The bacterial blight of cotton is also known as "black arm." This disease is caused by a bacterium that infects cotton plants and causes dark, sunken lesions to appear on the stems and branches. These lesions can spread and ultimately kill the plant. The name "black arm" comes from the appearance of these lesions, which often turn black as the disease progresses. Other symptoms of bacterial blight of cotton include wilting, leaf drop, and boll rot.