Fungus Gnats

My new enemy:

(Not to scale, thank God. They're about 1/8th of an inch in real life)

When I started growing my first few crops I had major problems with fungus gnats. They were everywhere in the greenhouse - flying around at soil level and swarming anytime a pot was disturbed. The primary cause is too much water (my kids really enjoyed water the plants several times a day...). Cutting back on water didn't help. I tried:

• Yellow pest strips. They caught plenty of gnats but never seemed to put a dent in the population. About once week I'd forget about the strips, only to have the gnat-infested pest strip stick to my head. Yuck.
• Apple cider vinegar. The gnats are attracted to the vinegar, fall in, and drown. It was rewarding to see a few dozen gnats floating in vinegar but it really didn't work.
• A mini bug zapper, capable of "...keeping 1000 square feet free from flying pests". Nope.
• Various organic insecticides, including pyrethrins and neem oil.

Nothing worked. I was getting really discouraged until I discovered  mosquito dunks. 

Mosquito dunks are cakes made from dried bacteria (Bt-israelensis). BT-i is ingested by the fungus gnat larvae while in the soil, where it kills the larvae before they mature into flying gnats. I ground up several cakes into a fine powder and sprinkled on the soil of all my plants. I also sprinkle a bit on any new pots I prepare for planting. Seven to ten days after applying it absolutely wiped out the fungus gnats, and I haven't had any major problems since. When I discover a gnat, I simply sprinkle a bit of powder on the soil of the affected plant to prevent an outbreak. Nothing like a bit of biological warfare against your enemy.