Thrips, Fungus Gnats, Mealybugs: Causes and Natural Solutions

Thrips, fungus gnats or mealybugs? These three pests are the number one enemies of houseplants. Understanding what causes them to appear is the key to preventing them effectively and knowing how to get rid of them naturally. In this guide, find out what attracts each pest, how to tell them apart and the most effective biological methods for fighting them.

How can you tell which pest is attacking your plant?

First step: correctly identify the culprit. Each pest has its own visual signature.

• Small silvery or bronzed dots on the leaves, fine black droppings → thrips
• Small black gnats flying around the pot, white larvae in the compost → fungus gnats
• White cottony clusters on leaves, stems and nodes → mealybugs

1. Thrips: causes and solutions

Why do they appear?

Thrips are attracted to warm, dry environments. They feed on the cell contents of plants by piercing the leaves with their mouthparts, which creates the characteristic silvery marks. Contributing factors:

• Air that is too dry (central heating in winter, air conditioning in summer)
• Lack of ventilation in the space (a permanently closed room)
• Stressed plants (lack of water, excess fertiliser, unsuitable light)
• Introducing a contaminated new plant without quarantine
• Bunches of cut flowers brought in from outside

Prevention and treatment

To prevent thrips:

• Maintain adequate humidity (40–60%)
• Ventilate your growing spaces regularly
• Quarantine every new plant for 2 weeks
• Inspect under the leaves once a week

To treat: combine nematodes (eliminate the larvae in the compost) + neem oil (sprayed on the foliage) + sticky traps (catch the flying adults).

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2. Fungus gnats: causes and solutions

Why do they appear?

Fungus gnats (sciarids) appear mainly because of soil that is too damp. The females lay their eggs in damp compost, and the white larvae feed on roots and decomposing organic matter.

• Chronic overwatering (cause no. 1)
• Poor-quality compost that already contains eggs
• Saucers permanently filled with water
• Poor drainage in the pot
• Decomposing organic matter on the surface of the compost

Prevention and treatment

To prevent gnats:

• Let the compost dry out between waterings
• Empty the saucers 30 minutes after watering
• Add a layer of clay pebbles on the surface to block egg-laying
• Use good-quality compost (avoid opened bags stored for a long time)

To treat: nematodes (Steinernema feltiae) are the most effective solution against the larvae. Combine them with fly traps for the flying adults.

Discover our full guide: How to get rid of fungus gnats

3. Mealybugs: causes and solutions

Why do they appear?

Mealybugs are attracted to warm, slightly humid environments. They feed on plant sap by piercing the stems and leaves with their mouthparts, weakening growth and encouraging sooty mould (a black fungus).

• Warm temperatures (ideal for their multiplication)
• Over-fertilising with nitrogen (sap that is too rich)
• Lack of ventilation (plants crowded together)
• Stressed or weakened plants
• Introducing new plants without quarantine
• Ants in the pots (farming mealybugs for the honeydew)

Prevention and treatment

To prevent mealybugs:

• Inspect regularly the hidden areas (undersides of leaves, nodes, leaf axils)
• Space plants out to improve ventilation
• Moderate fertiliser applications (avoid nitrogen overdosing)
• Clean the leaves with a damp cloth once a month

To treat: combine black soap (smothers mealybugs), neem oil (disrupts their cycle) and manual cleaning with a cotton bud dipped in alcohol on visible clusters.

Discover our full guide: How to get rid of mealybugs

The universal solution: Jungle Buddies nematodes

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Our Jungle Buddies contain beneficial nematodes (living micro-organisms) that specifically attack the larvae of all 3 pests: thrips, fungus gnats and mealybugs. Safe for you, your children, your pets and other insects. Easy to apply by watering.

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The 5 golden rules for preventing these 3 pests

1. Systematic quarantine: every new plant stays isolated from the others for 2 weeks so any infestation can be detected
2. Weekly inspection: 30 seconds per plant to spot the first signs early
3. Controlled watering: letting plants dry out between waterings prevents gnats and supports general health
4. Healthy plants: a vigorous plant (good light, good watering, a suitable fertiliser) resists pests better
5. Biological prevention: 1 application of nematodes in spring and in autumn drastically reduces the risks

FAQ: your questions about plant pests

How can you tell if your plant has pests?

Look for the signs: silvery dots (thrips), flying gnats around the pot, white cottony clusters (mealybugs), sticky patches on the leaves (honeydew), slowed growth or distorted leaves. Also inspect the undersides of the leaves, which is where most pests hide.

Should you throw away a heavily infested plant?

Not necessarily. Even a badly affected plant can be saved with an intensive treatment (nematodes + neem oil + black soap) and a little patience (3–4 weeks of treatment). If the infestation is spreading to your whole collection, put the plant into strict quarantine.

Can pests survive the winter?

Yes, especially in our heated homes. Thrips and mealybugs find a permanent tropical climate in winter. Treatments therefore need to be carried out all year round in the event of an infestation, not just in spring.

Do essential oils work?

Very little on established infestations. They may have a repellent effect but no curative action comparable to nematodes or neem oil. Use them only as a complement.

My neighbours have pests: am I at risk?

Not directly (indoor pests travel little from one flat to another), but be more vigilant when swapping cuttings or buying plants together. Always inspect and quarantine.

Which season is the riskiest?

Spring and summer for outdoor proliferation and the arrival of thrips in homes. Winter in our heated homes, where thrips and mealybugs thrive. Autumn is often the season when infestations come to light (after the summer multiplication phase).

In summary

Thrips, fungus gnats and mealybugs have distinct causes (dry air, overwatering, humid heat) but can be fought with common solutions: Jungle Buddies nematodes for the larvae, neem oil for the adults, black soap for mealybugs. Prevention remains the best strategy: quarantine new plants, inspect regularly and keep plants in full health.

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