Test Your Knowledge - July

Tomato spotted wilt virus (TSWV) symptoms on tomato foliage
Tomato spotted wilt virus (TSWV) symptoms on tomato foliage
Joey Williamson, HGIC, Clemson University.

Yes! This is a symptom of tomato spotted wilt virus (TSWV) on tomato foliage.

There’s really nothing tastier than a vine-ripe, home-grown tomato. Unfortunately, there is another tomato disease that may make this more of a dream than a reality. There have been an increased number of cases of tomato spotted wilt virus in the Southeast, and you may have experienced it in your garden, too.

TSWV is spread by a tiny insect called thrips, which acquires the virus by feeding on one of many infected weed or ornamental hosts, and then spreads it to the developing tomato plants. Several weeks after transplanting the tomatoes into the garden, random tomato plants may appear stunted, and younger leaves may be marked with bronze or dark spots.

TSWV symptoms on foliage
TSWV symptoms on foliage
Joey Williamson, HGIC, Clemson University.

Often the upper foliage will become twisted and cupped as the bronze areas expand. Younger plants may wilt and die, but older plants may survive and bear discolored fruit that may not fully ripen.

TSWV symptoms on fruit
TSWV symptoms on fruit
Meg Williamson, Plant Problem Clinic, Clemson University.

Eliminating weeds in the garden is the first step in reducing the chance of acquiring TSWV. Keeping the grass and weeds mowed in areas surrounding the garden may reduce the spread of thrips onto susceptible garden plants. Weeds in the garden area during the winter may harbor both the thrips and the virus. So, remove the old crop debris, till and mulch the garden for the winter to keep weeds and thrips down for the next year.

Reflective (aluminum or silver-colored) mulch beneath the tomato plants may reduce the number of thrips that arrive and feed upon the plants. If reflective mulch is not available, paint black plastic mulch silver before transplanting the tomatoes.

There is no cure for a plant with TSWV. Roguing or removing infective plants immediately from the garden may help reduce the incidence of disease on additional plants. However, feeding by thrips can transmit the virus to plants within minutes. Because of this rapid infection time, insecticidal sprays may be of no use for the home gardener.

Seeds of several TSWV-resistant varieties of tomatoes are available from mail-order seed companies. These varieties are resistant, but not totally immune. They may acquire the virus, but yields and fruit quality may remain acceptable. Look for varieties such as, ‘Amelia’, ‘Bella Rosa’, ‘BHN 444’, ‘BHN 640’, ‘BHN 685’, ‘Red Defender’, ‘Sophya’, ‘Talladega’, ‘Top Gun’, ‘Health Kick’, ‘Muriel’, and ‘Picus’. Contact the Home & Garden Information Center for assistance in locating seed for specific varieties.

For the best tomato fruit possible, it is important to keep the tomato plants healthy. For more information on how to grow tomatoes and on disease and insect pest control, please see HGIC 1323, Tomato; HGIC 2217, Tomato Diseases, and HGIC 2218, Tomato Insect Pests.

Joey Williamson
HGIC Extension Agent

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This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.