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HELP!!! Gnat Problem

Discussion in 'Marijuana Plant Problems' started by RedKasper, Jul 20, 2009.


    RedKasper Member

    My six plants have begun their second week of flowering and a gnat infestation has recently taken over the area. The gnats used to be a small problem, but now they've multiplied like crazy and their on every plant and everywhere. I can see tons of them coming out from the bottom of my pots and roaming around on the top soil. I already tried hanging a few sticky traps and I've only caught a few...the traps haven't made much of a difference.

    What should I do?

    I've heard that placing a layer of sand 1 - 2 inches thick will eliminate the problem. I've also heard that certatin mixuteres of garlic and other household products will work. I saw a bottle of Fox Farms Don't Bug Me Insect Spray and thought about getting that too. Does that work well against gnats?

    What has worked well for everyone else and their gnat problems? Thanks!

    itsgrowinglikeaweed Well-Known Member

    Sand works very good for all sorts of soil nesting nasties. I use sand on most of my houseplants and my MJ when i need too. I HAD a problem before the sand. It wont kill adults but it will keep them from breeding in the soil, and will smoother any eggs or larvae. Sticky traps should eventually round up the adults.

    Hayduke Well-Known Member

    If the problem is really really bad...like you are going nuts...1T/gal Dr bronner's Hemp-peppermint oil soap...make sure you adjust pH or it will defoliate your plant! (the gnats will be gone thought!!;)) Use at your own risk! I did not pH...and f'd up a couple...other strain did not seem to mind.

    Bugs hate peppermint oil...I had not seen larvae before using...they crawled out of media in bottom of pots and died!

    IMO Sand blocks the plant from breathing, and I see just as many gnats in bottom as in top....Just my opinion.

    If you use the peppermint oil, they will still return.

    To effectively manage (cuz I do not think you can get rid 100%) you need to periodically water in some predatory nematodes which eat the larvae.

    The sticky traps work if one of the dumb shits happens to run into one...I use some "tanglefoot" around the holes in the bottom of the pots...pick up the pots and tap them...gnats run out to see who's a knockin' and either smash with finger or let them just get stuck in the tanglefoot, and build up on top of each other....this must be de-moralizing to these little bastards!

    The nematodes work excellent for thrips also...the only problem is if you have a perpetual grow like I do...I am constantly introducing new pots which are nematode free, and need to buy more nematodes.

    I use ~2x during grow. When used I see a gnat here and there...when I have new pots I have not treated...I see one run across outside of pot every minute or so, reminding me I need nematodes.

    If you use the peppermint oil soap...make sure you adjust pH!!!!!!!!!!!!! It was highly effective (fungus gnats were temporarily GONE!) for my infestation but use with care!

    The soap is supposed to increase the plants uptake...maybe release salt bonds? and this also could have been the reason for the leaf drop. The buds were still excellent.

    itsgrowinglikeaweed likes this.

    RedKasper Member

    Thanks for the info! Very helpful.

    Mcgician Well-Known Member

    GoGnats worked well for me. I also heard that Ed Rosenthal's "zero tolerance" is good too, but much more expensive. Most like because of the amount of cinnamon oil he puts in it. GoGnats has several different ingredients, but the most pronounced is cedar oil. Seen those dog beds at Costco? The ones filled with fluff and wood chips? Well, inside those beds with wood chips is cedar. It's meant to ward off bugs, and put off a better smell. It may not be as nice as cinnamon, but it sure does work.

    bigwheel Well-Known Member

    Makey yourself a gnat trap. Take a 2 liter plastic bottle and stuff a banana peeling and a shot or two of bourbon in it. Stick a funnel in it and tape around the joint to make a seal. Leave it in the grow room. Should be full of gnats before long.

    Hayduke Well-Known Member

    Plant oils!!!!

    I love the gnat trap! My daughter had a banana for lunch...just retrieved the peal from the compost bucket and made a trap! Sounds devilishly fun:twisted:


    Crutch Member

    If you have fungus gnats, small black gnats about 1/16th on an inch. Their life cycle is about 23-30days, a good way to stop them is to interrupt their life cycle. When I had the problem I used Yellow Sticky cards(bugs love yellow), to attract and trap the adults, and then to make the soil less hospitable for them I spaced out my watering cycle. If you are over watering or not waiting for the soil to dry up in between waterings, you are making fungus for the larva to eat. In fact this weekend, it was about 100 deg. where i live, and while I was gone I placed my indoor plants outside as I had not planned for it to be that hot, this is only my second summer in the valley. I came back on sunday night, to find dry soil and not one fungus gnat.

    To summarize:

    1. Space out your watering cycles, don't give them fungus to eat, let your top soil become a little crispy before watering again.
    2. Disrupt their life cycle. Kill the adults before they lay eggs. Place red wine in a small container near your plants the gnats will smell the fermenting wine and investigate and drown. Or use Yellow sticky cards to catch them, this is also good for identifying your infestation.
    3. Neem Oil is also good for killing the fungus gnats, but I haven't been able to find it at a normal hardware / garden stores, only specialty shops, or the nursery around the corner.
    4. 1/4 inch of sand on your top soil. thumb out about 1/4inch of your top soil then replace it with sand. this will make your soil less inviting for them to lay eggs.

    Fungus gnats can bring some pretty nasty diseases, and most of these diseases will make you eradicate the infected plant to prevent spreading of the disease.

    Hope this helps you. :peace:

    chronicj69 Well-Known Member

    pickel juice and teatree oil works like a charm

    RedKasper Member

    Thank you everyone for your advice and assistance.

    I was afraid to sit around and wait for the problem to get worse...so I ventured to my nearest garden center and picked up a bottle of insect control spray that utilizes pyrethrum as its main ingredient. It's suppossed to be all-organic and can be used up until the day of harvest. So when I got home, I immediately tried some of the spray on the top soil and I'm already seeing a heavy reduction in total gnats. I suppose I'll give it a few weeks with this spray and my sticky traps, and if that doesn't work I'll try some sand as my top layer.

    The "gnat trap" sounds like a great idea and I'm gonna start working on that immediately!

    Thanks again for the help!

    Hayduke Well-Known Member

    Checked my gnat trap...no takers yet...I think this trap would work much better for fruit flies and may put it in the kitchen as they like the compost bucket...could be that the nematodes are doing such a good job that there are not enough fungus gnats to really be attracted to the trap yet...or maybe they do not like Scotch...being domestic pests...

    Pyrethrin will definitely work...I have used it for adult thrips (NO MORE! Spinosad works good). I have not used it on the soil...but airborne it will leave the garden void of any life above the soil...it is serious shit! Although pyrethrins are found in nature, the stuff we buy is not chopped up chrysanthemums, but a synthesized equivalent. I have it and won't use it again because of the perpetual and because I live around my plants and I am barefoot during the 2 weeks it takes to break down.

    The cinnamon oil sounds interesting...the long lost StoneyMcfried sprinkles lots of cinnamon on the top of the soil (I thought it was for fungus).

    To those that are having success with sand...What is happening to the ones on the bottom?

    And as for the water issue...maybe it is because I am in small pots, but I let my shit get really dry(they air prune themselves on bottom) and they are not 100% eliminated. but I have over-watered a patch of indoor grass for the late cat, and OMG they were way out of hand! I will let my Dracena's get bone dry...then over water with left over nutes occasionally...and a few always come back :neutral:

    Which makes me wonder...It was said to let them dry so that there is no fungus to attract the gnats...but I pay good money to add beneficial fungus on purpose...so are they only attracted to "bad" fungus?

    Also does anyone have a recipe or know of a product besides tanglefoot to make your own sticky traps?


    itsgrowinglikeaweed Well-Known Member

    QUOTE: "To those that are having success with sand...What is happening to the ones on the bottom?"
    Gee IDK. I never had a problem with bugs "on the bottom" So I'm not sure what thats all about. The sand i applied pretty much completely solved the tiny flying insect(maybe they were something other than fungus gnats?) problem I had. And as far as the sand keeping the soil from breathing... It kinda will at first. This is basically how it kills the bugs, smoothering them. It will hold in some moisture too so you wont have to water as often after you apply it. But after about a few weeks (when hopefully the bugs are gone) the sand ends up getting watered into the soil and mixed up with it, actually improving the breathability of the soil. So its all good in the long run. Some of my house plants i water more carefully so that the sand stays put on top of the soil.
    Also ive tried a few of the homemade sticky traps using molasses, and syrup and stuff like that but never has any luck attracting them. I do have some sticky traps that i bought at the local dollar store that round them up pretty good.
    I also use a trap that is just a glass with some apple cidar vinegar in it, with a saran wrap cover, that i stabbed with a fork to make 4 small holes in it. the bugs crawl in the holes and cant find the exit (morons LOL). I put this trap next to my bananas and other non refridgerated produce. It works really well.
    I'll also mention that i never see any bugs in my flowering tent. I have a DIY cooltube in there that is hooked up to a very powerful 6in inline fan and blows through a DIY carbon filter i made. Anyway the open end design of the cooltube is like a damn vaccuum sucking up any bugs that think that they are going to go up and check out the light. then they get slammed into the filter material and are not seen again. Ah ah ah ahhhhh!
    I'd like to know more about the nematodes. Where do you get them? how do YOU apply them. I've got some outdoor veggies that could use some bug protection too.

    Hayduke Well-Known Member

    The trap I made is going in the kitchen as fungus gnats are not drunks...Yeah I lose a few to the air-cooled hood, but I do not have enough exhaust to really suck them out good:twisted:

    I get my nematodes at the local hydro shop for $12.99(?)USD so the Nature's Control site looks pricey...shop around. They come in a little blue sponge that I often cut in half...you soak in a gallon of water...dilute more if needed...I do cuz I want them in more than the top 2"...they like the bottoms as much as the tops as they are of similar moisture levels, and I have LOTS of holes on the bottom of the pots, and coco lets it lots of air.

    store them in the fridge and do not let them dry out...you can not see them with the naked eye on the sponge at least...I have not seen them in soil either....they are really small.


    They may already be in your veggie garden...but it certainly would not hurt to add them...they eat pretty much any grub or larvae that are harmful to roots or whose adult stage is harmful.

    I have recently thought about figuring how to cultivate the sponge to grow the worms myself...can't be too hard...

    Oh and as for the adults...not sure how effective they will be, but I am hatching a Preying Mantis egg sack (in a paper bag) right now...the majority will be released in the veggie garden, but a couple may stay indoors to teach those lazy lady bugs a lesson:twisted:


    itsgrowinglikeaweed Well-Known Member

    Hey thanks for the nematode info. I had only just recently heard of them, and actually forgot to look them up untill i saw them mentioned here again.
    So the lady bugs weren't getting the job done huh? LOL Good luck with the mantis. :joint::peace:

    gavmac3777 Member

    you can get rid ov them very easy just go to shop buy a smoke bomb or fogger as they are sometimes known. set that of seal room for about 2 to 4 hours(make sure all ventilation is off. scrape about an inch off ov the top ov your soil and bin it, replace that with sand and then hey presto, within about a week or so you should be gnat free.

    RedKasper Member

    Interesting method gavmac3777...I might try that. Where can I buy a smoke bomb or "fogger"? Will it hurt my plants?

    The pyretheum-based spray I put on my soil worked very well yesterday......but this morning I awoke to another infestation....they were back!!!!

    I can't tell if the spray actually helped...but I'll try it again in 2 more days and see what happens. (Directions say to use every 3 days)

    I think I'm gonna go buy some sand and place a 1/2" layer on the top soil. Many people seem to think that's the best method.

    weedsmoke1221 Active Member

    got a organic grow going as well - I find neem oil and insecticidal soap works well to keep them under control, both organic made by schultz.. I found it in the gardening section at the grrocerie store - hey they are adding CO2 to the grow area right?

    katwoman2012 Well-Known Member

    I used that Eco-Sense bug crap with pyrothene and it didn't work. I have dishes of dish-soapy water in all my cabs. The dryer the plants, the more dead ones. It's a never-ending battle I clean out about 100 bugs in 3 cabs every morning. Gag. I've got pix of my plants in so much dish soap that they're foaming over. The assbites come back. Good luck. Tried GoGnat and Gnatrol. Waste of money IMHO.

    kevin Well-Known Member

    pickle juice = vinegar, will mess up the ph and kill your plant:peace:

    Hayduke Well-Known Member

    Dish soap is detergent not soap...there is a difference. Dr Bronner's Hemp-Peppermint Oil Soap works for sure...dead larvae crawl out of soil and die on pots....but this will raise your pH so adjust. This is somewhat extreme...but your situation sounds extreme. This works for the ones in soil...the flyers need to be dealt with separately yet simultaneously or the problem will not go away....honestly without regular use of pyrethrin...they WILL come back.

    This will work for the adults...the sand maybe for the babies (I don't do sand), but the "bomb" is a pesticide.

    For those that have used pyrethrin without success: Use the bomb type...I have used Pyrethrum TR (total release bomb...can just release some, but be careful...do not press down and lock or 3,000 sqft of insecticide will be released. I was recommended this by a bay area grower with 15 years exp. (for thrips) He uses periodically as needed. One of these cans will last for a couple of years with light periodic use.

    If you use this at 3-5 day intervals you can get rid of f. gnats and thrips for sure...as you will kill the hatchlings with the second shot before they can lay eggs (may need 3-4 applications).

    Do not spray directly on plants (you can spray some of the more dilute versions like "don't bug me" and there is a regular aresol spray that you can spray on by the same maker of the "TR" (but this was not recommended) spray at lights off...all ventilation off... Cover your skin, mouth...think ahead...hold breath...spray a little and get the f*ck out in a hurry...put a wet towel under door....let stay as long as possible...sneak in to plug back in ventilation (holding your breath!) and let vent for a couple of hours before you go in...it will still smell like Men in Black were hunting aliens for a day or so....poison breaks down in 2 weeks so use up till 6 weeks flower (only if absolutely necessary!)

    For me...my veg and flower box are in the master bath and I still use the sink/shower/toilet, and smoke most of my grow myself...I could feel the chemical through my bare feet...Anybody want a can of Pyrethrum TR? It WILL kill everything above ground in the room

    Personally...the nematodes for the larvae and tanglefoot sticky trap goo for the walkers/flyers works pretty good...they are not and will never be gone, but they are not even a nuisance any longer...as I add new untreated pots...the numbers increase a little reminding me I need to water in some new nematodes...if they disappeared entirely...the beneficials would starve (faster);)

    Also...the Neem label scared me...I know it is supposed to be cool...but still...I use Organic Hemp seed oil...cuz I do eat it! 1T oil/1T baking soda/1T DR Bonners to 1 gal water works for bugs and fungus (powdery mildew) though I am going to try Serenade (a bacillus) for the veggie garden cuz oil is bad in temps above 80f...and may use for the girlies when needed.

    I'll shut up now...hope this helps someone.


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