The soybean plant can be very susceptible to dicamba-based herbicides if the soybean variety is not tolerant. Just a small amount can cause damage to a field. Leaf cupping and curling are the first signs.
In Minnesota, the Department of Agriculture is reporting 210 off target reports and complaints related to dicamba application. Over half the counties in the state have some reported damage. So far, the only affected crop is soybeans that were not dicamba tolerant.
One of the responsibilities of the Minnesota Department of Ag (MDA) is to ensure farm chemicals are applied according to labeled guidelines. It is their job to investigate these off-target complaints and determine why they happened.
“We are really interested in trying to understand the how’s and the why’s of the damage issues that we are seeing,” said Josh Stamper, director of the Pesticide & Fertilizer Management Division at the MDA, during a recent phone interview.
Before any regulatory decisions can be made regarding dicamba use in the future, the MDA has to first know, what was the cause for the off-target movement this year.
“We do not want to put down rules and requirements and things that growers have to do if we don’t think they are going to be effective. We want to make sure that whatever we require on the label for a consistent application, we want to make sure that that is going to be effective,” said Stamper.
The 210 reported off-target complaints are being actively investigated by the MDA and Stamper was unable to comment as to what those investigations are finding to be the cause.
Typically, the MDA investigations cover products that have been used in a way that does not follow the labeled guidelines. In this situation with dicamba, the cause for product movement may not be the result of off label usage.
“A lot of the farm community is saying that when they talk to their neighbors across the fence or to the custom applicators that make these applications, they are saying we followed the label, we did everything that the label told us to do. As far as a regulatory agency, we respect that,” he said.
It is also likely that there is dicamba-related damage that is going unreported.
“A lot of growers do not want to go down the official investigative pathway, where you send out an ag chemical investigator, just because they want to maintain relationships with their neighbors,” he said.
Again, the main focus of the MDA in these off-target investigations it to understand why they occurred, to gather as much information as possible. Before any decisions can be made about the products, all the information has to be gathered.
“If they did follow the label and they have got the records and they can prove they followed the label, those guys do not have anything to worry about,” he said.
It is possible that properly-applied dicamba re-volatilized and moved on its own, through no fault of the applicator.
This was the first year that dicamba was applied to soybeans and applied this late in the growing season. With a leaf canopy just inches away from closing, those leaves would have intercepted and collected dicamba product being applied. The larger droplet size required with the dicamba applications would have contributed to more product being collected on the leaves.
“If that is applied when it is cool, the day time temperature heats up, the soil heats up and it drives volatilization. Dicamba can re-volatilize that product and it can move several hundred feet, sometimes it can move several thousand feet. That is where we have seen some cases this year, where it is just fence row to fence row leaf cupping,” said Stamper.
Stamper also explained that the issues we are seeing in Minnesota do not appear to be the same as those being seen in some other, southern states. In those areas, it appears that a handful of growers and applicators used older dicamba formulations and not the products approved for use on soybeans.
That does not seem to be the case in Minnesota.
Unfortunately, it will be difficult to assess the extent of the damage to non-dicamba tolerant soybean crops. The University of Minnesota has been putting together estimates of yield-loss potential based on historical data.
“A lot of this stuff is research that was done 40 years ago. The impacts to a modern soybean cultivar is going to probably be quite a bit different. If we go back to the 1970s, when maximum yields were maybe 30 bushels per acre and now, in a good year, we can consistently see 60-80 bushels per acre, it is a total unknown,” he said.
Historically, when a product’s label does not sufficiently ensure effective product use, the Commissioner of Agriculture can issue special instructions and restrictions on that product.
Stamper gave the example of a product called Command in the late 1990s. That product turned vegetable crops white and the commissioner at that time was forced to issue special instructions to prevent further damage.
“If everybody is following the label and we are still seeing this off-site movement, our primary interest is understanding why there is offsite movement and how we can prevent it,” said Stamper.
Source: Minnesota Farm Guide
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