What is in this article?:
- Bacterial blight could crop up in Mid-South cotton in 2011
- Mid-South outbreaks in 2011
Bacterial blight in cotton "isn’t what I’d term a limiting factor 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,” says Donald Blasingame, Mississippi State University plant pathologist emeritus. “To those growers, it’s not a minor problem — it’s a severe problem.”
BACTERIAL BLIGHT in cotton is most often the result of infected or contaminated seed. It affects primarily leaves and bolls and in the Mid-South is usually spread by rain and blowing wind. — Mississippi State University photo
Mid-South outbreaks in 2011
“Last year, we had outbreaks in the Clarksdale, Miss., area and adjoining counties, and also in the Wilson, Ark., area,” Blasingame says. “Of the seed samples sent in last year, about a third had the organism. It doesn’t take very many infected seed in a bag to cause a potential problem.
“For example, you have a bag of seed with only 2 percent or 3 percent of infected seed, and you plant it on 40 or 50 acres. When the canopy closes and the bacteria begin to multiply, if a storm comes through, all of a sudden instead of a few plants infected, you can have a spot as big as a tennis court. If there are subsequent storms, you may have a spot as big as a football field — which started from just a very small number of infected seed.
“Once you see bacterial blight in the field, you really can’t confuse it with anything else, because it doesn’t look like any other cotton disease. The angular leaf spot will begin as a small, water-soaked spot. It won’t be round like cercospera or other fungal-type diseases.
“Many times it’s restricted by some of the leaf veins; sometimes it will carry down the leaf and become almost systemic. It can go to almost any part of the plant.
“It normally enters through natural openings, the stomata, and once inside the plant begins to multiply rapidly, producing a chemical that breaks down cell walls as it moves through plant tissue. It can get on any plant part that is soft enough and has a natural opening. Many times, we’ll see bolls that may not have a lot of bacterial blight on the boll itself, but will have infection on the petiole, which will then drop.
“It doesn’t take a lot of bacteria to cause defoliation, and you can lose the bottom canopy very quickly under the right environmental conditions.”
Given the outbreaks in 2011, Blasingame says, “I think there is plenty of inoculum present for recurrences this year.”
He suggests looking at screening results for seed varieties and “stay away from those that are highly susceptible.” Also, where possible, debris in the field should be destroyed and turned under in order to limit carryover of the disease.
If there are areas where the disease is suspected after the canopy covers, he says, “Get out in the field and look into the lower part of the canopy for signs of the disease.
“Unfortunately, once infection occurs there’s not really much you can do except take good notes on the variety involved and seed lot so you can take precautions the following year.”
Cotton can tolerate a certain amount of defoliation, Blasingame says, “but once the disease gets on bolls, that’s when the losses start. Even if the boll isn’t lost, it may be hardlocked.”
Plant breeders have done a good job of identifying genes for resistance to the bacterial blight pathogen, he notes.
“There are at least 22 strong genes of resistance, but for most plant breeders, the first thing they look at is yield. And if they’re dealing with an organism that has a history of only 1 percent to 2 percent loss over 50 years or more, they’re likely not going to spend a lot of time on incorporating genes for resistance.
“So, when choosing your cotton seed, look at tests where varieties have been screened for this particular disease, and factor those results into your seed choices.”