Production Blog

Even More Dicamba Questions

Pam Smith
By  Pam Smith , Crops Technology Editor
Connect with Pam:
Soybeans are very sensitive to dicamba herbicide as many growers found out last year when varieties that were not tolerant to the herbicide showed injury symptoms. (DTN photo by Pamela Smith)

COLUMBIA, Mo. (DTN) -- Why wait to get to the issue if it is on everyone's mind? The University of Missouri Crop Management Conference kicked off last week by taking a head-on look at dicamba herbicide use.

Kevin Bradley, University of Missouri weed scientist, kicked off the meeting speaking on: "The Dicamba Dilemma: Where Do We Go From Here?"

It is the same topic we asked Bradley to address in November during a DTN-sponsored webinar that drew nearly 400 listeners. In fact, we had crammed so much content in that webinar that it left little time for questions. You'll find some of the questions and answers generated during that webinar at the end of this article.

The typically soft-spoken and intense Bradley openly admitted how difficult the uncertainties swirling around dicamba have made the past two years and how it has torn at the fabric of agriculture.

"Weed scientists that I talk to all agree that in our careers (and some of those span decades), we've never encountered any issue like this," said Bradley, who is also past-president of the Weed Science Society of America (WSSA).

The divisiveness, he said, is made more pronounced by the fact that few walk any middle ground with regard to attitudes on the technology. Calls to restrict applications of the herbicide because it cannot be contained are met with equally loud rebuttals that the herbicide is needed and beliefs that increased application precautions will control movement.

"There is such a debate going on in this industry right now, that it is unprecedented in scope," Bradley said.

The one thing experts seem to agree on is the need to learn as much as possible about the technology before applicators head to the field in 2018. Seed companies have not pulled back on dicamba-tolerant seed introductions, and industry estimates are acres devoted to the seed could double in the coming year.

The two-day Missouri conference, while not totally dedicated to dicamba, included summaries of field-related research related to the volatility of the new dicamba formulations. The information was presented in the context of reducing off-target movement in 2018. The University of Missouri Weed Science Department has a searchable database of their trial work at….

We'll be writing about many of the topics related to dicamba between now and spray season. We'll keep asking questions and trying to find answers for readers. If we want to keep this technology, it must be applied correctly.

Below are questions and answers from DTN's November webinar: "Dicamba: Where Do We Go From Here." The webinar is recorded and may be listened to here:….

Many of the questions are general to dicamba use. Some of the questions are specific to points made in the webinar; we've included some of those too should you listen to the webinar rebroadcast and wonder about those issues.

The answers have been reviewed by the webinar participants, Kevin Bradley, Jean Payne, Illinois Fertilizer and Chemical Association (IFCA); Jay Magnussen, Iowa farmer and agronomist; and additional weed scientists and industry experts.

Individual states continue to look at and issue local needs labels, so some information may have changed since the airing of the webinar.

Q: Has Missouri settled on an application window for Engenia, XtendiMax and FeXapan?

A: Applications are prohibited after June 1 in the Bootheel counties of Dunklin, Pemiscot, New Madrid, Stoddard, Scott, Mississippi, Butler, Ripley, Bollinger and Cape Girardeau. For the remainder of the state the cutoff is July 15. For more information go to:…


Q: Do you believe that application of older, non-labeled dicamba formulations to dicamba varieties was a contributing source of injury in addition to the other four buckets you listed?

A: It is possible that there were some applications of older dicamba formulations. However, older formulations do not explain away the scope and scale of this issue.


Q: Why are Missouri studies showing air sampling results with XtendiMax and not FeXapan?

A: FeXapan and XtendiMax are identical chemistries. DuPont has a distribution agreement with Monsanto to sell FeXapan.


Q: My understanding is you are not supposed to mix Xtendimax/Engenia with AMS herbicides. Why was that tested (in some of Bradley's Missouri plots)?

A: That is true that AMS is not to be used with these new dicamba formulations. AMS makes the compounds more volatile. It was included in the testing to show just how volatile it can make the newer formulations and compare to the older compounds such as Banvel and Clarity.


Q: I am an ornamental shade tree grower in Illinois with 90 acres. What perimeter around my nursery in miles do I need to be concerned about? How long after application to a nearby field can dicamba still continue to move and damage my trees?

A: No one really knows how far it can move. Some studies are showing we have seen off-target movement of at least 1 mile. On the second question, current data suggests 2 to 3 days after the application.


Q: Any comment on why the low incidence of problems in the Coastal states?

A: Some states were heavier users of dicamba technology than others and simply have more fields and bigger fields. The cropping mix might have kept some growers from totally embracing the technology. Perhaps they sprayed earlier in the season when temps were cooler. There was extensive training done in some states such as Georgia.


Q: My shade tree nursery was drifted by 2,4-D last year causing lots of damage. How will dicamba damage to trees be in comparison?

A: It depends on the tree species. The University of Missouri is doing long-term studies on trees, and there is still much to be discovered there. Initial studies have shown some differences in how different trees respond even though both dicamba and 2,4-D are both auxin herbicides. Typically, 2,4-D does not gas off and move like dicamba -- so when 2,4-D does go off-target, it is more likely a physical drift event and the concentration of the drift could be higher.


Q: Did the drift or crop response occur in both determinate and indeterminate (soybean) varieties?

A: Because all cultivars may handle injury from dicamba differently, the University of Arkansas studied differences in an indeterminate or determinate growth habit in regard to the plant's ability to recover from dicamba injury. You can find more about the study here:…

P[L1] D[0x0] M[300x250] OOP[F] ADUNIT[] T[]

In that study, the indeterminate cultivar was more sensitive in the reproductive stages, while the determinate cultivar was more sensitive to yield loss from early vegetative applications. In general, they determined soybean cultivars that are more determinate in growth habit may be more sensitive to dicamba and susceptible to higher yield loss from off target movement or tank contamination.


Q: What do the new EPA label restrictions do to address the movement of the product AFTER application? How will that be accountable?

A: The new EPA label does not address volatility. Accountability is an open-ended question and one reason this issue is very complex.


Q: Will education and label requirements reduce injury in 2018? Will increased planting of Xtend beans reduce or increase injury in 2018?

A: More education is a good thing, but there was a lot of education done prior to 2017. There are growers that say they intend to plant Xtend soybeans as a defensive move. That would protect those soybeans from off-target movement of dicamba. However, it does nothing to protect other sensitive plants and crops from physical drift and/or volatility. So much of what happens in 2018 will be weather dependent, and that makes it hard to predict.


Q: Any concerns or complaints from Enlist/the new 2,4-D choline product?

A: Cotton is extremely sensitive to 2,4-D. However, soybeans are not as sensitive to 2,4-D as they are to dicamba. Enlist herbicides also have an extensive label and protocols to follow. Enlist was only available in cotton in 2017, but will debut in corn and to a limited extent in soybeans in 2018. The new choline formulation has been shown to be less volatile in university tests than earlier 2,4-D formulations, but applicators will still need to be careful because there are plenty of sensitive crops and plants. Off-target movement of Enlist used in cotton appeared to be limited last year. However, the acreage was not nearly as large as with the dicamba products in 2017.


Q: What is the concern for organic crops? Will it put them out of the organic transition if they experience damage?

A: That's a good question and answers are unknown at this time. An organic grower testified at the Arkansas State Plant Board hearings that any amount of drift onto his crops would mean a destruct. We're trying to get more answers on how dicamba drift might violate the acreage as it relates to transition years. If you are an organic grower, you should ask the certifying agency for clarifications.


Q: In talking with peer association executives, are the IFCA survey results (discussed in the webinar) consistent with their perspectives?

A: We are not aware that other state associations performed a survey, but they did share at a September association meeting that the feedback they received from their members was consistent with what our survey showed. The survey results were shared with all the state associations. Those survey results can be accessed here:…


Q: Will the insurance industry force removal of dicamba by refusing to offer liability insurance for applicators?

A: The jury is still out on what insurance companies will do for the coming year. It is critical that growers check with their providers to see what is being offered for 2018.


Q: The dicamba label was only for two years, so how much better does 2018 have to be to overcome the issues of 2017.

A: Only EPA can answer this question. Everyone you ask will probably have a different answer. Some suggest that fewer cases in 2018 would equate to "success." Others have a much different definition of success.


Q: Is there a need to increase spray volume to higher gallonage to get better coverage.

A: We have seen the label be updated to 15 gallons minimum. Our farmer and retail participant Jay Magnussen said he used between 15-20 gallons on every field last year and was pleased with those results.


Q: Will Illinois be able to perform enough training to get all custom applicators educated? All private applicators?

A: Illinois will have enough venues to enable both customer and private applicators to receive training. IFCA is happy to assist any of our retail members with setting up training meetings and getting an instructor for you. You could include your applicators/operators and farmer customers in these meetings. They can be open to others (i.e. posted at, or you can keep this in-house just for your employees and customers. We just ask that you have 30 people minimum to justify getting an instructor there.


Q: All of the new label changes only address particle drift. If vapor drift is a potential problem, how is EPA addressing this issue? Are they buying into chemical companies' assertions that vapor drift isn't occurring?

A: You are correct. The supplemental changes in the label do not address volatility.


Q: What are the legal regulations for retailers regarding sale of dicamba? What can retailers do, concerning sales from an ethical standpoint, to assist with federal regulations?

A: Retailers can play a vital stewardship role by reminding persons who purchase these Restricted Use Pesticide (RUP) dicamba products to ensure they have training before they apply them, and direct them to any information available in that state regarding training opportunities. Retailers are not legally required to see proof of training before selling the RUP dicamba products, but they are legally required to record the purchasers' pesticide license number on the sales invoice, and to keep that invoice for a minimum of 2 years.


Q: How effective do you think the new technologies have become at reducing drift overall? Is there perspective on these new technologies being capable of completely reducing drift in the future related to the volatility concerns?

A: No technology brought to market thus far is completely capable of reducing drift 100%. While the new formulations have reduced volatility, there is no such thing as a no-volatility formulation. Also, adding some additives and other herbicides can influence the volatility of those new formulations.


Q: I've got a redbud tree in my yard that exhibited symptoms similar to dicamba. At least a mile to the nearest soybean field. Will the perception of urban homeowners be that dicamba was at fault, right or wrong, due to the visibility of this issue?

A: Diagnosing herbicide injury in ornamental plants can be difficult, but redbuds are one of the trees that are often noted for being sensitive to the auxin herbicides. It's important toward keeping other herbicides to show our urban neighbors that we can apply these products without issue. Here's a good resource on those symptoms from Purdue University:…


Q: Are (applicator liability) insurance companies rejecting both the coverage AND defense, or are they defending but reserving coverage?

A: Good question. We asked a specialist in the insurance industry for insight. Here's his response: "The denials I've seen are just that -- denials. I have not observed the parsing of policy benefits -- legal defense. If a suit has been filed against insured, the company likely would defend a groundless suit." There are differences in how insurance companies are handling claims too.


Q: After reviewing the label changes for these products -- do you believe those label changes will result in a significant reduction in the amount offsite damage in 2018?

A: Weather conditions play a big role in what happens. If more farmers plant soybeans earlier and are able to spray earlier in cooler conditions and before a lot of other sensitive crops are growing, then the year may be different. The labels, if followed, should help control physical drift and tank contamination issues. Volatility remains a question as nothing on the EPA's label changes addresses that issue.


Q: Do you expect that insurance premiums are going to go up next year for policies covering drift?

A: It seems likely that both private farm owners and custom applicators could see adjustments in coverage and/or premiums.


Q: The label now says sunrise to sunset, hypothetically, if you had to set a "time" (i.e. 8:00 a.m.), how early and how late would you suggest?

A: Missouri's new label says the three dicamba products cannot be applied before 7:30 a.m. or after 5:30 p.m. In North Dakota, the ruling is applications may only be made from one hour after sunrise to one hour before sunset. Other states are also making recommendations to further define this.


Q: I agree that industry can help address issues related to off-target movement that is traceable (applicator error, drift, label violations, etc.), but how does industry address off target issues that are not traceable to the source (volatility).

A: So far the industry has chosen to say that the injury caused this past year was due mostly to applicator error and that further education will solve the issue.


Q: As a pilot, I check local airport weather stations, as well as other weather stations such as DTN. The issue becomes that field wind speed and direction many times do not reflect similar direction and speeds, when compared, even just a couple of miles can make a difference of 20-60 degrees direction.

A: Whatever method an applicator can incorporate to record field conditions at the time of application, including wind speed and direction, is to their benefit. Even taking a written note of the wind speed direction at the start, during and at the end of the application is helpful from a recordkeeping standpoint and will be considered if an investigation is conducted.

Records kept by the applicator, especially if they are recorded in a consistent and professional manner, will go a long way in establishing the wind speed in the event of an investigation. The Illinois Department of Agriculture, for example, relies on airport and other wind-speed indicators mostly when they feel the applicator's records are not adequate, consistent, or vary widely from what was recorded at a nearby airport. But still they have to prove you wrong vs. prove themselves right, and a good record of in-field wind conditions is your best line of defense in an investigation.


Q: Dicamba affects the new growth of soybeans on the leaves that are there at the time of application. We see damage show up 14-21 days after depending on soybean growth?

A: Dicamba symptoms do not show up immediately after exposure, and as we saw last year, it often took up to 21 days for symptoms to appear.


Q: Isn't part of the problem related to what is sprayed in our neighboring corn fields? Such as the Status and Diflexx in commercial corn. Those folks also use AMS in their tank mixes plus on those particular labels, the rates used are much higher today?

A: Damage to nearby sensitive soybeans has always been a concern when applying dicamba to corn. However, we've sprayed dicamba on corn for years without widespread injury. In the past, dicamba in corn has typically been sprayed earlier in the season before the sensitive soybean was about. However, because the soybean planting window has moved into earlier months, it is a concern. In addition, several of the states where the symptoms were most severe, Arkansas for example, use very little dicamba in corn.


Q: Will the insurance industry force removal of dicamba by refusing to offer liability insurance for applicators?

A: The jury is still out on what insurance companies will do for the coming year. It is critical that growers check with their providers to see what is being offered for 2018. It's also important to discuss plans with your commercial applicator if you intend to have dicamba custom-applied. Some applicators had enough claims in 2017 that their insurance companies WILL NOT cover dicamba claims in 2018. Some applicators have said they won't apply dicamba or will only apply to limited acres in fear of issues with their insurers.


Q: Talked to a local seed dealer, major co. He has not sold any seed this fall for next year. Is this an automatic boycott by the grower?

A: Panel members agreed that Xtend soybeans will be in the field next year. In fact, they expect to see the technology double in use in 2018.


Q: What about effects of drought on soybeans affected by volitization?

A: Stress on the soybean after injury tends to increase yield loss. Areas such as Arkansas that had many dicamba injury claims also had a very favorable growing season this year. Many farmers think that helped control the yield losses from dicamba injury.

Pamela Smith can be reached at

Follow Pam Smith on Twitter @PamSmithDTN


P[L2] D[728x90] M[320x50] OOP[F] ADUNIT[] T[]