Effect of powdery mildew of pecan shucks on nut weight and quality and relevance to fungicide application

Abstract Powdery mildew of pecan, caused by Microsphaera penicillata (Wallr.:Fr.) Lev., infects pecan shucks but rarely infects other parts of the plant. Although common in orchards in the southeastern United States, it has not been a concern in irrigated pecans in the Southwest until recently. In the past three years, orchards in southern Arizona have been heavily infested. Infections were superficial but caused discoloration of much of the shuck surface. Trials were conducted in 1999 and 2000 to determine if powdery mildew affected nut quality in these orchards by comparing nut weight, kernel weight and kernel color from infected and non-infected fruits. Since powdery mildew infections were ubiquitous throughout the orchards, preventive fungicide applications were made to selected fruits to maintain disease-free shucks as non-infected controls. After harvest, there were no significant differences in whole nut weights, kernel weights, percent fill and kernel color ratings in infected fruits compared to non-infected fruits. Results indicate that powdery mildew infection of pecan shucks does not affect nut weight or kernel quality in irrigated orchards of the Southwest and that control measures for powdery mildew infections are not needed.