Fungus Gnats:
Image by Ot1: Fungus Gnat
Signs of an infestation:
Fungus Gnats are attracted to soils that are rich in compost and nutrients. They lay eggs on the surface, hatching into larvae. Those larvae feed on the root tissue, including root hairs, and the outer cell covering of the root; often leaving only the central tube of the root. External signs include discolored leaves, and systemic plant failure. Fungus gnat adults will often run across the medium and may fly if the plant is shaken.
Controlling Fungus Gnats:
Pyrethrum aerosols, as well as placing yellow sticky traps all around the plant will help control the emerging adults. Gnatrol (containing natural Bt) is highly recommended.