A day without wind is ideal for spraying for weeds in soybeans. So is one that’s not too hot. That doesn’t happen very often in some areas.
Farmers have a number of choices when it comes to controlling broadleaf weeds in crops like soybeans. One popular choice is dicamba, especially if dicamba-tolerant soybeans are being grown.
Three years ago, according to the Environmental Protection Agency website, dicamba formulations were first registered for “over-the-top” use on growing dicamba-tolerant cotton and soybean plants during the 2017 growing season. Allegedly there were a high number of incidents where sensitive plants were injured by the drifted spray that year. An agreement was reached with manufacturers on measures to help minimize potential for damage at the end of 2018.
As previously reported in High Plains Journal, “On Oct. 31, 2018 the Environmental Protection Agency announced a continued registration, including label changes, for XtendiMax herbicide with VaporGrip technology, according to Bayer Crop Services, St. Louis, Missouri.”
Thoughts about it now
University of Missouri plant science professor, Kevin Bradley, said just about every state has allowed a federal label to be what applicators are to follow when applying dicamba.
“I can’t speak for everybody, but I know that’s Missouri’s situation,” Bradley said. “I haven’t heard of any other states that have enacted any thing other than what the label says.”
One of the regulations makes dicamba only available for sale and for use by certified applicators.
“That was a big deal for some states,” Bradley said. “It wasn’t all that big of a deal for us because the Missouri Department of Ag had implemented that restriction already for the 2018 season.”
The regulation meant farmers had to have specialized training to buy and apply dicamba. But Bradley doesn’t see this as a “major impact” to farmers since many are hiring commercial applicators to apply these products to fields.
“For one, it will be their liability,” Bradley said. “The retailer that sprays it, it’s on them if they do it wrong. So a lot of farmers just deal with it that way and take it all off themselves.”
Liability pushes farmers to custom applicators, just because “some of them don’t want to add that to their plate of being liable for the injury,” Bradley said.
Bradley wasn’t positive of the exact number of cases in Missouri last year of crops that suffered injury from dicamba drift, but the number of complaints did go down. They’re still big numbers considering there was just a fraction of injuries reported several years ago.
“Three years ago a common year of herbicide injury in the state of Missouri would have been 30 or 40 cases,” he said. “And now we’re talking about 200 or 300 for just one active ingredient, dicamba. Last year in this state it was still a major issue.”
This year is a little unknown, Bradley believes.
“I think there are a lot of pieces of the puzzle that we continue to figure out and I think this thing is a puzzle,” Bradley said. “I don’t think we know everything yet. But we’re learning every year. Unfortunately universities are having to learn because we weren’t able to look at this before it came out from the standpoint of volatility.”
Bradley thinks they’ve learned how to help farmers and applicators reduce liabilities and keep the spray where it’s supposed to go and not drift.
“There’s a lot of things just in the last year that are coming to light as pretty significant things that are impacting the likelihood of volatility,” he said. “I just think we still don’t know everything but there’s a lot of good people working on it and trying to figure it out to be able to keep this product in the mix in the future.”
Helpful hints
Iowa State University Weed Science Professor Bob Hartzler agrees with Bradley and is equally concerned that nothing has been done to address volatility. He believes following the label recommendations helps keep the chemical where it needs to be.
“Evidence shows that the products can move either due to particle drift or vapor drift,” Hartzler said. “The label focuses on minimizing particle drift.”
He has no doubt that temperature inversions have played a role in many cases. The label has been changed to reduce the likelihood of spraying during inversions—for example, only spray an hour after sunrise and 2 hours before sunset.
His biggest piece of advice to keep dicamba from drifting? Follow the label.
“Which is very difficult to do since all of the restrictions result in very few hours that are legal to apply the product,” Hartzler said. “It is really important to scout all fields long before the spraying season to determine the location of sensitive plants adjacent to the field.”
Simply put, there are many fields which are not suited for the Xtend system due to susceptible soybeans or other plants near by.
“I would also try to avoid applications when temps are forecast to be higher than 85 degrees F.
When asked if soybean farmers will have to contend with this for years to come or if he thinks the problem will be remedied with regulations and restrictions, Hartzler was a little optimistic.
“Until the volatility issue is solved I think there will always be problems,” he said. “Applicators will learn how to avoid some of the problems, but there will be times when they are forced to make applications during ‘marginal’ conditions and problems will happen.”
Problems from dicamba drift for Iowa farmers have been miniscule compared to other areas—mostly due to differences in climate and a smaller percentage of the Iowa landscape being planted to Xtend crops.
“The most widespread problem is injury to adjacent soybean that are not Xtend varieties,” he said. “I have no idea how many acres were damaged, but complaints to our Department of Ag doubled in 2017 and 2018 following approval of the Xtend system.”
There has been damage to other plants and trees, but Hartzler doesn’t have a good feel for the extent of that.
“My concern is that if the acreage of soybean treated with dicamba continues to increase we will continue to see more damage to non-agricultural plants,” he said.
In Iowa, 95 percent of the dicamba will be used to help manage waterhemp, and Bradley said the same of Missouri.
“It has evolved resistance to many of the other products used in soybeans, and the dicamba provides more consistent control than the other post-emergence products,” Hartzler said. “Some growers will use it to manage marestail and giant ragweed.”
Hartzler thinks with the approval for export of the 2,4-D soybean (Enlist) gives growers another alternative.
“It will be interesting to see how the market shakes out after they are widely available in 2020,” he said. “Will a lot of growers shift to them due to lower risk of off-target injury, or will they stick with Xtend due to concerns of having non-dicamba resistant soybean injured by dicamba?”
Kylene Scott can be reached at 620-227-1804 or [email protected].
