How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS AND SIGNS

Fusarium wilt causes infected seedlings to wilt and possibly die. Inner tissues of affected seedlings are red or brown. In older plants, leaves turn yellow and develop tipburn. Internally, the vascular system is brown to black in the leaves and a reddish brown discoloration develops in the cortex of the crown and upper root. Plants may be stunted and fail to form heads.

COMMENTS ON THE DISEASE

In California, Fusarium wilt of lettuce occurs primarily in Fresno County. Recently, the pathogen has also been confirmed in coastal Monterey and Santa Cruz counties. The pathogen causes a disease only in lettuce but may be sustained on the roots of many plants. Once introduced into a field, the fungus will probably remain indefinitely. It exists in the form of three races, but only Race 1 is currently found in California. Fusarium wilt symptoms may resemble those caused by ammonium toxicity and Verticillium wilt.

MANAGEMENT

Cultural Control
Avoid infested fields. Do not move soil from an infested field into a clean field.

Organically Acceptable Methods
Cultural controls are organically acceptable.

PUBLICATION

UC IPM Pest Management Guidelines: Lettuce
UC ANR Publication 3450
Diseases
S. T. Koike, UC Cooperative Extension, Monterey County
R. M. Davis, Plant Pathology, UC Davis

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