We've all seen them. Those pesky, annoying fruit fly looking things. Besides being unappealing to have around your plants and home, they don't pose much of an issue for you or your plants. In very rare cases they can breed out of control and their larvae feed on damaged plant roots. So what can you do? We've composed some helpful information and tips on dealing with fungus gnats.
They can come home with your new plant, or sneak into your home from open windows and doors. They're not great flyers, so tend to hover around infected plants or light sources. Fungus Gnats will lay their eggs in soil (unlike fruit flies that do not need soil) with the larvae sustaining itself on decomposing plant material and other organic nutrients found in the soil. They tend to only live for 7 to 10 days, but within that period, a female gnat can lay anywhere from 200-300 eggs. Gross, right?
If you're developing a fungus gnat problem, there is a good chance you may be over watering your plant. They tend to only lay their eggs in moist soil conditions. Plants that require more humidity and moisture are more prone to fungus gnat infestations (although any plant can be effected if it's being overwatered). If you're noticing a lot of fungus gnats and want to check for larvae, a good trick is to place a thin slice of potato on top of the soil. The larvae will make their way to the surface to feed on the potato within just a few days.
The best thing to do if you start developing a fungus gnat problem, is letting the soil completely dry out for the top 2-3 inches before watering again. This will help kill off the larvae, stop further development of eggs and make the soil less appealing for females to lay more eggs.
You can also use food grade diatomaceous earth (that white stuff that looks like baking soda, but is like broken glass for insects). Sprinkle a few tablespoons on the top soil and let it sit for a few days. Using an insecticidal soap is also another option, as is setting up the classic apple cider vinegar trap around your infected plant.
Once you have a handle on the issues, take care not to overwater in the future and treat as soon as you see any gnats!
PS. What does 'overwatering' mean exactly? Overwatering is simply watering your plant too often. This way, the soil doesn't have a chance to dry out, and the roots are constantly wet and soggy. This type of environment is a big invitation for fungus gnats, root rot and fungal problems.