How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Leaves on one or more branches, often on only one side of the tree, will turn yellow and/or wilt early in the growing season. The symptoms progress until the infected shoots die and dry up later in the season. When shoot, branch, or trunk tissue of infected trees is cut in cross section, the vascular ring and often much of the heartwood will display dark discoloration. Foliar symptoms usually appear only on young trees (first to fifth or sixth leaf). Older trees do not normally exhibit symptoms of Verticillium wilt.

COMMENTS ON THE DISEASE

The causal fungus survives from season to season in soil, debris of previous, susceptible crops, and probably in roots and the lower trunk of infected trees. Often, the fungus can be isolated from living portions of infected tissue year around in the Central Valley. Research has shown that tree yields can be reduced by verticillium even when foliar symptoms are not readily apparent. Specific rootstock/scion varieties may vary in susceptibility.

MANAGEMENT

Orchards can be adversely affected by this disease even when low pathogen numbers in soil (two to three propagules per gram) are present. Avoid interplanting young orchards with susceptible cover plants, such as cotton, tomatoes, melons, etc. When replanting in an area where susceptible perennials were previously grown, try to remove as many roots of the previous crop as possible.

Soil Solarization. To solarize the soil before planting, cover the moistened soil with clear, UV-inhibited plastic sheeting in late spring. Leave the plastic in place during summer months. To solarize the soil after trees have been planted, cover the soil around trees with black plastic sheeting. Leave in place for one to two growing seasons.

Orchards may also be fumigated before trees are planted.

PUBLICATION

UC IPM Pest Management Guidelines: Almond
UC ANR Publication 3431
Diseases
W. D. Gubler, Plant Pathology, UC Davis
J. E. Adaskaveg, Plant Pathology, UC Riverside
Roger Duncan, UC Cooperative Extension, Stanislaus County
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center
Acknowledgment for contributions to the disease section:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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