Diseases of Pima cotton (Gossypium barbadense) ; upland cotton (G. hirsutum)
Angular leaf spot
This leaf spot disease, also known as bacterial blight, is caused by the bacterium Xanthomonas malvacearum. It occurs only in very moist conditions, usually during prolonged summer rains in the southeastern part of Arizona. Lesions on bolls are circular and greasy in appearance (photo 1) while those on leaves are water-soaked areas that take the shape of interveinal areas infected with the bacterium (photo 2). No control measures are recommended.
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2 
August 3, 2006