how do I kill black fly aphids without poisoning my plants or myself?

December 8, 2008 4:33 AM

Black fly aphids already got two of my house plants. I threw the plants out, but some flies still are buzzing around and my apartment stinks of Raid. I still have two orchids i love and don't want to part with. could they be housing the flies? What would be a good, organic way to get them off if they are?

I've sprayed the orchids with mild soapy water but i can't tell if the black flies are living on them. they don't appear to be. where else might they be living in an apartment? Also how might they have got in in the first place?

other bits of information: I live in the British isles, and the aphids only showed up in winter.

posted by iamnotateenagegirl to home & garden (7 comments total)

Spray with diluted washing up liquid in an atomiser.
posted by mandal at 4:57 AM on December 8, 2008

Sorry, I cut myself off.

Keep repeating this treatment, it should get them all sooner or later.
posted by mandal at 5:02 AM on December 8, 2008

I'm not sure what "black fly aphids" are. I'm guessing what you actually have are fungus gnats.

These would be tiny black flies that live in the soil of houseplants. They're a bit smaller than a fruit fly and a bit harder to swat. If poking around the soil of your plants causes a few flies to escape, that's what you have.

The best way to get rid of them is to let the soil dry out completely for a day or two. Most plants can survive it, and the flies can't. Soapy water won't do much good. Catching or killing the flies is pointless - they die in a day or two anyway. You need to take care of their larvae, which live in the soil.

No need to throw out plants.

If all else fails there are some bacterial solutions that you can get (they live in the soil and attack the gnat larvae).
posted by mmoncur at 6:20 AM on December 8, 2008

Mmm, I was going to ask if you were sure they were Aphids... and not Fungus Gnats? (also known as Root Gnats).

If they're still hanging around it's probably too late, but if not cover your plants! (Mosquito net, cake keeper?) As far as I know damp soil is the only place you'll find them but Google can help you out with that.

If you said Aphids - because you have Aphids.. there are insects that will make short work of them and then be on their way. Although you may not be set up to just release a bunch of Ladybugs in your home. I don't know?
Plus it's Winter up there huh? Mmm.
Google. (Ladybugs/ ladybirds/ ladybeetles.) I think other things eat them too, but they're the cutest!

Also ask your local Orchid Society!! (Trust me.. you will have one.)
posted by mu~ha~ha~ha~har at 7:34 AM on December 8, 2008

You can kill off the gnats by repotting the orchids in all new soil. It's probably past time to repot those orchids anyway. Turn pot over, tap plant out, gently rinse off the dirt, trim back any dead leaves (especially at the former soil line, which harbors those gnats) and roots, repot in a slightly bigger pot using an airy orchid potting medium. Do not reuse any of the old soil.

More details and photos here.

Despite their tropical appearance, orchids do not like to live in perpetually damp soil; they like having lots of air exposure to the roots and thrive best in very fast-draining materials (I have a bunch potted with styrofoam packing peanuts, for example). Watering is best done by drenching the soil and letting it dry for a day or so. Solving your potting/watering issues will also solve your gnat problem as fungus gnats can't survive in soil conditions that orchids favor.
posted by jamaro at 9:03 AM on December 8, 2008

If you had aphids on your orchid plants, you would see aphids on your orchid plants, as aphids spend most of their time sucking on plant juices and having hundreds of aphid children. Jamaro has perfect advice for dealing with fungus gnats, if that's what is actually going on.
posted by oneirodynia at 12:16 PM on December 8, 2008

I meant to add: chill out on the Raid until you actually figure out what you have and where it's coming from. There's no point in saturating your home with toxins when they may not even be applicable to the job. If you really have fungus gnats, you need to kill the larvae in the soil. Raid won't be effective, but Bt will. Bt is safe for humans, animals, and fish.
posted by oneirodynia at 12:29 PM on December 8, 2008