The 2021 cropping season may be seeing the high mark for off-target dicamba herbicide damage on non-tolerant soybeans, but it is tough to separate it out from drought, weed experts say.
Joe Ikley, North Dakota State University Extension Service weed specialist, in a July 19, 2021, interview at a field day at Casselton, North Dakota, said there appears to “a lot of off-target movement affecting non-Xtend (non dicamba tolerant) soybeans,” he said.
With soybeans early in their reproductive stages, it was the most important time to catch significant rains. And it was too early to determine the severity and breadth of this year’s dicamba damage, he said.
Dry conditions produce more leaf “cupping” symptoms at lower dose rates than in a normal rainfall season, Ikley said.
Cupped soybean leaves in fields across the Midwest are a problem this summer, and South Dakota State University Extension weed science coordinator Paul Johnson said off-target dicamba drift is the first conclusion many farmers jump to. However, the cupping really is a result of a combination of agronomic factors that have been magnified by this year's drought.
"No. 1, we've got a lot of drought stress across the state, and that is causing the plants to, in a lot of cases, look like they might have dicamba problems," he said about South Dakota's crops. "But we've also got a lot of plants out there that actually do have dicamba problems."
And the heat and lack of moisture has exacerbated any issues from dicamba spray drift injury, Johnson said.
“As the drought persists, it’s going to take longer for that soybean plant to recover, and start growing out of it,” Ikley said. Some areas of North Dakota had been catching some rains, which could allow some crops to recover, but too many have not.
“If there is injury from dicamba in the soybean fields, the injury can persist for longer this year,” he said.
Worst since 2017?
Dicamba-resistant soybeans were introduced to the market in 2017. That was the last year dry conditions were “close” to the impacts of the 2021 drought.
“But the primary soybean-growing areas of North Dakota — the eastern part of the state — was not as dry in 2017 as it is this year,” Ikley said. “So I’d say since the launch of this technology, statewide, it’s the driest and hottest year we’ve had since 2017 when the system was launched.”
"Complaint numbers to the North Dakota Department of Agriculture are not up, even though there’s quite a lot of injury out there," Ikley said. “It sounds like people are not, at least, turning them into the (North Dakota) Department of Agriculture, as a whole.”
The South Dakota Department of Agriculture and Natural Resources also has not received widespread complaints.
“The Department of Ag so far is below what they saw last year on complaints, and I think a lot of our farmers are out there and they understand they just have a severe drought situation and there isn’t much they can do about it,” Johnson said.
Johnson said in past seasons where there were a large number of complaints turned into the state regarding herbicide drift on crops, specifically with dicamba, nearly 95% of the cases did not see any yield difference at harvest time and so that settled the issue.
Other states have been getting more complaints, Ikley said.
Ikley perceives victims are becoming “pretty annoyed.”
“People are spending a lot of money on Enlist soybean seed and to have them be ‘cupped’ and really not be growing for a week or two or three, that’s really not something you want to be look at,” he said.
Ikley received one call from a farmer, saying his neighbor was spraying Xtend soybeans in winds with 30 mph wind gusts. Ikley urged the man and others to report incidents to the state, in case a field inspection agent is handy. He suggests they record any suspicious activity using their smartphone.
“Unfortunately, you have that documentation on the back end, but you can’t stop that application from being made,” Ikley said.
However, Johnson said dicamba drift in South Dakota was not a case of applicator error.
“Our applicators did a fairly good job this year. They fought through some very windy and very hot conditions and the problem is the applicator could do everything right and still in some cases it came out wrong,” he said.
Frustration is always higher during a drought year in the first place, Ikley said.
“I think if you look at our farmer population in general, you don’t always want to be turning in your neighbor, anyway,” Ikley said. “You might have an investigator come out to the field and they can’t really draw any conclusions of where the application came from. In that case there’s no recourse for the person who is affected.”
Ikley knows of no one in North Dakota who has gone to court to reclaim dicamba damage claims. He doesn’t know of any North Dakota victims in class action suits. Typically, legal action comes involving high-value, specialty crops.
Harry Stine, founder of Stine Seed, at Adel, Iowa, on July 17, 2021, complained to the Environmental Protection Agency, describing five continuous years of dicamba injury to the company’s non-dicamba-tolerant research and production fields. The manufacturers have expressed confidence in the safety and efficacy of their herbicide, when applied according to the label.
Ikley noted that application restrictions on dicamba make it exceedingly difficult to legally apply dicamba in real-world weather conditions. “You have to have the stars align,” he said. Chiefly:
It is illegal to apply it after a June 30, cutoff, nationwide.
Applications are illegal two hours before sunset to one hour after sunrise, to avoid temperature inversions, which allow the chemical to volatilize and move like a fog.
Wind speeds must be between 3 mph and 10 mph, limiting applications to the middle part of the day for the most part. “Below 10 mph is often hard to accomplish in our state ” Ikley said.
If downwind there is a sensitive crop (like non-Xtend-resistant soybeans), the application is prohibited. So, wind direction can be as important as wind speed.
Ikley said regulators don’t know how many Xtend seeds were planted and how many were sprayed with dicamba.
“I’d say statewide, about 40% to 50% of our soybean acres are probably Xtend, and at least half of those probably received a treatment of dicamba," he said.
With roughly 7 million acres of soybeans, he figures there may be 2 million acres to 4 million acres of the dicamba-tolerant varieties. He thinks that number may have declined because of increased adoption of Enlist, or 2, 4-D-resistant varieties, straight Liberty-Link and non-GMO soybeans and straight Roundup Ready ones.
Other causes of cupping
Unless farmers plant a “true check strip” in the field of dicamba-tolerant beans, where there were no symptomatic soybeans, it is difficult to prove that the damage came from the herbicide and not the general drought, Ikley said.
South Dakota Soybean Association leadership has been working with weed scientists at SDSU and officials with the South Dakota Department of Agriculture and Natural Resources on the issue of cupping. Jordan Scott, South Dakota Soybean Association president, said SDSU has been conducting tissue sampling and running lab tests to determine the cause of the widespread problem. He said they suggest farmers do the same kind of research on their own farms before they point to off-target dicamba drift.
“Different herbicides products can cause different types of cupping, and so farmers should send a sample to be tested at SDSU or work with their agronomist,” he said.
Johnson said farmers can scout their fields to determine what kind of damage they have. As a plant growth regulator, dicamba will cause symptomology on the newest leaves or newest trifoliate of the soybean plant. There is usually a cream-colored tip on the soybean leaf and Johnson said there will be stacking of the internodes on the plant or the spaces between the leaves will be closer together. He said drought stress will show regular spacing between the nodes. Dry soils are causing additional problems that are showing up in soybeans as puckering of the leaves, such as salt issues.