Description
Flower thrips (Frankliniella species) are tiny (1/20 inch long) insects that infest the flowers, flower buds, and growing points of many plants. They are able to distinguish different colors of flowers, usually preferring those that are yellow or light colored. The amber-colored adults and lemon yellow nymphs (immature thrips) feed by rasping the plant tissue and then sucking the released plant sap. The injured tissue dies, producing dead spots, distorted blossoms and new leaves, and balled flowers (flower buds that turn brown and never open). The larvae drop to the ground to pupate. Flower thrips are most abundant between late spring and midsummer. They reproduce mainly on the flowers of trees, grasses, and weeds, and then migrate to gardens nearby. In the western states, thrips are most damaging when uncultivated plants dry up in summer, forcing the insects to migrate to gardens where plants are still green. Thrips spread tomato spotted wilt disease, and often discolor flowers, especially roses.
Control
Flower thrips are difficult to control because they are usually protected in plant tissue, and they constantly reinfest garden flowers from nearby plants. Spraying ornamentals with a systemic insecticide (one that moves through the plant) will protect flowers for up to 10 days. Use an insecticide containing acephate at the first sign of damage. Control thrips on food crops with an insecticide containing malathion or carbaryl. Make sure your plant is listed on the label. Repeat the spray 2 more times at intervals of 7 to 10 days to control thrips as they hatch.
