Bradysia sp., and others
In the garden: A vast range of plants (usually potted) where the compost is maintained in a damp condition.
On Crops: A vast range of plants (usually potted) where the compost is maintained in a damp condition.
Throughout UK and Europe
The adults are small dark-coloured flies 3-4 mm in length, often seen hovering around the base of pot grown plants or flitting about on the compost surface where they mate. The small translucent eggs are laid in batches of 20-50 into the compost surface. These hatch into small cream-coloured maggots that have shiny black heads. The larvae live within the soil and feed on plant roots, lower stems and on leaves that touch the compost surface. When mature, the larvae are around 6mm in length.
Adult fungus gnats do not cause any damage to plants. The larvae feed on the plant roots and lower stems often causing young plants and seedlings to rot and die. Where leaves are touching the compost surface, larvae will often feed on the lower leaf surface.
Keep bags of compost tightly sealed to prevent fungus gnat infestation before the compost is used. Placing a layer of grit on the surface of the compost will prevent adults from laying their eggs.
Predatory mites that live within the compost and eat fungus gnat larvae can be bought commercially. Parasitic nematodes are also available that can be watered into the compost.
Sticky traps will provide an early warning of when fungus gnats are flying around pots.