[Image: Picture of leaf spot on cotton]
Symptoms
Cotton foliage is susceptible to a variety of leaf spots. These spots vary from a few millimeters to a few centimeters and from brown to tan to white, depending on the fungus involved and the stage of development. Many leaf spots may be surrounded by a red to brown halo. In some leaf spots, the center may drop out, giving a shot-hole appearance; or they may contain concentric rings with a bull's-eye appearance.
Leaf spots rarely contribute to crop losses in Louisiana. Under the conditions of high rainfall or high humidity; however, leaf spots can develop during the season and contribute to losses by defoliating plants. Some leaf spots are more severe on nutrient-deficient plants.
Causal Agent and Disease Development
Some of the fungi associated with leaf spots are associated with boll rots. The most common are Cercospora, Alternaria, Stemphyllium and Rhizoctonia. In Louisiana, most leaf spots develop early in the season shortly after planting or late in the season near harvest during periods of rainfall.
Control
Control of the leaf spots is not considered necessary because they seldom cause any crop losses. Maintaining good, balanced nutrition will reduce their severity.