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Take Control of Thrips

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Take Control of Thrips
Alton N. Sparks, Jr., University of Georgia, Bugwood.org

Thrips are a common plant pest that are sometimes described as worms with legs or fringe-winged insects. There are 264 species in North America that feed on plants. Some species, however, are beneficial insects as they feed only on mites and other insects.

Thrip Identification

  • Tiny – less than 1/16-inch long.
  • Black or yellow-brown, but may have red, black or white markings.
  • Long, slender and cylindrical bodies.
  • Most are winged with long fringes on their long, narrow wings.
  • Very active, move very quickly, are gregarious.
  • Often jump when disturbed.

Thrip Reproduction

  • Females are larger than males and, in many species, can reproduce without male fertilization.

  • Eggs are laid in slits the female makes in the leaf tissue, she can lay 25-50 eggs at a time which hatch within a couple days to a week.

Thrip Nymphs

  • Hatching nymphs look similar to adults, but are translucent light yellow in color, and have no wings.
  • They have short antennae and short legs.
  • These immature thrips are very active.
  • Within two to three weeks, thrips can reproduce, thus populations can build very quickly.

Thrip Behavior

  • Thrips feed on the foliage, flowers, and shoots of azalea, ardisia, dogwood, gardenia, hibiscus, magnolia, maple, palm and viburnum and other woody plants throughout the growing season.

  • Many species feed within the plant buds or furled leaves, so can be even more difficult to see.

  • Although thrips have wings, they are not strong flyers. However because they are so small and light, they can be carried on wind from infested areas. They are also often transported on infested plants.

Signs

  • The first sign is generally yellow or bleached spots on leaves, deformed leaves, dead blotches on petals.

  • Next you are likely to see silvery varnish-like look and black spots on the surfaces of the leaves, both of which are from the thrips excrement, or fecal matter.

  • Eventually, the leaves and petals will become thin, wilt and prematurely die and drop off.

    Because these signs can be similar to those of other plant-infesting species, it is important to accurately identify the insect prior to treating.

    Monitoring and Control

    The University of Florida provides the following recommendation to help determine if thrips are infesting your plants or garden:

    "To aid in detecting thrips, place a sheet of white typing paper beneath the leaves or flowers and shake the plant. The thrips will fall onto the paper and can be more easily observed and identified than when on the plant. Also look for the small spots of varnish-like excrement on the leaves. If plants are flowering, be sure to inspect the flower parts for thrips presence. Since thrips are so small, use a 10 to 15-power magnifying glass."

    Sticky traps can also be used to monitor plants for thrip presence, UF advises. However, it is beneficial purchase specially made blue traps rather than standard yellow-traps, because these traps seem to be more effective and light colored thrip nymphs can be more easily seen against the blue.

    If control is necessary and the thrip has been correctly identified, the University of California/Davis recommends an integrated pest management program be used, to include "the use of good cultural practices and conservation of natural enemies with the use of least-toxic insecticides, such as narrow-range oils."

    Pruning of damaged and infested leaves and plants can provide some control for some thrip species, particularly if only a few plants are in the area.

    In many cases the thrip damage is more cosmetic than dangerous, thus thrip presence does not usually warrant the use of pesticides. In addition, pesticides can kill off the thrips' natural enemies. But when needed, UF recommends systemics, defined as pesticides that cause death or injury to pests when ingested during feeding. The use of insecticides with short residual life will not provide effective control because the thrips can continue to invade throughout a growing season. Read and follow all label directions when using any pesticide.

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