Downy spot only occurs on the foliage. Symptoms usually become apparent in late June or early July. The lesions first appear as small, pale green to frosty spots on the lower side of the leaflet. 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.