Thrips are tiny, slender insects that feed on a wide range of garden plants and houseplants by scraping plant tissues and sucking out their contents. Although only about 1–2 mm long, they can cause significant cosmetic damage and may spread certain plant viruses.
Symptoms of Thrips Damage
Thrips feeding causes leaves to develop silvery, gray, or bronze streaks and patches where plant cells have been damaged. Tiny black specks of excrement are often visible on affected foliage. Heavy feeding can result in distorted or curled leaves, stunted growth, damaged flowers, and flower buds that fail to open. Some plants may show scarring on leaves, flowers, or fruit.
How to Identify Thrips
Adult thrips are narrow, rice-shaped insects that are usually yellow, tan, brown, or black. They have narrow, fringed wings, although these are difficult to see without magnification. Immature thrips resemble adults but are smaller, wingless, and often pale yellow or cream colored. Because thrips are so small, gardeners often notice the damage before seeing the insects themselves. Tapping foliage over a sheet of white paper can help reveal the insects.
Management
Cultural Controls
Inspect new plants before bringing them indoors or planting them in the landscape. Remove heavily infested flowers, leaves, or stems, and keep plants healthy through proper watering and fertilization. Managing weeds around gardens can also reduce thrips populations because many weeds serve as host plants.
Mechanical Controls
For houseplants, isolating infested plants can slow the spread of thrips. Washing plants with a strong stream of water may remove some insects. Blue or yellow sticky traps can help monitor and reduce adult populations.
Chemical Controls
Insecticidal soaps, horticultural oils, and products containing spinosad can help manage thrips when applied thoroughly to affected plant surfaces. Because thrips reproduce quickly and some life stages are protected within plant tissue, repeated applications may be necessary. Follow all pesticide label directions, and use chemicals only when needed as part of an integrated pest management program.
Photo credits: 1: Whitney Cranshaw, Colorado State University, Bugwood.org; 2: Whitney Cranshaw, Colorado State University, Bugwood.org; 3: Whitney Cranshaw, Colorado State University, Bugwood.org
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