Fungus Gnats caught on a sticky trap
One of the biggest problems with Fungus Gnats is that they can feed on the tender roots of young seedlings. I am currently growing hostas from seed and have just discovered Fungus Gnats. The Gnats can feed on the roots, stunt the growth of the seedlings or kill the seedlings. The Fungus Gnats (not adult) were in the potting soil the I recently purchased.
There are several way to control Fungus Gnats in the home. Always allow good drainage and don't over water plants in your house for winter. There are several sprays on the market to control the adults. Make sure you read the warning labels of all insect sprays before using and make sure that Fungus Gnats is listed on the container. I have installed several sticky traps around my hosta seedlings and have caught many of the adult Fungus Gnats in flight (and have caught myself in the traps several times - they are sticky!) I am now using Bacillus thuringiensis (var. Israelensis) or "Bti " to kill the larva in the soil. Bti is a biological pesticide that contains naturally occurring bacteria that target and kill specific insects - in this case Fungus Gnats. The Bti is eaten by the larva and then they die. Bti does not harm animals, fish, birds, beneficial insects or humans. It does not contaminate the environment. Bti is hard to find in stores and nurseries. You may want to seek it out on the internet and have it shipped to you. Several application of Bti in the soil should rid you and your home of Fungus Gnats.
The Creative Gardener