There have been several reports of high thrips populations attacking crops and bothering homeowners alike this spring (see KPN June 5, 2018, Thrips Can Be Cause of “Mystery Bites” and “Pool Miseries”). Despite their tiny size, various thrips species are serious direct pests in greenhouses/high tunnels as well. Thrips are also vectors of Tosopviruses, such as tomato spotted wilt virus. Producers are encouraged to monitor for thrips, along with symptoms of the viruses they might transmit. Pay particular attention to susceptible crops, such as tomatoes and peppers grown in high tunnels, as well as these same crops and other vegetable crops in production fields.
Thrips (Figure 1) often infest developing buds of plants. As new growth emerges from buds, it may be twisted or deformed due to thrips feeding. In greenhouses, it is common to find brown spots caused by thrips feeding on leaves of vegetable crops. Often there is black fecal matter in association with these feeding sites (Figure 2). Because thrips are so small and often hidden in flowers or plant buds, growers scouting for thrips can tap plant parts over a sheet of white paper or into a white cup in order to see them.
Insecticides are used to reduce thrips numbers when they are abundant, but producers need to be careful to select insecticides that have good thrips activity. For vegetable crops, Radiant, Sivanto Prime, Torac, Rimon, Venom, Assail, Admire, pyrethroid insecticides, Dimethoate, and Lannate can provide good to very good control of thrips; however, these individual products are not labeled on all vegetable crops and some cannot be used in greenhouses/high tunnels. Read the label before selecting and using a pesticide.
By Ric Bessin, Extension Entomologist