Experts Cite Only One Certain Cause of Soybean Leaf Cupping: Dicamba
In the summer months, U.S. farmers often see herbicide damage in their soybean fields.
Soybeans that are not tolerant to dicamba are extremely sensitive to dicamba drift. Off-target movement of dicamba — even at very low levels — can result in leaf malformation known as “cupping,” which can affect plant growth and yield.
Cupping is distinguishable from other leaf symptoms due to its distinct appearance and effect on leaves. Multiple university weed scientists, after years of study, have found no culprit other than dicamba that causes potentially damaging leaf cupping in soybeans without the dicamba trait.
Busting myths
Speculations have arisen that other causes, such as Enlist® herbicides, AMS and glufosinate, also may cause cupping. Weed scientists reject this speculation.
“There is no scientific evidence that AMS can cause leaf cupping in soybeans,” says Prashant Jha, a professor and Extension weed specialist with the agronomy department at Iowa State University.
In a 2022 blog post, Jha says: “At higher rates or under stress conditions, it may cause leaf burns, but not a cupping response. Nor will [applications of Liberty herbicide] on glufosinate-tolerant or Enlist [E3] soybeans cause cupping. Moreover, we have been using AMS with glyphosate for past several years over millions of acres of glyphosate-tolerant soybeans, but no leaf cupping has been reported.”
Jha goes on to address rumors of Enlist herbicides causing cupping.
“This is also not a valid speculation based on multiple studies conducted by university researchers,” Jha says. “The 2,4-D symptomology on soybean is very much distinct from dicamba symptomology.”
Soybean Symptomology
Soybean cupping misconceptions commonly pop up in grower chat rooms and across social media. University research has demonstrated that the only definitively known cause of soybean leaf cupping is exposure to dicamba, which is a restricted use product.
Soybeans without the dicamba trait are extremely sensitive to dicamba and may show symptomology from dicamba exposure at less than 1/800 of the standard spray rate, according to crop sensitivity research from University of Georgia. In recent years, universities and state regulatory agencies have documented many examples of off-target movement of dicamba.1,2,3 Dicamba motility can be extreme under certain conditions, sometimes moving more than a mile off target.
Dicamba cupping damage often shows up as late as seven to 14 days after application, especially in dry conditions. According to Purdue University Extension research, cupped soybean leaves will have a white-to-yellow leaf tip but no leaf strapping. These symptoms can remain for several weeks and can decrease yields in fields of soybeans without the dicamba trait. Other symptoms include reduced soybean plant height and apical meristem death.
Soybeans – and corn – without the Enlist traits are considered compatible crops because there is relatively low sensitivity to 2,4-D. Enlist E3® soybeans may show a temporary crop response following an Enlist herbicide application. Enlist E3 soybeans may have “drooping” or “sleepy” effect while the plant works to metabolize 2,4-D choline. It’s more likely to occur in conditions where the plant is stressed, including hot daytime temperatures and drought. The plants metabolize the 2,4-D choline and return to normal typically within 24 to 48 hours. Yield is not impacted when this occurs.
Enlist herbicides can also cause cosmetic and temporary leaf strapping, which is different in appearance from cupping. Strapping can occur within hours of herbicide application and dissipates in 12 to 36 hours. Again, yield is not affected.
In the pictures below, you can see the difference between soybean cupping, soybean leaf strapping and leaf drooping.
 Soybean Cupping |  Soybean Leaf Strapping |
 Leaf Drooping |
“Farmers can’t afford to guess about the cause of leaf symptomology. That would be like estimating harvest yield by looking out the combine window instead of checking yield monitor data,” says Eric Scherder, Corteva Agriscience U.S. agronomy lead for herbicides. “Corteva Agriscience strongly urges farmers to seek an objective, data-based approach to diagnosing leaf symptomology in their soybeans. The differences are distinguishable, and university sources can help identify the cause of leaf symptomology in a given field.”
More differences
There are other significant differences between dicamba and Enlist herbicides that can impact crop response in soybeans.
In-crop dicamba herbicides have time-of-day, temperature and calendar cut-off date application restrictions because of the increased risk for volatility and drift. In-crop dicamba applications can only be applied 1 hour after sunrise until 2 hours before sunset. Dicamba applications are completely banned when the forecasted temperature is 95°F or higher on the day of or day after application. If the forecast temperature for the day of or day after application is between 85-95°F, the user can only apply dicamba to 50% of untreated acres and must wait 2 days before treating remaining acres. There are even calendar cut-off dates in the states of Iowa (June 12), Indiana (June 12), Minnesota (June 12 south of Interstate 94; June 30 north of Interstate 94), Illinois (June 20) and South Dakota (June 30).
Enlist herbicides do not have any time-of-day, temperature or calendar cut-off date application restrictions.
In addition, Enlist herbicides do not require drift reduction agents (DRAs) or volatility reduction agents (VRAs). Whereas DRAs and VRAs are mandatory for every in-crop application of dicamba to minimize the risk for drift and volatility that could cause crop damage in neighboring or nearby fields.
More information on Enlist herbicides is available on Enlist.com.
1 Hager, A.. "2019 Observations from the Field: Dicamba." Department of Crop Sciences, University of Illinois at Urbana-Champaign, August 2, 2019.
2 Hartzler, B. “Dicamba: What does the research say?” Iowa State University Extension and Outreach, July 3, 2020.
3 “2020 Mizzou Weed Science Virtual Field Day Video 7: Environmental factors that Influence the Success of Dicamba Applications.” University of Missouri Integrated Pest Management, July 31, 2020.
Dicamba is a Restricted Use Product. The transgenic soybean event in Enlist E3® soybeans is jointly developed and owned by Corteva Agriscience and M.S. Technologies L.L.C. Enlist Duo® and Enlist One® herbicides are not registered for sale or use in all states or counties. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your area. Enlist Duo and Enlist One herbicides are the only 2,4-D products authorized for use with Enlist® crops. Consult Enlist herbicide labels for weed species controlled. Always read and follow label directions.