Cupping Soybeans: Iowa Farmers Question the Cause, Some Point Fingers

Soybeans exhibiting cupping leaves.
Soybeans exhibiting cupping leaves.
(Lindsey Pound)

In the past two weeks, Iowa farmers have taken to Twitter to show fields of soybean leaf cupping and debate what’s contributing to the problem this season.

In some cases, growers say the culprit is dicamba drift. Others ponder whether the cupping is caused by some mixture of herbicides and crop oil, fertilizer and salts. Still other growers are pointing at Enlist technology which provides three herbicide tolerances – 2,4-D choline, glyphosate and glufosinate – as the issue.

Lindsey Trippett TwitterOn Tuesday, Corteva pushed back on those speculations, encouraging farmers to not make a rush to judgment about Enlist.

“I've done the research myself, starting in 2008, and we have no internal data – nor are we aware of any external data from universities – that would support any of these allegations or speculations. It just has not been happening, based on our data package,” says Eric Scherder, crop protection launch manager for Corteva.

Iowa State University (ISU) Extension field agronomists say they have found off-target dicamba drift to be causing injury in some fields.

Paul Kassel notes in his July 7 report (available at https://bit.ly/3hBwVdl) that “off-target movement of dicamba products is fairly widespread in many Enlist, Liberty Link or conventional soybean fields. The dicamba drift injury symptoms began to appear around June 20 and have persisted since,” writes Kassel, an ISU field agronomist based in northwest Iowa.

Phil KIn that same July 7 report, ISU field agronomist Rebecca Vittetoe says the main concern or issue she had the first week of July was herbicide injury in soybeans due to a “growth regulator or group 4 herbicide.” Paul Kassel photo

Group 4 herbicides are plant growth regulators, also referred to as synthetic auxins, and include dicamba, dichlorprop (2,4-DP), mecoprop, MCPA and picloram. These herbicides represent three chemical families that make up the group 4 herbicide category.

The International Herbicide-Resistant Weed Database offers more information about Group 4 and other herbicides via its online Herbicide Classification System. Information on the site notes that, to date, weeds have evolved resistance to 21 of the 31 known herbicide sites of action and to 164 different herbicides.

Along with herbicide drift problems, application error – whether in mixing, spraying or poor tank clean out when switching technologies – has been cited this season as a cause of crop damage. Virgil Schmitt, ISU field agronomist based in southeast Iowa, says the herbicide injury he was made aware of last week resulted from “mostly tank contamination.”

Regardless of what factors are contributing to soybean leaf cupping this season, Corteva’s Scherder encourages farmers concerned about off-target herbicide movement to report that information to their local state agency.

Hartzler and his colleague, Angie Rieck-Hinz, ISU Extension field agronomist, have provided these resources by state:

 

 

 

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