Thrips

Overview 

Thrips are small (1/5th inch), fringe-winged, pale-colored insects. With magnification, you can identify the adults that range in color from yellow to black and have four long, narrow, fringed wings. The young nymphs are smaller, wingless, and range in color from yellow to white. Many thrips are plant feeders attacking flowers, leaves, fruit, twigs, or buds.  

Symptoms and Diagnosis 

Thrips are rarely seen because of their small size. The insects feed by puncturing the surface of the plant parts with their single large mandible and slurping the plant juices that seep from the wound. Flowers or leaves may develop silvery streaks. Heavily infested leaves appear brownish or silvery, and growing points may become contorted. Some species of thrips leave sooty spots of black fecal matter on the leaves. Thrips also vector plant diseases. A few species are beneficial predators of mites and small insects including other thrips, and some feed on fungal spores. Several species may bite people. Some species act as vectors of plant disease. Thrips are poor fliers, so damage may first appear in one location and then slowly spread over the plant. Thrips will be most apparent on flowers, especially white, yellow, and other light-colored blooms. 

Life Cycle 

Female thrips lay their eggs in tiny slits cut into the surface of leaves, flowers, fruit, bark, and stems. In warm, indoor conditions, the eggs can be laid any time of year and hatch within a few days. The young, called nymphs, are cream to pale green and only visible with magnification. They feed for 7–14 days. Full grown nymphs, in most species, drop off the plant to the soil where they burrow down and pupate. Winged adults emerge to complete the cycle. Some species enclose the pupa in a cocoon on the ground or on the host plant. The winged adult thrips emerge from the cocoon or pupal stage. Outdoors, generations may occur every two to three weeks, but the largest populations are present from late spring to midsummer. Thrips overwinter in the egg stage. 

Integrated Pest Management Strategies 

1. To limit future problems, inspect plants regularly. With regular inspection, pest problems can be caught when just beginning and control is easier. It is also recommended to isolate newly acquired plants for 2–3 weeks to limit the introduction of pests indoors. Bringing plants indoors in the fall is another way of introducing insects indoors. 

2. Knock off thrips with a forceful spray of cold water in small gardens, preferably early in the morning. Use a nozzle that produces a fine spray of water, and thoroughly wash off the undersides of affected leaves. The control is most effective when repeated at least 3 times, either daily or every other day. 

3. Keep plants moist. Plants that are kept too dry are more likely to be damaged by thrips. To limit damage or reduce future damage after other initial control measures are used, keep plants moist and increase humidity. 

4. Prune and destroy injured and infested plants. Do not compost them. 

5. Predacious spiders, mites, and pirate bugs help control thrips. Conserving naturally occurring populations of beneficial insects by avoiding persistent pesticides is important to biologically controlling thrips. 

6. Insecticidal soap. Insecticidal soaps, which are considered nontoxic to humans and pets, give good control. Be sure that flowers and growing tips are well covered with the spray. Frequent sprays may be needed until the problem is under control. 
 
7. Use superior horticultural oil sprays. Highly refined oils sold as superior or horticultural oils will also control thrips. The oil suffocates the insects. These oils are highly refined and under proper conditions, can be applied to plants in foliage without damage. Follow label directions to avoid damage to some plants that may be sensitive. Superior oils are also considered nontoxic and are less likely to harm beneficial insects. When spraying indoors, protect surfaces that may be damaged by an oil residue. 

8. Use chemical insecticides. Many insecticides registered for use indoors are available. Sprays containing pyrethrins, a plant-derived insecticide, are effective and more benign than other chemical pesticides. Follow label directions and, if possible, spray out-of-doors or in a garage, weather permitting. 

Organic Strategies 

Strategies 1, 2, 3, 4, and 5 are strictly organic approaches. For organic approaches to Strategies 6 and 7, consult the Organic Materials Review Institute (OMRI™) for appropriate products. 

Pesticide Disclaimer: 

Always follow the product's label and ensure the product is effective against thrips. Not following the pesticide label before usage is a violation of federal law.