Tomato Diseases: How To Fight Tomato Spotted Wilt Virus

by Matt Gibson

About Tomato Spotted Wilt Virus

Tomato Spotted Wilt Virus is a plant disease that is now quite common in any temperate, subtropical, and tropical environments around the world. The virus affects over 1000 different plant species and has become a major concern for tomato farmers. The virus affects many ornamental plants as well as vegetable plants such as tomatoes, peppers, basil, lettuce, beans, peas, and potatoes.

There is no known cure for the virus once it has taken hold of a plant. Luckily, there are plenty of preventive methods that you can implement to reduce the chance of it occurring in the first place. The scientific name for this disease is tomato spotted wilt Orthotospovirus (TSWV), and tomato chlorotic spot Orthotospovirus (TCSV).

Causes And Symptoms of Tomato Spotted Wilt Virus

Tomato spotted wilt is caused by thrips, which are actually common garden pests. The small insects feed on a number of plants by puncturing the leaves and sucking out the plant’s contents. Thrips get the virus when they are in the larval stage while feeding on infected plants, such as weeds. Once contracted, they transmit the virus to adult thrips which fly from infected plants to healthy plants.

While the virus can be contracted only by the larval stage of thrips, the transmission of the disease is almost exclusively due to adult thrips. Larvae can acquire the virus in as little as 15 minutes and cannot transmit the virus immediately, but only after a latent period of incubation which lasts anywhere from three to 10 days depending on the vector species.

Once transmission occurs and thrips become infective, they can transmit the virus to adult thrips for a period of 22 to 30 days, or for the remainder of their adult lives. Adult thrips do not pass the disease down to their progeny, but overlapping stages in the insect’s life cycle tend to account for the continuous spread of the virus.

Several biological characteristics of the insect make control especially difficult. Thrip eggs are inserted into the leaf or plant tissue, so they are protected from insecticides. After two to four days, the eggs hatch into larvae that remain in protected areas, such as flower buds or terminal foliage. Toward the end of the larval stage, the insect usually stops feeding and moves down into the soil to pupate, where they miss insecticides that are directed at the foliage of the plant. The adult thrips, which live for approximately 30 to 45 days and lay anywhere from 150 to 300 eggs, feed primarily in flowers and terminals, which are protected parts of the plant.

Infected tomatoes have a number of noticeable symptoms. Visible characteristics of the disease include dark-spotted or bronze-colored foliage, dark streaking within the plant’s terminal stems, noticeably stunted growth, and the plant’s growing tips may experience die-back. The fruit which the infected plant produces will likely appear deformed or wilted, and there is usually a significant reduction in quality as well as yield. Ripe fruit looks distorted and may be covered with distinctive red and yellow ring-like markings.

Treatment and Control of Tomato Spotted Wilt Virus

Once spotted wilt has infected a plant, there is no treatment options that will save the plant, but there are actions that you can take to reduce and control the spread of the virus from plant to plant.

Tomato spotted wilt is not easy to control in fields of tomato plants because of the virus’s large plant host range, which includes weeds and perennials. Once the disease is noticed, remove infected plants and destroy them immediately. This is not always a foolproof solution, however, as the virus has often spread before symptoms ever appeared or became noticeable.

If you live in an environment with a high occurrence rate of the disease, or an area with a high population of thrips, planting resistant tomato varieties is a wise option. It is also important to keep your tomato plants away from susceptible plants whenever possible, especially if you are growing tomatoes in your home garden or in flower and grain fields.

At the end of each crop’s harvest, remove all thrip sources, like weeds. After removing all plant debris that could be harvesting thrips, plow your garden areas and let lie fallow. In approximately three to four weeks, thrips should have emerged and dispersed, but it is still smart to reduce cultivation and avoid moving thrips from already infected plants.

If you are growing your tomatoes in a controlled environment, such as a greenhouse, it will be slightly easier to control the virus. Use yellow sticky cards to mark areas where you notice early infestations, placing the cards above the crop canopy. These cards will allow early detection of an infestation, which will improve your chances of removing the infected plants before the disease begins to spread. You can also lower thrips exposure through the control practice of applying a fine mesh cloth to doors and air vents.

Using insecticides to control thrips is not effective in the field or controlled environments like the greenhouse, as thrips are known to develop resistance to common insecticides very quickly. Pesticide rotation helps to lower thrips resistance capabilities. Several applications made in five-day intervals are necessary for this method to have much effect.

Before the growing season begins, plant disease resistant tomato varieties with the Sw-5 gene. These varieties do not require insecticide applications for thrips in order to control tomato spotted wilt. Use virus and thrips-free transplants from greenhouses that inspect transplants and actively manage thrips. Check transplants thoroughly for any signs of infestation before planting,

During the growing season, avoid planting near any crops that are infected with the virus and continue to monitor for thrips and tomato spotted wilt symptoms. If thrips are spotted or symptoms observed, manage thrips to minimize the spread within the field by removing all infected plants and seedlings, and by controlling weeds in and around the fields.

After the growing season, promptly remove and discard all old tomato plants and any other host crops after the harvest is complete. Control weeds and volunteer plants in non-cropped or idle land near next year’s field, as well as in fallow fields.

Common Questions and Answers About Tomato Spotted Wilt Virus

Can you eat tomatoes with tomato spotted wilt virus?

Tomato spotted wilt virus may prevent your tomatoes from maturing or developing the flavor you’re used to getting from homegrown tomatoes, but they are safe to eat. That said, it’s best to remove the plants from the garden and destroy them to prevent spreading the disease. Remove and discard any weeds growing near this part of your garden as well, and clean and sterilize your gardening tools. You might choose not to plant in this location in the next few coming years to ensure you’ve overcome tomato spotted wilt virus.

How do you treat tomato spotted wilt virus?

As it is not possible to cure infected plants, once plants begin to show symptoms of tomato spotted wilt virus, they must be removed from the garden and destroyed. Weeds growing near infected areas of the garden should be removed as well, as the weeds can provide shelter for the thrip insects that spread tomato spotted wilt virus. When removing weeds, pay particular attention to annual sowthistle, buttercup, chickweed, dandelion, and plantain weeds. To ensure not contracting the disease in future years, gardeners may choose not to plant in areas where plants that had tomato spotted wilt virus previously grew. Silver reflective mulch can be used to further discourage tomato spotted wilt virus. If the silver reflective mulch cannot be found, you can paint black plastic silver with spray paint.

Is tomato wilt a viral disease?

Tomato spotted wilt virus is a viral disease that is spread by small insects called thrips.

What are the symptoms of tomato spotted wilt virus?

Tomato spotted wilt virus causes the upper side of leaves to be discolored to bronze, eventually developing necrotic spots on their foliage. Some plants will experience tip dieback, will have leaves that are cupped downward, or will show other signs of deformation. You can see signs of the virus on green fruit as concentric areas and raised zones become visible, or on ripe fruit, the virus’ signature pale blotches and chlorotic spots are easy to notice. In addition to the yellow ring-like spots that are easy to diagnose, some plants also produce sunken, brown necrotic areas.

What causes tomato spotted wilt virus?

Tomato spotted wilt virus is spread through the movements of small insects called thrips. Controlling thrips will help control the virus, but gardeners should be aware that once a plant is infected with tomato spotted wilt virus, it is not possible for it to recover. Removing and destroying the plant is the only solution to prevent spreading the virus throughout the garden. Gardeners dealing with tomato spotted wilt virus should also remove weeds around the parts of the garden that are infected, as several types of weeds can be host to the thrips that carry tomato spotted wilt virus.

Have you seen tomato spotted wilt virus on your tomato plants? If you have pictures of the impact on your tomatoes, send them our way.

Want to learn more about tomato spotted wilt virus?

Clemson University covers Tomato Spotted Wilt Virus

Growing Produce covers Tomato Spotted Wilt Virus

University of California covers Tomato Spotted Wilt

Science Direct covers Tomato Spotted Wilt Virus

Cornell University covers Tomato Spotted Wilt Virus