Summary: Thrips are small insects that can be pests when they feed on garden plants or valuable crops. Thrips often jump when you touch them and they sometimes bite. Without proper care paid to plants, thrip populations can get out of control.
Thrips seldom have a big influence on human affairs. It's not that it doesn't have an economic impact from damage caused to commercial crops and garden plants. It's just that it is rarely seen. Thrips are smaller than one millimeter and often hide in curled up leaves or within buds of flowers. It is yellowish brown or black in appearance, but can have brightly colored spots, as well.
There are many different species of thrips, but they all share some common features such as thin bodies, feathery-looking wings, and elongated feeding tubes used for puncturing and sucking. When it feeds on plants it prefers new growth found on new branches or younger plants. Some fruits and vegetable plants that are sources of food for thrips are avocado, tomato, rose, onion, and citrus trees. Normally, thrips do not damage the fruit of these plants, but do cause cosmetic damages to the leaves. Woody plants like azaleas, dogwood, gardenias, and magnolia are planted for their aesthetic appeal, so thrip damage to leaves or flower buds can leave these plants unsightly.
Some species of thrip are predators and feed on other thrip species or small mites. Predator thrips can actually help keep the pest species of thrips under control. Other insects that prey on thrips include the aphid wasp and predator species of mites. These natural predators are often the best form of pest control for thrips. Pesticides can be ineffective against thrips due to their small size and their tendency to hide in buds of furled leaves where pesticides may not reach. Their eggs are laid in protected cases inside slits they create in leaves, or on the outside of a plant stem or leaf. The thrips nymphs develop underground where pesticides would have difficulty reaching them.
Thrips have a high reproduction rate and under the right circumstances they can have a population explosion. This can be a problem because thrips will feed on the fruit of a plant instead of just the leaves, causing economic damage. This impact can be accentuated because thrips are capable of spreading plant viruses such as the tomato spotted wilt virus.
Thrips can also be a nuisance because of their small size. They are able to get into strange places like the inside of a picture frame or LCD television. Imagine the expense of taking your TV apart to extract a wayward thrip. And, to top it off, thrips can bite. The bite is not dangerous, but can create an irritating, itchy bump. Talk about adding injury to insult.
Treatment to prevent thrip damage can be difficult because the damage is often not evident until sometime after the thrips have been present. The thrips and the damage to the leaves are often unnoticed at first because of the thrips small size and the fact that the damage is not noticeable until the plant tissue grows and expands. A plant virus will have become well established by the time it becomes noticeable. Then, over-reacting, you grab your can of pesticide spray, exacerbating the problem by killing the good-guy predators while leaving the bad-guy thrips unharmed. What a mess!
The most effective way of preventing thrip damage is to promote the survival of thrip predators. Predatory mites and nematodes added to gardens or crops will aid this cause. Predatory nematodes feed on the thrips while they are in their larval stage, which usually occurs underground.
Trimming away dead branches will keep a plant healthy and help it survive damage caused by thrips. Learn how to properly trim your ornamentals because improper trimming promotes new growth that the thrips like to feed on. Proper feeding and regular watering will also benefit plant health. Some cultivars, or variety of plant species, will be more resistant to thrips than other varieties of the same plant species. Find out from your local garden supplier which plant cultivars are more resistant to thrips.
If you have a continual problem with thrips you might want to try using reflective mulch. This mulch is usually silver or grey in color and helps protect young plants. The reflective light from the mulch makes it hard for the thrips to locate the plants. As the plants grow and cover more ground the mulch becomes ineffective, but by this time the plants are often mature enough to survive some thrips damage.
If you want to protect adult plants you might try using a row cover that excludes insects, but not light and air. These covers can be attached to a wood, wire, or plastic frame and are made of muslin, nylon, or other mesh cloths. Floating row covers are often made of a woven, synthetic plastic. These are not attached to a frame, lying loosely over the plant. Plants have room to grow under the cover. Aluminum foil can also be used in a small, home garden.
If you insist on using insecticides, try neem oil, pyrethrins or insecticidal soap such as Safer. Products like Conserve, Spinosad, and Monterey Garden Insect Spray are more potent, but also effective. Avoid using organophosphate insecticides such as Malathion, carbamates such as Carbaryl, and pyrethroids such as Cyfluthrin, Fluvinate, and Permethrin. These pesticides can kill beneficial insects and last longer in the environment. Any pesticide you choose will probably only need to be applied once or twice in a given year. As always, read the label.