Dealing with fungus gnats

An update on Fungus gnats

In a previous post, I mentioned that I would experiment with hydrogen peroxide to kill off fungus gnats. I have since tried using it, and must say I am “reasonably “impressed”.   When I say reasonably impressed, I must qualify that. It definitely works, but maybe just not as well I would have hoped for. No matter how many times I apply it, the gnats might disappear for a while, and then before you know they are back again.

Now believe me, fungus gnats are not my friend by any sense of the imagination. I absolutely detest them. Not only are they bothersome pests, but if they are not brought in check, they can also create massive problems in the health of seedlings. So, there is no leeway here.  I will not be happy until I have done all I can to get rid of them.

So again, it was back to the drawing board. I began doing some research to try and figure out why I wasn’t being as successful as I hoped I would be. There had to be answers out there somewhere. Surely!

I didn’t take long to find out that while I had most bases covered, there were a few things I missed. One glaring omission was the dosage of the H202 I had been using. I understood that the 3% hydrogen had to be mixed in the ratio of one-part H202 to four parts water.  This was right, but not for the purpose I had used it. It turned out that the one to four ratio should be used for foliar spraying, rather than for a soil drench. I had been using the one to four dilutions for soil drenches.  For a soil drench, the ratio should be far stronger. It should be mixed at one-part H202, two parts water. This solution then gets poured on top of the potting soil and is allowed to drain through it

More possibilities

Multi directional approach

So, this has become my new way of doing things, but I am not stopping there. In addition to the stronger H202 mix, I am now also using cinnamon. I sprinkle cinnamon powder liberally over the surface of the potting soil.  I do this because cinnamon has strong anti-fungal properties. This means that the fungus that gnat larvae need to survive will not grow as readily. Insufficient food for the larvae can only mean one thing. They will not survive

It has come through loud and clear that tackling fungus gnats needs to be a multi-directional approach. Nothing will work on its own. It must be a combination of measures that must be adopted simultaneously if the war is to be won.  These include preventative measures, as well as striking directly to eliminate the problem.

My strategy now is to use sticky fly paper and cinnamon together with restricted watering as preventative measures. For the offensive, I will use H202 both as foliar spray (at the 1: 4 ratio) and as a soil drench at the new ratio of one to two parts water. If this doesn’t work, I will be trying two other offensive measures.

The first of these is the use of mosquito bits. I mentioned these in my previous post, but have not had the opportunity to try them out. They are apparently a bacterial approach to tackling fungus gnats using a bacteria called Bacteria Thuringiensis. It is a genus that kills many pests. Bacillus Thuringiensis Israelenis is said to be effective in killing off fungus gnats. The bacteria apparently affect the stomach lining of mosquitoes, black flies, and fungus gnats. The larvae of fungus gnats eat the bacteria, and they are killed even before they can turn into adult flies. It certainly seems like something I will need to try.

Diatomaceous earth

The other thing I will look at is using diatomaceous earth. Diatomaceous earth is the sharp fossilised remains of microscopic sea creatures. It contains microscopic shards of silica. These shards of silica are like broken glass to fungus gnat larvae. It pierces their skins, and in the process they die.  If I try this method of controlling gnats, I will ensure that I use food grade diatomaceous earth. The pool grade contains far more silica and is far more dangerous to use. I will also wear a mask when I apply it.

Something I have tried in the past is nematodes. Unfortunately, I didn’t find them particularly effective. I didn’t notice any particular improvement, even though I followed the suppliers’ instructions to a tee. Besides not finding any benefit in using nematodes, I also found them pricey. In view of this, it is unlikely I will try using them again.


It’s all very well throwing money at the problem, but somewhere along the line the most cost-effective method needs to be found. I am now fairly confident that I will get rid of fungus gnats sooner or later. I am certainly throwing enough at it, and something (or combination of things) will prove successful. However, the trick now will be to figure out what work’s the best without breaking the bank! That will definitely be my next mission


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