Tospoviruses in Tomatoes and Peppers

Thanks to Dr. Celeste Welty, OSU Department of Entomology, for contributing to this post.

We have seen an unusually high number of tomato and pepper samples with Tomato spotted wilt virus and related Tospovirus diseases this spring and summer. Symptoms on foliage include necrotic and/or chlorotic spots, and necrotic spots or streaks on stems and petioles. Ringspots may be observed on leaves. Plants tend to be stunted and may wilt. Fruits develop a range of symptoms, from chlorotic blotches to ringspots.

TSWV on pepper – notice necrotic spots on leaves.

Closeup of TSWV on pepper leaf – note ringspot symptoms.

Tospoviruses are transmitted from plant to plant by thrips. Thrips larvae feeding on plants acquire the virus and become infective for the lifetime of the insect. The viruses overwinter in infected plant debris and weeds. Plants infected at the seedling stage are likely to have more severe symptoms than plants infected later.

These viruses are managed differently than aphid-transmitted viruses because they have a longer development cycle within the thrips, so there is hope of getting the problem under control if prompt action is taken. If isolated plants show symptoms, these should be rogued and destroyed as soon as possible. Insecticides can be effective if applied as soon as the problem is diagnosed, however, note that thrips are one of the more difficult pests to kill with our current choices of insecticides. We have Radiant (spinetoram), Movento (spirotetramat), and Exirel (cyantraniliprole) that generally do the best; beware these are quite expensive. Lannate (methomyl) can do ok; the pyrethroids (such as Warrior, Mustang, Baythroid, Asana) are generally poor for thrips control. Movento is systemic but needs an adjuvant such as Dyne-Amic or LI-700 to get it into the plant. Note Radiant and Movento are not allowed in greenhouses or high tunnels.

TSWV symptoms on green tomato fruit (cluster type) in greenhouse (photo courtesy of Anna Testen).