If you are seeing tiny bugs on your plants that look a bit like worms with legs, you may have thrips. These fringe-winged insects are a common plant pest. There are 264 species in North America that feed on plants, but there are also other species that are actually beneficial insects because they feed only on mites and other insects.
- Tiny (less than 1/16-inch long)
- Black or yellow-brown, but may have red, black or white markings
- Long and slender with cylindrical bodies
- Usually winged, with long fringes on their long, narrow wings
- Very active and move very quickly
- Social creatures, generally found in groups
- Easily provoked, often jumping when disturbed
Is It Okay If I See Only a Few Thrips?
Seeing any amount of thrips is not really ever a good sign. This is because:
- Females thrips, which are larger than the males, can reproduce without male fertilization.
- They make slits in the leaf tissue to lay their eggs.
- A single female can lay 25 to 50 eggs at a time, which hatch in less than a week.
- Once hatched, the thrip will mature to adulthood, able to reproduce themselves within three weeks, so populations can build very quickly.
- Hatching babies (nymphs) look a lot like the adults, except they are translucent light yellow in color, and have no wings.
- They have short antennae and short legs.
- These immature thrips are very active.
What Do Thrips Do?
- Thrips feed on woody plants throughout their growing seasons, including the azalea, ardisia, dogwood, gardenia, hibiscus, magnolia, maple, palm and viburnum throughout the growing season.
- Many species feed within the plant buds or curled leaves, so they can be very difficult to detect.
- Although thrips have wings, they are not strong flyers. But because they are so small and light, they can be carried by the wind from plant to plant. You also can unknowingly bring them into your home on a plant that was already infested.
- The first sign of thrips is usually that of yellow or bleached spots on leaves, deformed leaves, or dead blotches on petals.
- Next, the leaves are likely to take on a silvery varnish-like look and black spots, both of which are from the thrips' excrement, or fecal matter.
- Eventually, the leaves and petals will become thin and wilt, then 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.
Because thrips are so little, they can be difficult to see until infestations become large. So, one way to determine if thrips are infesting plants in or around your home is to put a blank sheet of white paper beneath the flowers or leaves of the plant and shake the plant. If there are thrips on the plant, at least some will fall off, and their dark bodies will be easily seen on the white paper.
By doing this, you also will be able to collect samples of the insect for identification. Whether attempting to identify the insects as thrips on the paper or simply inspecting plants for thrips, a 10- to 15-power magnifying glass will help enlarge your viewing of the thrips enough to see detail.
You also can use sticky traps to capture thrips for monitoring and identification. This will not provide control of the thrips, but it will let you know if a plant is becoming infested. It is recommended that specially made blue traps be used, rather than standard yellow traps; the blue traps seem to be more effective and it is easier to see the light-colored nymphs on blue than on yellow.
Control and Prevention
Early detection and integrated pest management are the best options for preventing a wide-ranging infestation. This includes:
- Regularly inspect your plants for thrips or other plant pests and take action immediately if any are detected.
- Prune all damaged and infested leaves and plants.
- Spray or wash the plant with a soap and water solution (about 2 teaspoons detergent in a gallon of water), making sure you get the solution on all the leaves and other areas of the plant.
- Hose down resilient plants with high-pressure water, focusing on the bottom/underside of the leaves. This can knock the thrips off the plant and can be repeated as often as the plant can handle it.
- If none of the above work, a low-toxicity contact insecticide that is labeled for thrips and for plants or a narrow-range oil can be used. However, pesticides are rarely warranted, and are usually not very effective, because of the way they feed, their activity, and the fact that their eggs are pupae are in protected areas. Additionally, thrips will continue to invade throughout the growing season, so a one-time use is unlikely to have a great deal of effect. When using any pesticide, always carefully read and follow all label directions, using only those specifically labeled for the pest and situation.