natural pest control

how to control fungus gnats organically

fungus gnats

Are you being tormented by tiny dark gnats in your house, particularly around plants and windows? You might be dealing with fungus gnats. The plant pests are not harmful to humans but can wreak havoc even kill younger and weaker plants. Nearly everyone that has grown houseplants or worked in a greenhouse has experienced them.

Beyond the nuisance of the gnats flying in your face, they can wreak havoc on your plants. Fungus gnats cause damage to plants through multiple stages in life. They are particularly deadly to young plants and seedlings.

identifying fungus gnats

Fungus gnats (Sciaridae spp.) are easily distinguished from the common fruit fly (Drosophila spp.) by their darker color. The gnats are almost black similar to a mosquito while fruit flies are a lighter brown color.

If you are still unsure, you should scope out the area where they are hanging out. Fungus gnats are attracted to wet plant soil and standing water. You will see them hanging out in bathrooms and around sink drains. They flock to windows especially when the room lights are off. Fruit flies are attracted to the sweet swells of fruit and any rotting fruits or vegetable. They usually stick to the kitchen and pantry areas but are sometimes attracted to the smells from sweet smelling shampoos and soaps.

life cycle and damage

While the adults can still sometimes spread pathogens to plants, they are mostly just an annoyance. The adults live about 10 days during which they seek moist soil to lay their eggs in. Within 8-10 days, the eggs hatch and develop into larvae that feed on the finer roots of plants. Larvae can also tunnel into the base of plant stems causing more severe damage. After 12-14 days, the larvae develop into a pupa still feeding off roots and fungi in the soil. The young adults leave the soil 4-6 days later. The whole cycle speeds up with warmer temperatures and excess water.

Fungus gnats infest potting soil where the larvae feed on fungi growing in the soil and small roots. This can stunt growth in plants and spread plant pathogens. This contact allows fungus gnat larvae to spread the fungi that cause damping off in young seedlings. If you have ever tried to start your own vegetable seeds inside, there is nothing worse than seeing one little plant after another reach up to the sun only to topple off succumb to disease.

management solutions

Fungus gnats prefer a constantly moist, warm, and shaded environment. The simplest way to prevent fungus gnats is to water your plants properly. If you allow the soil to dry out between watering, it decreases the amount of fungi and decaying material in the soil that they feed on. Sometimes even perfect watering isn’t enough, so you have to take fungus gnat control more serious. Here is a rundown of the best options we go to when dealing with a fungus gnat infestation.

physical controls

Before you begin to treat fungus gnats, take measures to prevent any standing water in the areas infested. Don’t let water pool in trays beneath plants, bathrooms, or kitchens. As their water (and food) supply dwindles, the gnats will begin to seek it wherever they can.

Yellow sticky traps are a very simple and effective method of ridding yourself of the adult fungus gnats. Place them around plants, windows, and lights. The traps can also help with a number of other plant pests but are non-selective and can sometimes catch the good guys.

organic pest control yellow sticky traps

biological controls

Beneficial nematodes

The most effective solution I have found is using beneficial nematodes (Steinernema feltiae). These are microscopic worm-like parasites that feed off fungus gnat larvae as well as many other pests in the soil. They are not harmful to the plants or people and continue to work for over a year and a half. After drenching the soil once with the mixture, the treatment is complete. Once the adult fungus gnats die, the infestation is over. The nematodes continue to kill off the population until they are completely gone.

Bt – (Bacillus thuringiensis)

Another effective method of managing fungus gnats is treating affected areas with Bt. This bacteria is naturally occurring and actually kills worms, caterpillars, larvae, and insects. It takes a few treatments but eventually will take out all of the fungus gnat larvae. It also works great against mosquitoes. The downside is that they kill off most everything in the soil even the beneficial insects. Believe it or not, even the soil in your houseplants is alive with microorganisms. Avoid using Bt unless nothing else works.

bacillus thuringiensis fungus gnats

Diatomaceous Earth

We have found so many uses for this amazing substance. DE (Diatomaceous Earth) is a soft sedimentary rock that is used in powder form to control all kinds of  insects (roaches, ants, fleas, etc.). It basically acts like microscopic razors that dehydrate insects from the inside out. DE works incredibly well against fungus gnat larvae. It only stays effective as long as it stays dry. In areas that get rain or watered often, it can take a few applications of it to really knock out all of the fungus gnat larvae. DE can also kill off many other organisms. It, however, is perfect for treating areas around the bathroom and kitchen (and it works great against many other pests you don’t want in these areas). We keep some on hand at all times for its versatility.

diatomaceous earth fungus gnats

Carnivorous Plants

Growing carnivorous plants can be a fun way of fighting against the gnats but not greatly effective. Select types of plants that best match your conditions (sunlight, temperature, etc.). I have had great success growing butterwort and hardy sundew plants. Venus flytraps are a popular option but are typically better at catching larger insects. Most carnivorous plants require a great deal of sunlight. The most effective types for fungus gnats attract insects to land on their sticky leaves where they become trapped. The plant actually digests them to obtain nutrients that allow them to thrive in low nutrient environments. Kids love seeing what these cool plants can do.

We have gone through many moves for school and work. Inevitably every time we move, we end up catching some fungus gnat hitchhikers along the way. Soon after moving in, we usually end up managing a full blown fungus gnat assault. We lucked up and avoided this on the most recent move.  A few months later, a new plant was gifted to us complete with a full infestation that quickly spread.

Because we always keep it around, we tend to use DE for so many common household insects. It’s always our first go to treatment for fungus gnats, but sometimes we have to call in the heavy hitters. They may be a bit more costly, but nothing beats beneficial nematodes for completely knocking out the problem when it’s bad. It works every time and lasts for years. Rid yourself of these pests easily and organically and don’t look back.

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