How to Prevent & Treat Thrips on Your Plants

Have you seen tiny silvery-white spots on your plant’s leaves? Are your plants growing more and more slowly? Perhaps you’ve spotted little black balls sitting around the plant? It sounds like thrips could be responsible!

Thrips are tiny insects that roam around your garden but can also get indoors, affecting your house plants. 

In this article, you’ll learn how to spot thrips and what to do when you identify an infection.

Let’s get started! 

What are thrips?

Thrips are also known as thunder flies, storm flies, thunder bugs, corn flies, harvest bugs, or by their Latin name, Thysanoptera. 

These tiny fringe-winged insects belong to the Thysanoptera family, of which there are around 5500 species worldwide. Measuring as little as 0.5mm in length (up to 14mm), their dark brown bodies can be challenging to spot.

Their diminutive size and the fact that they reproduce asexually make it difficult to spot an early infection, which is problematic because thunder flies spread quickly. They’ve even been known to get inside household objects, such as furniture or computer monitors, where they sit between the front glass and the LCD screen. 

The name “thrips” originates in Ancient Greek, meaning “woodworm”, and refers to both the singular and plural. So, it’s not “one thrip, two thrips”; it’s “one thrips, two thrips”.  

What do thrips and their larvae look like?

The adult insects are yellow at the head end and dark brown at the hind end. Their distinctive cigar-shaped bodies accommodate six “bladder-like” legs and four feathery, fringed wings with compound eyes and asymmetrical mouthparts. 

Their eggs are almost invisible to the naked eye, laid into plant tissue, but the tiny, sausage-shaped larvae (around 1mm long) are colourless or white until they mature after feeding into the second instar stage, where they turn yellow.  

Thrips tend to appear completely static until you look closer, where you’ll spot tiny movements. 

While thunder flies have wings, they’re not great flyers. They can fly weakly and have developed a “clap and fling” approach to flight, where they create lift by using an unsteady wing pattern. Nonetheless, their feather-like wings aren’t suitable for conventional flight. 

The life cycle of thrips

Female adult thunder flies lay up to 70 eggs on leaves or plant stems during their lifetime. They can reproduce either sexually or asexually. 

Amazingly, the plant on which the eggs are laid influences the speed at which they hatch. For example, on Chrysanthemum, they hatch after just three days if the temperatures are between 18-36℃, but other plants vary their gestation period. 

The egg hatches into the first instar larvae before developing into the second instar larvae after three days of eating. This second stage lasts for around ten days, depending on the ambient temperature, until the larvae are fully grown. At this stage, it pupates — usually in the soil —  lasting for around a week, when it emerges as the adult thrips. 

Adult thrips live for around 45 days. 

Damage caused by thrips

Thunder flies use their mouthparts to drill holes into leaf surfaces, allowing them to suck sap from the plant’s cells. This turns the leaf yellow with prominent vines. 

Later, the leaves turn brown, and in the case of severe infection, the entire plant shows significant growth disorders or stunted shoots. 

Which plants are affected by thrips damage?

Thrips infect a wide variety of indoor and outdoor plants, including:

• Orchids
• Cyclamen
• Club lilies
• Chrysanthemums
• Monsteras

Additionally, they can hit vegetable crops quite severely, particularly:

• Cucumbers
• Peppers
• Tomatoes
• Aubergines

Recognising a thrips infection

One of the main problems with thunder fly infections is that they’re difficult to spot early. And we all know that if we catch a condition early, it’s easier to treat. 

Typical signs of infection are:

• Silvery-white spots on the leaves
• Growth retardation
• Small black balls on the leaves of stems
• Stunted shoot growth

Fighting thrips infection

Act as soon as you identify the infection. Here’s how to fight them:

Rinse the infested plant

Place the infested plant in the shower or bathtub and rinse the foliage thoroughly with insecticidal soap. Repeat this process regularly to eliminate the pests. 

Use beneficial insects

You can buy packets of Amblyseius cucumeris (a.k.a. thrips killer mites), which are predatory mites that eat thunder flies. 

You can buy these online or in garden centres, and they are effective in the fight against thrips. Once the infestation has gone, the mites die off. 

Neem oil for thrips infestations

Neem oil is a natural insecticide that’s effective against thrips. Simply dab infested plants with the oil to kill the pests. 

Fly papers for killing thunder flies

This isn’t recommended as a stand-alone approach to catching and killing thrips, but hanging fly papers around the home and garden can help attract the tiny critters. Remember, they’re not great flyers, so this approach will only catch the insects in flight.

Replace the soil

Once the eggs have hatched into their larval form, they often drop off the leaves and land in the soil substrate. So, replacing the top layer of soil or compost can help interrupt the reproductive cycle of thunder fly infections. 

Use olive oil detergent

A mix of olive oil, washing up liquid and water can be effective against thrips. Spray the plants regularly with this mix; the thrips will struggle to cling to leaves. 

Cut off the younger leaves

In case of severe infection, removing a plant’s young leaves may be necessary, as the thrips often use these to hide. 

Plant care after infestation

After eliminating the insects, your plants will need some extra TLC. 

Check all foliage for any signs of reinfection, and remove the insects manually if you spot a fresh outbreak. Use a magnifying glass to help spot these sometimes microscopic insects. 

Remove any remaining thrips by wiping the leaves with a damp cloth and a little insecticidal soap. 

Then, keep the plants well watered, placing them in a sunny spot (if they’re sun-lovers) and feeding them with an appropriate fertiliser. 

Keep monitoring the plant for signs of reinfection. 

FAQs

Any questions?

I hope this article has helped you identify and tackle those troublesome thrips, but if you have any questions, drop us an email.

Or explore our comprehensive Help & Advice section for everything garden and lawn care related!

Thanks for reading.  

Louis Hooft

Founder & Lawn expert

Introducing Louis Hooft, the founder of MOOWY and your reliable expert. With a profound love for stunning lawns and extensive experience in garden maintenance, Louis is here to assist garden enthusiasts in achieving a greener and livelier outdoors than ever before. Count on Louis for invaluable tips, clever tricks, and top-notch products to make your garden flourish!