5 Steps to Get Rid of Fungus Gnats

You know how I know you're a gardener? You've got fungus gnats. These pests are a near inevitability when starting seeds indoors in a non-sterile environment. Fortunately, they are more of a nuisance than anything and we can apply the principles of Integrated Pest Management (a step-by-step approach to managing many garden pests and diseases) to keep them under control!

1) Identify - What do fungus gnats look like?

One of the most common mistakes that's made with pests and diseases is jumping immediately to solutions - only to later realize the problem was misdiagnosed from the beginning.

To avoid this, slow down and take one step back to properly identify the pest at hand. 

While there are four stages to fungus gnats (egg, larvae, pupa, and adult), only the adult stage is visible to the naked eye. Adult fungus gnats are small black flies (order: diptera, families: Mycetophilidae and Sciaridae) that look nearly identical to fruit flies. 

As such, when inspecting your young seedlings if you noticed small black flies in the seed starting area then this is your sign that fungus gnats are present and that we must now evaluate the severity of the infestation. 

fungus gnat stuck on yellow sticky tape

Yellow sticky tape has proven to be a very effective method for trapping adult fungus gnats. 

2) Evaluate - Where do fungus gnats live?

The preferred environment for fungus gnats is a warm, moist environment where decaying organic matter (i.e. compost, worm castings) is present. The challenge that this presents is that for our seeds to germinate they need very similar conditions - which is why ending up with fungus gnats is an inevitability that every gardener is sure to experience.

We cannot evaluate the fungus gnats as eggs or larvae because they are too small to be seen by the naked eye, but they would be living and hatching in the soil. Once they are able to fly, we will be able to identify them in the air and evaluate the severity of the infestation.

One of the best ways to evaluate how many fungus gnats are present is to use yellow sticky tape (which fungus gnats are attracted to) to trap them and count how many flies are on the sticky tape at the end of the first day (keep track of this in your garden journal as we will related back to it in page 5). 

 chart showing the number of fungus gnats observed per day before taking action

Before taking action, track the number of fungus gnats you observe per day. This will allow you to see whether or not your actions are having an impact.

3) Tolerance - Are fungus gnats bad for plants?

Some pests and diseases that we will encounter in the garden can cause damage or kill our plants if we don't quickly begin to manage them. Fortunately, it is very rare that fungus gnats will reach the point of causing any noticeable damage to our plants. 

Adult fungus gnats don’t damage plants or bite people; their presence is primarily considered a nuisance. Larvae, however, when present in large numbers, can damage roots and stunt plant growth, particularly in seedlings and young plants. - University of California Agriculture & Natural Resources

Because of this, the level of action to take comes down to your tolerance of them. If they don't bother you, then very little action is required. If you find they significantly disturb you, then a greater number of more intensive measures can be taken to keep the fungus gnat population under control. 

Based on your Evaluation in Step 2, establish a tolerance level that you hope to accomplish with the actions that you take. 

4) Action - How to get rid of fungus gnats

Recall that the ideal environment for fungus gnats is a moist, warm environment where decaying organic matter is present. Therefore, to manage this pest we can take several proactive steps to make it a less ideal environment:

  • Fan: Utilize a fan to help dry your seedling mix between waterings. 
  • Sand: Once your plants have germinated (approximately 7-14 days) apply a small layer of sand on the top of your seed cells. Sand does not retain water and will create a physical barrier that prevents the fungus gnats from reaching the organic matter.
  • Cheesecloth: Tape cheesecloth around the bottom of your seed cells create a physical barrier to the watering holes at the bottom of the seed cell. 
  • Bottom Water: Once your plants have germinated, shift from watering the top of the soil to bottom watering. Additionally, do this in a separate tray and separate environment to keep as little moisture in the seed starting area as possible. 

Using sand as a physical barrier against fungus gnats

On top of those proactive strategies, there are numerous reactive steps we can take to target the population of fungus gnats: 

  • Yellow sticky tape: Because fungus gnats are attracted to the color yellow, yellow sticky tape (which can be purchased at nearly all nurseries) is highly effective at keeping the adult population under control. This is my preferred method. 
  • Neem Oil: Mix 1litre warm water, 1tsp of neem oil, and 2-3 drops of Dr. Bronner's soap and spray the soil thoroughly to target the eggs and larvae. 
  • Beneficial insects: Two beneficial insects (Steinernema nematodes and Hypoaspis mites) are both beneficial insects that will target the fungus gnats as a host insect before killing it. 
  • Carnivorous plants: Cape Sundew's (Drosera Capensis) are a highly effective carnivorous plant that attracts the fungus gnats with their brightly coloured tentacles and then traps them in a sticky mucilage that is secreted from the tentacles. 
  • Pesticides: Lastly, you can explore chemical pesticides. This is not something I have explored nor is it part of my natural and organic approach to gardening so I can't speak to which options might be available! 

Based on what interests and fascinates you, pick a few of the options above to begin taking action on the fungus gnat population. 

Picture of Cape Sundew carnivorous plant for fungus gnat management

Consider using carnivorous plants, such as this Cape Sundew, to manage fungus gnats and other pests. 

5) Monitor - Will fungus gnats go away? 

Using the same Yellow Sticky Tape as Step 2, monitor and record the number of fungus gnats on it each day. This will show you the impact of your actions.

If the number continues to climb and exceeds your tolerance level, consider trying one of the other actions. If the number decreases below your tolerance level, then clearly the actions have been successful!

How do I manage fungus gnats? 

For myself, I can tolerate a few fungus gnats flying around - especially knowing that it means I can keep my plant babies in a microbial rich and biologically active environment. To accomplish this, I use a combination of Yellow Sticky Tape and Cape Sundews and have been very pleased with the results! 

I trust you'll also find a combination of actions that get the population to a level you can tolerate - let me know what works best for you in the comments below! 

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