How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Leaves and petioles on plants infected with tomato spotted wilt exhibit numerous, brown necrotic spots. Margins of leaves wilt and become yellow. Often only one side of the plant is affected, which results in a twisted appearance of the lettuce head. Plants infected early may die.

COMMENTS ON THE DISEASE

The Tomato spotted wilt virus has a very wide host range (over 500 species). The virus is transmitted by several species of thrips. The western flower thrips, Frankliniella occidentalis, is the most important vector. Larvae acquire the virus during feeding and remain infective throughout their life.

A tospovirus related to the Tomato spotted wilt virus (Impatiens necrotic spot virus) has recently been found on lettuce in coastal areas.

MANAGEMENT

Avoid planting next to infected crops. Control populations of thrips with insecticides and fallow fields to allow thrips to emerge from infected* crop debris and disperse from the field. Practice crop rotation to nonsusceptible crops such as small grains.

PUBLICATION

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

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