Several have asked me how to control fungus gnats when they are rooting cuttings. Crop King (330-302-4203 has a nematode (Steinernema feltiae) that feeds on their larva and stays around till they pretty much wipe them out. Warm wet conditions encourage the gnats and also blow flies. You get 15 million (be sure and count them!) for $24.48 and shipping. If you want to check and see if you have fungus gnats larva (they eat the new roots), just put some raw potato on the top of your mix. The larva will feed on it and you can see them when you lift the potato. They are small, cream colored with black heads. Hope this helps.
LOL!!!
This is the damage fungus gnat larvae can cause to an entire rose embryo, let alone roots:
…and this is the way they like to do it!!!
Here one such critter caught in the act, ready to feast:
I wish I had some of your stuff a few months back, I lost 99.99999% of ~100+ embryo-seedlings (all from USA), because the seedling mix I used was infested with fungs gnat larvae.
I thought I got over it, however clearly it is still a raw wound in my mind!!!
I still cannot believe the degree of damage these tiny hiddeous things can do!!!
George, you exaggerate!!:). Was it 99% or 100%? [I know its painful either way, like when I killed a 20 yr bonsai by neglect of watering after a vacation].
Watch for hungry roly-poly pillbugs too. Though they are good at eating the aphids off your rose plants, they’ll consume your lettuce and other delicate seedlings.
LOL!! I can be a loud one, I know!
Since you asked for clarification 
, 2 seedlings had lived out of a hundred or so, and now these also have died. I had boiled the media after discovering the gnats, then I reused it to tansplant into it again…this was a mistake…the boiled media after being boiled, gradually became smelly, “acid” and eventually everything I replanted into it looked “burned”. The reamining two surviving seedlings also burned, and died, jus tlast week!!
So the real answer is 100% loss, most of which was directly attributable to the gnat larvae, the other losses due to stupid re-use and hot water-treatment of the afected media.
Yes stupid!!!
Fungus gnats dislike Bounce. Yes, those dryer sheets with fake perfume on them. Put a small piece of a sheet whereever you don’t want the gnats. It’s a great repellent.