Fungus Gnats and Fly Larvae
PestsAct soon
Small dark winged flies, 1–6 mm long, around the growing area and on the substrate, with small larvae feeding in substrate or mushrooms.
Likely causes
- Open substrate or casing attracting egg-laying flies
- Flies entering through unscreened doors, vents or windows
- Moist organic waste or spent substrate left in or near the room
What to do
Screen vents and doors, keep the room clean and remove spent substrate and waste promptly. Use sticky traps; one study found that both UV light (about 370–398 nm) and green light (about 526 nm) attract the main mushroom fungus gnat, so a light trap with both works best.
Easily confused with
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Sources
- In search of the spectral composition of an effective light trap for the mushroom pest Lycoriella ingenua (Scientific Reports (2021)). Sciarid fungus gnats are small (1–6 mm) dark winged insects and among the most important pests in mushroom production; larvae cause direct crop damage and adults are vectors of dangerous fungal pathogens; both UV (about 370–398 nm) and green (about 526 nm) light are recommended for trapping.
- Agrodok 40: Small-scale mushroom cultivation: oyster, shiitake and wood ear mushrooms (Agromisa Foundation and CTA (Peter Oei, 2005)). Mushroom flies are attracted by the odour of mycelium; they lay eggs between the gills and on the mycelium and the larvae spoil the crop; the remedy is to remove old and contaminated bags consistently and clean the rooms.
Last updated: 2026-10-19