Corynespora 'target Leaf Spot' in Alabama Cotton: Fungicide Effect and Variety Response.

The pathogen Corynespora cassiicola causes target-like necrotic lesions on cotton, Gossypium hirsutum, leaves – it is commonly known as “Target Leaf Spot” and can cause complete defoliation of the plant. A study conducted during the 2013 and 2014 growing seasons helps determine the effect of fungicide treatment and variety in target leaf spot management. An irrigated field study was initiated in May of 2013. Treatments were arranged in 2x7 factorial experimental design with main plots being the fungicide treatments (with or without) and the sub-plot treatments being the variety (7 varieties). Treatments were replicated 4 times. The appearance and severity of the leaf spot was rated on the Florida 1-10 scale every 2 weeks beginning after first bloom. Final results reflect that some varieties are more susceptible to C. cassicola and fungicide is effective in decreasing some leaf spotting, but there is no concrete link to yield in either case. This information can be valuable to Alabama farmers for management of this disease. Field study inputs were supported by a grant from the Alabama Cotton Commission.