Thrips may be really tiny, and they often disappear before you get a good look at them, but they can suck the life from plant leaves, growing tips and buds.
There are thousands of different varieties of thrips worldwide. A few of them are beneficial insects, eating mites and other pests, but most thrips are pests. They are commonly found in greenhouses. These species have piercing mouthparts used to puncture leaves and siphon out nutrient rich sap. Thrips are also vectors for other plant pathogens (diseases).
Thrips generally stay hidden, feeding on the underside of leaves, new shoots, buds. or under the sepal (the green bit at the base of a flower). Thrips attack avocados, beans, blueberries, citrus, figs, grapes, marijuana, and countless other valuable crops.
Usually, the damage is seen before thrips are noticed. Damaged leaves may look pale, splotchy, stippled, and silvery, eventually turning brown. Frass (tiny black bug poop) is often present. Shoot tips and leaves may also be curled or distorted.
As heat tolerant varieties of many crops are being developed, thrips are adding them to their diet. Just because a host plant isn't listed today doesn't mean it won't be thrips food tomorrow!
Thrips are really tiny - often less than 1/20” long. Thrips bodies are thin. They have fringed hairs on their wings, but you won’t see this without a hand lens. Adult thrips can range in color from white, yellowish, pale green, to brown or black. Immature thrips, both larvae and nymphs, look like tiny pale green caterpillars. To make sure that thrips are causing the leaf damage, shake damaged leaves while holding a blank sheet of white paper underneath. A magnifying glass can help identify the culprit. Yellow sticky traps can also help you detect the presence of thrips. If possible, identify the species attacking your plants. Watch this UC video to learn how to collect thrips for identification.
Unfortunately, thrips are difficult to control. Natural predators are your best line of attack, so avoid using general purpose pesticides. This will allow pirate bugs, green lacewings, and parasitic wasps to take care of the problem for you. Thrips have protective larval stages and the ability to fly away, so insecticides are not effective. A strong spray from the hose can displace many thrips. Also, removing weeds and surrounding plants can make life a little less comfortable for these tiny invaders. Once thrips have infested an area, reduce the amount of nitrogen or other fertilizers applied, to limit the amount of vulnerable new growth.
Preventing thrips infestations
Reflective mulch can confuse incoming thrips, but it won’t help once they are established. Row covers can also protect vulnerable plants. When pruning, avoid shearing susceptible shrubs, as this can provide many points of entry, both for thrips and other uglies. Be sure to deadhead flowers and remove dead or diseased tissue, as these areas can also provide a hiding place for thrips.
Healthy plants are better able to defend themselves, so be sure to irrigate properly to avoid water stress.
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