TROUBLESHOOTING
FUNGUS GNATS

 

FUNGUS GNATS

WHAT TO LOOK FOR:

Fungus gnats can be a nuisance both inside and out. Tiny flying insects that slightly resemble a very small mosquito, fungus gnats only grow to about 1/16” long. You may also note their tiny larvae in the soil, which look like very tiny maggots (oh no!). Fungus gnats are easiest to spot when the adults are flying or hopping around on the soil, especially when you water, as that’s when they buzz around the most.

Plants with fungus gnats may suddenly wilt, will appear stunted, or have yellowing leaves.

HOW IT HURTS:

The primary way in which fungus gnats can affect your plant is through their larvae. The larvae feed on the plant’s roots and fungi near the top of the soil. This harms the roots ability to take up nutrients or moisture from the soil effectively. Fungus gnats are especially harmful to young plants and seedlings that do not yet have a vigorous root system established.

Adult fungus gnats only live about 1 week, but they breed quickly (an adult can lay up to 300 eggs in its lifetime!), so it is best to treat as soon as you notice them.

HOW TO HELP:

It is not recommended to use synthetic or harmful pesticides—especially inside! You don’t want those kinds of chemicals on the food you eat, or to breathe them in if you spray inside your home. Outside, pesticides (including organic ones) can harm beneficial insects such as bees, so it’s best to use sparingly — or try to find other methods.

  1. Do not overwater:
    Fungus gnats thrive in overly damp soils. Allow plants to dry out a bit between watering. Larvae and eggs will die in dry soils.

  2. Use yellow sticky traps:
    You can purchase yellow sticky traps online, through a local home improvement store or plant nursery. These work by trapping flying insects in a sticky substance. Be aware that sticky traps can trap beneficial bugs as well.

  3. Cover the top of the soil with sand:
    A light layer of sand (use horticultural sand, not play sand from a sandbox!) on the top of the soil may prevent adult fungus gnats from laying eggs. This effectively ends their life cycle. Let the sand dry out completely before watering the plant again.

  4. Diluted hydrogen peroxide:
    Create a mixture of one part 3% hydrogen peroxide to four parts water. You might already have 3% hydrogen peroxide in your house, but be sure it is not a higher percentage than 3%, or industrial grade, both of which can cause harm. Let the top of the soil dry out for a few days before applying. Water the plant like normal with the hydrogen peroxide mixture, which will eliminate larvae on contact. To get rid of the adults, you can use the same solution to spray the leaves and the plant.

    NOTE: Be sure that this mixture does not come into contact with furniture or flooring, as it can bleach items in your home. Excessive use of hydrogen peroxide can also strip organic compounds from the soil, so best to use sparingly.