As the lesions age, a pale green-yellow spot develops on the upper side of the leaflet. The spots on the underside of the leaflets become light brown with a somewhat diffuse margin. 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.