Downy spot can cause serious, premature defoliation. The cultivars Stuart and Moneymaker are very susceptible. The downy spot fungus overwinters on infected leaves. Powdery mildew occurs on the green shucks and occasionally leaves of most pecan varieties. This white-gray dusty growth is also seen on infected shucks.
Powdery mildew is most common in hot, humid weather.
The cultivar Pabst is very susceptible. Brown leaf spot occurs on mature pecan leaflets. Diseased areas appear as reddish-brown, small more or less circular lesions. As the lesions develop, they may become more irregular in shape and cross over veins in the leaflet. Brown spot is seldom a problem in properly sprayed groves, but can cause some premature defoliation in poorly sprayed groves or groves where a fungicide program is terminated too soon in the summer.