I'm new to this site, so I' m sure the answer is here some where, but is there a systemic way to control fungus gnats? I have been using rubbing alcohol, but have many passifloras and hoyas plus other plants that are infested. I spend half my day dabbing those pesky little critters. Thanks.
I don't think Keyring is around very much anymore... Here is my very humble 2 cents worth of ideas, and I'm sure someone else will come along with other suggestions. :-)
What has worked for me is to let the soil dry out completely, which means not watering for quite a while and trying to ignore the plants' shrieking at me. (grin) When the soil is as dry as can be without actually being rock, water everything with a little bit of hydrogen peroxide in the water. After that I go back to a regular watering routine, but I try to be careful not to let the soil stay too soggy. The fungus gnats are there because of the water. They don't actually hurt anything, other than being very annoying, but their larva are in the pots, eating at the roots. The hydrogen peroxide helps get rid of any larva that survived the desert experience, and discourages any remaining gnats from laying eggs in the pots.
This works very well for me, but I have mostly very easy houseplants. If yours needs constantly wet soil and letting them dry out like this will do irreversible harm, maybe you can try doing the hydrogen peroxide in the water first and see if that takes care of them. Squish any gnats you see to cut down on the number of eggs they can lay (and because it's satisfying!) And, most of all, be careful not to over water.
I hope that helps! I didn't write the above article; I just edited it together from a bunch of Keyring's threads in various forums with her permission, so I am not nearly as expert as she is. :-)