Plant problems · Pests · Seedlings · Act this week
Fungus gnats
What you see
- Small black flies around the soil surface
- Larvae (tiny white worms) in the top layer of soil
- Seedlings wilt because larvae eat the young roots
Why it happens
Gnats breed in wet topsoil. They are a sign of overwatering more than a disaster in themselves.
What to do
- Let the top layer of soil dry between waterings
- Yellow sticky traps catch the adults
- Water in Bacillus thuringiensis israelensis (BTi) or use beneficial nematodes against the larvae
- A layer of sand on top of the soil stops them laying eggs
Next time
- Do not keep the surface wet
- Bottom water seedlings
Easy to confuse with
- Overwatering: The whole plant droops with leaves that feel firm and swollen, not limp
- Root rot: The plant wilts even when the medium is wet
Not sure?
Take a photo of the soil surface and a sticky trap and ask the Grow Doctor, or send it to the grow companion on Telegram.