Fungus Gnats? Used Diatomaceous Earth any suggestions next?

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Well-Known Member
May 28, 2021
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east coast
hey guys hows it going, so i recently encountered some fungus gnats im pretty sure. started seeing some holes in the leaves a week or two ago and shrugged it off didnt see pest. well yesterday i was staring and talking to the plants and just hangin in the room. I see my soil movin, im like whoa whoa whoa i get up close and i see some small bugs with wings in the soil crawling around on top. look to other buckets a few in there. Now i dont mean i have swarms by any mean just a few in each bucket or crawling around. i go home depot buy some DE for the top of the soil and i put a light layer on the top. i also bout a spray bottle of ortho bug/insect killer preventer and went around the room and sprayed the sides of the tent and around the walls and corners of the basement. basements clean mind you nothing downstairs but the boiler and storage of bins so nothings bringing the gnats to them food wise or people wise noone lives or goes down there, just growing. so back to the story i lay the DE down on the soil, light fan one blowing overnight, soil was dry as **** before adding i read all the reviews soil must be dry and DE must be dry to work so no worries there. I have seen DE turn into mud, clog the roots or trays and everything wen u water normal again, i will be keeping the DE on for a few days and then try to remove as much as possible i dont want lockout or any issues never had to use DE before but everyone says it works amazing just turns to mud and causes some issues? kind of wondering if this is true or is there anything else i can do like a shop vac and suck it off in a few days... plants are growing good im a month and a week into growing i just trimmed the plants back we flip in two weeks so please any words of wisdom before i flip with bugs or prevention.. i use (2) bags of foxfarm ocean forest, (1) bag FF light warrior some perlite all mixed together as the recipe maybe the soil brought them in but why didnt they show up more until now. who knows, thanks everyone


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I've had the gnats before, but never noticed that they attack leaves. It's usually the little larval gnats that attack the root systems and will eventually kill the plant. Diatomaceous earth works to kill the adults, but it's a double edged sword. Inhaled, the stuff will cut up your lungs like asbestos does.
I found hanging the old fashioned no pest strips works, but they're not too good to be breathing in, either.
Get some yellow cardboard or yellow fly swatters and put Vaseline all over the cardboard or fly swatters and put them buy your girls. They are attracted to the yellow. They will be stuck to it in no time. Stop top watering for awhile and only bottom water and they will die. You need the top 2" of soil dry to get rid of the little pain in the asses.
Hey thanks for the reply yeah I have been wearing a K 95 mask since I put down yesterday. And then I just finished watering from the bottom letting them sit in containers and absorb it up for at least 15 minutes and then put back in the 10 they seem to absorb a good amount I haven’t watered in the last few days so Monday will be the real watering day where I will probably scratch off some of the top layer of the DE.... and try and suck it out with the vacc hose the best i can before I water again on Monday before lights off, but this DE will sit on top of soil for 4 days before being touched and removed I squished that big gnat with my hands today haven’t seen any other big ones... I will get the yellow fly swatted trick and Vaseline And I will also go get mosquito dunks and some strips to hang tonight. They absorb the water pretty fast from the bottom I can say I’ve never done that before in the last 11 years that I’ve grown it was pretty cool to see that 5 gallons of water absorb from the bottom there was only about 2 to 2 1/2 gallons left after 15 minutes or ten min tops I let em sit in it, was that long enough? I want to flip in a week or so and get this all resolved, and once the top layer is dead of gnats, will the larvae Still be in the roots or in the side of the pots or at the bottom at all? Is there a formula I should feed them from the top after I remove the DE? Thanks for the reply’s so far
Lmfao yea I got bad allergies so I wear the regular white mask to cut the grass just used another to top the soil and sit and check the room out until I get it up in a few days and water again
Azamax for the win. Little pricey. I have some other stuff, starts with p. Pangine or something. Can look in closet.

They are organic.

Just put up two fly traps in the basement from Lowe’s one literally on the side of the door to the grow tent and one in the room next to it hanging from a hook... i gotta hit a dollar store or order a yellow fly swagger on Amazon lmfao
Just so we on the same page, we’re meaning the fly traps I posted in the pics??? LOL

Just did these two brands blackflag(brown bag)

and raid (blue) bag fly traps the blackflag gave better details and what it was used for then the raid so I picked up one of each and gonna go from there


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Well in my other post I ask another question like how long do you let them sit in the water to absorb up for? It’s pretty cool watching it soak up everytime it got low I added more water
By Monday I’m gonna suck out what I can of the powder from DE and give a nice big feed cuz I’m flipping, does DE effect ph at all should I go alittle lower like 6.0?
okay so here we are, i took my house vacuum and with the extension hose and tiny tip added on i sucked 90% of the DE out and off the soil in the plants. The DE had already hardened up on the top layer and had some mud spots or maybe were the gnats came up and died but some spots were dotted on the layer so I'm guessing the left over gnats tried to rise and get away and died there lol...anyways soil looks good, dry as F** and no bugs seen in or around the grow so doing good so far.....So i flipped the light schedule yesterday, today i fed, did a nice grow big, tiger, big bloom cal mag feeding 5 gallons of water used and between them all no drainage and they really needed that drink since its flip mode now theyll use that energy and shoot right up... i can post pics of the before and after if anyones interested in my photography haha

PS - anyone lookin at this in the future, DE is a MESSY white powder that gets everywhere with the fans on and moving and sitting on the top of the soil for days. Be prepeared to clean and vaccum and wipe down alot of the room wen you remove the DE from the soil, i have seen it be mud and turn into slime and harden on the plants and mess up the feeding and lockout the plants, removing the DE is my personal best experience instead of watering ontop of the product and soil. USE it, clean it/Vacc It, Water, And in the middle of watering and removing ya plants from the grow tent and room wipe everthing in and around ya tent and floor and walls ect. my 2 cents
so heres some updated photos after my top soil watering and foiler feed, i was trying to rinse off whatever DE was left on the plant leaves and sides of the pots and soil.. whatever was in the soil left over seemed to wash away but the pots and leaves are stained with the white residue and its all over the plants, i have not scrubbed or rubbed the leaves but looked tainted with white across them, as all the plants have left over residue. im glad i did this in veg before the flip. but besides that the plants have no bug, no issues as of yet in the soil or around it.. no traps caught anything yet either.... update by next week see if residue goes away.


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PyGanic is your friend.
ill have to google it, thats a new one never heard of it. will have to check it out, but DE was quick and powerful and organic just didnt like the residue buildup and the way blew around my whole basement and it sticks to everything lol

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