Published: June 1, 2017

One of the challenges on detecting plants that get a virus is noticing the symptoms early. A grower in Morgan County noticed plants randomly scattered around his greenhouse were not growing normally. The plants had symptoms that might be considered a physiological disorder, a nutritional imbalance, a foliar disease or even a combination of these. The plants were tested using an immunostrip assay (Agdia: Elkhart, IN) and were positive for Tomato Spotted Wilt Virus (TSWV). More severely infected plants would have some of the classic symptoms like swirling patterns on the fruit or severe stunting and purplish color.

left Tomato plant is slightly stunted, somewhat yellowish and with some brownish foliar spots (bronzing). right Tomato plant in foreground has TSWV. (Photos by Joni Harper)

Infected plants can't be 'cured' so had to be rogued out to lessen the spread of the disease. Other control methods are to apply insecticide to reduce thrips and eliminate weeds. Thrips are known to vector the disease and weeds can harbor both thrips and the virus. The virus can be hosted by many types of landscape and garden plants. This link provides a long list of hosts: https://scholarspace.manoa.hawaii.edu/bitstream/10125/5893/1/RES-078.pdf.

left Green tomato fruit, with several circular white marks, from a plant that tested positive for TSWV. right Green tomato fruit, also from plant referenced above, with bumps due to TSWV. (Photos by Patti Hosack)

Thrips are a common greenhouse pest that occur on a wide range of ornamentals. Tomato transplants are frequently raised in this environment, thus should be watched for the occurrence of thrips. If many plants get TSMV and they are scattered around the production greenhouse, it indicates that the transplants may already have had the virus or a thrips problem. Plants getting a virus infection after planting in a production greenhouse are often located in certain areas, like adjacent to open vents or in a corner where weeds weren't controlled.