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« on: April 28, 2021, 09:00:42 AM »
I like to start most of my trees from seeds or cuttings I get from friends or forum members here, as most of the trees I buy locally turn to be not true to type.
About 2 years a ago, I found a fungus gnat flying around in my grow room and I thought nothing of it. Fast forward a few months and there were hundreds! Those pesky things are annoying as hell, but the real issue is their larvae. They nibble on the roots of my seedings and rooting cuttings and stunt or kill them.
So after many hours of research on how to get rid of them I found many suggested solutions online and I started applying them.
Not everything I used during this fight that lasted 2 years worked. I'll try to summarize my experience as follows:
1. Cider-vinegar traps: I learned how to make them and put up 5 of those. Had 0% success. not a single gnat fell in. Complete and utter waste of time.
2. Only Water the pots from the bottom: I started doing this even though I had a large number of pots. This made it very time consuming to water the plants but I never stopped doing it. It seems like it is a good practice but you will not get rid of gnats completely this way, as they will still crawl into the pots from the drainage holes, or the sides as the potting soil shrinks a tiny bit when its dry. Furthermore, this made it more difficult to tell if a plant needs watering or not as the soil always looks dry from the top.
3. Hydrogen Peroxide: I drenched the soil with Hydrogen Peroxide as the larvae is said to die on contact with Hydrogen Peroxide. This had no effect at all. Had to stop after a few weeks. In fact I found a video on YouTube where a guy puts Hydrogen Peroxide directly on a gnats larvae under a microscope and the maggot is not even phased by it.
4. Mosquito Bits (dunks): I first sprinkled few bits on top of the soil on each pot so that every time I water, more of the stuff dissolves into the soil. However, after a few days the bits got moldy which attracted more gnats. So I started pre-dissolving the bits in water, and use that water to water the plants. Gnat population decreased after a few weeks, but then recovered back even though I never stopped using the bits. I think they might have built up some sort of immunity against it if that's possible.
5. GnatrolŪ Biological Larvicide: This is basically the same stuff in Mosquito Bits but much easier to use (powered form). I used it for 4 months with the same results as Mosquito Bits. In fact, the population started getting out of hands quickly. Note that I never watered my plants with plain water while using the Gnatrol. I always use a water and Gnatrol mix every time.
6. Sticky Yellow Cards: These are very effective at trapping the adults and reducing their numbers. However, this will not get rid of the gnats completely. I highly recommend using these yellow sticky cards since it can reduce the adult population reliably.
7. Pyrethrin: This is the holy grail of gnats killers. This is an organic compound that is extracted from the chrysanthemum flowers and can be used on produce till the day of harvest. It is one of the safest insecticide according to the research I made online so I felt ok using it indoors in my grow room. I mixed it with water and I used it to water my plants. It has been a week now, I only saw 2 gnats since. I'll continue using this stuff and update you guys if it finally kills off all of the gnats for good. It is sure looking amazing right now with almost not gnats flying around. Its a bonus that Pyrethrin also kills aphids.
In conclusion: Using yellow sticky cards and drenching the soil with Pyrethrin might be a reliable method to get rid of fungus gnats completely.
P.S. I hear Pyrethrin is toxic to cats.
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