fungus gnats

What can help control fungus gnats in indoor plants?

First I would back off on watering--I have never had trouble with them unless I've been watering a bit too much. The excess water will do more harm to your plants in the long run than the gnats will.

For the adult gnats, most insecticide sprays can take care of them, or if you prefer to avoid chemicals you can put up yellow sticky traps. In addition to treating the adults though you also need to deal with the larvae in the soil--Bacillus thuringiensis (Bt) is one good approach for them. It's found in mosquito dunks and products like Gnatrol.

Some plants may be sensitive to this approach: A soil drench can be made using 1 to 2 teaspoons of horticultural orange oil per 1 gallon of water. This will kill the fungus gnat larvae living below the soil line where they damage plant roots.

The ultimate fix is not to over water plants. If plant roots take up too much room in the pot preventing drainage it's time to bump up to a larger pot or use new media and root prune if using the same size pot. The latter method requires top pruning to balance the plant (root>top growth).

I like sticky traps too, better the little buggers meet a "sticky end" than plague your plants!

I found a "never before" infestion after I used an organic citrus/vegetable fertilizer. They apparently were in the fertilizer and when water was added they bloomed.

I moved the infested plants out of the GH and let the gnats run their life cycle they've not come back and I won't use that fertilizer till the plants go back out.

I'm sure many of you will disagree, but I soil drench all potted plants with Sevin 24 hrs before I bring them in the house for the winter. I also lightly syringe and wipe all the vegetation with plain water just before they come in. This advice was from The University of Michigan Cooperative Extension. After battling them using all the home remedies and organic remedies I found this to be the fastest and most effective. 1/4 tsp Sevin to a quart of water. Water plants until the potting soil is thoroughly saturated and water runs out the bottom. The plants are then free of all soil pests and remain that way for the duration.

My infestation began with a potted gift amaryllis from White Flower farm 3 Christmas's ago. Inspite of following all the proper cultural practices, such as allowing the soil to dry throughly between waterings, the little buggers thrived and spread. I buried slices of potato in the soil to trap the soil larva. I used the yellow sticky traps for the flys. I tried the organics, which in my opinion are a complete waste of money and time. I could knock down the population levels but never eradicate them. Then, in utter desperation, I soil drenched with Sevin. I've not had a fungus gnat since.