Abstract
Two years of observations on water availability, black aphids and leaf scorch provides evidence of substantial interaction among these factors. Foliage of irrigated trees of `Desirable', `Cheyenne', and `Wichita' cvs. exhibited much less leaf scorch, black aphid damage, free nitrogenous substances, and sugars than did nonirrigated trees. Water stress appears to predispose foliage in such a way so as to greatly increase the ability of black aphids, and certain fungal pathogens to grow and/or reproduce on/in the affected foliage. This appears to be associated with the organisms ability to induce biochemical changes that increase levels of free nitrogenous substances and sugars. The level and degree of chlorosis and area of foliar damage by black pecan aphids was much greater on nonirrigated trees. Two years of observations on the relative resistance of about 50 cultivars resulted in genotype related differences in susceptibility to leaf scorch.
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