by Stan Wise
Farm Forum Editor
If I had to guess, I would say that many of you are going to plant some dicamba-tolerant soybean seed this year.
If that’s the case, you might be interested in something the South Dakota Secretary of Agriculture said this week. Mike Jaspers spoke in Aberdeen on Feb. 27 at the Precision Agriculture Conference. There, he was asked what the state would do if off-target dicamba damage became a problem again the way it was in 2017.
Jaspers pointed out that while South Dakota did not impose many of the state-specific restrictions on dicamba that neighboring North Dakota and Minnesota imposed (such as a cut-off date for applications), the state reserves the right to do so at any point in mid-season if officials start seeing the same problems with dicamba they saw last year. He also said the Department of Agriculture will be keeping a close eye on Southern states early in the season. If they see a lot of dicamba-damage problems despite the additional federal label restrictions and training requirements, Jaspers said the state may decide to pull the label early in the season.
I can already hear you: “If everyone follows the label, we’ll be fine.”
Maybe. Maybe not.
It comes down to the difference between physical spray drift and volatility. I’m sure we all know the dangers of physical drift, but volatility is a different animal. When a chemical volatizes, it turns into a gas. At that point, we’re not talking about a tiny liquid droplet blown on the wind at the time of application. We’re talking about a chemical that has been sprayed on a field and then turns into a gas hours — maybe even days — after application. At that point, it can be blown on the wind and damage plants wherever it ends up. That means you might have applied the chemical perfectly, but it can still leave your field.
The companies that manufacture the new lower-volatility formulations of dicamba say that volatility isn’t an issue with their products. They’ve visited hundreds of farms where off-target dicamba damage occurred, and they say these cases were caused by several different application errors.
However, Extension and university researchers have found that while those errors can cause off-target dicamba damage, volatility can cause damage with the new formulations, as well. One University of Missouri study showed that damage due to volatility was occurring up to three days after application of dicamba. And while a new formulation of dicamba (Xtendimax) caused less damage due to volatility than an old formulation (Banvel), it was only a 20-percent reduction.
Can you guarantee the wind won’t be blowing in the direction of your neighbor’s fields three days after you make a dicamba application?
According to a December “Successful Farming” article, the issue of volatility is so concerning to Iowa State University weed scientists that they are recommending farmers make no post-emergence applications of dicamba and reserve the herbicide for pre-emergence use only.
What this year will tell us about the effectiveness of the new restrictions on the use of dicamba and the issue of volatility is still up in the air. However, Mike Jaspers made a good point in his presentation this week. He said that when you compare the new dicamba label weather- and time-based restrictions to typical June weather patterns in South Dakota, there are not very many in hours in which it will be safe to apply the chemical. Your crop may need to be treated for weeds in a time when you cannot legally use dicamba.
Therefore, if you plant dicamba-tolerant soybeans, dicamba cannot be the only weed management tool in your arsenal.