Scab

Scab affects foliage, young shoots, and fruit, but damage is the result of fruit infections. Fruit infections appear as dark lesions on ripening fruit, most commonly on the upper surface, and may grow together to form large blotches. Lesions may have green or yellowish blotches that turn grayish when spores are produced.

Primarily a problem on cling peaches in the northern San Joaquin Valley during wet spring weather. The fungus that causes scab overwinters in lesions on first-year twigs. Spores are produce in these lesions when humidity exceeds 70% beginning at bloom and lasting several weeks. Spores are spread by air movement and splashing water and will infect developing fruit, although it may take several weeks for lesions to appear.

In orchards with a history of scab, applications of a fungicide within 3 weeks after full bloom to protect developing fruit, and again at 5 weeks if disease was severe the previous year, will reduce fruit infection. Fungicides applied during bloom for brown rot and at petal fall to control shot hole will also reduce the spread of scab if appropriate fungicides are chosen.

Take a fruit damage sample at harvest to assess the effectiveness of the current year's IPM program and to determine the needs of next year's program. For procedures, see FRUIT EVALUATION AT HARVEST. Record results for the harvest (PDF) sample.

• Fruit sampling for pest damage at harvest (PDF)