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Since 2016, soybean farmers have quickly adopted dicamba- and 2,4-D-ready crops in their fight against herbicide-resistant weeds. However, the expanded use of these herbicides during the growing season has led to an increased threat of drift damage for neighboring specialty crop growers. Several high-value crops can be damaged by concentrations of 1/300 the labeled rate or lower. Crops with especially high sensitivity to dicamba and 2,4-D include grapes, tomatoes, and soybeans that are not engineered for dicamba-resistance. Recent legal issues have limited the use of three dicamba products for the 2020 growing season, but 2,4-D and other dicamba products are still in use and will continue to pose a risk in areas with diversified or organic production.
A new fact sheet series is available to help specialty crop growers prepare for and respond to possible dicamba and 2,4-D drift. The series provides tips for being proactive, detailed steps for documenting and responding to damage, and a brief background on why dicamba and 2,4-D have been especially problematic. A Frequently Asked Questions fact sheet highlights various concerns pertinent to specialty crop producers. The series sought input from a variety of crop and herbicide specialists across the United States, as well as state regulatory agencies.
Fact sheets are available online at go.osu.edu/ipm-drift.
Preparing for drift
“Vigilance and communications are the two big things,” says Ohio State weed specialist Doug Doohan, “Knowing who your neighbors are, talking to them about your plans, talking to them about their plans, being aware of who’s doing what on the land and when.”
But who is your neighbor when it comes to drift? Just how far can dicamba drift travel? Most spray droplet drift will move short distances. This type of damage is generally limited to adjacent fields. However, dicamba and 2,4-D are likely to drift as a gas or via a temperature inversion. Temperature inversions can be especially damaging, moving suspended pesticides in a fog-like layer for longer distances.
“There’s all kinds of circumstantial evidence of much greater movement,” says Doohan. “When you’re talking inversions, if an inversion is motivated by a 2-3 mph wind, it could go miles—especially if the conditions persist through the evening.”
Doohan has helped investigate several drift cases and was one of the co-authors for the new fact sheet series. He encourages growers to establish a Standard Operating Procedure to prepare for a drift incident, just as they might for food safety concerns. He also stresses the importance of documenting suspected drift quickly, thoroughly, and repeatedly. The new fact sheet series offers detailed suggestions for these activities.
“If you see something, document it,” he advises. “Use your cell phone. You can always delete unneeded photos later, but you can’t go back in time and get the picture you wish you had taken.”
The new fact sheet series was cowritten by specialists at The Ohio State University and Purdue University, with support from the North Central IPM Center Working Group on Herbicide-Drift Risk Management. The working group organized in the fall of 2019 and plans additional projects in the coming year, including more resources and an anonymous survey of specialty crop growers to better assess the extent and frequency of drift damage throughout the north central region. The North Central IPM Center serves Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin and is supported by the USDA National Institute of Food and Agriculture through agreement 2018-70006-28884.