Today I’m going to discuss some of the difficulties I’ve encountered recently regarding fungus gnats. These pesky things resemble fruit flies but tend to be incredibly annoying and their larvae seems almost impossible to kill. Although growing terrariums can be very rewarding, containers that are kept constantly moist will almost inevitably be infested at one point by these creatures. Water-loving plants are a risk to these things and it doesn’t matter if they are kept inside or outside, the gnats somehow manage to find a way to your beloved plants.


Life cycle of the fungus gnat

Fungus Gnat Larvae

If you’ve been infested, you’ll see small worm-like white critters in your clear terrarium container. They move slowly and sometimes can go unnoticed. One single fungus gnat can lay 200 eggs at a time. Larvae thrive in moist conditions and feed on decaying plant matter. They have also been known to eat and destroy plant roots while spreading viruses and disease to your plants. So, you can imagine how loved these things are by yours truly. Plus, they look disgusting. Also, forget using a wide spectrum insecticide as these things are totally unfazed.

The lifecycle of the fungus gnat takes about 20 days from egg to maturity. So, killing them overnight is not likely.
Here’s what I’ve tried:

1. Hydrogen Peroxide

I read online that 1 part peroxide to 2 parts water would kill larvae on contact. While this may seem like the case, it certainly also kills certain plants on contact too. I tried this and successfully killed several of my maidenhair ferns. The best part is that the larvae still seemed to survive.

2. Steam

I have a steamer and I read that this also kills larvae on contact. The larvae is said to live in the first 3 inches of topsoil and applying steam should kill them. Yes, this did kill a lot of them but not all. It also successfully killed some of my plants too, which definitely was not ideal.

3. Azamax

Azamax is like a concentrated version of neem oil and this too was unsuccessful. This was very harsh on the plants so I don’t recommend trying this to get rid of fungus gnats. Azamax would be best for treating thrips, spider mites and other types of pests that neem oil could remove. However, Azamaz should be reserved for severe infestations since neem oil is usually more than capable most of the time.

4. Gnatrol

Gnatrol is derived from the same bacteria that beneficial nematodes are known to spread when killing gnat larvae. Since I applied a wide spectrum insecticide when I originally planted my terrariums, the use of beneficial nematodes were out of the question. The insecticide kills beneficial nematodes, which is why you should opt for growing organically 100% of the time. Gnatrol is bacteria that kills larvae by making them stop eating. Larvae takes around 2 weeks to grow and Gnatrol isn’t an overnight solution, but it seems to be the most effective. I’ve seen complete eradication in some of my containers but I will need to continue to reapply the solution once every 5 days to the containers where I can still see larvae.

Gnatrol comes in a powder form and you need to mix it with water for application. Please note that if you are using tap water for the mixture, the bacteria that kills gnats will not be viable if mixed with chlorinated water. Most tap water is chlorinated, so this shouldn’t be too much of a surprise. In order for successful Gnatrol application, put water in a container and leave it open so the chlorine can evaporate. No need to filter the water in any special way… you just need to leave the container lid open or ajar for a day or two so the chlorine can escape.

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