Late last growing season, Arkansas soybean fields experienced a rash of green bean syndrome cases.
“This is the same thing that has occurred across the Mid-South periodically and a lot of people, including researchers, are having trouble finding out (its cause),” said Roger Leonard, LSU AgCenter entomologist, at the recent Tri-State Soybean Forum held in Oak Grove, La.
“We're examining this at several levels of study, including varieties, planting dates, abiotic stresses like moisture deficits, as well as effects of herbicides, insecticides and fungicides. My area of study, of course, is insects and insecticide use.”
The problem surfaces when areas of fields, or entire fields, refuse to mature. This often is accompanied by excessive leaf retention on otherwise mature plants, uneven maturity of pods on individual plants, green stems with mature pod and other combinations of abnormal plant development.
“For example, on the same plant, 50 percent of the pods may be ready for harvest and 50 percent are still green and maintaining high moisture.”
Don Boquet, an LSU agronomist, is reviewing the effect of planting dates on this malady. He used the same varieties planted on several dates. For the same variety, one of those dates exhibited green bean symptoms and the others didn't.
“So, the planting date — or at least the conditions during that interval between planting dates — played a role in these symptoms.
“(Boquet) also evaluated his entire soybean variety trial (Louisiana OVT) for green leaf retention and green stalks. It was interesting that the highest yielding varieties in the test also had the highest green stalk grades. Leaf retention was not a factor and they were able to (remove) what few leaves they had with Gromoxone. There appear to be a number of different variety responses that can produce some of these symptoms as well.”
Leonard pointed to a photograph of a soybean field that looked like a patchwork quilt made of green and brown material. “Soybean insect pest studies are the easiest to create a (green bean syndrome) scenario. This is an example of a study where plots were treated for stink bugs and others were left non-treated. Those that weren't treated exhibited green stems, uneven pod maturity and excessive green leaf retention. It was a row-to-row effect.
“We know that stink bugs can create these symptoms but that pest is also one of the easiest to prevent. Just scout and spray according to action thresholds prescribed by the Mid-South entomologists.”