Evidence of off-target movement of dicamba in the Midwest

According to Prashant Jha, professor and Extension weed specialist at Iowa State University (ISU), ISU Extension field agronomists, commercial agronomists, and others across Iowa have observed non-dicamba tolerant soybean showing injury symptoms in line with dicamba.

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"As long as we have dicamba, it's not a question of if we ever will see off-target injury in a year, the only unknown is how extensive it will be," says Aaron Hager, associate professor and faculty Extension specialist at the University of Illinois Urbana-Champaign.

In Illinois, dicamba-related complaints peaked in 2019 at over 700. This summer, there are reports of widespread damage to soybeans in southern Illinois and complaints of pesticide misuse that specifically mention damage to trees. The signs are cupping in soybean leaves and bare trees in July and August.

Hager says that with a significant switch away from dicamba technology to Enlist technology this spring, many were hopeful for less off-target response.

"The amount of dicamba sprayed in soybeans was less, but on the flip side, a higher percentage of acres are now sensitive to off-target movements," he says. "When there is widespread use of a volatile product like dicamba at times of the growing season where temperatures are much higher than normal, we continue to see the effects across the landscape."

Dicamba injury in soybeans.

How to manage damage

Unfortunately, managing off-target movement is beyond a farmer's control.

But the question if there is anything you can do to recover from damage has been asked before.

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Brian Dintlemann, M.S. student, and Kevin Bradley, professor of plant science and technology at the University of Missouri, conducted a research trial over three seasons to determine if there may be any treatment for dicamba-injured soybeans.

The recovery treatments they tested included common foliar fertilizer products (PercPlus, Megafol, YieldOn, etc), a fungicide (Priaxor), urea with Agrotain, a plant growth hormone (Radiate), and weekly irrigation.

In their research, published in 2021, weekly irrigation was the only recovery treatment that resulted in yields that were higher than the dicamba-injured control. However, none of the recovery treatments resulted in yields that were as high as the non-treated control.

Results from all three years of the study indicate that if your soybeans have become injured with dicamba, the best thing to do is to irrigate. This will help them recover some, but not all.

In alignment with this research, Prashant Jha at ISU says that in areas of the state that have received rain, affected soybean plants with low levels of dicamba exposure are likely to outgrow the injury.

"However, injury from dicamba drift is an ongoing concern and jeopardizes the use of this product as one of the few postemergence herbicide options left for controlling waterhemp in dicamba-tolerant soybean. Enlist One or glufosinate are also effective on waterhemp when applied over-the-top in Enlist E3 soybean," Jha notes.

University of Missouri Extension horticulturist Michele Warmund says there are few short-term solutions to prevent herbicide drift, but a long-term option is to plant protective structures, like a living windbreak.

"Sorghum-Sudan grass is an annual plant that grows 5-12 feet tall. Multiple rows can provide an inexpensive annual barrier to protect low-growing crops against herbicide drift," according to Warmund.

Another option is a windbreak with multiple rows of perennial trees and shrubs. In a three-row windbreak, for example, one row of evergreen trees, a second row of shrubs, and a third staggered row of shrubs in a planting about 40-50 feet wide, will provide greater protection against herbicide drift than one with fewer rows.

However, even a single row of tall plants with dense foliage will help minimize damage, she says. You might consider American plum, silky or red twig dogwood, witch hazel, ninebark, and American filbert.

While there may be continued concern over off-target movement, weed control and resistance is at the top of the list for farmers too.

"Dicamba is an important tool, especially right now, when growers need access to safe and effective crop protection," says Kyel Richards, Bayer Crop Science.

If you have experienced a suspected herbicide incident, contact your state's Department of Agriculture or call the Bayer hotline number at 1-844-RRXTEND to report off-target movement or suspected resistance issues.