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Signs of dicamba damage to soybeans Photo by Mark Loux.

The dicamba dilemma

With more acres of dicamba resistant cotton and soybeans growing in fields around the country, there is more potential for postemergence dicamba applications during warmer, more humid conditions and more chances for the controversial herbicide to move off-target.

The situation has been particularly heated in in the South. An Arkansas man was shot and killed in 2016 over a neighborly dispute concerning off-target dicamba damage. Missouri and Tennessee have also been reporting off-target dicamba damage on significant acres.

Available for 2017 planting were the Monsanto Xtend soybeans and cotton that are resistant to Monsanto’s XtendiMax with VaporGrip, which is also sold as FeXapan by DuPont. In addition, BASF developed the Engenia dicamba formulation. The long-needed new tools are finally available to help tackle tough weed control situations but are bringing with them (not wholly unexpected) logistical and management issues. Arkansas and Missouri have even banned any additional dicamba applications for the remainder of the growing season, although subsequent label changes will allow some continued use in Missouri. Some examples of this have been showing up in Ohio too.

“I’ve walked a few fields and looked at some injury issues. There has been some off-target movement of dicamba from treated fields of Xtend soybeans. What I looked at I would characterize as more of a volatility issue than a particle drift issue,” said Mark Loux, Ohio State University Extension herbicide specialist. “Certainly it’s an effective tool. We needed some new tools and it’s an effective one but as individual growers and applicators, you’re going to have to be a little more careful about where and when you use it.”

Loux has seen the curled up leaf fringes indicative of dicamba damage on soybeans in multiple Ohio sites. The good news for non-dicamba resistant soybean damage is that significant yield loss is not a common occurrence.

“Exposure to dicamba in the vegetative stages has less long-term effect and potential to reduce yield compared with exposure in the reproductive stages. Our experience with injury during the vegetative stages is that it rarely leads to yield loss, unless there is a significant reduction in plant height,” Loux said. “I know my counterpart in Tennessee is concerned about fields getting hit multiple times. What we don’t really know about yields is the loss if you do have an instance where you’re getting the same field with multiple instances of exposure and injury. What does that do to yield? If you have a continued exposure, that would be an issue. One of the fields I looked at has second round of exposure so we had symptoms develop initially on the fourth trifoliate, followed by some recovery and then injury showed again several weeks later on the newest growth.”

Beyond nearby soybeans, dicamba is also deadly for countless other horticultural, vegetable, and fruit crops. In such cases of off-target movement, the costs can escalate quickly.

In addition, the damage can be hard to track and document because it can show up days or weeks after the initial application and can be misdiagnosed. Cases often go unreported.

“One of the things that’s happening is that most of it is not being reported. It’s a neighbor not wanting to file an official complaint against a neighbor so unfortunately it’d be nice if the Ohio Department of Agriculture got to document some of that, but I understand what’s happening there,” Loux said. “We are a very populated state we have vegetables, we have vineyards and things like that and so the concern we have is if we have a high dollar situation like that happen here that’s going to raise red flags and get everybody more excited.”

Dicamba damage can also be challenging to diagnose (and pinpoint the source of) because it can move off-target in multiple ways for multiple reasons. There are many ways the dicamba herbicides can be applied off-label.

“They have an approved list of what you can and can’t mix on their website and you have to go by that. It’s all there, you have to go by the website and it’s all on label. If something happens, they’re going to come out and say, ‘OK you were off label on this.’ One of the things that has happened is that some guys have decided they don’t need to use the approved dicamba products. That was a big problem in the South last year,” Loux said. “The label is complicated. We talked about it this winter and tried to make information available and I know BASF and Monsanto did training too. And you can only use certain nozzles and they specify pressure range for that. There is a whole series of things about leaving a buffer and I have to say in a lot of the fields that I have looked at there is no buffer being left. That’s one of the first things being ignored, because it’s a pain in the neck. Then there is not spraying when the wind is in the direction of a susceptible field and not spraying in certain wind speeds. In some cases I looked at, all of those are being ignored except the right nozzle.”

And, of course, dicamba is known for being volatile.

“Historically dicamba is a volatile product. It’s one of the most volatile herbicides that we have worked with and it’s been difficult for companies to reduce that volatility. Weed scientists have no information on how volatile these new formations really are. We don’t test volatility ourselves, so we have to take companies really at their word on this,” Loux said. “I think our assumption on this was that we weren’t going to completely reduce the volatility. You had to sort of go on good faith and assume that they wouldn’t sell a product that has considerable potential for that.”

That assumption was not made by southern weed scientist Ford Baldwin, who has been very vocal about his dicamba concerns. Baldwin works with Bayer and the Arkansas State Plant Board and has been in the thick of the steamy dicamba debates in the southern states.

“We’ve got over 600 complaints right now and our plant board proposed to the stop the sale of dicamba because we’ve got about 34% Xtend beans and a lot of the counties where there is heavy Xtend use, every other soybean there is being hammered. We have two kinds of soybeans — dicamba beans and those that have been nuked by dicamba beans,” Baldwin said. “We’ve got about half the people that want to grow Xtend beans. They like the technology and they like the weed control. The problem is we’re not keeping it on target. When you go look at a field that has been hit by dicamba the first time, you see the physical drift pattern. Then things bump along and you think you’re pretty good until about two weeks later it’s like a bomb goes off in the air. Then every single field that is not an Xtend field in a given area looks the same. There is no pattern to it. Every plant and field looks the same. There is no doubt in my mind that it is vapor volatility. Even though these are lower volatility products they are not non-volatile. In these 90-degree temperatures when you get a whole bunch of it on the ground in a given area, the vapors are cooking off and going into the air. It is accumulating and there are inversions at night and it is going all over.”

The challenge, Baldwin points out, in many of these situations appears to be by-the-book label-following with a volatile product.

“If it is moving off target due to drift, then you did not apply the product properly and that is an applicator issue. On the other hand, if you put it out in your field and you followed the label and got it perfectly on target and then the next couple of days it turns into a gas and moves off target and goes and kills a bunch of red gold tomatoes, is that an applicator problem or a chemical problem? I personally believe that the technology cannot be used in the form that it exists today,” Baldwin said. “If we can’t use it, that is a bad deal. That takes away a technology. But it has to be all or nothing. You cannot intercrop dicamba in non-dicamba soybeans and you all will learn that up there in Ohio probably around the first of August. You have to be either zero dicamba or 100% dicamba. It is all or nothing. Then if you go to 100% dicamba you are putting even more of it into the air and our trees will be rolled up, our gardens will be rolled up and our horticulture crops will be rolled up.”

The other challenge is that more dicamba means more potential for dicamba resistant weeds.

“We’ve already proven you can develop a dicamba resistant pigweed in as little as three years. If you’re a farmer out there planting 100% dicamba, you’re going to be happy for a year or two but then you’re not controlling your pigweed and waterhemp with dicamba and you’ll have drastically reduced yields. And if you don’t plant dicamba, then your neighbors are going to kill your beans,” Baldwin said. “On one side you have these farmers that say, ‘Look I paid the trait fee and bought this technology in good faith and now you’re taking it away from me in the middle of the road?’ On the other hand, for every acre of that you have two acres that are being severely affected and they don’t have a chance of getting any compensation for anything. What is the effect on the million acres of soybeans we’ve got that have been hit with dicamba and have a 10% to 15% yield loss on a 60-bushel yield average? Do the math.”

But the dicamba issue is more complicated than simple math. The labels for the new reduced-volatility dicamba are more complex than most applicators are used to and it creates significant potential for accidental misuse. There is also cost incentive for purposeful off-label use or use of unapproved dicamba products which can directly cause some of the issues being observed, said Monsanto Crop protection lead Ty Witten.

“There have been reports of off-target movement or damage from dicamba but we don’t necessarily have good data behind this. That is the part that is troubling to me,” Witten said. “Good data is really important to have regardless of how this is playing out to know what is going on. We know there are difficulties with application making sure that growers do the right thing. There are questions as to when to apply it with regard to weather patterns for inversion. That becomes an important piece. We have reports of off-label use and unapproved products. It is a lot of information and we don’t have clear line of sight on and we want to make sure everybody is well informed before we have immediate actions taken.”

Witten said Monsanto has a hotline set up for these exact issues that is helping to provide insights into the issue.

“We are hearing reports from the Boothill area of Missouri, Tennessee and Arkansas. That is really where most of the reports are coming in. The calls we have received in the call center are not indicative of what we are hearing in the media,” Witten said. “We have had some calls from growers with questions and we are investigating those actively.”

One of those cases illustrates part of the dicamba dilemma.

“Volatility of XtendiMax TM with VaporGrip is the lowest on the market but it is still not zero. Unapproved tank mixes can cause problems, ammonium sulfate, for example, is not approved and it can increase the volatility of dicamba. AMS has almost become a staple on some farms for hard water and use of glyphosate but it can increase the volatility of dicamba. If a grower uses dicamba with an AMS product they are not going to have a good experience,” Witten said. “We got a call from a grower in Iowa and they went above and beyond and absolutely did the right thing. They left an upwind buffer and then went and treated that space with a small tank mix with about 35 gallons in their tank after they’d been treating other parts of their farm. In our field inspection he said he had two or three gallons of AMS left in the tank, would that cause the issue? That absolutely caused the issue. Even compounding that, it was late in the afternoon when they applied that and it went to a dead calm after the application. With AMS and the weather pattern, even though that grower did the right thing, he ultimately did something that could potentially harm the neighbor. With new technology we need to have good information so we can properly train and inform as the product moves forward.”

Witten also stressed that good, clear communication is important when sorting these issues out.

“There is nothing better for this than good communication as we move forward with more diversity in the future. With some of the reports that happened last year with off-target movement and illegal applications of dicamba, growers were reluctant to notify others that they were using dicamba for fear of getting the finger pointed at them if a problem did happen,” he said. “‘Flag the technology’ is a great tool out there to help, custom applicators especially. A flag can help identify those fields. Texas employs the use of flags for the technology. Being a good neighbor is important and the wonderful thing about this dicamba technology is that growers have more choice than ever before to combat weed resistance. That choice is an awesome thing but at the same time we really need to respect what is sprayed on the farm.

“I have been involved with this technology for over a decade and I am excited about the success stories and the opportunities for effective weed control. There are approximately 20 million acres of Xtend crop product out there between soybeans and cotton. We have been seeing really good success and weed control. The growers that are having success are just moving on and farming.”


Photo by Mark Loux.
Photo by Mark Loux.


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