Mycosphaerella caryigena

Author: Paul Bertrand, University of Georgia

Symptoms

Downy spot symptoms (Figure 3) are usually first seen in late June or early July. The first symptoms appear as frosty white or pale green circular spots, about 1/8 inch in diameter, on the undersides of the leaflets. The upper side of the leaflets may not show symptoms at this time. In mid-summer the lesions turn yellow. Small faded spots become visible on the upper side of the leaflets above the lesions. In late season, the lesions on the underside of the leaflet become more or less brown with an irregular margin. Faded spots are now clearly visible on the upper leaflet surface. Infected leaflets begin to drop noticeably in August.

Control

Downy spot overwinters on leaves infected the previous season. Most infections occur before pollination but do not show up until late June to early July. The key to downy spot control is a good prepollination spray program. The varieties Stuart and Moneymaker are very susceptible to downy spot and may be used to check for its occurrence. Fungicide treatments for downy spot after symptoms become obvious in July do not have much value and will not prevent drop of infected leaflets.