Watch for Thrips in Vegetables
I have gotten reports from flower growers of an inundation of thrips into their flower crop in the last week or so. I know, I know flowers are not vegetables, but many of the Flower thrips species that get into flowers will get into and on vegetables. Thrips are tiny, thin yellowish-orange insects the size of metal filings with fringed wings. They feed by puncturing the outer layer of plant tissue and sucking out the cell contents, which results in stippling, discolored flecking, or silvering of the leaf surface (fig.1). Thrips feeding is usually accompanied by black flecks of frass (thrips poop) (fig. 1). Pest thrips are plant feeders that discolor and scar leaf, flower, and fruit surfaces, and distort plant parts or vector plant pathogens. There are several species of vegetable thrips with the most common being the Eastern flower thrips, Frankliniella tritici, Tobacco thrips Frankliniella fusca, Western flower thrips, F. occidentalis and Onion thrips Thrips tabaci. The last three species are the ones most likely to transmit tomato spotted wilt virus, TSWV. Feeding results in various tissue responses, including scar formation and distorted growth (fig. 2). Thrips hatch from an egg and develop into two larval stages and then the ‘prepupa and pupa’ stages, before becoming an adult. Females of most plant-feeding species lay their kidney-shaped eggs on or into plant tissue. The prepupae and pupae of most species drop to the soil or leaf litter to pupate. Thrips have several generations (up to eight) a year. When the weather is warm, the life cycle may be as short as 2 weeks.
It is difficult to identify thrips to species in the field. Thrips color, size, markings will not separate the different species found in our vegetable fields from one another to any great extent. Thresholds for vegetables are: flowers of tomato, pepper or watermelon can tolerate 5 thrips/flower with no fruit developmental problems. Squash and pumpkin flowers can tolerate 5-10 thrips/flower with no effect on fruit quality. One or two applications of a pyrethroid or neonic or spinosad (see 2018 Mid-Atlantic Commercial Vegetable Production Recommendation Guide) applied with enough water (80-100 gal/a) should control most thrips infestations. Spraying more than 4- 5 times for thrips in a 4-5-week period will usually lead to an even worse thrips problem. This is because the sprays will reduce eastern flower thrips and other thrips species, but usually not western flower thrips that are often resistant to many insecticides. Once the thrips population consists mostly or entirely of western flower thrips it may not be possible to get the population under reasonable control.
