How To Get Rid of Thrips

How To Get Rid of Thrips

What Are Thrips?

Thrips, also known as 'thunder flies', are a significant problem in greenhouse horticulture. These tiny brown or black sap-sucking insects are attracted to many indoor plants. These tiny insects jump from plant to plant, leaving silvery smudges in the leaves. These smudges are indications of their feeding holds where they've pierced through the top layer of the leaf to feed on the plant tissue. Small dark dropping will be seen around their feeding sites; these are their digestive waste. These bugs can distort the plant's growth whilst transmitting diseases through the feeding holes.

What Do Thrips Look Like?

The adults are tiny, thin, black insects, around 1-2mm long. You'll find them crawling slowly across the plant's leaves. Some species have a pair of narrow wings fringed with long hairs, while others are wingless and often paler. There are many species of thrips (Western flower thrips [Frankliniella occidentalis], Plague thrips [Thrips imaginis], Tomato thrips [Frankliniella schultzei], Onion thrips [Thrips tabaci]) but most commonly found on indoor plants are the Greenhouse thrips (Heliothrips haemorrhoidalis). These insects have specialised mouthparts for cutting through the outer layer of leaves and sucking the plant tissue for nutrients.

The Life Cycle of Thrips

The thrips eggs are kidney-shaped and are laid in leaves, flower petals, and the soft parts of stalks. A female thrip will deposit her eggs through a small opening in the plant tissue that she has cut prior. After hatching, the larva immediately feeds on plant tissue, sucking out its nutrients. The second stage larva is large and has more colour as they've eaten more plant tissue. At the end of the second instar, the nymph usually falls to the ground to pupate. The adult thrips has a fully developed pair of fringed wings and will imminently start searching for new plants.

Do Thrips Cause Damage to Indoor Plants?

Yes, thrips cause damage to the plant's leaves, buds and stems by piercing the cells of the surface tissues and sucking out their contents. This causes the surrounding tissue to die, resulting in silver-grey patches on leaves and the black dots of their body waste. The black dots indicate their presence in the crop and are the remaining leaf tissue. Thrips are also responsible for the transmission of viruses and diseases.

How Do You Control Them?

There are many natural enemies to thrips, including predatory mites, predatory bugs, predatory thrips, lacewings, ladybirds and parasitoid wasps. You can use q-tips with alcohol for small infestations and remove any adult thrips by hand. Whipping the leaves with neem oil or a treat wash is the most effective control method. Sticky traps are great for attracting flying adult thrips; blue traps have a higher success rate, although green and yellow equally work.
The secret to controlling thrips is to discover them early. Keep a close eye on your plants for silver-grey spots and continuously spray plants with neem oil to prevent them from landing and breeding.
As thrips breed rapidly, they are notoriously tricky insects to control; a full-plant wash and whip will be the most effective system. If it's a bad infestation, repeat weekly.
Consistency is the key.