Strawberry leaf spot is caused by the fungus Mycosphaerella fragariae. Characteristic leaf symptoms make this disease easy to identify. At first, small purple spots develop on the upper leaf surface. As the spots enlarge, the centers turn a brown color and are surrounded by a dark, reddish border. These spots may coalesce as they enlarge, and cause death of leaves.
Because the fungus is spread primarily by splashing water, wet spring weather can lead to higher disease incidence.
Control: Plant resistant cultivars; many are available. THIS IS THE MOST EFFECTIVE CONTROL MEASURE. Where practical, remove infected leaves and leaf debris, because the fungus overwinters on infected leaves. Protectant fungicides (benomyl, captan, or thiram) can be applied when susceptible cultivars are grown. Begin fungicide applications after symptoms start to appear. In dry growing seasons, fungicides are generally not required.
This article originally appeared in the May 26, 1993 issue, p. 79.