Tomato Spotted Wilt Virus a Local Problem
There has been a lot of tomato spotted wilt virus (TSWV) found recently in our area. TSWV is a virus that is spread by at least seven different kinds of tiny insects known as thrips. It takes only a few minutes of feeding for a tomato plant to become infected, and once TSWV is acquired, there is no cure.
TSWV is sporadic in nature with some years having high disease pressure and other years having relatively little disease pressure. The virus has locally been found in tomatoes, tobacco and peppers. Because of the unpredictable nature and the broad host ranges of thrips, controlling TSWV can be very challenging.
TSWV can be a major problem both in greenhouses and in the field. It can affect plants like tomatoes, peanuts and peppers along with many ornamentals. On tomatoes, symptoms may be found on leaves, petioles, stems and fruit. Early symptoms include upward rolling of leaves and off-colored bronzed foliage. Later, leaves may show small, dark spots and eventually die. Dark brown streaks can be seen on stems and petioles. Plants may be severely stunted and new growth can be deformed. Sometimes the plant may exhibit one-sided growth and the tops of the plants may turn yellow and wilt.
Fruit symptoms are very distinctive. Immature fruit have mottled, light green rings with raised centers. Mature fruit has a unique red/orange mottling that can make the fruit undesirable. Brown sunken areas may also be produced on fruit.
In North Carolina the most common vectors are tobacco thrips (Frankliniella fusca) and western flower thrips (F. occidentalis). Tobacco thrips are able to spread the virus from nearby weed hosts before insecticides can kill them. Infections when the plants are young usually result in the greatest impact because early infections can prevent flowering and fruit set. Western flower thrips are extremely difficult to control because they are highly tolerant to insecticides. Western flower thrips reside deep within the blossoms, which makes them difficult to reach with insecticides.
The feeding of thrips can damage plants by the collapse of plant cells. This leads to deformed plant growth, flower deformation, and on foliage silvery areas with flecking.
Controlling TSWV is very difficult. In the home garden there is usually little secondary spread after the first wave of infections in the spring when virus-bearing thrips are moving from winter weeds to garden plants. You may wish to remove infected plants, especially those that were infected before fruit set, because they will not recover.
Remove weeds around the garden to reduce the locations that harbor both the thrips and the virus. Specifically target these weeds: dandelion, chickweed, buttercup and plantain. Removing infected plants may slow the spread if they are destroyed when symptoms appear. Many TSWV resistant varieties are available and can be effective. Organic growers may want to consider the use of silver reflective mulches to repel thrips.