By Judy Sedbrook, Colorado Master GardenerSM, Colorado State University Cooperative Extension, Denver County
Thrips are small insects, only about 1/20", but they can cause a lot of damage. At maturity, they are yellowish or blackish with fringed wings. Nymphs have a similar shape but lack the wings. They are usually yellowish to white. Thrips are poor flyers. As a result, damage often occurs in one part of the plant then slowly spreads throughout it.
Size of thrip compared to a dime
Thrips feed in buds, folded leaves, and other unexposed areas of plants. This makes them difficult to treat with an insecticide. They feed by sucking juices from the plant causing stippling, or small scars, on leaves, flowers and fruit. This results in stunting of the plant, leaf distortion and premature leaf drop. Flowers may be deformed and fail to open properly. Petals may show brown streaks and spots. Their excrement is black and shiny, which may be a clue to their presence. In addition to this physical damage, thrips also transmit tomato spotted wilt virus and impatiens necrotic spot virus, for which there is no control.
Brown streaks and spots seen with thrips
Control of thrips is difficult. To look for their presence, shake the plant out over a sheet of white paper. If you find thrips there are a few steps you can take to dispatch them.
Photos: Judy Sedbrook
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010