The relationship between Alternaria leaf spot and potassium deficiency causing premature defoliation of cotton

Investigations into the relative roles of Alternaria leaf spot and potassium deficiency in causing premature defoliation of cotton showed that severe leaf spotting developed only on plants already showing deficiency symptoms. Defoliation was delayed or reduced by either the application of potassium fertilizer or by fungicide sprays, but significant yield increases required both fertilizer and fungicide. Removal of flowers also prevented the development of deficiency symptoms and prevented the leaf spot disease. Differences between cultivars in susceptibility to the disease were linked to their sensitivity to low levels of available potassium.