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Rid of Gnats in Plants by Natural & Chemical Methods

How to Get Rid of Gnats in Plants by Natural & Chemical Methods

Plants, whether indoors or outdoors, bring joy and liveliness. They add beauty, fragrance, and appeal to interiorscapes with their brightly colored flowers and leaves. Suddenly you observe small mosquito-like insects surrounding your beautiful plants. These tiny flying insects are gnats or, more specifically, fungus gnats or plant flies. Luckily these adult flies (fungus gnats) do not cause harm to your indoor and outdoor plants. However, their larvae wreak havoc on the garden and indoor houseplants.

The fungus gnat larvae feed on the roots of young plants and seedlings. They bore into the plant roots and encourage the invasions of soil-borne fungal pathogens, leading to a slow decline. This guide will cover all information on how to get rid of gnats in plants.

Although there are many ways to control gnats in plants, natural methods such as vinegar traps, raw potato slices, food-grade diatomaceous earth, and sticky cards are the most effective. Another best approach to prevent the fungus gnat infestation is to let the soil dry out between waterings; otherwise, overly wet soil provides a home to these bugs. To learn more, keep on reading!

What Are Gnats (Fungus Gnats or Plant Flies)?

Fungus Gnats or Plant Flies
Fungus gnats are small flying insects that invade houseplants when the potting medium is overly wet and rich in organic material.

Fungus gnats (dark-winged flies) are tiny, mosquito-like insects of the genus Bradysia and Orfelia that primarily infest the potting soil mix of indoor houseplants. They belong to the Sciaridae family and appear from garden leaf litter, compost, and debris. They do not cause any harm to houseplants but are mainly considered a nuisance.

These dark-winged flies have delicate bodies with slender legs and long, segmented antennae extending from their heads. Their large antennae distinguish them from more robust shore flies (greenhouse flies) that actively work on decomposing organic matter. Adult flies are 1/16 to ⅛ inches long and have a “Y-shaped” pattern on their wings.

Note: Fungus gnats are not strong fliers like common houseflies and mosquitoes. They do not move much around indoor plants, remain near potted plants, and rest on top of potting soil mix.

Life Cycle of Fungus Gnats

Fungus gnats develop through four stages—eggs, larvae (comprise of four instars), pupa, and adult. The female gnat flies lay their eggs in the damp potting soil that hatches into larvae within three days of laying when temperatures are 75 degrees Fahrenheit. The fungus gnat larvae appear as semi-transparent, worm-like creatures with blackheads.

These translucent creatures vigorously feast on soil fungi and tender roots and undergo four larval stages within ten days. Then they enter the pupal stage and, after four days, emerge as adults.

Life Cycle of Fungus Gnats
Fungus gnat larvae feed on host plant roots in large clusters, causing rapid yellowing and wilting of host plants. Credit: Flicker

The life cycle of fungus gnats from female to female completes in 17 days when the temperatures are warm. The more favorable the weather conditions are, the faster they will develop and produce more generations per year. Therefore, fungus gnats have more overlapping generations, like whiteflies, aphids, and spider mites.

Note: The infestations of gnat flies are more common in gardens during winter and indoors during spring and summer. While in coastal regions, fungus gnats infestations can occur at any time of the year indoors and outdoors.

What are the Signs and Symptoms of Fungus Gnat Infestations?

Fungus gnat flies do not damage the plants, except they use their crevices and leaves as home. These adult gnat flies lay eggs in moist potting soil and leaf debris. On the other hand, their larvae feed on plants’ root systems when present in large numbers.

Fungus gnat larvae feed on young roots and expose them to secondary pathogens such as root rot fungi.

The following are the common signs and symptoms of fungus gnat larvae damage, so keep an eye out for proper plant care.

Fungus gnats stunt plant growth: When fungus gnat larvae feed on the feeder roots, houseplants stop growing because plants cannot absorb water and nutrients from the soil.

Fungus gnats lead to plant yellowing and wilting: The high populations of fungus gnat larvae cause significant root damage and poor nutrient absorption. Under severe root damage, the foliage turns yellow and begins drying. Even it leads to premature leaves falling and entire plants wilting. 

Root rot: This is also the expected sign and symptom of fungus gnat infestations. Their larvae vigorously feed on the plant root system when the potting soils are too wet due to poor drainage and overwatering. It leads to slow plant decline that can only be treated at early stages with repotting.

What Causes Fungus Gnat Infestations?

One of the most common factors that promote fungus gnat infestations on indoor and outdoor plants is too little or too much water, improper soil conditions, and poor garden sanitary practices.

How to Get Rid of Gnats in Plants

Indoor and outdoor fungus gnat infestations are associated with moist conditions around gardens and houseplants. However, proper plant care practices and organic insecticide applications can easily control these flies.

Following are the proven practices to get rid of gnats in plants:

Natural Ways to Get Rid of Gnats in Plants

Let the Soil Dry

The most effective strategy to control the adult fungus gnat flies around houseplants is to allow the drying of the growing medium, particularly the top 2 inches of the soil. Dry soil will minimize the survival of eggs and newly hatched larvae. It will also prevent the root system from decaying and plants from wilting.

Report the Potted Plants

Another best way to control the higher populations of fungus gnats is repotting your potted plants every two years. Repotting benefits the plant by providing a fresh potting mix and a new planter. Ensure to choose a container with drainage holes; so that the excess water drains freely without suffocating the root system.

Remove the Excess Decaying Material

Remove the houseplant containers with an abundance of decaying leaf litter, dried bulbs, and roots because these materials serve as food sources and hiding places for fungus gnat flies.

Excess Decaying Material

Use Bottom Watering Technique to Avoid Fungus Gnat Infestations

Bottom watering of potted plants prevents fungus gnat infestations. It keeps the top layer of the potted plant’s soil dry, thus discouraging the fungus gnat egg-laying process. 

This practice involves setting a planter with a drainage hole onto a water-filled bowl. So the roots soak up the water through holes, and the topsoil layer never gets wet (which is common in top watering).

Note: Be cautious about employing the bottom watering technique for moisture-loving plants such as Calatheas, Money tree, Spider plant, and African violet. Because these plants only thrive and survive in consistently potting soil.

Use Vinegar Trap

Pour one cup of vinegar into the bowl with one teaspoon sugar and a few drops of dish soap. Cover the bowl with perforated plastic wrap and situate it near the houseplants. The strong scent of vinegar will attract adult flies and minimize their nuisance around indoor plants.

Use Yellow Sticky Traps

Yellow sticky cards also play a vital role in managing fungus gnat flies. These cards help plant parents in the monitoring of adult gnats that infest houseplants. So place sticky cards attached with small wooden sticks in potted plants to capture the fungus gnats.

Use Raw Potato Slices to Detect Fungus Gnat Larvae Infestations

Place raw potato chunks in the potting soil to attract and trap the fungus gnat larvae. Once trapped, remove the infested potato chunks and properly discard them. Make sure to replace them with healthy ones.

Cinnamon Powder Applications Starve the Fungus Gnat Larvae

Cinnamon is a natural fungicide that prevents fungal infections in houseplants when applied as a soil drench or foliar spray. Its applications eliminate gnat larvae’s food source and lead to their starvation.

Apply Dish Soap Spray as an Insecticide

Castile and other liquid dish soap functions as effective insect killers. These detergents kill soft-bodied insects such as whiteflies, aphids, and fungus gnats through suffocation and dehydration.

For effective fungus gnat management, mix two teaspoons of dish soap per liter of water and apply once a week during spring and summer.

Introduce Beneficial Insects to Control Fungus Gnats

Beneficial insects are also natural enemies or beneficial bugs that prey on pests. These natural predators feast on all stages of harmful bugs and prevent houseplants from damage. These beneficial bugs are lady beetles, green lacewing, and praying mantids.

how to get rid of gnats in plants
Seven spotted ladybugs on a flower and searching for food

Apply Chemicals to Get Rid of Gnats in Plants

Applying insecticides to control fungus gnats is only practical for outdoor plants over large areas. These insecticides ensure the rapid elimination of insect pests and prevent plants from severe damage. The most valuable insecticides are;

Hydrogen peroxide functions as larvacide and prevent plants from root rot. Mix one part of 3 percent hydrogen peroxide with four parts of water. 

Apply this solution to the leaves and top soil layer with the help of a spray bottle. Make sure not to over it because it will damage the leaf buds and prevent them from opening.

Neem oil is the most effective and environment-friendly insecticide that kills all life phases of insect pests ( from egg to adult). It functions as an antifeedant, disrupts hormonal balance, and negatively impacts their growth and reproduction. In addition, plant oil-based insecticides rapidly kill houseplant bug infestations.

To make a neem oil spray for fungus gnat control, mix one teaspoon per three parts of water and pour it into a spray bottle. Apply this solution once a week as a foliar spray and soil drench to deter the adult fungus gnats and their larvae.

Use biological control pesticides such as Bacillus thuringiensis subspecies israelensis (commercially available as Gnatrol) and Steinernema feltiae (beneficial nematode) to get rid of gnats in plants. These biocontrol agents successfully control the larval stages of fungus gnats as they lay eggs inside the larvae. For effective control, repeat the applications of Gnatrol every two weeks during the growing season (spring and summer).

Note: Beneficial nematodes provide season-long control of harmful bugs when applied as soil drench because they reproduce actively in moist and organically rich soils. Then actively search for fungus gnat larvae and munch on them.

5 Helpful Tips to Prevent the Infestation of Fungus Gnats

To prevent the invasion of fungus gnats in houseplants during the active growing season, follow these essential prevention tips;

  1. Quarantine the newly purchased plants for at least one to two weeks to examine the pest infestations thoroughly.
  2. Avoid overwatering and poor soil drainage because it favors larvae growth and their spread.
  3. Always use pasteurized potting soil mix to kill the fungal spores and fungus gnat eggs.
  4. Plant your indoor potted plants in a well-aerated potting soil mix. To improve soil aeration, add perlite or sand as two parts per one part of garden soil.
  5. Maintain good garden sanitary practices, such as discarding dried and fallen leaves; otherwise, they will act as food sources and hiding sites.

FAQs on How to Get Rid of Gnats in Plants

What is Fungus Gnat Attracted to?

The potting soil that is overly wet due to overwatering and rich in decaying organic matter attracts the fungus gnat flies and acts as a breeding site.

Does Overwatering Cause Fungus Gnats?

Yes, overwatering causes fungus gnats because moist soil is a primary source of attraction and provides food by encouraging fungal spore growth.

What Kills Fungus Gnats Instantly?

Neem oil and hydrogen peroxide spray kills the eggs, larvae, pupae, and adult fungus gnats instantly.

Do Fungus Gnats Come from Soil?

Yes, fungus gnats come from soil because female gnat flies lay eggs in the moist potting soil, and they complete all their life cycle stages in it.

Can Fungus Gnats Bite Humans?

Adult fungus gnats do not cause any harm to humans, pets, and plants. However, their soil-inhabiting larvae harm the plant’s feeder roots and promote fungal infections.