Stop fungus gnats: Control larvae and adult flies

Fungus gnats are common indoor pests that both damage roots and are a nuisance:

**Identify fungus gnats:**

*Adult fungus gnats:*

- 2-4mm small, black flies

- Fly around slowly and sluggishly

- Particularly active during irrigation

- Like to sit on moist soil

- Live only 7-10 days

*Larvae (the main problem):*

- 4-5mm long, white maggots

- Transparent with black head

- Live in the top 5cm of the soil

- Eat root hairs and fine roots

- Development time: 2-3 weeks

*Recognise damage:*

- Small flies around pots

- Slowed growth

- Yellowish leaves for no recognisable reason

- Roots with feeding marks

- Substrate with small tunnels

**Immediate measures:**

*Reduce watering:*

- Allow soil to dry between waterings

- Keep the top 2-3cm dry

- Water only from below (saucer)

- Improve drainage

- Stop overwatering immediately

*Set up yellow traps:*

- Sticky yellow traps

- 2-3 per large pot

- Directly on substrate surface

- Catch adult flies

- Renew weekly

*Cover substrate surface:*

- sprinkle 1-2cm of sand on the soil

- Use quartz sand or perlite

- Prevents egg laying

- Larvae cannot move upwards

- Dries faster

**Biological control:**

*SF nematodes (Steinernema feltiae):*

- Microscopic roundworms

- Parasitise fungus gnat larvae

- Mix into the irrigation water

- Keep substrate moist for nematodes

- Effect visible after 1-2 weeks

*Predatory mites (Hypoaspis miles):*

- Eat fungus gnat larvae

- Live permanently in the substrate

- Also effective against other soil pests

- A single application is usually sufficient

- Can be combined with nematodes

*Bacillus thuringiensis israelensis (BTI):*

- Bacterial toxin against mosquito larvae

- Mosquito dunks in the irrigation water

- Harmless to plants and humans

- Apply every 2 weeks

- Can also be used in water tanks

**Mechanical methods:**

*Hoover method:*

- Vacuum adult flies daily

- Irrigate when they are active

- Drastically reduces egg laying

- Simple and immediately effective

- Can be combined with other methods

*Substrate replacement:*

- Complete replacement in case of severe infestation

- Carefully remove old soil from the roots

- Repot in new, sterile substrate

- Dispose of old soil (do not compost)

- Most radical but safest method

*Water bath treatment:*

- Place pot in warm water (40°C) for 30 minutes

- Larvae drown or float up

- Only for robust plants

- Alternative to repotting

- Then apply sand mulch

**Chemical options:**

*Neem oil watering solution:*

- 5ml neem oil per litre of irrigation water

- Systemic effect via roots

- Apply every 10 days

- Also against other pests

- Organic and plant-compatible

*Azadirachtin preparations:*

- Active ingredient from neem tree

- Pour into the substrate

- Inhibits larvae development

- 2-3 applications necessary

- Professional preparations more effective

*Pyrethrin spray:*

- Against adult flies

- Spray on substrate surface in the evening

- Kills