Fungus Gnats

Lately my houseplants have been infested with fungus gnats. I've tried it all from the sticky traps, potatoes,l etting the plants dry out, to putting sand ontop of the soil, using houseplant insecticide spray, to quarantining all infected plants. They just keep coming back! I've done much research but I can't find a product that will kill the larve deep in the soil because this is where the problem lies. They multiply quickly in the soil and then as adults fly around above the soil. What an annoying sight! I do not want to throw away the plants but this is a last resort. Please help!!!

What are you using for fertilizer?

Al

First I would check on your watering--anytime I've had a problem with them I was keeping things a little too wet. Then to take care of the larvae in the soil you can use Bt (Bacillus thuringiensis). Here's one product that's available--there are probably other places that sell it too if you google Gnatrol. http://www.planetnatural.com/site/gnatrol.html

Get a package of "Mosquito dunks". Break one in quarters and put a quarter of one in your watering can. This will kill the larvae in the soil. I use sticky traps and Sundews (carnivorous plant) to get the adults.

Thanks for the replies and advice. I use name brand fertilizer, from Miracle Gro to organic brands. It's hard not to keep the soil moist with the tropical plants, which is where the problem lies. I try not to over-water, yet not have them dry out completely. The gnats are annoying buggers! I also use a plant watering probe so I can be sure when to water them. I will try both prodeucts and be back with results!

Fungus gnats LOVE organic fertilizers like fish emulsion and any of the 'meals' - cotton seed, blood, hoof/horn, feather, etc. I would suggest that you adopt any 3:1:2 ratio fertilizer like MG or Peter's 24-8-16, MG 12-4-8, or Foliage-Pro 9-3-6 (very good because it contains ALL the nutrients, including minors, and even Ca and Mg, which most solubles lack).

I would also dispense with any inexpensive moisture probes. They don't measure moisture levels, they measure electrical conductivity and are better at detecting fertility (salt) levels than moisture levels. Illustration: Dip the probe in a cup of distilled water & it will read DRY. Add a tsp of salt, and all of a sudden the water is wet. Feel the soil at the drain hole, or insert an absorbent wick into the drain hole, when the soil there, or the wick feels dry, it's time to water. Soil feels dry to the touch at 40-45% moisture content, but most plants are able to continue to extract moisture from soils until moisture is locked too tightly in particles at about 30% moisture content. This gives you a considerable buffer between when soils FEEL dry and when they actually ARE too dry, and should act as a stand-alone cure for your gnat problems.

Al

Al,
Do you work with plants for a living? You are very educated on the topic and I have many more plant questions to follow. This is my first year where all summer I've aquired a large collection of unique plants and it's my favorite hobby to care for them and watch them grow. The houseplant insecticide spray only killed the adults above the soil. Sand did not work so then I used Yardsafe ceder granules ontop of the soil. Although this product is for the yard, it's been working and I guess suffocating the gnats below. The product is for the yard but it works and my plants are slowly growing again and looking better. The plants without granules are infested with the gnats.
I'll try the probe test with water and salt. It made a great gift but I was unaware it is that deceiving.
I have a few unidentified plants I'd like to post pictures of if you can help name them for me!

I don't work with plants for a living, but in order that I might be reasonably sure I'm making the right decisions about the plants I grow as bonsai (and all the other plants I tend), I've dedicated a considerable number of years to learning about their physiology, and the various areas of science that relate to their care.

FWIW - I don't think the cedar mulch is suffocating the gnats. The natural bio-compounds in cedar (terpenes, cedral and camphors) act as a temporary repellent.

If I could make an observation: You can advance your growing abilities considerably and reduce your level of frustration considerably if you take some time to learn a little about soils and how to make a good one. Whenever the problem is not light related, almost all problems you encounter in container culture can be traced directly to the choice of soils or involve soil choice in large part.

For more details: http://davesgarden.com/community/forums/t/796311/

Al

WOW thanks AL I learned a lot too, I'm have the same problem .
Thanks

Well I live in Northeast PA so recently the weather has quickly become cooler.in mid summer almost every plant I had was completely infested with fungus gnats and every plant was slowly dying! It was a nightmere! Today I cannot find one gnat and the plants are beautiful!
My crazy method worked of isolating the plants, and pouring 1-2 inches of yardsafe granules ontop of the soil. The product is for the yard but it works on plants! I also power washed the top of the plants with a hose and later sprayed the plants with insecticide spray to kill any adult gnats on contact. I also think the change in temperature with less humdity helps. I will never water the plants too much either to avoid them coming back!

Antoinette

Al's right on. But if you're still having a problem, the traps that work best are the ones that plug in with a u-shaped fluorescent, under which you slide a sticky paper. When it's dark, they're attracted to that light, and will get stuck. They actually work very well. Worst case scenario, you can try a 'screntch' which is basically spraying the soil until it's a little bit drenched with a pyrethrum insecticide or something like that that's labeled for indoor use.

AL said to get the Gnatrol , he gave the web site well they have stopped making it .
Now I did the play sand works while you have in on your soil , a few things wrong some plants get root rot sand keeps it wet so make sure you don't water them untill you check , than to check soil you move the sand now there is a opening for them . after a month ,the work getting the sand out if you only have a few plants thats fine. Than as soon as the sand comes off one or two might still have some and you start over .
GOD I HATE THEM

Mosquito dunks have the same stuff in them as Gnatrol, those are usually fairly widely available.

Ecrane3,
Can i get this dunk at home depot or lowes ?

Maybe, try local non big box centers. I get mine at Adams in Poughkeepsie. They really work.

Around here they usually have them at Lowes & HD but I don't know if that would be the case everywhere or not.

I tried everything I could think of or read.. My gnats just wouldn't go away. I have alot of house plants... so as a last resort, I spent an entire weekend... baking new soil at 300 degree for two hours, being sure with a meat thermometer that the middle of the soil had reached 180 degrees... I re-potted every single plant with the new, baked medium and though it was alot of work, I am proud to announce that I am GNAT FREE for about 3 weeks now..

Note: Be sure to wash all the old medium off the roots, but be prepared to put it in the new medium immediately. Also be sure that your soil/medium has completely cooled before you use it.. I'm sure 180 degree soil would surely kill a houseplant.

I have my home back.. and I can drink a glass of soda without gnats ending up in my glass. : D