Bacterial blight is like that really bad case of the flu you had one time years ago: It doesn’t happen often — but you never forgot it. In cotton, it can be just that bad.
It is an opportunistic plant disease in cotton, says Jason Woodward, Texas A&M AgriLife Extension pathologist at Lubbock. “The pathogen has been reported in every country where cotton is grown,” he said at the Red River Crops Conference at Childress, Texas.
“No matter where you go in the High Plains or the Rolling Plains of Texas, you see it somewhere, even in 2011.” Recent reports also indicate frequent and somewhat widespread occurrences in Oklahoma.
Losses can be significant — from 35 percent to 59 percent in field epidemics reported in the late 1950s (before use of acid-delinted seed), Woodward says. “Currently, negligible losses have occurred; however, sporadic outbreaks do occur (they have been more frequent recently).”
The pathogen thrives under high moisture, high heat, and high humidity environmental conditions. It is specific to cotton, and may persist in field debris for a limited time or survive on seed. Cotton is susceptible throughout the growing season, and infections may occur on foliage and bolls.
DAMAGE INCREASES SUSCEPTIBILITY
“If the plant is damaged, it’s possible infection may take place more easily,” Woodward says. Blowing sand, hail, insects feeding on bolls, even herbicide injury, may make the plant more susceptible to bacterial blight.
“If you had the disease last year, there is a good chance it will show up this year. But weather plays a significant role. The pathogen can survive in arid conditions, but disease development is highly dependent on environmental conditions; high humidity is required for infection.” A dense canopy and rainfall, or high irrigation capacity, can also create favorable conditions for infection.
“We saw a lot of acres infected across the region last year, a result of the prevalence of susceptible varieties and conditions favorable for development of bacterial blight. In Texas, we typically see the disease late in the season.”
Farmers can manage the disease, Woodward says. “Since we have a number of resistant varieties, bacterial blight is the easiest disease we have to manage. Choosing resistant varieties is the easiest way to manage it.”
Some of the newer varieties with at least partial resistance to bacterial blight include DP 1518B2XF, DP 1639B2XF, DP 1646B2XF; FM 1830GLT, FM 2334GLT, FM 1900GLT, FM 2007GLT, FM 1888GL, FM 1953GLTP; NG 3500XF, NG 3640XF, NG 3699B2XF, NG 4545B2XF, NG 4689B2XF; PHY 223WRF, PHY 490W3FE, PHY 300W3FE, and PHY 243WRF.
Cotton varieties vary in tolerance to bacterial blight, Woodward says, ranging from resistant, which can equal immune, to partially resistant, partially susceptible, susceptible, and extremely susceptible.
He recommends that growers look at field history, production challenges, and management capacity — including irrigation — in choosing varieties. And he suggests recording seed quality, keeping seed tag information for different seed lots, and saving sub-samples of the seed for testing later, if needed.
Crop rotation may be a useful management tool, he says, and planting date may be a factor if producers can reduce the exposure window for infection.
“We have no economical chemical control,” he says. “Resistant varieties, residue management, and crop rotation are the best options.” Woodward also notes that some resistant varieties have shown limited susceptibility (10 percent) in recent years. “We need to know if this problem increases so we can keep our thumb on the pulse of the issue.”
Like a flu shot, prevention is less painful than dealing with the disease.