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Fungus Gnats: What Are They? And How Do You Control Them?

Fungus gnats or fungus flies are fruit fly–sized insect pest that primarily affects indoor houseplants which are overwatered.

Fungus gnats can be difficult to spot due to their tiny size. The adult fungus gnats are considered harmless as they do not bite or feed on plants. But they are known for their fast reproduction systems. 

Fungus gnat larvae (baby fungus gnats) feed on plant roots and soil. This can cause severe damage to houseplants. They love damp soil. And can get into your home or gardens through slight openings or opportunities. 

Identifying Fungus Gnats

It can be easy to identify the adult fungus fly. The gnat insect resembles a mosquito. It features a grayish-black body and a pair of transparent wings. Its entire body size is ⅛ of an inch and it features long thin legs. 

As larvae, they can be found in damp soil or organic materials. They measure up to ¼ of an inch and have elongated white bodies with shiny black heads.

Damages Caused By Fungus Gnats

The adult fungus gnat is considered more annoying than harmful to all plant bugs. They can be seen flying all over the affected plant which can be a bit distracting. The larvae of fungus gnats are harmful to indoor plants. 

This is because they target young and tender houseplants. Feeding on its roots and even causing delays in the development of new roots.  Visible symptoms of a damaged plant would include;

  • Wilting
  • Poor growth 
  • A complete loss of vigor, and 
  • Yellowing. 

Some plants are more prone to damage by fungus gnats, a few of these plants are; 

  • African Violets 
  • Poinsettias 
  • Geraniums, and
  • Carnations.

Fungus Gnat Life Cycle 

Fungus gnats reproduce more females than they do males. A female fungus gnat can produce a total of 300 fungus gnat eggs a week. These eggs are laid in moist or damp soil. Within a period of 4 to 6 days, the eggs hatch into larvae. 

The fungal gnat larvae then last for a period of 2 weeks. In this period they feed on plants to gain strength. After 2 weeks, they grow into the pupal stage. This should last for a  period of 3 to days before they become adults. Then the process is repeated. 

On average, it takes the fungus gnat insect a period of 3 to 4 weeks to complete a life cycle. The length of this period also depends on soil temperature. 

Controlling Fungus Gnats

To control fungus gnats in houseplants, you have to do the following; 

  1. Inspect any plant you intend to purchase for signs of fungus gnats. This can be done by doing a thorough check on the soil for larvae. If you notice flying gnats hovering around the plant, send it back.  
  1. Reduce your watering frequency. This can help by making the soil conditions inhabitable for gnats to lay their eggs. 
  1. If you do notice the presence of fungus gnats, then let the topsoil dry out for a bit. Doing this can lead to the death of a few larvae and even eggs. It could also make the soil less inviting to fungus flies. 
  1. Fungus gnats have an attraction towards the color yellow. This can be used to set a trap for them. Place yellow sticky tape around possible areas they could perch on. This method could work on a large number of fungus gnats. 
  1. You can make specific fungus gnats insecticides to control large-scale infestations. Products containing Bacillus thuringiensis var. Israelensis are great options.  It is considered safe for both humans and wildlife.
  1. Nematodes can be introduced to the affected houseplants. These are beneficial insects that are known to feed on larvae fungus gnats.
  1. Make use of organic pesticides like neem oil and horticultural oil for getting rid of gnats. Ensure you use them every week when treating large-scale infestations.

Frequently Asked Question

How long does it take to kill fungus gnats with neem oil?

With proper application of neem oil, fungus gnats infestations can be cleared in 2 months. 

What causes fungus gnats?

Excess moisture in the soil is the primary cause of fungus gnats.

Do fungus gnats mean mold?

Fungus gnats love damp or soggy soil. The presence of mold in the soil can indicate signs of fungus gnats. 

Do fungus gnats turn into worms?

No, they do not. But they do have a larvae stage in which they look like small worms.

Does cinnamon deter fungus gnats?

Yes, Cinnamon can make a powerful pesticide when used well.