Help with Gnats!!!

Discussion in 'Growing Marijuana Indoors' started by iloveindica, May 23, 2010.

  1. :mad: Fucking gnats. I had a bad feeling about the local grow/hydro shop I went to, and this is what happens for not trusting my instinct.

    I have some gnats in my FFOF soil. Just a couple so far but I need to know how they can damage my plants and what I need to do to contain them QUICKLY!
  2. i had a problem with gnats too, they were flying all over getting stuck in my buds, really pissed me off, so one day, i put a 2 inch layer of play sand on top of my soil it solved my problem.
  3. I have had a horrible problem with them too. Go get some fly traps - ones that can set on the same level as your grow pots are the best. I have tired all sorts of insecticide and it never really worked. What worked for me is sand. Get some sand from your local hardware store. If you are not 100% sure it's sterile bake it for a few hours at 350 degrees and let cool for a few hours. I like to make sure i have more ready then i need ready.

    Put your sand about half an inch deep on top of your soil. This will keep your soil moist for longer than you are used to because it stops evaporation a good deal. When you water your plants you will have to do so carefully because the soil and perlite will float up, you have to pour slowly. I like to move my sand to the side till i get to soil then slowly pour the water and move it back.

    Even being careful you will have to change the top sand every few weeks because the soil will float up and mix in making a home for those gnats again. Just carefully tilt your pot when the sand is nice and dry and brush it out and replace with new sand.

    Also make sure after you water you watch it over the next few days - sometimes the soil will pull away from your pot's walls and the sand will fall down the edges exposing soil on the edge. just push some more sand down the crack and that will stop, add more sand as needed.

    Just be careful not to over water with this but it WORKS better than anything else - just don't leave any other breeding places (bags of soil - piles of soil, anything moist and dirty really).
  4. Pick up some mosquito dunks from the hardware or garden store. Crumble one up, and sprinkle 1/4 tsp or so on each plant. Water, and give it some time. It'll stop the bugs from breeding, and they should be completely gone within 2 weeks. Then just add as needed or if you bring new soil into the grow room.

  5. Thanks for the responses everyone. Gonna get these suckers before they spread too much.

    So mosquito dunks? From like Lowes? My plants are just seedlings right now will this be safe?
  6. Yep, just the plain mosquito dunks from Lowes are fine. They're in a red package with 6 dunks. Avoid the new Off! brand dunks since they aren't organic. It's also sold as Gnatrol for use on gnats, but apparently that formulation is harder to use.

    I've been having a hell of a time with gnats, too. Sticky strips do help, but they'll only catch adults. The females lay 200 eggs each go round. That can get nasty QUICK! You can also catch them with bowls of sweet vinegar with a few drops of dish soap mixed in. (Add a teaspoon of sugar to white vinegar if you don't have apple cider vinegar.)

    If you try the sand, make sure it is thick and only use play sand. The industrial stuff can contain asbestos.

  7. You are a scholar and a gentleman sir, thank you.

    I will make sure these suckers die a horrible death before damaging my babies.
  8. Go to Lowes/Home Depot.
    Read the label of the product for pyrethrum, neem oil, and I forget the third ingredient but it basically speeds the delivery of pyrethrum. Get the concentrated once you mix with water. It's like 7 bucks. Don't go to a hydro shop and pay 13 to 20 bucks for crap.
    Go to Walmart/Target.
    Get 3% Hydrogen Peroxide.

    Mix the H202 with 50/50 water.
    Pour it through the the pots using the H202/H20 mix. One mix per 3 gallon pot. Adjust accordingly. This will kill all the larva and has the benefit of oxygenating your plants roots and also curing root rot and killing fungus. The negative is that it will kill all the beneficial bacteria in the soil, but if done once before applying pyrethrum your plants will be fine and the beneficial bacterial will re-populate.

    Do not use H202 on seedling less than 2 weeks old.

    Mix the pyrethrum/neem oil according to instructs (2 tbls per gallon).
    Put it in a spray bottle. spray the top of the pot and the drainage saucers liberally. This will prevent any newly laid eggs from maturing to flies. The spray has pyrethrum and will kill the flies on contact so use to kill the flies you see. It is safe to spray on the plant. Do NOT spray flowering plants leaves only the pot. Veging plants can be sprayed all over. Do NOT spray young seedlings. Spray weekly until no flies.

    Problem solved.

    There are also other methods such as adding sand to the top of the pot which causes the larva to cut themselves to death and the flies cannot lay their eggs in the soil. However, this method has a drawback in the the flies will enter the pot from the drainage holes.

    You can also make a potting mix with diatomaceous earth. The larva will cut themselves burrowing in the soil. You can only do this for new plants or when transplanting to new pot.
  9. DM can be used on existing plants as a top dressing. It's pretty effective. Only works when dry, so it would probably be more effective on top 1-2 inches of the soil. (Like the dunks, it still works, but in this case it needs to dry out some. Bonus - that helps keep back flies, too.)
  10. #10 Dankafied, May 23, 2010
    Last edited by a moderator: May 23, 2010
    BLAH BLAH BLAH...all those methods metioned above are just mere controling factors. the fact is once u have a fungus gnat infestation in the soil it becomes a serious problem. some people get lucky and dont start see any the affects until late flowering. usually when you see the leaves start to look some what burnt with dead blotchy spots, thats when you know the infestation has taken its toll. not even azamax can cure an infestation. the best way to be fungus gnat free is to seal up any leaks around the grow space area. kill all off flyers with bombs and yellow sticky traps and then replant into new soil or just ride it out and hope the best. everything else is just a control method. just remember once the soil is infected there is no cure!

    look for larvae in the drain pans, thats how youll know if its real bad.
  11. I had a gnat problem... I dunno about in the soil, but I killed all the adults and most of the eggs...

    I use 50/50 91%iso alcohol and water. Spray the plants VERY well. and the dirt!

    I havent, nor would I do this while in flowering, but it works GREAT on my veg plants and has no effect on leaves or anything ;)
  12. Make sure to knock out the problem BEFORE flowering if you can . It is super nasty to pick the dead bugs off of the trichomes. They stick to resin like, well, fly paper.
  13. Gnatrol, recommended-5ml/pg, than 10ml/pg, than 15ml/pg, I use 5ml/pg every other watering, sold in 5-gal buckets only, the finer hydro stores will sell it in small amounts, it looks like a tan sand, stickie traps, diotumacious earth on top of the soil, and the various organic insecticides I use for spider mites every 3-7 days.
    Hot shots work pretty good also.
    I usually notice a few and thats it, with in a week or so I don't notice them around.
    They lay eggs in the soil and when they hatch the lavae works on the root system, the flays are the least to worry about, its the larvae that kills.
  14. I like this guy's method and it seem to work. [ame=]YouTube - Flying Gnats in your Marijuana Plants - How to Win This War ~SUPER TIP~[/ame]

    I would use some Hygrozyme after to clean out the dead roots the larva killed and promote new growth.

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