From the Digest

Fungus Gnats

By Barbara Rengers (October 2009)

This year, I’ve been having problems with fungus gnats. Is this from the area in which I live, the mix I purchased or something else I’ve done? I’m not sure, but I am sure that I will be going after them vigorously.

Fungus gnats are little hopping bugs you see when you water. They have black or gray bodies and clear wings.

Plants grown under cover and in peat mixes are most susceptible to the pests. Their larvae feed on dead roots and leaves, but sometimes consume tender new roots.

To deal with them, consider the following:

  1. Look for small insects on the surface of the soil. They will be active when you water or move the plant. The larvae are one-quarter-inch. white-bodied maggots with black heads that can be found just under the surface of the soil.
  2. Keep plants clean of debris. Fungus gnats feed on dead plant material.
  3. Use yellow sticky traps placed near the infested plant to catch adult fungus gnats.
  4. Water with a solution of Bacillus thuringiensis, an organic control for caterpillars, to kill the insect larvae. B. thuringiensis is a bacterium that is safe to use around people and pets.
  5. Drench the soil with a solution of pyrethrin, an organic pesticide made from chrysanthemums.

University of Minnesota Extension Service
Ohio State University Extension Service