Thrips – how to fight them in your plant collection

Like many plant owners recently, I investigated a few poorly-looking plants and was horrified to find a pretty extensive thrips infestation. 

What are thrips?

Of the plant pests that I’ve dealt with in the past (mainly fungus gnats and spider mites), thrips are definitely the worst. They seem to cause the most widespread damage, stunted growth, and lurk in hidden places waiting to make a comeback after you think they’re eradicated.

The RHS describes thrips as small insects, many of which feed by sucking sap from leaves and flowers. The larvae live on the underneath of the leaves, and the adults are able to fly, meaning they can spread to new plants around your home. 

How to tell if you have thrips

Generally if you spot any damaged leaves or stunted growth, on any plant, it’s worth inspecting leaves and stems closely to see if you have any pests. Thrips are no exception – their damage causes mottling and discoloured patches on existing leaves, and weak new leaves.

In some ways it’s quite easy to spot if you have thrips living on your plants:

Thrips on a philodendron shangri-la
The culprits at work on a philodendron Shangri-La -adult thrips (black insects) and larvae (cream blobs)

5 signs of thrips

  1. Small and creamy-yellow coloured larvae, about 1mm long. If you poke one with your fingernail, you’ll see it scurry away
  2. Small thin black insects, which also move around the undersides of leaves
  3. Black specks around the areas of damage (their excrement)
  4. A brown/rust coloured tinge on the underside of leaves
  5. Mottled, browned or damaged new growth

They also seem to have favoured plants, which in my collection have been all my philodendrons, tradescantia, swiss cheese plants (monstera deliciosa), pothos (epipremnum aureum), rubber plants (ficus elastica), and even carnivorous plants.

How to treat thrips

Like most pests, thrips populations can be suppressed and eventually eradicated through a couple of physical measures:

Option A: Smothering with an oil mixture

Dilute a few drops of neem oil or castille soap in a sprayer. I usually add a drop of eco-friendly washing up liquid to help emulsify the mixture. Shake it up, and spray down the surfaces and stems. This smothers the insects and eventually kills them.

Pressurised sprayer for treating plants
Pressurised sprayer for treating plants

Option B: Targeting with rubbing alcohol

Alcohol will ‘melt’ most insects, so you can make up a well-diluted mixture and spray or wipe down leaves, which will almost immediately kill any insects you apply it to. I like to spray and then use an old brush to physically remove the pests off the leaves.

Repeat or alternate between these methods every few days, and keep your plants out of direct sunlight while they dry.

Remember to give your plants a break between treatments because it can be harsh to them too. Oil will also smother plants’ leaves and affect their ability to ‘breath’ and photosynthesise. Similarly, alcohol, especially in too high dilutions, can damage the leaves.

As soon as you have no more signs of pests, stop the treatments and switch to a less harsh preventative treatment like SB invigorator.

Different pest treatment options
Different ‘natural’ pest treatments – SB Invigorator and castille soap

Other treatment options

As a last resort I sometimes used off-the-shelf pest sprays like Bug Clear or Provanto. These aren’t ideal because they’re harsh to plants and us, often systemic (meaning the plant takes in the poison and the insects die when dining out on it), and can be less effective over time because pests develop resistance to it. 

In many ways it’s a slow process treating with oil / alcohol, but more likely to be effective over time because you’re physically killing and removing the insects.

Good luck in your battle against thrips!

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