Ugh.. I don't know what it is but EVERY year I get these darn gnats. This is the first year I was able to find out more information about them though. These little buggers can kill a seedling off in 2 days and an almost ready to transplant plant in about a week.
Normally when they started flying around I was able to spray and get them killed before I lost all of my plants. This year it's a little bit harder. They have invaded my aquaponics systems. I have all my seedlings and almost ready to transplant plants in my grow beds. I can't use any of the normal pesticides (and Corey and I agreed starting this year everything as close to organic as we can get) Yet I also can't afford to loose all 150 plus seedlings!
So I'm doing a 4 step approach. 1st thing I did was get the mosquito dunks. They are safe for plants and fish. These went into the fish tanks. I researched them ad the BT is commonly sold in jugs for Aquaponics.
Then tank by tank I am taking all the plants out, pumping almost all the water out into the fish tanks (the fish love bug larva) and then adding enough rock to get rid of any standing water spots. The Fungus gnats lay eggs where it's wet and the larva live and grow in the moist environment where they eat plant roots and fungus.
Then I am replanting the seedlings. Please note a few things. First make sure you get the roots into water. Second if your seedlings are really small, immediately transplant into another box, they can't take the 30 mins out side of their watery environment and will litteraly melt in front of your eyes.
I have also hung up one of the sticky flying bug traps over the beds to help catch the adult gnats. I realize this could take up to 6 weeks to get them all gone.. but hopefully I'll have saved my plants. So far the beds I've fixed are doing really good.
So if you see little white things that move like crazy when you blow gently on the surface of your dirt or other growing medium strike fast or you could loose your seedlings
More info and picture of fungus gnats