Gardeniarose,

I start seedlings indoors under lights and fungus gnats occasionally breed in the peat moss growing medium. I control them by adding some BT (bacillus thuringiensis) to the water that I use for the plants. However, it is effective against the fungus gnat maggots, but not the adults. You might want to use a non-toxic flying insect spray, based on pyrethrum, on the adults. Or you might find it effective to suck them into a vacuum cleaner hose. I found that to be effective against white flies.

MM

Fungus Gnat larva only grow in a growing medium that is too wet, they cannot grow in dry soil mixes. Let this soil dry and they larva will die. To determine when it is time to water the plant again insert your index finger into the soil to the first knuckle nad if the soil is still damp do not water but if the soil is dry soak the pot and let it dry to that stage again. To get rid of the adults, which will be laying more eggs that will become more larva when the soil conditions are right, place some yellow sticky traps around the plant.