Pest

Fungus gnats

Bradysia spp.

Small dark flies whose larvae live in moist media, feeding on fungi, organic matter and young roots. Mostly a nuisance on established plants, but larvae injure seedlings and cuttings and spread root rot.

Signs

• Weak-flying, mosquito-like adults around the media and on yellow sticky cards.
• Clear larvae with shiny black heads in the top 1-2 inches of moist media.
• A slice of raw potato laid on the media for a day or two collects larvae underneath.

What favors it

Media that stays wet at the surface, and mixes with unfinished compost or other fresh organic matter.

Prevention

• Let the top inch of media dry between waterings.
• Bottom-water, or top-dress with coarse sand or gravel.
• Store bags of media closed; avoid half-composted additions.

Often confused with

Sources

• Fungus GnatsUniversity of Maryland Extension
• Fungus Gnats and Shore FliesUMass Amherst Extension
• Fungus Gnats and Shore Flies (E-111)Purdue Extension
• Fungus Gnats: Tiny Pests in Houseplants and How to Control ThemNC State Extension

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