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Scab, also known as peach scab (Cladosporium carpophilum), results in superficial lesions on skins of peaches and other stone fruit. Small, velvety, olive-green spots form on young fruit, usually near the stem end. Fruit can become infected anytime during the season, especially if conditions remain wet. Spots become darker, expand to 1⁄4inch diameter, and may crack. Lesions may run together if disease is severe, and fruit may drop in extreme cases. A corky layer underneath the skin develops but does not expand into the flesh. Twig infections cause raised lesions on current season’s wood; they resemble bacterial leaf spot lesions. The fungus overwinters in twig lesions. Leaf infections are uncommon. Infection is more severe when conditions are wet after petal fall. Symptoms develop 6 to 12 weeks after infection occurs.

Peach scab lesions on small branches.

(Photo: USDA-CES Slide Series, Clemson University, Bugwood.org)

Peach scab lesions on fruit.

(Photo: John Strang, University of Kentucky)

Management:

• Increase air circulation to encourage drying of plant tissues (pruning, thinning, spacing).
• Use proper sanitation (remove infected fruit; remove diseased twigs; discard debris away from orchard).
• Use fungicides either at petal fall or at shuck split.
• Peel fruit to remove diseased skins.

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