How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS AND SIGNS

Verticillium wilt becomes apparent when leaves on one or more branches, often on only one side of the tree, turn yellow and/or wilt early in the growing season. The symptoms progress until the infected shoots die and dry in a curled position often called a "shepherd's crook". When shoot, branch, or trunk tissue of infected trees is dissected, the vascular ring and often much of the heartwood will display dark discoloration. Foliar symptoms usually appear only on young trees (2nd to 4th leaf). Older trees do not normally present symptoms of Verticillium wilt.

COMMENTS ON THE DISEASE

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

MANAGEMENT

Orchards can be adversely affected by the disease even when low pathogen numbers in soil (2–3 propagules per gram) are present. Verticillium is very common when orchards are planted in soil formerly planted to susceptible row crops such as cotton, tomatoes, melons, etc. Avoid interplanting young orchards with these susceptible crop plants.

Inoculum levels can be reduced by flooding in summer, solarizing the soil, growing several seasons of grass rotational crops (especially rye or sudangrass), or a combination of these treatments. When replanting in an area where susceptible perennials were previously grown, try to remove as many roots of the previous crop as possible. Fumigating with chloropicrin* before planting will reduce inoculum.

Soil Solarization
Preplant. Beginning in late spring, cover the moistened soil with clear, UV-inhibited plastic sheeting. Leave in place during the summer months.

At planting. Cover soil around trees with black plastic sheeting. Leave in place for one to two growing seasons.

PUBLICATION

UC IPM Pest Management Guidelines: Apricot
UC ANR Publication 3433
Diseases
J. E. Adaskaveg, Plant Pathology, UC Riverside
W. D. Gubler, Plant Pathology, UC Davis
W. W. Coates, UC Cooperative Extension, San Benito County
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center, Parlier
J. L. Caprile, UC Cooperative Extension, Contra Costa County
B. A. Holtz, UC Cooperative Extension, Madera County
Acknowledgment for contributions to Diseases:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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