August 27, 2014
Louisiana cotton farmers need to be on the lookout for target spot, a fungal disease that can quickly defoliate plants.
Trey Price, LSU AgCenter plant pathologist at the Macon Ridge Research Station, said target spot is present in all cotton-producing areas of the state, with the most severe cases in Franklin, Madison and Tensas parishes.
Price recommends that farmers with late cotton crops scout for target spot now, paying close attention to the lower canopy of plants. The disease produces tan- to brown-colored lesions that have concentric rings like a bull’s-eye. Infected plants may look healthy from the road, so it is important to check lower leaves, where the first lesions usually appear.
"It will start with only a few spots but after that, the disease will progress with more lesions, and it doesn't take long for it to start defoliating cotton," Price said. "I've seen some fields go from a few spots to 50 percent defoliated within two weeks."
Impact depends on the stage of the crop. Mature cotton plants probably will experience minimal effects that do not warrant treatment. However, late crops of cotton with bolls that still need to fill could take a significant hit.
Ground application of fungicides such as Quadris, Headline and Twinline can slow disease development, but Price said it is unclear if late-season applications of those products will be economical or result in increased yields.
There also are no known target spot-resistant varieties, although some varieties seem to fare better than others because of their plant structure.
"If you have a variety that's prone to getting tall and having really dense foliage, the disease will probably be more severe on that type of cotton," said Price.
The disease occurs every year in Alabama and Georgia, but has only been an occasional problem in Louisiana. Price said it is more widespread in Louisiana this year because of warm, rainy weather favorable for disease development.
In 2013, Louisiana cotton was valued at $185 million and was grown by 285 producers.
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