Nearly everyone, whether grower or gardener, will experience thrips pressure at some point.
There are many species of thrips that attack an array of different plants but typically the culprits are Frankliniella occidentalis, or Western flower thrips (WFT), the most common species found in horticultural settings.
Surprisingly enough, thrips are commonly mistaken for both root aphids and fungus gnats due to their small size (1/25 of an inch or 1mm). This, combined with their hyper-reproductive capacity and resistance to common pesticides have made WFT increasingly harder to control. They develop in climates between 47–95F and feed on plant material of many kinds, causing damage and spreading diseases. Their reproduction and general activity are kicked into overdrive by the presence of pollen.
How To Spot Thrips: Damage And Symptoms
Because WFT are small and the juveniles are tiny their presence is usually detected by the damage they leave in their wake. These pests can cause serious harm through their feeding behaviors: piercing plant cells, removing the contents with their rasping/sucking mouth parts, and feasting on the sap that seeps from the wounds. Symptoms of damaged plant cells that collapse include disfigured foliage and deformed flowers. Affected leaves may appear puckered and/or twisted, with pale spots and/or silvered patches and flecking visible.
Thrips often leave specks of black frass, a type of waste material they produce when they feed, on the surface and undersides of leaves as well. Be sure to turn leaves over to check both sides when examining them. You can also tap branches of the plant onto a sheet of white paper and look for any thrips that become dislodged.
As the Western flower thrip goes about puncturing plants with its single mandible it also poses another threat: the winged adult is a primary vector for transmitting diseases, such as plant viruses. An infected thrip is able to transmit tospoviruses, including tomato spotted wilt virus and impatiens necrotic spot virus, to at least one plant a day until its death in approximately thirty days.
What Do WFT Look Like?
WFT are long, slender winged insects that can resemble grass seed to the naked eye. Through a magnifying glass adults are long and slender with two sets of narrow, clear, nearly veinless wings that have dark, hairy fringes. Typically the pests can be found crawling on plants, especially within the flowers and growing points where the bugs shelter, feed, and reproduce. Females can range in color from almost white to yellowish-orange to nearly black.
Thrips Life Cycle
Warning: This video has been rated SQ for graphic content. If bug closeups make you squeamish, watch through parted fingertips.
WFT have six life stages—they can go from egg to adult in 9 to 13 days, under optimal conditions (77 to 86F). Also keep in mind that there will be thrips at different life stages at the same time within any given setting. Both the larval and adult stages actively feed on plants.
Egg: Eggs are deposited into plant stems, petioles, and leaves by females using a saw-like ovipositor over the course of 2 to 4 days per batch of eggs.
Larval Phase 1: Larvae do not have wings when they emerge but are able to feed on the plant. For 1 to 2 days they are like little lumps that can’t wiggle around so this is the ideal time to release predatory insects.
Larval Phase 2: Larvae in this second phase are larger than in the first, feeding on the plant before entering the pupal stages. For these 2 to 4 days they can wiggle around a lot, trying to get away from predatory mites, whipping their abdomens at them and spraying them at the same time.
Note that larval phases 1 and 2 are the only life stages that can contract a virus from a host plant; it takes about 30 minutes for the larvae to acquire the virus. The second larval phase, along with the adults, is capable of spreading any virus that is acquired.
Swirski-Mite or Thripex sachets are best for prevention and control during these early stages of thrips presence. Isarid™ is also effective for control at all stages.
Prepupa and Pupa Stages: Larvae normally drop to the soil to pupate over 1 to 3 days; however, they can pupate on the host plant if its architecture provides places to hide. Pupal stages do not feed.
At this stage, Entonem is a go-to solution for soil application, as it kills the pupating thrips in the soil. Entomite-M is another fantastic choice that can be added as potting mix. These can be used together. Atheta is also a good option, especially for growers with potted plants or with thrips spread out in hard to reach places. Atheta is a flying predator that patrols soil for pupae and is able to reach crevices and corners.
Adult: Winged adults emerge after pupation, ready to feed and preparing to oviposit eggs in about 30 days, depending on the environment. Adults must feed for 5 minutes in order to transmit any virus they may be carrying.
Thripor-I, Thripex, and Swirski-Mite go after all life stages of thrips.
I See Thrips, Now What?
Thrips fly everywhere and survive in all kinds of climates which is why they’re so pervasive. For this reason we offer a range of predators to fight thrips in different types of conditions. When choosing a biosolution, whether in a commercial or home setting, the humidity of the plants’ environment is an important factor to consider.
In hot, muggy areas like the Carolinas, Mississippi, Alabama, and the Deep South, Swirski-Mite is the best choice. If it’s cool or dry where you are, like some areas of the Southwest or in the Northeast, go with Thripex. For an all-around indoor greenhouse solution we recommend Thripor-I.
I Don’t See Any Thrips, How Do I Prevent Them?
In general, maintaining good plant health with regular water and fertilizer/soil amendments helps keep plants from getting stressed so they are less susceptible to thrips infestation. Regular cleaning and disinfecting of any surfaces or equipment in the plants’ environment helps keep thrips from setting up shop as well. It’s also important to inspect all incoming plants and cuttings carefully because in addition to being capable of flight, WFT can travel far distances being carried in by the wind or hitching a ride in on plants.
Beneficial insects cannot survive if no thrips are present for them to feed on, so only use them at the first sign of WFT—deformed flowers, puckered or twisted leaves, pale spots, silver patches, flecking, or black frass left behind. When you see that first sign it’s important to act immediately because WFT can double their population in four days. We recommend Swirski-Mite as a fast-acting biosolution that nips thrips in the bud.
To make life easier we’ve gathered all of our Natural Enemies thrips-fighting products on one page. Simply select Thrips under the by Pest dropdown menu up top. Click on a product and scroll down to find details, uses, and shipping information.
Deeper Dives:
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