Bacterial blight is a cotton disease that, over decades, has accounted for an average loss of only about 1 percent across the U.S. cotton belt, and many younger growers and consultants may never have seen it in the field, says Don Blasingame, Mississippi State University plant pathologist emeritus.

“It isn’t what I’d term a limiting factor in cotton for most producers — unless they happen to have one of the ‘hot spots’ where it occurs, and in those cases losses can be as high as 25 percent to 40 percent, or more,” he said at the annual meeting of the Mississippi Agricultural Consultants Association.

“To those growers, it’s not a minor problem — it’s a severe problem.”

The organism for the disease, which has been known since late 1800s and occurs in all cotton producing areas of the world, is most often the result of infected or contaminated seed, Blasingame says.

“When I was in graduate school at Texas A&M, we saw bacterial blight quite often. Back then, producers would ‘brown bag’ seed from the previous year’s crop. If the field had bacterial blight that year and saved seed was planted the following year, it would occur again.

“The first outbreak I saw in Mississippi was in 1972, and it was pretty severe. Fields were affected from Rolling Fork up to Clarksdale, with thousands of acres involved. At that time, growers were primarily using mechanical/flame delinted seed, which did a good job of removing lint, but it didn’t control some of the disease organisms that were on or in the seed.

“Then the move was made to acid delinting, which did a good job of removing some of those pathogens from the seed, and for a number of years we saw very little bacterial blight.”

In recent years, however, he says the system of acid delinting has changed from the old type of turning seed over in an acid bath to a mist-type application, “which sometimes can’t adequately penetrate the cracks and grooves of the seed to destroy the bacteria.” The bacteria can be carried internally as well as externally, he says.

Three conditions are necessary for a severe disease outbreak, Blasingame says: the virulent pathogen, a susceptible host, and the proper environmental conditions.

“For most Mid-South producers, the environmental conditions favorable to bacterial blight — rain and blowing wind — occur at some point in the season almost every year. In 2011, we had plenty of inoculum, and a few cotton varieties were fairly susceptible to the pathogen.

“Under certain conditions, the disease can carry over in the field from one year to the next, if there is a mild winter and field debris isn’t destroyed or turned under — but I consider that a fairly minor means of getting the organism into the field. It is most commonly seedborne.”

When an infected seed is planted, Blasingame says, the bacteria “grow right along with the cotyledon and the plant until about mid-season, when the canopy overlaps and produces a greenhouse effect in the bottom of the canopy. The bacteria then grow and multiply, and when a storm comes through with rain and blowing wind they can be dispersed throughout the field, causing seedling blight, damping off, or boll rot.”

The organism for bacterial blight is fairly easy to isolate and identify in the lab, he says, and in the field it “isn’t difficult” to spot the resulting defoliation and loss of bolls that occur in the lower part of the canopy.