Symptoms and Signs
Plants infected with Tomato spotted wilt virus exhibit bronzing of the upper sides of young leaves, which later develop distinct, necrotic spots. Leaves may be cupped downward. Some tip dieback may occur. On ripe fruit chlorotic spots and blotches appear, often with concentric rings. Green fruit show slightly raised areas with faint, concentric zones.
Comments on the Disease
Tomato spotted wilt virus is transmitted by various species of thrips, including the western flower thrips, Frankliniella occidentalis, the onion thrips, Thrips tabaci, and the chili thrips, Scirtothrips dorsalis. Tomato spotted wilt virus also infects the thrips vector. Nymphs that acquire the virus by feeding on infected plants will retain the ability to transmit it for the remainder of their lives. Tomato spotted wilt virus cannot be passed from infected females through the eggs.
The virus has an extremely wide host range, including many weeds and ornamentals as well as crop hosts. It is one of the few plant viruses with a host range that includes dicots and monocots (e.g., tomatoes and onions). Recent outbreaks have occurred in the San Joaquin Valley where they are believed to be associated with nearby infested crops or weeds.
Management
Management of tomato spotted wilt is generally not practiced in California, but in areas where it is known to occur, plant resistant varieties and control western flower thrips and onion thrips when the virus is detected early.
Before the Growing Season
- Plant resistant tomato varieties with the Sw-5 gene. Resistant varieties generally do not require insecticide applications for thrips to control tomato spotted wilt.
- Use virus- and thrips-free transplants from greenhouses that manage thrips and inspect transplants.
- Manage thrips on transplants before planting.
During the Growing Season
- Avoid planting near crops infected with Tomato spotted wilt virus.
- Monitor for thrips and tomato spotted wilt symptoms.
- If thrips are present and symptoms are observed, manage thrips to minimize the spread of the virus within the field.
- Consider removing infected plants at the seedling stage.
- Control weeds in and around fields.
After the Growing Season
- Promptly remove and destroy old tomato plants and other host crops after harvest.
- Control weeds and volunteer plants in fallow fields, non-cropped, or idle land near next year's tomato field.