Bacterial Blight (Angular Leaf Spot) of Cotton

Cotton Disease Information Note No. 3
Steve Koenning, Plant Pathology Extension Specialist



Bacterial blight of cotton (also called angular leaf spot) is an important and potentially destructive bacterial disease. The disease is caused by a bacterium, Xanthomonas campestris pv. malvacearum. Cotton yield losses in excess of 10% have been reported in the past, although significant losses to this disease in the United States have not been reported in many years. The disease has only been detected sporadically in North Carolina.

Symptoms


Figure 1. Bacterial blight (angular leaf spot) caused by Xanthomonas campestris pv. malvacearum.



Figure 2. Bacterial blight lesions on leaf and the blackleg symptom on the leaf petiole.

Bacterial blight starts out as angular leaf spot with a red to brown border (Figure 1). The angular appearance is due to restriction of the lesion by fine veins of the cotton leaf. Spots on infected leaves may spread along the major leaf veins. As disease progresses, leaf petioles and stems may become infected resulting in premature defoliation (cotton black leg, Figure 2). Black cankers may girdle the stem or branches causing the portions to die above the canker. A white waxy crust containing the bacterium may form on old leaf spots or cankers. Bolls may become infected causing boll rot which results in rotted seed and discolored lint. Infected bolls have round, rather than angular, lesions that initially may appear water-soaked. As infection proceeds, bolls lesions will be sunken and dark brown or black.

Disease Impact

The extent to which bacterial blight will impact cotton yield in infested fields will depend on environmental conditions during the season. High rainfall, and humidity as well as warm temperatures favor disease development. Yield losses of greater than 10% have been reported.

Management

Remedial actions to arrest disease development are not available. The only positive action growers can take is to use growth regulators to prevent rank growth. Keeping the canopy as open as possible to reduce humidity and promote drying of the foliage may prove beneficial in limiting the progress of this disease. Do not cultivate or move equipment through fields when foliage is wet. Infested fields should be harvested as soon as possible. The cotton variety, seed lot and a rating as to disease severity should be determined. Stalks should be shredded at the first opportunity. Fields that have bacterial blight this year should be planted to a blight-resistant variety next year or rotated to a different crop.

Preventative Actions for Bacterial Blight of Cotton:

Plant high-quality, disease free, acid delinted seed.
Plant blight-resistant varieties if available.
Scout fields and identify infected plants and varieties.
Shred stalks and incorporate cotton debris.
Do not cultivate or move equipment through fields when foliage is wet.

Other Links

Cotton Pest Management Strategic Plan for the MidSouth
NC Agricultural Chemicals Manual

Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact your county North Carolina Cooperative Extension Service agent.

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This webpage last updated January 29, 2004 by Tom Creswell.