Question
After I re-potted I over watered and now have bugs. Gnats and these
mini flies. I never see the flies until they end up in the vinegar soap
mixture I have placed around the plants for the gnats - who rarely take
the bait. They look like fruit flies but I don't have any fruit out.
What could they be? One of my plants, my favorite, also seems to be the
favorite spot for all the damage. It has long draping vines and sort of
heart shaped leaves some varigated greens and yellows some all green.
Some of them look eaten on the edges and shrivel up some just turn yellow
to brown in a spot that spreads then die altogether. I've thought
about trying the no soil potting mixture. H- E -L- P I'm new at this.  

Answer
Hi Aliyah,

First, you need to identify your plants. If you don't know what you have, you can email photos to me at [email protected]. Only then can I tell you how to properly care for them.

Adult fungus gnats look like tiny flies and fly around and are an annoyance, but they are not harmful to people. Each gnat lives for about 5 days. The trick is to get rid of the next generation - the gnat larvae that live in the top layer of the soil. The larvae feed on decaying organic matter. Decaying pine bark in potting mixes and decaying plants roots feed the larvae. Try to keep the soil as dry as possible. Remove all loose soil from the surface and put a light layer of coarse coir (coconut husk) or sand or diatomaceous earth on the soil surface. These substances have sharp edges that carve up the larvae. (Recent studies indicate that fine-textured peat moss also deters gnat larvae.)

Another safe technique is to place ?inch slices of raw potato on the surface of the soil. After a day or so, discard the slices along with the larvae inside. Repeat this until there are no more larvae in the potato.

For more serious infestations try Knock-Out Gnats to treat fungus gnats available from Gardens Alive for about $20. See http://www.gardensalive.com/item_display.asp?ProductNumber=1962

Detection trick: Add a little water to the soil and then look very closely for tiny fungus gnat larvae swimming in the water as it pools on the surface. You need good light and good eyes to see them. If you don't, then your plant is probably gnat free.

Prevention is often the best remedy. Use sterile potting mixes that are free of bark chips. The potting mix should have ample drainage material, such as perlite so that it drains well and allows the soil to dry out frequently. Fungus gnats can nearly always be traced back to overwatering and/or poor soil quality.

To attract and capture the adult flying gnats, pour a little red wine into a small glass (cooking wine will work, if you don't want to waste the good stuff!) and leave it out for the day. Repeat the treatment as necessary.


Please let me know if any of this is unclear or if you have any additional questions. If you would like to e-mail me some photos, I may be able to provide some additional insights.

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Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

You can E-mail me directly at: [email protected]