fungus gnat control and eradication

Discussion in 'Growing Marijuana Outdoors' started by thezephyr, Aug 10, 2015.

  1. Hey everybody,

    I've got a nice outdoor grow going, but made the mistake of mixing in an older bag of soil I had laying around along with my various organic amendments. Fast forward, and now the three plants that got a bit of that soil now have rather intense fungus gnat infestations in the soil media. I have had totally successful harvests even with fungus gnat problems in the past, but this time around I really just want to get rid of them. My plants are just starting to form pre-flowers at the tips of the branches so I have some time before the fungus gnats become a problem for anything other than the root zone, but it sucks going out every morning to pluck those little bastards off my sticky buds so I'm hoping to resolve this problem and eliminate the infestation before I get too far into flowering.

    So far, I have given each of the affected plants a neem oil soil drench. theoretically, neem disrupts the feeding of the larvae, weakens the adult population, and should cause birth defects and weakness in the subsequent generations. Additionally, I'm letting my soil dry out pretty thoroughly between neem drenches. I know from experience that although this slows their reproduction, it doesn't get rid of them entirely. And although my plants are still strong as ever, consistently adding neem like this will put a strain on them.

    So now I turn to the experts here at grasscity. I'm looking for recommendations and advice from anyone who has successfully eradicated a fungus gnat population. My grow is all organic so far, but I would be willing to use inorganics if they are non-toxic to humans and pets and would dissipate/flush from my plants root system before harvest. I cannot work with diatomaceous earth because of respiratory problems.

    Here are a few options I am currently considering, and I'd love to hear any other suggestions or successful techniques from everybody:

    A neem seed meal top dressing- I'm hoping this would either discourage or make it impossible for the adults to lay more eggs. Has anyone used neem meal for this prupose?

    Predatory nematodes- This seems like a great organic option, has anyone on here used predatory nematodes succesfully against pests in the root zone?

    Gnatrol- as I understand it, this product is an insecticidal bacteria similar to BT in a granular powder which is then diluted in water for a soil drench. has anyone used this product on cannabis? should I be worried about my plant uptaking it systemically? is there any chance of toxicity from this product remaining in my plants at harvest time a few months from now?

    Thanks everyone, hoping to get some good information together here. most of the people on these forums use pre mixed soil for their grows in some capacity, so fungus gnats are something we all deal with from time to time. hopefully this information can be a useful resource for others as well. I'll be sure to post the results of whatever treatment I end up using.


Share This Page