This tomato plant tested positive for Tomato Spotted Wilt Virus (TSWV) using an on-site test kit. Note the blackened color of the foliage and markings. It was difficult to see the ringspot markings of the virus in the sample. Holding the leaf sample up to the light can help to see the lines of ringspot.
Tomato Spotted Wilt Virus (TSWV) and Impatiens Necrotic Spotted Virus (INSV) are two members of the Tospoviruses which are vectored by Western flower thrips (Frankliniella occidentalis). These viruses have an extremely wide host range (more than 600 species of plants are susceptible). There is no cure or chemical treatment for plant viruses. Discard affected plants, eradicate weeds that may be hosts, and control thrips populations. Inspect plant material at arrival or quarantine new shipments. Do not grow vegetable transplants and ornamental bedding plants in the same greenhouse.
For more information see the fact sheets:
New England Greenhouse Floriculture Guide, A Management Guide for Insects, Diseases, Weeds and Growth Regulators.