Fungus gnat larvae usually are located in the top 2 to 3 inches of the soil, depending on moisture level, and primarily feed on plant roots, fungi, and decaying plant matter. Gnats are not strong fliers and emerge from soil when disturbed.
Fungus gnats are tiny, delicate flying insects that resemble miniature mosquitoes. They are present any time of year, but they tend to be more common in fall and winter. The pesky gnats aren't selective about when they lay eggs, which they deposit in the top 2 to 3 inches (5-8 cm.) of potting soil.
Adult fungus gnats only live for about a week, but the eggs they lay will sit in the soil for three days and hatch into nymphs, which will live in the soil for about two weeks before growing wings.
Rest assured, however, that you can get rid of fungus gnats without having to trash all of your plants. If the infestation is new, let the soil of infected plants dry out completely, which kills the larvae. If the infestation is beginning to grow, however, you'll need to take more serious action.
Drench the soil with microbial insecticide, such as bacillus thuringiensis, more commonly called Bt. This is the most effective way to kill any fungus gnat larvae. Allow the soil to dry out for a few days, so that the top 2 inches (5 centimeters) are really dry. The larvae of fungus gnats cannot survive in dry soil.
Eradicate your fungus gnat infestation for good with the following method: Put up a bunch of sticky traps, top-dress the soil with sand and do nematode soaks every 10 to 14 days until the problem is resolved. Also, stop overwatering your plants and eliminate any unnecessary sources of moisture. That's it.
Using boiling water to hydrate the seed starting mix will kill the fungus gnat eggs 99% of the time. Most seed starting mixes have little, if any, microbes in the mix. They are typically peat moss and vermiculite based.
Remove the gnat infested soil
Just keep in mind that gnat eggs in soil could still hatch and mature after you remove it from your plant, so make sure you take it outside to the trash.
Hydrogen Peroxide
A peroxide solution apparently kills larvae and eggs on contact, effectively killing off all infant gnats and disrupting the lifecycle. You should be able to buy hydrogen peroxide from any high street pharmacy or online. Mix 1 part 9% hydrogen peroxide with 6 parts water.
“These pests are attracted to moisture, so you may see swarms in areas with damp soils, standing water, or even houseplants that have been overwatered,” Ludwiczak adds. “The breeding habits of gnats are most active during warmer months, which is why they seem to be especially prevalent during summer.”
Fungus gnats go through complete metamorphosis (egg, larva, pupa, adult) and reproduce in moist, shaded areas within decaying matter. One generation takes about 4 weeks. Mated females lay 00 to 200 microscopic eggs. Eggs are oval, smooth, shiny white and semi-transparent, and hatch in 4 to 6 days.
Cinnamon is a powerful natural fungicide, which kills off the gnats' primary food source, therefore making the soil inhospitable. You can also use a cinnamon stick, just pop it straight into the soil. You can grab either cinnamon sticks or powder next time you're doing your supermarket shop.
Because fungus gnats thrive in moist conditions, especially where there is an abundance of decaying vegetation and fungi, avoid overwatering and provide good drainage. Allow the surface of container soil to dry between waterings.
Fungus gnat management is a cultural matter and not soil dependent. All potting soils must contain organic matter, be porous, and hold water well for effective root growth, and any soil that's moist and high in organic matter will attract fungus gnats.
Use natural predators. Nematodes (Steinernema) and predatory mites (Hypoaspis) feed on fungus gnats and their larvae and can be applied to the potting mix as eggs that will hatch and begin to feed. They will gradually attack the problem until there is nothing left for the predators to feed on.
Repel them with Scent.
Or, you can switch up your favorite scent with something they don't like. Try Lighting citronella candles, using lemon or vanilla sprays. While gnats are a fan of sweet-smelling fruit, they can't seem to stand vanilla, lemon, or even lavender. A little spritz can at least keep them at bay.
Bleach Your Drains
If you notice gnats around your kitchen sink or bathtub, pour a cup of diluted bleach down the drain to kill the gnats. Be sure to pour the cup of bleach down each drain or garbage disposal very slowly until there are no more gnats in your line of sight.
Hydrogen peroxide will kill the gnat larvae and not injure your plant. Keep reapplying weekly until you notice the gnats are gone.
Neem oil is superb when used as a preventative and very effective in eliminating infestations. The great news is that it targets major pests like spider mites, mealy bugs, aphids, and fungus gnats.
Coffee grounds repel pests. Most pests do not like the smell of coffee, so they will stay away- Fungus Gnat is no different. If your coffee grounds are not repelling them, you're not doing it right. One thing you would have to do is to avoid spreading the coffee grounds on the face of your potting soil.
Life Cycle
They prefer to lay eggs where fungus is growing. Indoors, they occur anytime of year. The larvae feed for about 2 weeks and then pupate near the soil surface within thread chambers. After 3 to 7 days in the pupal stage, adults emerge and live for about 8 days.
Vinegar works through a process of dehydration. It breaks down the waxy cuticle on the bugs, which causes them to dehydrate and die. It's simple, effective, and safe for food plants.
To get rid of fungus gnats, mix a solution of one part hydrogen peroxide with four parts water. Pour the mixture onto the soil around the infested plant.
Or, if the pot is big enough, place this trap inside the pot on top of the soil. The gnats will be attracted to the scent of the vinegar and fly in for a sip. Meanwhile, the dish soap works to cut the surface tension of the vinegar, causing the fungus gnats to fall in and drown.