Why Are My Tomatoes Dying?
Since the mid 90’s, tomato spotted wilt virus (TSWV) has become one of the most serious diseases of tomatoes in our area. Infections of TSWV in our region usually first appear in May and peak in June. Always deadly, there is no way to treat TSWV and infected plants should be pulled up and discarded.
Tomato plants infected with TSWV may at first appear stunted and pale. Upon close inspection, you may notice unusual markings on the leaves. Sometimes these marking look like brown or black spots, other times they look like tattooed lines or circles. Spots may or may not be surrounded by yellow leaf tissue. The leaves of infected plants may curl inward, while the veins may turn purple, and plants often take on a bronze color. Usually these symptoms show up in the top leaves of the plant first, while most other tomato diseases show up on the lower leaves first. As the disease progresses, infected plants wilt and die, usually within a week of the first symptoms appearing.
SPREAD BY THRIPS
Like most plant viruses, TSWV is spread by insects. The insects that spread TSWV are 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. Because thrips survive the winter on weeds, controlling weeds around your garden may help reduce TSWV infection.
One practice that has been found to reduce this disease is covering the ground under plants with a reflective plastic film. These films, which look like aluminum foil, are available from online retailers. Because they block water from entering the soil, drip irrigation lines must be installed under the film. Thrips are less active in our area in the late summer and fall. As a result late crops of tomatoes and peppers, planted in July for fall harvest, are less affected by this disease, though other disease and insect problems are more prevalent then, causing problems for later planted crops.
The most effective way to combat TSWV is to plant tomato varieties that are resistant to the disease. Unfortunately, tomato favorites like ‘Celebrity’ and ‘Better Boy’, and heirloom varieties such as ‘German Johnson’ and ‘Homestead’ have no resistance to this disease. There are several tomato varieties that have been bred for TSWV resistance and may be available from garden centers. These include ‘Amelia’, which is the most widely available resistant variety, ‘Crista’, ‘Talladega’, ‘BHN 444’ (sometimes sold as ‘Southern Star’), ‘BHN 640’, ‘Primo Red’, ‘Fletcher’, ‘Mountain Glory’, and ‘Red Defender’.
If you have lost a tomato plant to TSWV this year it is not too late to replant with a resistant variety. Since this disease is spread by insects and does not persist in the soil, it is safe to replant in areas where infected plants were removed.
Replanting 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 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.
If your tomato plants begin to wilt, develop spots, or show other unusual symptoms, it is important to have the cause of the problem correctly diagnosed so you will know how to treat the problem this year and how to best avoid it next year. To have vegetable problems diagnosed, bring a sample of the infected part of the plant, or the whole plant if possible, to your local Extension office. Make notes about when the symptoms first appeared, how they have spread, recent fertilizer or chemical applications, and plant variety.
Learn more about tomato spotted wilt virus from these websites:
- Clemson Extension: https://www.clemson.edu/public/regulatory/plantproblem/factsheets/tswv.htm
- Cornell Extension: http://vegetablemdonline.ppath.cornell.edu/factsheets/Virus_SpottedWilt.htm