Soybean growers in several states are puzzled by soybean cupping that has recently come to light. There are three probable causes, according to Paul Johnson, extension weed science coordinator at South Dakota State University, including the cupping that is familiar to producers who have had injury from off-target dicamba.
“Yes, we do have dicamba cupping out there, we also have clopyralid cupping that looks a lot like dicamba,” said Johnson. “And basically due to it being so dry late [last] summer and this spring, we have some carryover from some corn and wheat herbicides that have the clopyralid chemical in them. We have also some acetanilide injury like from Dual and Warrant, or things like that.”
Grower Kevin Deinert at Mount Vernon, South Dakota, is one of the farmers whose soybeans are affected.
“We’ve had some varied spots from field to field that have some cupping throughout the county and throughout some parts of the state near me,” said Deinert, second vice-president of the South Dakota Soybean Association. “We have seen some wide-spread fields affected by cupping.”
Each of the three herbicide classes results in subtle differences in the appearance of the cupping, but, said Johnson, “to be 100 percent right, you’d be doing tissue samples from those leaves if you’re within about 45 days of the application happening, or if you’re right after you see the carryover happening,” adding that farmers will want to consider whether that determination is worth the cost. “You can have them analyzed, but it’s about $300 a test.”
While some herbicide injury is exacerbated by hot, dry weather, Johnson has observed that some of the cupping resulting specifically from dicamba injury is delayed by the dry weather.
“What we see is that the top leaves cup, but that is only happening after those leaves have grown out from the growing point and showed that type of injury,” said Johnson. “So consequently, being it’s dry, we’re not growing the bean plant as quick as normal, and so it’s two to three weeks before we see that happening.”
It’s been Deinert’s experience that soybeans cupped to the extent seen in his fields will be ok.
“As long as we continue to receive favorable rain and favorable growing conditions,” said Deinert, “I’m fairly optimistic a lot of these soybeans will pull through and still do very well.”
Johnson concurs, characterizing most of the cupping he’s observed as “minor, and on the top of the plant.”
“As long as the growing point on the soybean plant continues to grow,” said Johnson, “very, very seldom do we see a significant yield reduction.”