Written by: Charlotte Glen, Horticulture Agent

There are many plant diseases that make growing tomatoes a challenge in the southeast. One of the worst is tomato spotted wilt virus (TSWV). First found in our area in the mid 1990’s, this disease is different from most tomato diseases because it is caused by a virus rather than a fungus or bacteria. In addition, unlike most viruses, TSWV kills the plants it infects and it has started showing up on tomato plants in our area in the past few weeks.

Symptoms
Tomato plants infected with TSWV may at first appear stunted and pale. Upon close inspection, you may notice unusual markings on the leaves of infected plants. Sometimes these marking look like brown or black spots, other times they look like tattooed lines or circles. The leaves of infected plants may curl inward, and plants may take on a bronze cast. Usually these symptoms show up on the top leaves of the plant first, whereas most other tomato diseases show up on the lower leaves first. As the disease progresses, infected plants wilt and die, usually within a few weeks of the first symptoms appearing. There is no way to treat TSWV and infected plants should be pulled up and discarded.

Spread by Thrips
Like most plant viruses, TSWV is spread by insects. The insect that spreads TSWV is called thrips, and they are very small and difficult to control. Treating for thrips will not prevent them from transmitting the disease to your plants. This is because thrips transmit TSWV very quickly when they begin to feed on a plant with their needle like mouth parts. The disease is transmitted before pesticides are able to kill the insect. Thrips often overwinter on cool season weeds growing around gardens and yards and move into vegetable gardens as these winter weeds die. Controlling weeds around your garden can help reduce TSWV infection. TSWV does not persist in the soil like many tomato diseases, so if you lose your tomato plants to this disease this spring you can replant tomatoes in the same area.

Resistant Varieties
The only way to combat TSWV is to plant varieties of tomatoes that are resistant to the disease. Unfortunately, old favorites like ‘Celebrity’ and ‘Better Boy’, and heirloom varieties such as ‘German Johnson’ and ‘Homestead’ have no resistance to this disease. There are several new varieties that have been bred for TSWV resistance and may be available from area garden centers. These include ‘Amelia’, ‘Crista’, ‘Bella Rosa’, ‘Talladega’, ‘BHN 444’ (sometimes sold as ‘Southern Star’), ‘BHN 640’, ‘Quincy’, ‘Top Gun’, ‘Nico’, ‘Mountain Glory’, and ‘Red Defender’. Other vegetables that can be affected by TSWV are potatoes, eggplant, peanuts, and peppers. The bell pepper variety ‘Heritage’ is resistant to TSWV.

Other Diseases
If you have lost your tomato plants to TSWV this year it is not too late to replant with a resistant variety, but that does not guarantee you will not have other disease problems. Both bacterial wilt and southern blight cause tomato plants to wilt and die and there are no tomato varieties resistant to these diseases. Unlike TSWV, both of these diseases persist in the soil from year to year, so if you have lost tomato plants to either bacterial wilt or southern blight in an area of your garden in the past you should avoid replanting tomatoes, peppers, or eggplants in that area. There are also several diseases that infect the leaves of tomato plants, causing them to turn brown or yellow. Many of these foliage diseases can be controlled with fungicides such as mancozeb, daconil, copper, or immunox. If your tomato plants begin to wilt or show other disease symptoms, it is important to have the symptoms correctly diagnosed so you will know how to treat the problem this year and how to best avoid it next year.

Learn More
In Pender County, samples of diseased tomato plants can be taken to the Cooperative Extension Office, located at 801 S. Walker St. in Burgaw, Mon-Fri, from 8 a.m. to 5 p.m. If you have questions about growing tomatoes or other plants, call us at 910-259-1235, or  //pender.ces.ncsu.edu

Learn more about tomato spotted wilt virus from this Extension article:

• Louisiana Extension: http://www.lsuagcenter.com/en/lawn_garden/home_gardening/vegetables/disease_pest_management/Tomato+Spotted+Wilt+Virus.htm

To find out more about tomato insect and disease problems, consult these Clemson Extension Fact Sheet:

• Tomato Diseases: http://www.clemson.edu/extension/hgic/pests/plant_pests/veg_fruit/hgic2217.html
• Tomato Insect Pests: http://www.clemson.edu/extension/hgic/pests/plant_pests/veg_fruit/hgic2218.html