Green soybeans problem in Louisiana

Farmers in Louisiana are beginning to see signs of a problem called "green bean syndrome" in their soybeans, according to Ken Whitam, a plant pathologist with the LSU AgCenter.

"The problem is scattered around the state but not as big a problem as we have had in the past," Whitam said, adding, however, that individual fields with the problem are often a total loss.

The problem arises when soybean plants are damaged by insects or disease and continue trying to make seed rather than mature and dry down for harvest, according to David Lanclos, an LSU AgCenter soybean specialist.

"The plant is 'confused,'" Lanclos said, explaining the damage occurs during the growing season but doesn't become apparent until harvest — when other undamaged plants begin to dry naturally.

The problem often is attributed to missed insecticide or fungicide applications — such as when power lines or buildings prevent aerial applicators from spraying the affected areas.

"The problem is a little high, because insect pressure was high this year," Lanclos said.

Whitam explained green bean problems can be attributed to several causes, and identifying the culprit in any individual field is tricky.

But the experts said one cause of green beans is associated with stinkbug injury.

"This damage can be recognized by the punch marks of the insects, and fungi may follow the damage," Whitam said. "Punch marks are evident on the beans and on the hulls."

Whitam said stinkbug-damaged beans often germinate in the hulls before drying. In those cases, the seed is full-sized, and the germinating tips are green, he said.

Some growing conditions also can be another cause of green beans, Whitam said, pointing out the variety DPL 5414 is reported to have green stalks in some fields.

"These beans will cut normal yields but will be difficult to combine because of the green stalks," he said.

Whitam also attributed plant injury to early aerial blight, which can kill flowers and young pods.

"When this happens, the plant tries to flower again," Whitam said. "If the primary pod set is lost, the physiology of the plant is screwed up."

Whitam said this injury can be identified by corrugated, ribbed stems and enlarged nodes and stems, which remain green and are brittle. In such cases, little or no seed are produced, and pods may number 20 to 30 at a single node, he explained.

"Sometimes you can see a few of the primary pods on the plant that are normal, and sometimes they are dead and cling to the plant," Whitam said, adding that stinkbugs may obscure the diagnosis.

Whitam added that other stresses can cause pod drop.

"If this happens, the results are similar to that of aerial blight," he said.

Lanclos said approximately 35 percent of the Louisiana soybean crop of about 800,000 acres remains to be harvested.

And the LSU AgCenter expert said he is worried some of the plants now ready to harvest will have some seed sprouting because of the high moisture — and that harvesting with combines will be difficult because of plants falling over.

"Most of the loss will not be in quantity," Lanclos said. "It will be in quality at the elevator."

Soybean production in Louisiana contributed more than $100 million to the state's economy last year, according to the 2001 Louisiana Summary of Agriculture and Natural Resources from the LSU AgCenter.

Rick Bogren writes for the LSU AgCenter.

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