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Fungus gnat problem getting out of control help!! Top Feed Hydro

Discussion in 'Bugs' started by ran4it2, Mar 11, 2011.


    ran4it2 Active Member

    Alright to start I have 25 plants in 2 4x4 under 2 1000w lights. 2 gallon pots filled with hydroton and drippers going to the center of each pot. I water for 30mins every 4 hours and it goes on 3 times when lights are one.

    Plants are in the first week of flowering. Earlier I went into my growroom to look at my plants. I hadnt seen too many gnats flying around. When I Moved the hydroton around in one pot i seen like 10 adult gnats crawling around.

    Ive tried AZAMAX,H2O2 in my res. I tried the 4 Hour cycling to let the hydroton dry out. Im stumped.:-( I dont have alot of money for pesticides that dont work.


    Hillcrest Active Member

    chemical free.....
    Get some diahydro... crush it up a little sprinkle on top of medium.
    This stuff due to it's structure SHREDS the little bastards and they basically bleedout , drying up.
    Or buy 'Gant off'

    ran4it2 Active Member

    how about mosquito dunks?

    Indicator Active Member

    Mosquito dunks (Bt, Bacillus thuringiensis subspecies israelensis) worked well for me in soil. Pack of 10 for @$7 at local feed store. I would think if you strain out the bits, it would prob. work in hydro as well. Plants didn't mind it. Otherwise, I know you can find some at hydro stores in a pre-made liquid. Obv. will cost a lot more.

    IVIars Active Member

    You probably have aphids and not gnats. Alot of people think they are gnats because they fly and look like them, BUT when a root area gets overpopulated with aphids they grow wings and fly away trying to find somewhere less crowded. Azamax is just going to help keep them in check with repetative use. If youre in veg you can use spectracide and Bayer tree and shrub (both at home depot).

    ran4it2 Active Member

    Ive been using 1/2 chunk of the dunk in my rez of 15 gallons?

    Can i put Diatomaceous Earth on top of my hydroton rocks?


    TheTimeKeeper Well-Known Member


    In the past when growing with coco, I've used a 1-2inch thick layer of perlite on top of the coco, this prevents the bugs getting in to breed, I presume the same could work for you (this is a pretty commonly used preventative for coco and soil growers).

    I've also experienced the same problem as you which is one of the reasons I never grew in hydroton again.. I got serious root-rot caused by critters, local shop reccomended a few products to help in recovery & killing off - hydrogen peroxide (small doses) and BudLink (silicon additive), however it was too late and my yield was seriously reduced. This infestation, together with the amount of work it took to get the hydroton clean and root-free for re-use, as well as ensuring (and holping) the roots didn't clog up the return hoses etc, I just bagged the stuff up and moved to coco!

    For a 'surface' gnat control I used to mix neem oil with pyrethrum and water, and spray on top of the coco or perlite.

    Good luck with getting them down, I hope they don't affect your overall yield as much as they did mine!
    scroglodyte likes this.

    IVIars Active Member

    They most likely arent gnats. Ill bet they are Root Aphids. Look for a product called Evergreen, its 6% pyrethrum.

    Root Aphids will grow wings and fly to another pot when the root zone is overcrowded with them. Google a Root Aphid and a Fungus gnat to see the difference

    comeonplantgrow Well-Known Member

    a grabbed my vaccum hose and sucked about an inch and a half of the top of the soil and never seen a gnat since(knock on wood).

    IVIars Active Member

    Lots of misinformation in this thread too. The dunks didn't work so let's keep going back to them being gnats? I bet they have 6 legs and look like a tick? People mistake RA for gnats because they fly.
    Let me break it down for ya.
    Exhibit A - you have fliers. RA will grow wings and fly to a different plant when they are overcrowded
    Ehibit B - you move the soil around a couple inches deep and can see them crawling
    See the correlation between the two?
    bruce barnwell

    bruce barnwell Member

    I was wondering if anyone knew if avid would kill the fungus gnats. i have some left over from a spider mite problem last year and was gonna try it out. I have had gnats for like 5 months and have tried everything. I have used the mosiquto dunks, H202, predaroty nemotoads, pryethrum bombs, sticky traps and i can't get rid of them and just want a sure fire way to have them gone. I do think that the nemotoads and mosquito dunks might work i used tap water when i used them and found out later that it will kill the bacteria and nemotoads because there is chlorine in it and you have to used Disttled water. I have also heard that liquid pryethrum will work but want something that works for sure and i had such great success with the avid i wondered if i sprayed all the hydroton and rockwool it would get rid of them

    ran4it2 Active Member

    just looked it up its def not root aphids they are fungus gnats. They seem to be under control at this point only cause the pump didnt come on for two days so the hydroton dried out.

    BobCajun Well-Known Member

    Fungus gnats are the worst weed killing bastards around. It's pretty much impossible to completely get rid of them in soil but you can get the larvae numbers down enough so they won't kill the plants by using neme oil and mosquito dunks crushed up in the water. Also sticky traps kill some of the adults but there are always ones that just never go on the traps for some reason. Anyway, in regard to your case, where you are using Hydroton instead of soil, simply change to perlite as the medium. It cuts them up when they try to crawl down through it. You can see the dead bodies on the top. At least I think that's what's happening. Possible they just happened to die on top of the perlite or they got fried on a light and dropped in there. It does seem to less desirable for them to live in though, whatever the reason. I've had whole crops killed by gnats in soil and that never happened with perlite so it must be objectionable to them for some reason. It wouldn't surprise me if it cuts them up though. Perlite is worth a try anyway.

    Perlite works great as a hydro medium and you can reuse it a few times if you pull most of the roots out. Some dead roots in it actually help to hold water. I don't know what kind of watering system you are using but perlite works well in top watered pots. You just put a plastic bag inside the pots and poke a few drain holes about an inch up from the bottom. You want about an inch of reserve water in the bottom of the pots so you only have to water once a day when on 12/12 light, twice with longer days. As long as it is an inch or less the roots won't die from sitting in it. How did I poke holes an inch up? I used those thin plastic pots that you can buy in bulk that have like big holes on the edges of the bottom rather than right on the bottom. I could access the bags through those big holes and poke through the bags at the tops of those holes, so they were about 3/4" from the bottom I guess. You could just use buckets instead and poke the holes in the sides of the buckets if you can't find those pots with the big holes or don't want to have to keep putting bags in them. You water to runoff, of course, to prevent fertilizer buildup.

    With smooth clay pebbles anything can crawl down through it to the roots but I doubt there's many flies or insects that could stand crawling through the sharp edges of perlite. I never had a fungus gnat problem using perlite at all. One thing you have to be careful of though is the perlite dust that can be stirred up in the air when handling dry perlite. That's why you wet it down first by pouring water into the bag. Dry perlite will get glass dust all over the place and it is bad for your lungs.

    IVIars Active Member

    Did you try h202? Or 6% pyrethrin, kinda pricy but you can use it in flower also
    bruce barnwell

    bruce barnwell Member

    I used h202 and didnt work what dose did you use of it i used 3 ml per gallon

    fabfun New Member

    try BT...........

    stevejones Member

    Figure I'd give my exp with fungus gnats, or rather the larvae from them. Problem started in soil, finished the grow changed to hempy for next grow. bleached the room. 2-3 weeks into next grow, nute defficiency? maybe, fungus gnats.. yes

    100% perlite hempy buckets

    tried the following:
    diatomaceous earth, put on top, fed through drain hole. - no dice
    neem oil - nothing
    whole bottle of h202 - nothing
    BTi 2 mosquito dunks ground finely disolved into 1 gal of water - nothing
    BTi mosquito dunks finely ground spread into 1/4 inch layer ontop of perlite - no joy

    Its rare to see an adult these days but every watering there are thousands on the surface of the perlite

    next up - no pest strip with WW2 nerve agents. Lets get crazy.

    silverserf Well-Known Member

    Hey all,

    I hate those little bastards too...here's what i've been doing.

    I keep sticky strips up at all times..catches tons of the adults.

    Don't over water...I always let my plants dry out well before watering. The worse the infestation the more I let'em dry, to the point where the plant is drooping.

    Cover the soil with about an inch of perlite or play sand. This really helps, the adults will be looking for a moist spot where there is rotting organic material to lay their eggs, the sand and perlite are inert so make poor hatching grounds. I'm not sure about perlite cutting them up, but i hope so...death of a 1000 paper cuts.

    I grow mostly dwc with hydroton which the gnats seem to leave mostly alone, but i keep my clones and mothers in soil.


    stevejones Member

    silver, have you noticed any bleaching of leaves on the plants that are affected by them? I've got some new plants that are in a 80/20 perlite vermiculite blend and the ones that are affected are bleaching out on the bottom most leaves.

    also, they love perlite I heard diatomaceous earth cut em up, tried that ONTOP of the perlite and it didn't seem to help at all.

    roidrage152 Active Member

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