Fungus Gnats Can Be Controlled With Special Bt Formulation

Q. I recently transplanted two house plants and now  have gnats coming out of the soil and infecting my entire house.  Is there any way to kill these little buggers or do I have to get rid of all the dirt and start over?

A. Fungus gnats can be a serious problem with houseplants as they can feed on plant roots as well as the decomposing organic matter left in potting soils. The life cycle of fungus gnats (egg, larva, pupation and adult) are fairly short, perhaps two to three weeks.

The destructive stage is the larva or worm stage. The pesky stage is the adult which can fly and be bothersome. These stages are overlapping so they will not all be flying at once but some will be in the egg stage, some in the larva stage, some pupating and some flying.

You can attract the larva living and feeding in the soil to decaying vegetable pieces like small pieces of potato. You can lay pieces about the size of a French Fry on the soil surface and these larva will start feeding on them. You can collect these pieces and dispose of them and it will help get rid of a few of the buggers.

Let me point you in the direction of an organic product that may work for you. This is supposed to be available at hardware stores and home improvement stores. It was originally labeled for controlling mosquitos but is now approved for fungus gnats.

This is an “organic” product made from Bt (a bacterium) with a homeowner trade name of “Mosquito Bits”. There have been a few other homeowner products made from this Bt for indoor plants in the past but they have disappeared from many marketplaces I assume because the homeowner didn’t know about them and how to use them.

Mosquito Bits is a formulation of a special Bt for controlling fungus gnats.

A word of explanation. As I said, this is a Bt product. I have mentioned Bt in the past but this one is a DIFFERENT form of Bt so it will not work to use the Dipel or Thuricide product that you would use for grape leaf skeletonizer, tobacco hornworm, tomato fruitworm and other garden pests.

This form of Bt is rather unique to certain types of insects such as mosquitos and fungus gnats. The commercial formulation of this product is called Gnatrol. Apply this product according to the label directions.

Below I have pasted a document that explains the different types of Bt and how they might be used.