LSU AgCenter researchers are using a multidisciplinary approach to study soybean green plant problems across Louisiana.
In recent years, the frequency of plants retaining green leaves, green stems and green pods in fields of mature soybeans has increased significantly.
Research scientists and soybean production specialists believe these symptoms, commonly called "green bean syndrome" or "green stem syndrome," can be induced by a number of what they call abiotic and biotic factors. But there is no definitive research demonstrating these effects within current production systems, said LSU AgCenter entomologist Dr. Rogers Leonard.
Leonard is studying the problem along with LSU AgCenter weed scientist Dr. Jim Griffin, agronomist Dr. Don Boquet, plant pathologists Dr. Boyd Padgett and Dr. Ray Schneider and fellow entomologist Dr. Jeff Davis.
Schneider called the disorder "one of the most serious afflictions to plague the soybean industry," and the researchers say learning more about the exact cause is the key to moving toward the solution.
Green stem syndrome is said to occur when stems remain green and moist after the pods mature. The condition can result in delayed harvest, reduced harvest speed and contamination of harvested seed with green plant material. Mature pods that remain in the field during wet conditions can cause the seed to develop secondary problems or shatter onto the ground.
"The exact cause of the syndrome is unknown but has been attributed to fungal and viral infections, insect feeding that results in delayed maturation and in some cases drought," Leonard said.
The end result of green plants in a field of mature soybeans ready for harvest is a direct yield loss, reduced seed quality and reduced harvest efficiency, according to the experts, who say it also occasionally results in increased use of harvest aids.
Leonard and other LSU AgCenter scientists say their initial research project is needed to clearly reveal the causes that may be associated with this late-season soybean malady.
"Until we are able to clearly define the problem, it will be difficult to recommend a catch-all solution," Leonard said. "Because so many factors at one time or another have been associated with some of the green bean symptomology, this appears to be a complex series of interactions that are not well understood."
That’s why these LSU AgCenter researchers are taking a team-oriented approach and are coordinating and summarizing results from several similar studies across Louisiana.
The current experiments at the LSU AgCenter’s Macon Ridge, Dean Lee and Central research stations are examining the effects of cultivar (Roundup Ready and conventional), plant stress (water deficiency), insects (stink bugs) and fungicide treatments on the incidence of green leaves, green stems and green pods. The core test is with 12 varieties, including two that are older lines developed prior to the Roundup Ready ones.
At the end of the season the various experimental plots will be evaluated for the frequencies of plants exhibiting green leaves, green stems and green pod. All plots will be harvested, and seed yield and quality will be compared to adjacent plants in the plots that are not showing the symptoms.
"For Louisiana’s soybean industry to maintain and even improve production, we need to develop a better understanding of these late-season disorders and determine their effects on soybean yield and quality," Leonard said.
"‘Green bean’ problems encompass a wide range of symptomology and can be in spots or whole fields – but in some cases can cause complete yield loss," he said, adding, "We hope to associate individual treatments in the study with specific symptoms and then figure out what is going on at the farm level."–Mary Ann Van Osdell
(This article was published in the 2008 edition of the Louisiana Soybean & Grain Research & Promotion Board Report.)