Best Insecticide for Fungus Gnats

Best Insecticide for Fungus Gnats

Fungus gnats are small flies that can become a nuisance to both outdoor and indoor potted plants. If left untreated, they can cause irreparable damage to plants as they lay their eggs in soil or growing mediums and feed on plant roots. To help protect against their development, an insecticide must be used. Here is a rundown of your best options for eliminating fungus gnats.

Neem Oil

The first option for controlling fungus gnats is using a product containing neem oil. Neem oil is a organic and natural insecticide, derived from the neem tree in India. It causes damage to certain hormones in the developmental cycle of gnats, disrupting their life cycle and stopping further reproduction. To apply, simply dilute the oil and spray it onto the foliage of your plants.


A professional grade pesticide with Pyrethrum is also effective for fungus gnats. Made from dried chrysanthemum flowers, it has properties which act as a nerve toxin to insects and will kill them on contact. Make sure it is applied directly to the fungus gnat larvae and eggs in the soil.


Avermectin is an insect-killing ingredient that is found in many insecticides. It works by targeting the insect’s nerve cells and interfering with the chemical signals that make them function. By doing so, it will stop the fungus gnats in their tracks.


This powerful insecticide is often found in many professional grade pest control products. It works by affecting the nervous system of fungus gnats and other insects, resulting in paralysis and ultimately death.

Other Control Measures

In addition to insecticides, other control measures can be used to help reduce the population of fungus gnats.

  • Remove and dry out infected plant material.
  • Wash infected pots and plant materials with soapy water and allow them to dry.
  • Provide adequate drainage for potted plants so that soil does not become waterlogged.
  • Introduce beneficial predatory nematodes to help control the population.
  • Ensure the soil pH is in the 6.5 to 7.2 range.

By using the correct insecticides, together with other control measures, you should be able to successfully eliminate fungus gnat infestations.

Fungus gnats can be a nuisance in the home and in greenhouses, as they feed and reproduce in the moist soil of potted plants. One way to combat these tiny pests is with insecticide.

Insecticides containing neem oil or pyrethrins are the most effective treatment for fungus gnats. Neem oil is derived from the neem tree and can repel and kill gnats. It’s able to provide residual protection against insects for up to four weeks. Pyrethrins are natural compounds found in certain chrysanthemum flowers, which are toxic to fungus gnats. Pyrethrin-based products can kill a broad range of common insects, and can be used indoors or outside.

For best results, it’s a good idea to apply an insecticide toward the end of the day, after the gnats have left the soil to feed on the leaves. If a product is labeled as a contact killer, it’s a good idea to spray it directly onto the insects. Preventative measures, such as keeping soil dry and ventilated, can also help to keep the gnats away.

Insecticides containing neem oil and pyrethrins provide the most effective treatment for fungus gnats, whether indoor or not. They can repel, kill and provide residual protection, making them ideal for combating these pesky pests.

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