Originally discovered in Australia in 1915 and found on U.S. soil in the 1970's, tomato spotted wilt virus (TSWV) is a highly impactful plant disease that can result in both aesthetic damage and significant loss in crop revenue. This Tospovirus has one of the widest known host ranges, with over 1000 susceptible species in 85 families. As it is unable to move on its own, TSWV is primarily transmitted by thrips. Due to the easy spread, broad host range, and economical loss caused by TSWV, it is important to understand how to identify and manage infected crops.

The symptoms of TSWV may vary from different host species or different cultivars within a single host species. The plants frequently appear as stunted, wilting, bronzing with cupping of younger leaves, and chlorotic and necrotic spots with or without a bull's-eye pattern. Symptoms can also be manifest on fruit, frequently as ring-shaped chlorotic blotches.

Bronzed lesions on tomato leaves (A) and yellow ringspots on tomato fruits (B). (Photo: MU-PDC)

TSWV is transmitted by at least 10 species of thrips which allow the virus to replicate inside their bodies. The adult thrips move the virus from one plant to another while feeding. TSWV infection makes a plant more susceptible to thrips infestation, so the adult thrips will choose to lay their eggs on an infected host. When the eggs hatch and the nymph feeds on virus-infected plant, it becomes a vector for TSWV and will transmit it for the rest of its life.

The host range for TSWV is extremely broad. It includes specialty crops such as most Solanaceae family of plants, which include tomatoes, peppers, and eggplants. It can also cause significant damage to peanut and tobacco crops, and economic damage to ornamentals such as chrysanthemums and ornamental peppers.

How to manage TSWV:

TSWV is a viral disease and there is no known cure for infected plants. However, good cultural practices can help reduce the damage caused by this disease.

First, start with healthy plants. By selecting virus-free seedlings as well as inspecting all plant materials for TSWV symptoms and thrips infestation, the growers could avoid introducing TSWV by accident. There also are TSWV-resistant varieties to choose from, especially when the growers have this disease and are preparing for the next season.

Second, manage thrips. It is very challenging to control thrips. Using yellow sticky cards and to monitor them allows a rough estimation of the population and helps to informed management decisions. Choose an insecticide with ingredients such as azadirachtin, spinosad, and spirotetramat. Always read and follow label directions. Insecticide rotation is vital because continuous use of one single pesticide may cause the development of resistance.

Third, control weeds. Throughout the growing season, many species of weeds can host different kinds of pests, and some are reported to host TSWV and thrips. Therefore, maintain a vegetation-free border around the greenhouse or high tunnel and remove any weeds that might have overwintered inside. This will help to reduce the potential introduction of disease problems.

Finally, discard diseased plants. Any infected plants should be eradicated as they may serve as a source of infection to other plants. Plant debris such as fallen leaves and fruits should not be used for compost either.