Fungus gnats :(

[naturalgirl]

Ugh!! There are little flies on some of my plants, including my precious orchids, which I'm quite sure are fungus gnats. HOW do I get rid of these?? It would be great if there were some easy-ish remedies that don't involve harsh pesticides as I have a cat, rabbit, and toddler niece.
Do they actually cause harm to the plants? Or are they just annoying? I have one orchid in a room on its own and it seems to be declining, and I can't figure out any reason other than these flies! My others are doing ok but I want to make sure they don't start failing too!

[Dorothy]

Check out this past thread - Ugggh, fruitflies/gnats!
I hope this helps

[naturalgirl]

Thanks, Dorothy...

I also just read that pouring water with a bit of dish soap through the media will kill the larvae... Anyone have any experience with this?

[Dorothy]

You are very welcome ..
I think you are talking about 'mouse milk' - check out this past thread - http://www.orchidboard.com/community...ouse-milk.html

[Jerry Delaney]

If you really want to get rid of them for good, do a Google search for "beneficial nematodes". There, you will find several sources for these small plant harmless nematodes. The ones you want to look for are Steinernema feltiae. These nematodes are small, microscopic round worms that infect the larvae of the flies. Once they do, the larvae become kind of a reproduction plant for the nematodes and the larvae eventually disintegrate which releases thousands of more nematodes. Eventually, the nematodes die out because there are no more larvae to serve as hosts. These nematodes are absolutely harmless to anything but insect larvae. In your orchid potting media, they may get flushed out to some extent during watering. Most likely, the smallest amount you can purchase will be sufficient for several treatments. If you keep the extra amount in the refrigerator, they may last for weeks or months. Just remember, you are not dealing with a chemical here so don't expect them to eradicate your larvae population overnight. In a couple of weeks, your plants should be "fly free"!!

[goodgollymissmolly]

You generally get fungus gnats from peat based potting mixes although you can also get them from your own outdoor soil mix if it is damp and contains a lot of decaying organic matter. The larva do eat roots so they can be damaging. The adults are just a nuisance but they do lay eggs in damp decaying potting mix.

It is unlikely that your orchids are the original source or a place that eggs are being deposited unless your orchid mix is rotting. If you want to avoid pesticides, you can do the following but remember it will take time. If they are in your orchids (try apple below) then your orchids probably need repotting because the mix is rotting.

First the adults are attracted to yellow. You can buy sticky yellow strips to put in the area and catch the adults. To lure the larva to the surface, put strips of peeled apple on top of your mix and throw out the captured larva each day (don't leave them there or they will become adults). Third, put a layer of coarse sand or crushed granite (sold as chicken grit) on top of your potted terrestrial plants (not you orchids!!). This will prevent the adults from entering and laying more eggs.

Pesticide drenches work better, but I understand your concern. The above steps will probably not totally eliminate them in the short run, but the population will become less annoying.