How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

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.

COMMENTS ON THE DISEASE

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.

MANAGEMENT

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 and record results on a monitoring form (100KB, PDF).

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PUBLICATION

UC IPM Pest Management Guidelines: Peach
UC ANR Publication 3454
Diseases
W. D. Gubler, Plant Pathology, UC Davis
J. E. Adaskaveg, Plant Pathology, UC Riverside
J. K. Hasey, UC Cooperative Extension, Sutter/Yuba counties
Acknowledgment for contributions to the diseases section:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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