Complete Guide on How to Get Rid of Thrips Effectively

Thrips are one of the more difficult-to-detect pests for gardeners because the damage they cause often appears to be the result of a nutrient deficiency or a disease rather than an insect infestation. There are more than 6,000 thrips species sucking the life from plants all over the world.

A common pest found in greenhouses and indoor/ outdoor gardens, thrips damage plants by sucking their juices and scraping at fruits, flowers and leaves. Plant leaves may turn pale, splotchy, and silvery, then die. Injured plants are twisted, discolored and scarred.

Adults are very small (less than 1/25 inch) straw-colored or black slender insects with two pairs of feathery wings. Without the use of a hand lens, they resemble tiny dark threads.

What are Thrips?

Thrips are tiny insects about the size of a sewing needle that feed on a variety of plants. Thrips, also known as thysanoptera or thunderflies, are sucking insects that can cause damage to plants. But when they spread viruses to plants, the damage they cause can multiply exponentially.

Despite having mouthparts made for piercing and sucking plant juices, thrips are too small to pierce human skin and are not drawn to bite people because they do not feed on blood.

Life Cycle of Thrips

The life cycle depends on the species of thrips as well as the location, host plant, and other factors.

Adults and pupae overwinter in garden soil. In spring, newly emerged females insert eggs into the tissues of flowers, leaves or stems. Female thrips, which are larger than males, can reproduce without male fertilization.

Each female can produce up to 80 eggs, which hatch within days in warm weather or weeks to months in colder weather. They become wingless larvae (nymphs), which feed on plant sap. After two or more nymphal stages, many thrips drop to the soil to pupate.

As soon as they reach maturity, nymphs pupate by forming cocoons on the plant or in the soil. Adults with wings emerge from cocoons after several days to begin the cycle again.

The population will be at its peak from late spring to midsummer. There may be 12-15 generations per year with the entire cycle from egg to adult requiring less than 16 days in warm weather.

Adult thrips overwinter in decaying plant debris, bark, and other materials. In early spring, they become active and lay eggs in plant tissue. Since thrips can survive the winter in the egg stage, removing plant debris is critical for thrip control.

How to Identify Thrips

Adult thrips are 1/50 to 1/25 inches long and slender. They may be yellow, brown, or even black, and if you approach them too closely, they will probably leap or fly away. Their wings are narrow and fringed.

The nymphs resemble even smaller adults, though they are lighter green or yellow in color rather than darker in color. Sometimes their eyes will be red, and their wings won’t be fully developed.

The thrips that are on your plants will look like very small, dark slivers. It’s difficult to see their bodies without a magnifying glass, but they resemble lobsters up close. To see them clearly, shake them onto a white background.

Since there are various different types of thrips, they may differ slightly from one another.

Adults of the western flower thrips and onion thrips are significantly larger than adults of the avocado and citrus thrips, so their mature body size helps to differentiate them when they co-occur on the same host plant.

Damage Caused by Thrips

Extremely active, thrips feed in large groups. They leap or fly away when disturbed. Host plants include onions, beans, carrots, squash and many other garden vegetables, and many flowers, especially gladioli and roses.

Both adults and the wingless larvae are attracted to white, yellow and other light colored blossoms and are responsible for spreading tomato spotted wilt virus and impatiens necrotic spot virus.

When thrips congregate in large numbers, they leave black, varnish-like fecal deposits on the undersides of leaves.

To feed, they use their single large mandible to puncture the epidermal layer of the host plant, then sip the cell sap as it flows into the wound. The foliage appears dusty or silvery and dull as a result of their feeding.

Some species are able to feed by burrowing between the upper and lower leaf surfaces. Blossoms can develop brown flecks and wither prematurely. Leaves that have been damaged become twisted, discolored, and scarred.

These symptoms resemble those of various fungal or viral diseases, and thrips are frequently responsible for the spread of plant viruses and other plant diseases. If the plant damage is caused by thrips, the leaves will almost always have black spots caused by the pest’s excrement.

Thrips Control: How to Get Rid of Thrips Effectively

Thrip management is a matter of garden maintenance — reducing the places where thrips may breed — and requires removing plant debris while it’s still on the ground and green. Thrips lay their eggs in slits they cut in live plant stems.

Vigilance — spotting problems early and responding to them — is also required. Check your plants for damage and clusters of the pests at the place where leaves are attached to stems.

Don’t wait to take action. Take the measures listed below to keep thrips populations under control. And be sure to use the safest, most proven products.

Inspect and Monitor Plants

Inspect all plants you import into the garden for signs of thrips or their damage. Discard any infested plants by securely bagging and putting in the trash.

If found, use the Bug Blaster to hose off plants with a strong, encompassing spray of water to reduce pest numbers. Blue sticky traps are also helpful for monitoring adult populations and for identification.

Remove Weeds and Grass

To get rid of thrips remove weeds and grass from around garden areas to eliminate alternate hosts. Clean up crop debris in the garden, especially onion leaves after harvest. (Dry mulch will not attract thrips. Green mulch will.)

Encourage Beneficial Predators

Release commercially available beneficial insects, such as minute pirate bugs, the effective thrips predator (feeds on eggs and larvae before they can become adults), ladybugs, and lacewing, (especially effective in green houses) to attack and destroy all stages of this pest.

For best results, make releases of natural predators after first knocking down severe infestations with water spray or other method.

Consider Reflective Mulch

Using reflective mulch can reflects light and interferes with the ability of thrips to locate plants. This may be feasible on smaller plants, but can become increasingly less effective as plants grow bigger.

Aluminum foil is another alternative that can be used for small gardens but it can get expensive and difficult to reuse since it’s delicate to handle.

Apply Insecticidal Soaps and Neem Oil

Safe, smothering insecticidal soaps made from naturally occurring plant oils and fats, are also effective for knocking down heavy infestations (and won’t harm most naturally occurring beneficial insects). Spinosad and neem oil can be used to spot treat heavily infested areas.

Use Biological Insecticides

BotaniGard ES is a highly effective biological insecticide containing Beauveria bassiana, an entomopathogenic fungus that attacks a long-list of troublesome crop pests – even resistant strains! Weekly applications can prevent insect population explosions and provide protection equal to or better than conventional chemical pesticides.

Apply Pyrethrin

Severe populations may require a least-toxic, short-lived botanical insecticide (pyrethrin) to reduce pest numbers. Follow-up with predatory insects to maintain control.

Tip: Thorough coverage is necessary when using natural contact insecticides, especially on the undersides of leaves and where leaves attach to stems, a favorite place for thrips to congregate.