Tomato Spotted Wilt Virus (TSWV) was confirmed on tomatoes grown for production in a greenhouse in northern Indiana.
Symptoms of TSWV on tomatoes include dark, brown necrotic spots on leaves, dark streaks on stems, stunted growth and discolored fruit. Symptoms vary according to host. Other vegetable plants affected by TSWV include tomato, pepper, potato, eggplant, lettuce, spinach and cucumber. Several ornamental plants are also affected by TSWV and many weeds may serve as hosts.
TSWV is spread from plant to plant by thrips. Thrips are insects less than 1/20th of an inch long. TSWV can be vectored by western flower thrips, eastern flower thrips, and onion thrips. The western and eastern flower thrips are the most efficient vectors, but they don’t survive our cold winters well. Onion thrips survive just fine in our climate, but they are not as effective in vectoring TSWV. The TSWV is acquired by thrips in the larval stage, however the adults are responsible for most of the spread of the disease. Adults cannot pass on the virus particle to the larvae. The entire life cycle of thrips is about 30 days. Insecticide control of thrips is complicated by the fact that eggs are inserted into the flesh of the plant host and the larvae pupate in the soil-both spots are beyond the reach of insecticides.
TSWV has usually been a more serious disease of vegetables in tropical and subtropical climates than areas of the Midwest such as Indiana. This is because the thrips vector does not overwinter well here. Greenhouses provide an excellent opportunity for thrips survival and population growth. Where thrips are abundant, TSWV can become a problem. TSWV can move from a greenhouse to a nearby field of susceptible crops, such as tomato. If you have TSWV and thrips in a greenhouse near where you plan to grow field tomatoes, you should make every effort to eliminate the virus and thrips before you plant in the field.
Management of TSWV centers on controlling the thrips vector.
- Preventing TSWV is easier than halting the spread of this important disease. Do not plant ornamentals and vegetables in the same greenhouse. TSWV may be introduced on ornamentals that are propagated by cuttings. The disease can then spread to vegetables.
- Use transplants known to be free of both TSWV and thrips.
- Plant resistant varieties if possible. For example, there are a few tomato cultivars with resistance.
- Use yellow sticky traps to monitor thrips populations or by direct observations on the flowers.
- Thrips should be managed with insecticides when populations reach an average of 5 thrips per flower. However, if plants show symptoms of TSWV and thrips are present, control measures should be implemented. Effective insecticides that can be used in the greenhouse include Conserve®, Rimon®, and Venom®. When using insecticides to control thrips, coverage is critical. Thrips are very small and often will hide in seams and crevices, so make sure you have sufficient water and pressure to get the insecticide mixture to where the thrips are. If TSWV symptoms are suspected, send samples to the Purdue University Plant Pest and Diagnostic Laboratory.
- Remove symptomatic plants from a greenhouse with TSWV. Do not compost such plants; instead destroy them. Avoid crop debris in the greenhouse such as older leaves that have fallen or pruned leaves.
- Keep the area clear of weeds that may serve as hosts for TSWV.
Vegetable growers, particularly those who produce greenhouse tomatoes, should be on the look out for TSWV symptoms and implement the preventative measures above.
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