September 20, 2010
Diseases In Soybeans Could Cause Yield Loss At Harvest Time
As soybean fields are ready to be harvested, many in Indiana still show symptoms of sudden death syndrome and brown stem rot, says a Purdue University crop disease expert.
Yield losses from both are hard to predict and depend on the variety planted and growth stage of the crop when symptoms first appear, said Kiersten Wise, assistant professor in the botany and plant pathology department.Sudden death syndrome is a fungal disease caused by the soilborne fungus Fusarium virguliforme. Symptoms of SDS include yellowing and discoloration of the upper leaves. The first symptoms typically appear in a few small strips or areas of the field, usually in wet or compacted areas. As the disease progresses, the leaf tissue between the major veins turns yellow, then dies and turns brown.
"There are several management practices that may prevent SDS damage, but once symptoms are present, there is not much that can be done," Wise said.
Producers should plant varieties that are less susceptible to SDS in fields with a history of the disease. SDS is typically more of a problem in early-planted soybeans, like those planted this year in April or early May, Wise said. Planting fields with a history of SDS last and avoiding compaction in those fields may reduce risk of disease development.
Symptoms of brown stem rot can often resemble those of SDS, so it is important to split the lower stem of suspected plants to determine which disease is present, Wise said. BSR can cause internal stem browning, resulting in a dark brown discoloration of the pith at the lower nodes of the plant. If SDS is present, the pith will remain white, and the cortex will be gray or brown.
"It is important to determine if the diseases are present in fields and, if they are, keep good field notes to identify problem areas and plan to manage these fields accordingly the next time soybeans are planted in these fields," Wise said.
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