Thrips in Potting Soil

Damage and Detection

• Thrips damage the plant by cutting into the plant's surface layer with their strong mandibles and sucking the plant's sap. The plant’s leaves exhibit white or silvery streaks where the insect's fed. There may be areas of black spotting, which is the thrip's excrement. Bulbs often sustain damage from thrips while in storage. The thrip's feeding wilts and deforms the plant. Thrips often invade the buds of flowering plants and destroy them with their excessive feeding before the buds open. The insects require potting soil to pupate.

Reproduction

• Thrips reproduce naturally, but females can also reproduce without fertilization by a male. The female thrip produces 150 to 300 eggs. She inserts the eggs into the plant's tissues or lays them on the surface of the leaves. The eggs hatch in two to eight days. The larvae feed on the plant's sap and then drop to the soil. They burrow into the potting soil and pupate. Thrip larvae often carry viruses -- tomato spotted wilt virus or impatiens necrotic spot virus, which they pass on to the plant while feeding on it.

Prevention

• Thrip larvae require very little soil to successfully pupate. They can pupate in potting soil that has fallen to the floor and benches, according to the North Carolina State University. Promptly clean up any spilled potting soil, especially in the greenhouse. Closely inspect new potting soil before bringing it into the home or greenhouse. Thrips often gain entrance into a home or greenhouse via open windows or doors. They can invade the home on a newly purchased plant or through infested potting soil.

Control

• Never reuse potting soil that shows signs of a thrips infestation. Keep the potting soil around a plant evenly moist and avoid allowing the soil to dry out completely. Thrips prefer moist potting soil. If a plant shows signs of thrips infestation, repot the plant in new potting soil. Dispose of the infested potting soil. Thrips appear to quickly develop a resistance to insecticides, according to the Montreal Botanical Garden. Use insecticide sprays and soaps only when required to control the infestation.