Late season K deficiency and cotton leaf spot due to fungal organisms such as Stemphylium have been investigated by Georgia scientists. In almost every case, leaf spot problems investigated in Georgia involved low soil K, low petiole K and/or low plant tissue K. Low petiole K was the best indicator. Small brown lesions were caused by the fungal organisms Cercospora, Alternaria and Stemphylium. The leaf spot was found to be secondary to the primary problem of K deficiency. Leaf cells low in K are more susceptible to secondary fungal infections. Best management practices minimize K shortages include soil testing, split K applications, petiole analysis, and multiple applications of foliar fertilizer with K during the pinhead square to fourth week of bloom period.

For more information please see: Potassium Deficiency in Cotton Linked to Leafspot Disease