Thrips are one of the most frustrating pests to deal with on houseplants. These tiny insects can cause considerable damage, spreading quickly from plant to plant and often going unnoticed until leaves become silvered, distorted or covered in unsightly marks.
If you've been battling a persistent thrips infestation, repeatedly spraying your plants most likely isn't working. Fortunately, biological pest control offers another approach: using beneficial predatory insects and mites to tackle thrips properly.
To get them under control you need a combination of thorough plant cleaning, a large initial release of beneficial predators, ongoing biological protection and blue sticky traps to monitor pest activity.
Here's how to approach a thrips infestation and the products you need.
Step 1: Give your plants a thorough clean
Before introducing beneficial insects, it's important to get your plants as clean as possible.
Thrips can hide in all sorts of places, including:
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The undersides of leaves.
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New growth and tightly folded leaves.
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Leaf joints and stems.
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Flowers and flower buds.
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Cracks and crevices around the plant.
Product needed - Horticultural Soap
Treat all affected plants, paying particular attention to leaf undersides, stems and areas where thrips are likely to hide. Remove badly damaged leaves and any dead plant material where appropriate.
Test sensitive plants first and avoid treating in strong sunlight.
An important point: Horticultural soap is a contact treatment, so it needs to reach the pests. It won't provide lasting protection against thrips that hatch or emerge later.
Allow treated plants to dry before introducing beneficial insects. This soap does not leave behind residues but other pesticide residues can harm your newly introduced predators so leave 6 weeks if you have used this kind of spray.
Step 2: Introduce a large release of beneficial predators
Once your plants have been cleaned and are ready for biological control, it's time to introduce the beneficial bugs.
For an established infestation, you should considering a shaker tub of either Amblyseius cucumeris or Orius predators.
These are two different biological control agents, and each has its own advantages.
Amblyseius cucumeris – predatory mites
Amblyseius cucumeris are tiny predatory mites that feed on young thrips larvae.
They are particularly useful because they actively search through the foliage for young thrips before they have a chance to develop into adults.
One important thing to understand is that Amblyseius cucumeris do not target adult thrips. They concentrate on the early larval stages. So you will have needed to clean the adults from the plants and continue to remove them by hand.
What a substantial initial release does is put pressure on the developing thrips population and disrupt its lifecycle.
They are also a cheaper option than introducing Orius predators.
Orius – minute pirate bugs
Orius, sometimes called minute pirate bugs, are predatory insects that actively hunt thrips.
Unlike Amblyseius cucumeris, Orius can attack a wider range of thrips life stages, including adults.
They are particularly useful when dealing with an established infestation, although their effectiveness depends on conditions such as temperature, light levels and the availability of prey.
Both options have a place in biological thrips control. The best choice depends on the severity of the infestation, the growing environment and your budget!
Step 3: Add slow-release sachets for ongoing protection
Once you've done your clean up and maybe made your initial release of beneficial predators, I recommend adding slow-release Amblyseius cucumeris sachets.
These little sachets are an excellent way to maintain a continuing population of predatory mites on your plants.
Each sachet contains a breeding population of beneficial mites and a food source. The predators emerge gradually over several weeks, providing ongoing protection rather than relying on a single release.
This is particularly useful because thrips have a lifecycle that makes them difficult to eliminate with one treatment.
Eggs can be protected within plant tissue, while developing stages may be hidden in foliage, flowers or growing media, depending on the thrips species.
By maintaining a population of beneficial predators, you have a much better chance of catching newly emerging larvae before they develop into adults.
Your will need to replace the sachets every 6 weeks. Avoid positioning them in direct sunlight or somewhere they will become excessively hot or dry.
Shop slow release sachets and subscrptions
Step 4: Use blue sticky traps to monitor adult thrips
Blue sticky traps are another important part of this approach.
Thrips are attracted to blue, and sticky traps provide a useful way to monitor and catch adult thrips.
We recommend positioning them around your plants, close to the foliage, where they can help you:
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Monitor adult thrips activity.
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Identify whether an infestation is increasing or decreasing.
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Catch some of the adult population.
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Assess how well your biological control programme is working.
Don't expect sticky traps to eliminate an infestation on their own. They are a monitoring and supplementary control tool, rather than a replacement for beneficial predators.
Keep checking your traps regularly. If you're still catching large numbers of adult thrips, it may indicate that the infestation needs further attention.
Finally, be patient and keep monitoring
Biological control is not an instant fix.
Unlike a contact pesticide, which may kill exposed insects quickly, beneficial predators need time to establish and feed on their prey.
You may continue to see adult thrips for a while after introducing beneficial insects. This doesn't necessarily mean the treatment isn't working.
The important thing is to monitor the overall population and look for signs that new damage is reducing.
Continue checking:
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New leaves and growing tips.
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The undersides of older leaves.
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Flowers and flower buds.
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Blue sticky traps.
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The condition of your plants.
If thrips numbers remain high, review the predator choice and release rate.
Real customer experience: Biological control versus pesticides
We regularly hear from customers who have become frustrated with repeated attempts to control thrips.
One Ladybird Plant Care customer shared their experience of running two different approaches in separate plant rooms: pesticides in one and beneficial insects in the other.
Here's what they had to say:
"I’ve been fighting a big thrips infestation for a few months now. In one plant room I am using pesticides and in another I am using beneficial bugs. I have found the bugs to be a lot more effective and less labour intensive, but more expensive. I’ve found a combo of amblyseius cucumeris slow release sachets and a large release of amblyseius cucumeris works very well, they don’t target the adults but with a big release of them you should disrupt the life cycle enough at the early stages, and they are cheaper then orius laevigatus which I have had less success with. Ladybird Plantcare have given me some really good advice I would recommend"
This is a really interesting comparison because it highlights something important about biological pest control.
Although the initial cost of beneficial insects can be higher, they can offer a more sustainable and less labour-intensive approach to managing a persistent infestation.
The customer's experience also demonstrates that you don't always need to choose the most expensive predator to achieve good results. A well-planned combination of a large initial release and ongoing slow-release protection can be very effective.
Of course, every infestation is different, and results will depend on the thrips species, plant types and growing conditions.
Bundle Deal
To help you get started you can now buy a special bundle of products
Horticultural Soap + 10 x Slow Release Sachets + Blue Sticky Traps £16 (excluding shipping)
About the Author
Tessa Cobley is the owner of Ladybird Plantcare, a specialist supplier of biological pest control and beneficial insects for gardeners, houseplant enthusiasts and professional growers.
With a passion for helping people grow healthier plants naturally, Tessa shares practical advice on identifying and tackling common plant pests, using biological controls and creating a healthier growing environment. Her aim is to make effective, environmentally conscious plant care accessible to everyone.
If you would like to know more about working with Tessa, please visit www.tessacobley.com
