Small, dark, mosquito-like flies hovering around the soil surface and flying up when the pot is disturbed; larvae in the soil can damage fine roots of seedlings or already-weakened plants.
Cause & development
The most common fungus gnat species affecting indoor and greenhouse-grown houseplants in North America. EPPO code BRAIIM.
Favorable conditions
•Consistently overwatered, moist potting mix
•Organic matter in the topsoil that larvae feed on
•Poor drainage keeping the surface soil wet
Management
1Let the top 1-2 inches of soil dry out between waterings
2Use yellow sticky traps to catch adults
3Apply a Bacillus thuringiensis subsp. israelensis (BTI) soil drench to target larvae
4Top-dress with sand or diatomaceous earth to discourage egg-laying