A Gardeners Forum Forums Gardening Reference Gardening in 2005 Gnats

I have noticed small gnats flying around my house plants. I've been told that this could be due to over-watering so I've let the plants dry out, however I still have the problem. Any suggestions? Thanks.

Fungus gnats are a real pain in the butt. They love moist conditions, so letting your plants dry out is a step in the right directions. They can lay up to 300 eggs at a time, so once they are a problem it can be hard to git rid of them.

You can trap the larvae by pushing slices of raw potatoes into the soil, and then gathering them up and throwing them away....

Not quite so messy is to attach a piece of yellow plastic or poster board to a little stick or skewer. If you coat the paper/plastic with petroleum and put the stick in an infested houseplant near a lamp or light it will trap them on there so they can't get off--for some reason they are attracted to these yellow sticky traps....

Last time I had them I used some plastic cups full of dishwashing bubbles and I caught a lot of them that way...I'd put them near the plants and under the lights....once they flew in the bubbles they couldn't get out.....

Repotting of the plants should be a last resort.....

I use butterworts, carniverous plants with sticky leaves and pretty flowers I got from California Carnivores (they have a mail order web site). I've got a bunch of Ping. Moranensis around and everybody's happy but the gnats.

Thank you both. I will definitely try "everthing". I especially like the idea of carnivores and will check out the web site. However, I will have to keep an eye on my husband. He fed my Venus Flytrap hamburger and killed it!!!!!!
nikisue

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 ½ inch slices of raw potato on the surface of the soil to attract the larvae. 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.

Another bio-control method is Gnat Not, a parasite that destroys gnat larvae and other soil pests. It comes on a sponge in plastic (5 weeks shelf life) that is rinsed into water and applied to the soil. For information, go to http://www.goodbug-shop.com/gnatnot.htm

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.

Carniverous plants may attract a few of the flying adults, but they will not affect the unending supply of gnats coming from the larve living in the soil.

Sorry if this is a question, but can you SEE that there's larvae in the potato slices? Fighting a battle at the moment, and doing my homework to defeat the pesky enemy! Thanks, Will.

That's a good question, Mary. If there are gnat larvae in the soil, they will be attracted to the potato slices and take up residence there. They look like very tiny worms and they leave little tell-tale squiggly marks in the potato. It should be obvious if they are there.