How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS
Young blossom spurs and associated leaves collapse to form shoot blight. Gum exudes at base of infected flowers. Cankers on blighted twigs have tan centers with dark margins. Gray brown spore masses form on diseased flower parts and twig cankers under high humidity.

Monilinia fructicola overwinters on mummified fruit that either fall to the ground in late fall or early winter, or remain in the trees. In spring, apothecia form on mummies that are on the ground; these apothecia release ascospores at the same time as the trees bloom. Ascospores serve as primary inoculum for brown rot in many orchards. Mummies in the trees as well as those on the ground may also produce conidia, which may serve as the primary source of inoculum in some years. Twig lesions apparently do not produce spores.

COMMENTS ON THE DISEASE

Although all flower parts except the sepals are susceptible to infection by M. fructicola, only infection of the stamens leads to the development of blossom and twig blight.

MANAGEMENT

Bloom sprays to reduce blossom and twig blight help minimize loss to ripe fruit rot at harvest. Removal of remaining fruit from trees soon after harvest will help reduce inoculum the following spring.

Take fruit samples every other week after color break (see PREHARVEST FRUIT SAMPLES) to detect any developing problems in the orchard and 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 (see FRUIT EVALUATION AT HARVEST).

Chemical Control
Make a treatment at 20 to 40% bloom and again at 80 to 100% bloom if heavy rainfall or other conditions are occurring that result in high susceptibility to infection. Aerial applications are generally not as effective as properly applied ground sprays but may be necessary when the orchard floor is wet. To help prevent development of resistance to fungicides, be sure to rotate chemicals that have different mode of action group numbers.

More information on peach fungicides

• General properties
• Efficacy on peach diseases
• Treatment timing

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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