Fungus Gnats

Info for the Indoor Gardener

The first step in eradicating fungus gnats is identifying them correctly. The second step (and third...and fourth...) is to take appropriate, responsible action. These are one of the most common garden pests the Indoor Gardener will eventually face, especially if you don't let your soil dry out between waterings. Read below to learn how to avoid them, find them, and get rid of them.

DESCRIPTION

• fungus gnats are tiny - about 1/10 - 1/8 inch
• black or grayish
• looks like flies
• single pair of transparent or light gray wings
• long legs like mosquitoes
• antennae - often longer than their heads
• fly, crawl, jump along the planter's surface
• eggs are oval, smooth, shiny white or transparent
• larvae - legless, white, shiny, black heads
• can see through the larvae to the food in their stomachs
• pupae - silk-like cocoons in the soil

LOCATION

• adults on the soil surface
• larvae and pupae in top 1/4" or so of soil
• fungus gnats love wet soil that doesn't dry between waterings

MULTIPLICATION

• female can lay upwards of 100 eggs in the week of her life
• eggs laid in rows in soil
• larvae grow in rich soil

DESTRUCTION

• adults to minimal destruction to plants
• fungus gnats can drive the indoor gardener crazy by being such a nuisance in the air around the plant
• they multiply quickly and fly throughout your home
• larvae can eat root hairs and deplete the plant's energy
• adults can spread diseases from plant to plant

DETECTION

• you'll notice small fly-like insects close the soil
• you'll see them - especially around windows, try to swat them, and eventually swallow these garden pests as they multiply from room to room
• examine soil surfaces as you check your plants regularly
• notice insects that jump from the soil surface as you water
• plants wilt, poor growth, loss of leaves, yellowing

SOLUTION

• easy
• insecticidal soap: spray on soil
• let soil dry and then spray again
• remove top soil to 1/4 inch; add new soil
• be sure to let soil dry between waterings
• if you move plants from outdoors to indoors you may want to change the soil; at least the top half inch
• get rid of dead leaves, twigs, etc. immediately
• yellow sticky cards (for adults); check and replace every other day
• pesticides: pyrethins, pyrethroid insecticides (used frequently) for adults; organic Bacillus thuringiensis var. israelensis to soak soil and kill larvae; Neem products
• chemicals: chlorpyrifos, cyfluthrin, oxamyl, diazinon, resmethrin, among others
• potato traps for fungus gnat larvae (cut 1-1/2 inch squares white potato; place on soil surface; lift in a few days; discard with larvae; repeat until no larvae found)

ORDER: Diptera

FAMILY: sciaridae

Bradysia specie Bardysia coprophila (black-winged fungus gnats) Also: Sciara spp., Orfelia spp.

• adult lifespan = a few days to a week
• reproduce in decaying organic matter, warm temperatures
• generation = about a month (egg, larva, pupa, adult)
• female can lay about 100 eggs in her week of life
• 3-40 eggs laid in strings around plant base and in cracks in soil
• eggs hatch in about 5 days
• "maggot stage" - pale larvae (max 1/4 inch); distinguished by their shiny black heads
• maggot stage lasts about 2 weeks
• larva then spins a silk-like cocoon much like a butterfly (pupa stage)
• generations overlap
• nutrition from fungi and decaying organic matter in soil, or small root hairs or new roots
• natural predators of these garden pests: nematodes, predatory mites
• can spread such plant diseases as: pythium, cyclindrocladium

Return to Garden Pests

Return to Home Page