Causal Agent
Turnip mosaic virus (TuMV)
Distribution
Worldwide, especially in temperate regions
Symptoms
Leaves of cabbage, cauliflower and broccoli infected by the cabbage black ringspot strain of TuMV have 2-5 cm (¾-5 in.) of circular, light green lesions, which can best be seen on the abaxial leaf surface. Later, these lesions turn necrotic and may coalesce, resulting in large necrotic areas, which lead to defoliation. In cabbage, the outer leaves may develop necrotic spots which can occur throughout the head. In Chinese cabbage, symptoms manifest as vein necrosis and necrotic spotting of head leaves, and are often on one side of the plant. In turnips, radishes and mustard, leaf distortion, blisters, mosaic and stunting are commonly seen symptoms with any strain of the virus.
Conditions for Disease Development
Turnip mosaic virus is generally transmitted mechanically and in a non-persistent manner by more than 80 species of aphid. Cruciferous weeds are hosts for both the virus and aphid vectors. Generally, virus symptoms are more severe at temperatures between 20-28°C (68-82°F). Simultaneous infections of TuMV and Cauliflower mosaic virus result in severe stunting and vein clearing in cool weather. During warm weather, mottling and stunting are more common.
Control
Implement an insecticide spray program to help control vectors. Eradicate cruciferous weeds and volunteers. Incorporate plant residues immediately after harvest. Isolate transplant beds from crucifer crop fields.
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