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Plant pathologist: Bacterial blight unlikely to lower yields

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Written Tuesday, July 26, 2011  

While reports of bacterial blight in soybeans are high this year, a Purdue Extension plant pathologist says the disease is unlikely to hurt yields.

Soybean leaves with bacterial blight have angular lesions surrounded by a yellow halo. The top priority for producers should be identifying the disease so they can prevent unwarranted fungicide applications to manage it, Kiersten Wise said.

"The lesions will turn dark brown and fall out of the leaf tissue, giving the leaves a tattered appearance," she said. "It's pretty hard to distinguish from brown spot, so if you are seeing symptoms and are unsure, send in a sample to the diagnostic lab."

Bacterial blight, caused by the bacteria Pseudomonas, is most common in injured plants. Wise said this summer's thunderstorms and hail might have caused microscopic tears on the surface of the leaves, which allow the bacteria to enter the plant.

"Crop rotation and tillage can help prevent outbreaks of the disease by reducing the amount of bacteria that overwinters in soybean stubble," she said.

Producers can do little to manage bacterial blight during the season. Fungicides are ineffective against the disease.

"It all depends on the weather, and if the conditions are right, there is not much you can do," Wise said. "Hot, dry weather will limit disease development which will reduce the likelihood that the disease lowers yield."

"Even though it looks bad, growers don't have to spray," she said. "Knowing this will save time and money."

There are varieties that are less susceptible to bacterial blight. Wise recommended that farmers talk with their seed providers.

More information can be found online at the Purdue Pest and Disease Diagnostic Lab, http://www.ppdl.purdue.edu/PPDL/index.html or in the July 1 issue of the Pest and Crop Newsletter, http://extension.entm.purdue.edu/pestcrop/

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