Where do fungus gnats come from??

I'm referring to indoor growing, at least in the seedling stage.  Are fungus gnat eggs found in bagged potting soil, lying dormant until some unsuspecting dupe like me uses the soil?  i can't figure out how they get into my basement, unless their eggs are in the bagged potting soil.  I took some potting soil from the bag, and put it in a plastic bucket with foil on top.  Several days later, the foil looks a bit damp on the underside, and the soil has gnats all over it.  What to do?  I could toss it, but it would just happen again if the eggs are in the bagged soil.  Or, I could still use the soil, but plan on adding mosquito dunks to the watering can.
 
yeah I thinks there just kinda one those pests that are everywhere. In any soil i swear. This is what I did to kill the bastards indoor.
 
Tried neem oil, they loved it.
 
So go get a sack of good clean sand home depot. Water you plants first if they need it or are close to needing it.  Put a good inch, inch half layer of sand on top soil up your stem of the plant up to edges of the pot. Leave no bear spot what so ever. you don`t want to see soil.
 
Then take a fly strip hang it next to the plants.
 
The sand will kill the larva they cant come up through it. The fly strip is to kill adults leave sand for at least three weeks I left it for months dint hurt plant. Water in one area and recover with the sand as needed.
 
Best non poison way worked great for me. I took couple days for all the adults to die but no more.
 
here is there life cycle.
http://www.ext.colostate.edu/pubs/insect/05584.html
 
I had a brief run in with them this year, I know exactly where they came from...I have overwinters that I stick out on the patio when it's warm outside and they laid eggs in the soil while they were out there.  I got rid of them by using fly paper, bottom watering, and using a 1:4 hydrogen peroxide and water mix...no harsh chemicals.
 
Id ditch it. If not use the above peroxide and try to let the soil dry completely. Its not worth it honestly, I've been fighting them bad since december.
 
all soil cheap or otherwise can have fungus gnats in it. Supposedly you can sterilise it, but to be honest I find the solution far simpler. Just keep them at bay with 
a) watering from the bottom and
b) get some carnivorous plants (NOT venus fly trap) and/or
c) some yellow sticky cards.
 
IF you let them get out of hand, they become a problem. Then you can resort to sand next I guess. Otherwise, meh... 
 
Mosquito dunks, at least in this instance, appear to be working, though I am still getting a few fliers. You can crumble them into the soil or top dress at 1/4 tsp per gallon. I've heard good things about sand/perlite/DE top dressing, haven't gotten that far myself. Yet.
 
I use perlite in place of sand, and, hanging fly strips
 
The manufacturer told me to use mosquito dunks at the rate of 1 tsp per gallon.  I added it to my AACT tea, so I'll see how this works out.
 
Roguejim said:
I use perlite in place of sand, and, hanging fly strips
 
The manufacturer told me to use mosquito dunks at the rate of 1 tsp per gallon.  I added it to my AACT tea, so I'll see how this works out.
 
Let us know how the perlite works. I would think it to coarse and might allow them to escape still.
 
plaisir8 said:
I've learned to live with them...
 
Yeah there kinda one of those things. But on the other hand.
 
 
THEY NEED TO ALL DIE
 
Roguejim said:
How about a link?
 
Fungus gnats are a result of a unhealthy soild food web. If you have healthy soil, then preditors will eat the larva before they can turn to gnats.
 
 
Try mixing in some native "live" soil to your potting mix to see if it helps kill off the gnats.
 
 
 
Honestly in the 2 years I have been on this site I have seen this topic many many times. People always seem to think they can just bomb the soil and eveything will be ok.  
 
Also traping the adults will help speed up the process.
 
Cayennemist said:
 
Fungus gnats are a result of a unhealthy soild food web. If you have healthy soil, then preditors will eat the larva before they can turn to gnats.
 
 
Try mixing in some native "live" soil to your potting mix to see if it helps kill off the gnats.
 
 
 
Honestly in the 2 years I have been on this site I have seen this topic many many times. People always seem to think they can just bomb the soil and eveything will be ok.  
 
Also traping the adults will help speed up the process.
Well then, I guess "Happy Frog Potting Soil" , which I am using, is unhealthy, and devoid of predators that eat fungus gnat larva, by your criteria. 
 
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