My houseplants are infested with fungus gnats

(Question)

I recently transplanted three very large tropical plants, that I have cared for over many years. I purchased the soil from a well-known store in Toronto. Now the pots are infested with bugs. When I water, every Saturday, these flying bugs, like fruit flies, leap out of the soil.  I have hundreds and hundreds of them on my windows.  Someone suggested I put out dishes of apple cider vinegar near the pots, and they are now full of these flies. But they keep coming out of my plant pots. Help!

(Answer)

Not to be discouraged: patient detective work is often required to correctly identify, and deal with, pests.  It appears, though, that your plants are infested with Fungus Gnats. These will cause little, or no, injury to your plants, but can be a real household nuisance. The gnats lay eggs on the soil surface, and the larvae feed on decaying plant material in the soil. So, the key is to reduce the moisture levels in your plant soil and remove any plant debris on the surface. You mentioned that the flies come out of the soil when you water, so perhaps consider dialing down the frequency, and volume, of water you give your plants, albeit in the name of love. Let the soil really dry between watering, and ensure the bottom saucers are not sitting in water.

You may wish to refer to a prior reply to a client question about fungus gnats at:

http://www.torontomastergardeners.ca/?s=fungus+gnats

The following references provide excellent information on bi0logical control, water & soil management and trapping of these pests: http://www.ext.colostate.edu/pubs/insect/05584.html  ,            http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7448.html

Proper water management and removal of plant debris  will break the life cycle of these pesky gnats and will allow you to continue enjoying your houseplants.