Fungus gnats are small dark flies (about 1/8″ in size) that look similar to mosquitoes and are often confused with fruit flies . They thrive in humid environments and breed in the damp soil of houseplants.
The larvae is what causes damage by eating the roots, root hairs and stems. The symptoms of an infestation can be stunted plant growth, wilting, yellowing leaves and rotting roots.
The adults feed on fungi at the top of the soil (where they lay their eggs) while the larva feasts on the roots.
Here is a collection of remedies to get them out of your house along with some tips for trying to control them:
- Dry Them Out: Allow the soil to dry very well to the point that your plants start to wither before watering again (approximately the top one to two inches of soil is completely dry). It needs to get this dry so the larvae in the soil will dry up completely (ending their cycle), the adults cannot breed in the dry soil so the cycle ends.
- Sticky Traps: You can purchase yellow sticky cards for houseplants with the purpose of indoor insect control, these will work with fungus gnats. The idea is that the color yellow 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 the card to a straw or chopstick and stick into the soil. Another easy sticky recipe is to mix equal parts petroleum jelly and liquid dish soap then use the goop to cover the yellow card.
- Killer Soap Spray Recipe: Mix 2 tablespoons Ivory liquid soap or lemon dish detergent with 1 gallon of water, use this mixture to water and drench the soil that is hosting them. After about an hour, lightly spray the leaves with clear water to rinse the soap off.
- DIY Trap: Pour a tablespoon or two of apple cider vinegar into a small cup, top with water. Leave the cup near the plant with the problem. They will be attracted to the vinegar and will be killed by drowning.
- Vodka Spray: Mix 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 the leaf after a day or two it should be fine).
- Rubbing Alcohol Spray: Mix 1 cup rubbing alcohol with 1 quart of water, pour into spray bottle. Spray 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 soil, the nicotine will repel them. Do not use on herbs or plants that are eaten and watch that pets don’t have access to the tobacco.
- Try putting a layer of sand on top of the soil, this may help deter the little pests from setting up home.
- How to tell if a plant has the little critters? Here’s a trick to find out if you’re not sure: slice a chunk of raw potato and leave it on top 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.
- To prevent another infestation, reduce watering as gnats are usually a sign of over watering. Also make sure to remove any water from the saucer underneath the pot. Make sure soil is dry between waterings.
- Remove fallen leaves and plant debris so there’s no organic matter resting on the soil to attract them to feed on.