Target spot a ‘seasonal’ disease in west Tennessee cotton?

Heather Kelly says she doesn’t want to sound too many alarms about target spot in cotton just yet.

Kelly, Extension plant pathologist with the University of Tennessee, gave growers attending the 2014 Cotton Tour an update on the disease and an opportunity to observe its symptoms in a trial she’s conducting at the West Tennessee Research and Education Center.

There’s no doubt that target spot, which is caused by the fungus Corynespora cassicola, can cause premature defoliation and yield loss in cotton. But, the question is, will it rise to that level in cotton fields in west Tennessee.

“I haven’t really raised a lot of alarm on it; I haven’t put out a news blog on it because I don’t want to raise any flags just yet,” said Kelly. That’s because of research by scientists at Auburn University and the University of Georgia, which indicates the disease may pose different levels of risk depending on location.

“What they (Drs. Austin Hagan of Auburn and Bob Kemerait of Georgia) predict are these different kinds of zones of risk for target spot,” said Kelly, referring to a map of the Delta and Southeast states showing the potential for heavy infections of corynespora disease. “Where they see the loss of 300 to 400 pounds of lint to this disease is in the southern portion of Alabama and Georgia.

“They’re seeing a response to fungicides – usually two applications – here in this high risk area of the Deep South.”

Currently, Hagan and Kemerait consider central Alabama and north Georgia to be areas of medium risk for target spot and the risk in the northern reaches of the Cotton Belt in Tennessee and northern Arkansas to be low.

Target spot symptoms were reported for the first time in Tennessee last year, both on the West Tennessee Research and Education Center at Jackson and in Cotton Grove, she said. She was also investigating a complaint that it had been found in Lauderdale County in west Tennessee this season.

The timing of the disease can make a big difference in its destructiveness.

“In this northern, low risk area, it might only be certain years we see the disease come on early enough it can actually affect yields,” she said. “Here in the area (lower South)where they are seeing an impact on yields it comes in in the first or second week of July.”

In Tennessee last year, scientists at the station in Jackson first saw the disease in the last week of August and the first week of September. “This year it did come in about two weeks earlier here on the station.”

Kelly says most cotton varieties are susceptible to the disease. Some varieties are more susceptible than others, but the latter often are among the higher yielding varieties, and the yield loss is not as pronounced.

“In this trial here at the station, every single variety does have target spot,” she said. “The ones that have reduced susceptibility or slightly less target spots are those where the canopy hasn’t closed, or the ones on the end where there is probably more air circulation.”

Kelly is testing one fungicide – Headline – at different application intervals to try to determine the impact the chemistry can have in preventing the disease from infecting plants. Next year, she plans to try another fungicide that has been shown to be capable of eliminating the disease after it appears.

For more information on the cotton industry’s efforts to address the target spot issue, visit http://southeastfarmpress.com/cotton/public-private-sectors-search-answers-about-target-spot-cotton.

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