ROANOKE, Ill. – It’s a practice not commonly seen north of the Mason-Dixon Line: forced defoliation of soybean plants prior to harvest. However, late season defoliation merits consideration by some Illinois soybean growers, according to Mark Schultz and Jason Carr, technology development representatives for Bayer U.S. Crop Sciences. The company does not currently offer a defoliation product for soybeans.

“This is really forward thinking,” said Schultz, pointing out that Mississippi cotton and soybean growers have utilized defoliation products for decades. “The more we talk with growers, the more ways they share with us on how they might use this.”

Carr said there are a couple of reasons why Midwest soybean growers might want to consider late season defoliation.

“Sometimes we have varieties that have amazing late season health and yield and the stems stay green, making it more challenging to harvest. We thought if we could spray those and dry them down to make them easier to cut that there might be some benefits there,” he explained. “Another potential benefit is if you are in an area where you want to try to take advantage of a little bit fuller season bean, you could spray that with a defoliant and harvest it at the same time frame you would have your normal bean. If you are in an area that you usually plant at a 2-9, you could instead plant a 3-3 for a little more yield potential.”

In discussions with farmers, one grower told Bayer crop technicians he could envision utilizing a defoliant on early planted beans to clear his field for fall work and be one of the first to the elevator with his beans.

Defoliation was conducted on soybean plants at R6 and R7 growth stage during Bayer’s 2020 field trials, concluding that R6 applications resulted in apparent yield loss due to smaller beans. With R7 timing, however, two potential benefits were apparent to Bayer researchers.

“We were able to harvest about a week earlier and we kept the same yield potential as the untreated beans. We actually saw about a bushel an acre increase in yields, but it is too early to draw any conclusions from that. But it is interesting enough that we are looking at it again this year on a lot broader acres,” Carr said.

“This might be something used in conjunction with fungicide, because some worry that (fungicide) will keep their beans green (past due harvest time),” Schultz added.

Fungicide has been added into defoliation products Bayer is testing this year, allowing for yield comparisons between fields sprayed with defoliation and fungicide products, and those treated only with defoliation agents. “We are looking at both yield and maturity,” Carr said.

Moisture counts on defoliated soybeans have remained consistent with non-defoliated beans during Bayer’s field trials, according to Carr. 

In high-yielding cotton, defoliants are often used to remove leaves for easier harvest, inhibit regrowth and reduce lint staining. Then a desiccant is applied to speed up the drying of stems and remaining leaves, according to the Texas A&M extension. Common defoliation products for cotton include the adjuvants Inergy®, InterLock® and MasterLock®.

Carr and Schultz met with dozens of farmers in Woodford County, Illinois on August 26-27 to talk about soybean defoliation and other Bayer field studies during the company’s 2021 Roanoke FOCUS Tour.