbicide-resistant weeds
Farmers planting dicamba-tolerant soybeans mainly for protection against dicamba damage are in a better situation, Bradley says.
If they aren’t struggling with pigweed species like waterhemp and Palmer amaranth that are resistant to multiple herbicide sites of action, farmers can revert back to herbicides they’ve previously used to control these pests, such as group 9 EPSP synthase inhibitors (glyphosate) and group 14 PPO inhibitors (lactofen, fomesafen, etc.).
Regardless of your situation, Bradley says it’s important to be mindful of the dicamba application requirements before and during applications to preserve this technology for future use.
“On Nov. 9, 2018, the EPA will make a decision about what will happen with these herbicides and whether or not we’ll be able to apply them in the future. Approved products will expire and a big decision will be made,” says Bradley. “If people want to have this technology available to control those weeds, I suggest using them as labeled so we do not have a repeat of last year.”
