Gnats driving me gnuts

Help! My office is inundated with gnats! Must have gotten a "bad" batch of potting soil. What do I use to get rid of them? My plants include Ferns, Hoyas, Begonias, African Violets, Christmas et-all cactus and the usual tropical house plants. I did get a genuinely great laugh the other day when one flew up DH's nose and he did the "gnat-up-nose hack-n-dance" around my office....but other than that I can't find any good to them! (that was one GREAT "holding sides...might-wet-pants" laugh though!!!) Thanks! K

I'd be interested to know too. I have a couple around, but nothing serious. In the far distant past, before I grew wary of chemicals, I used Diazanon (sp?) mixed in the watering can and watered the plants with it, then repeated it a week later. That always took care of the critters. However, I always lost 10% of my plants. I dread the problem returning and would like to know what others have done that doesn't automatically kill some plants too.

I was considering a Malathion drench, that might do it since the larvae must be soft-bodied. I was thinking I would use it then 24 hours later leech the soil with water to clean it out....but I wanted to check and see what others do. I used the "over the counter" wimpy housplant bug spray last year and it was worthless. Someone mentioned that if I cover the soil with sand it would keep the gnats from reaching the soil to breed, I tried that last year too, but that didn't work either.....because they're back! My 8 year old enjoys sucking them up with the little hose that came with my Mini Shark vaccuum (like a Dustbuster) but even she gets bored with that! I use Diazanon for hard-bodied pests like ants, beetles, etc...

Put an inch or two of sand on the soil....in a weeks time the gnats will be gone. The mommy gnats won;t dig in sand to lay their eggs, and so the life cycle ends with the ones flying around now.
Works wonders!

Hi Marc! I tried that last year, but they're back again. Perhaps I did it too late and they had already laid eggs. Milan had some ideas that sound a tad more lethal...LOL.....

http://davesgarden.com/forums/t/482480/

In another thread Capt found it to work.....

http://davesgarden.com/forums/t/473962/

Thanks all........I will soon be free from watching my husband and clients do the "gnat up your nose hack-n-dance"!!!! LOL I don't think I'll ever get that vision erased from my memory......I die laughing every time I think about it!

Karen

Well if you removed the sand and exposed the soil again your gonna get gnats again. The eggs incubate for only 10 days, so the ones you have now are not from last years parents.
Also make sure that each time you water you do not expose soil, as they only need a tiny way in to lay those eggs.

I used neem oil on my pot of Passi's this past week they were ate up with the nasty little things.
I let it dry out and then watered with a mix of water and neem oil that took care of them i lost a few leaf's but no harm done to the plant's.
Robbie

Also cut back on the watering a bit if you can . They really like wetter as opposed to drier soils.
I use the sand and it works really well. Malathion stinks so bad I can't stand it especially for indoor plants.

I will add to what Caron says. Let your plants dry out. Gnats will only lay eggs in wet soil, and the larvae will only flourish in wet soil. But you need to really let the top couple inches dry out. I had them all over the house for a while, so I just quit watering. If you have something that can't handle the drying out, try bottom watering it until the problem clears up. Worked for me. I am now gnat-free, but it took a couple weeks.

Wonder what adding a solution of H202 would do. Has anyone tried that? - -Pen

Well, I looked on the Net and found that H202 (hydrogen peroxide) is indeed a treatment for gnats. It will kill the larvae in the soil, but you still need to kill the adults to break the cycle. For exterminating the adults, it is recommended to use a soap spray (few drops of dishwashing liquid in a spray bottle). Spray the foliage and all around the planting area, and be sure to spray the top of the soil. Repeat until adults have disappeared.

For the H202 solution, I read varying recs. Some say a couple tablespoons per gallon of water, but some say as much as 1 part H202 to 5 parts water. I think I would prefer the weaker solution but continue it with every watering for at least 10 days.

As a side benefit, I bet you see your plants perking up from the H202. --Pen

While fungus gnats love wet soil, I have heard that submerging your plants in water for an hour or 2 (lonf enough to kill larvae) can help get rid of them - but you'd have to have a place where your plants can dry out quickly. I've never tried it...
Mara