How to Manage Pests

UC Pest Management Guidelines

Almond

Verticillium Wilt

Pathogen: Verticillium dahliae

(Reviewed 3/09, updated 3/09)

In this Guideline:

SYMPTOMS AND SIGNS

Leaves on one or more branches, often on only one side of the tree, will turn yellow or wilt early in the growing season. The symptoms progress until the affected shoots die and dry up later in the season. Affected young shoots often resemble a shepherd's hook. 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, in 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-round 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 or scion varieties may vary in susceptibility. Second-to fourth-year trees are usually the most susceptible to Verticillium wilt.

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.

Fumigation

Orchards may also be fumigated before trees are planted.

Common name		Amount/Acre
(trade name)
When choosing a pesticide, consider its usefulness in an IPM program by reviewing the pesticide's properties, efficacy, application timing, and information relating to resistance management, honey bees (PDF), and environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
REPLANT SOIL FUMIGATION
A.	METHYL BROMIDE*/CHLOROPICRIN*	Label rates
	COMMENTS: Any use of methyl bromide must be allowed under a current Critical Use Exemption. Fumigants such as methyl bromide are a source of volatile organic compounds (VOCs) but are not reactive with other air contaminants that form ozone: methyl bromide depletes ozone. Fumigate only as a last resort when other management strategies have not been successful or are not available.
*	Permit required from county agricultural commissioner for purchase or use.

PUBLICATION

UC IPM Pest Management Guidelines: Almond
UC ANR Publication 3431

Diseases

J. E. Adaskaveg, Plant Pathology, UC Riverside
W. D. Gubler, Plant Pathology, UC Davis
Roger Duncan, UC Cooperative Extension, Stanislaus County
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center, Parlier
B. A. Holtz, UC Cooperative Extension, San Joaquin County

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