These small dark insects (about 1/8″ in size) look similar to mosquitoes and are often confused with fruit flies. They thrive in humid environments and breed in the damp soil of potted plants.
Why they’re harmful: Aside from being annoying, fungus gnats are actually quite destructive. The larvae is what causes the most damage by eating the roots, hairs and stems which then affects the vibrancy and health of the plant.
The symptoms of an infestation can be stunted vegetation/growth, wilting, yellowing leaves and rotting roots.
The adults feed on fungi at the top of the dirt (where they lay their eggs) while the larva feasts on the roots.
How to tell if your favorite houseplant is infested? Here’s a trick to find out if you’re not sure:
- Slice a chunk of raw potato and place it on surface of the soil where you suspect they are thriving (lay it cut side down).
- After seven days, lift the potato up–if you have them you will see larvae on the potato.
The good news is that they’re not that difficult to get rid of. I’ve put together a collection of DIY remedies below to help banish them from your house along with some advice for trying to control them.
Ways To Get Rid Of Them
Mimic Drought Conditions: Allow the soil to dry very well to the point that plants start to wither before watering again (approximately the top one to two inches of dirt is completely dry).
Why this works: It needs to get to this state so the larvae will dry up completely (ending their cycle). The adults cannot breed in these conditions so the life cycle ends.
Sticky Traps: You can purchase yellow sticky cards with the purpose of indoor insect control, these will work with fungus gnats. The idea is that the bright color will attract them and when they come to investigate, they will be stuck or trapped by the sticky substance on the card. Look for these in home and garden centers or greenhouse supply stores.
If you’d like to try making your own: Cover bright yellow index cards with Vaseline or Honey. Tape it to a straw or chopstick and imbed into the soil. Another easy recipe is to combine equal parts petroleum jelly and liquid dish soap then use the goop to cover the card.
Killer Soap Recipe: Combine 2 tablespoons Ivory liquid soap or lemon dish detergent with 1 gallon of water, use this mixture to drench the dirt that is hosting them. After about an hour, lightly rinse off.
DIY Trap: Pour a tablespoon or two of apple cider vinegar into a small cup, fill with water. Position the cup near the houseplant with the problem. They will be attracted to the vinegar and when they go to investigate, they will be killed by drowning. Wine should also do the trick.
Vodka Treatment: Combine 1/2 cup vodka with 1 1/2 cups water, pour into spray bottle. Spray (first test a leaf to make sure the alcohol isn’t too harsh for it, if it doesn’t burn it after a day or two it should be fine).
Rubbing Alcohol Solution: Mix 1 cup rubbing alcohol with 1 quart of water, pour into spray bottle. Spritz and treat every three days for two weeks. Make sure to test a leaf first to check the mix isn’t too harsh for it.
Tobacco: Break open a few cigarettes and make a light layer of tobacco over the top of the dirt, the nicotine will repel them. Do not use on potted herbs or anything edible and watch that pets don’t have access to the tobacco.
Tips For Control
- Try putting a layer of sand over the surface, this may help deter the little pests from setting up shop.
- To prevent another infestation, reduce watering as gnats are usually a sign of overly soggy/saturated conditions. Also make sure to remove any excess liquid from the saucer underneath the pot.
- Remove fallen leaves and botanical/debris so there’s no organic matter attracting them to feed on.