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PHOTO: Eran Finkle/Flickr
Tomato spotted wilt virus is a feared disease in many gardens, quickly turning once healthy crops into ruin. The classic symptoms of the virus on tomatoes include a yellowing or “bronzing” of the top sides of tender leaves, which quickly will lead to spotting necrosis and curling. Ripening fruit will show blotching with brown raised spots on green fruit and yellow spots and rings on mature fruit. Infected plants will be stunted with very limited fruit production.
This virus not only attacks its namesake, the tomato plant, but also a wide range of your favorite summer crops, including peppers, eggplants, lettuce and cucumbers. Symptoms of tomato spotted wilt virus differ among host plants and can only be positively identified through professional testing, which is readily available through your local county extension agents.
The Insect Link
It turns out that this destructive plant virus is almost solely spread by thrips, a tiny pest that is nearly invisible to the naked eye. The process begins when immature thrips are infected by feeding on wild or cultivated plants that harbor the virus. After maturation and a brief incubation period, adult thrips can then begin to transfer the wilt virus to any susceptible plants they feed on, including your vulnerable tomatoes, peppers and lettuces. In North America, only a few species of thrips, such as the western flower thrip, the onion thrip and the tobacco thrip, are capable of spreading the noxious virus. Unfortunately, many of these particular thrip species are quite widespread across the continent.
Controlling Tomato Spot Wilt
There is no treatment for plants infected with this wilt virus, so any plants that show signs of infection need to be removed immediately to help slow the spread of the disease in your sensitive crops.
If tomato spot wilt virus is an issue in your area, especially in the Southeast, take proactive steps to both prevent the virus and limit the population of thrips:
- Select and plant cultivars resistant to or tolerant of TSWV. Fortunately, there are many hybrid tomato and pepper cultivars available today that fit this need.
- Use reflective mulch and cultural weed control strategies to help keep thrip populations low.
- Control native weeds around the farm or garden that may be hosts for thrips and TSWV. Some of the worst weed offenders are chickweed, dandelions, cheeseweed, purslane, sow thistle and buttercups, many of which show no visible signs of TSWV infection, but controlling all weeds in and around the garden will help lower thrip populations.
Sadly, organic and conventional insecticides that are available to home gardeners are largely ineffective for controlling thrips because of their moderate innate resistance due to their sheltered feeding sites inside flowers and vegetation.