How to Manage Pests
UC Pest Management Guidelines
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.
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.
Organically Acceptable Methods
UC IPM Pest Management Guidelines: Lettuce