Let's first make sure what kind of critter you have. Fungus gnat adults are attracted to the organic based potting mixes we have, especially if kept nice and moist. It is the larvae that may nibble on plant roots along with the organic matter....the adults don't feed on anything, I don't think. They do NOT bite humans or animals. I guess I should say that they not only DO not, they CANNOT. Fungus gnats are not attracted to fruit juices or vinegar put out as baits.

Fruitflies try to find ripening or overripe fruit in which to lay their eggs. They also do not/cannot bite people.

There are also annoying little drain flies that can flutter around all over the place...but do not/cannot bite or sting people.

If you DO have fungus gnats, you should purchase some larvacide in the form of Gnatrol or even mosquito dunks you can dissolve in water. The active ingredient is the biological agent Bacillus thuringiensis var. israelensis (Bt-i). Used in your watering regime, this product will kill larvae. The adults live for about 10 to 15 days, so you will have to keep watering with this brew until you don't see any more adult gnats.

Be sure about what you are trying to control, though. Bt won't help you with anything but the fungus gnat larvae.

try the search function at the top of the page,

for:

indoor pests
gnats
fungus gnats
bug bombs
fumigation
indoor insecticides
soil sterilization
IPM
integrated pest management

and try it in each forum ... i dont recall if the search is specific to the forum.. or for all forums .... check it out ...

and try your county Ag agent.. and a master gardeners class ... if you havent done so already ...

ken

There are several ways to check and see if you are actually having a fungus gnat problem. The quickest and simplest is to pick out a plant ot two and unpot it. Look all around the bottom of the stems where the roots meet it with a magnifying glass. If you see larvae they likely are fungus gnats. rhizo is right, Gnatrol is safe and effective and will eliminate them. They can and will kill your plants if left to run amock, as well as slow any growth.

Here is a link that might be useful: Fungus gnat photos

I have been growing lots of plants from a seed, and using various store-bought soils like Miracle-Gro etc. In the past I have had problems with storebought soil and their guaranteed fungus gnats. So this time I looked up how to prevent them and went with the microwaving the soil method (50% power for 15 min) Nevertheless, it's so easy for even one to find its way in if someone gives you cut flowers or you open a window. So of course I got infested. It was crazy -- in no time I had tons of visible clear skinny fungus gnat maggots in the soil, not to mention tons of flying adults. Drying out the soil doesn't work b/c they can suspend their development to wait for moisture to return. Plus my plants were using a lot of water.

I tried everything else: dishsoap solution, BTI, hydrogen peroxide, rubbing alcohol, cayenne, etc. Nothing made a difference.

THEN I read about hot water. Yes, simple hot water! You might think it will damage/burn your plants but no, they tolerate it very well. What doesn't tolerate it at all are the fungus gnat maggots! If you don't believe me, you can test it yourself -- pluck a few out of the soil when they come to the surface at night. Put them in a dish and put some hot water on them. They die instantly.

How hot? Hand hot. In my apt, it's as hot as the water is allowed to get. But the temp is one that doesn't burn you but it's too hot to keep your hand under the faucet for more than 15-30 at a time.

To apply to plants, you dont need a lot. Just enough to cover the entire surface and take a few seconds to soak down through. With small pots, maybe a 1/2 cup or a cup.

I've tried this on all my plants (marigolds, irises, morning glories, vincas, four oclocks, mint, basil, pansies, petunias, impatiens, snapdragons, etc.

I was so excited about the results, I had to post -- this is my first post! Just a few days ago I had complete infestation in several pots (pulled out 20 maggots each and still had tons more writhing around) and tons of adults flying around. ONE treatment of hot water wiped the maggots out almost entirely -- there are even very few adults left now b/c no babies are taking their place. But I will keep it up in case they are laying any eggs. The plants don't seem to mind the hot water treatment one bit and I've already done it 2-3 times for many.

p.s. Yellow sticky traps work really well too to catch the adults and hurry the process along.

Just to clarify the comment above regarding fungus gnats not being able to bite. This is true of the adults, whereas 12 species of fungus gnat (LARVAE) have turned to a carnivorous diet and all 2000 species can bite through hard seed casings. The carnivors can penetrate the exoskeleton of insects.

@ORANGEUGLAD: Wow... this is the first time i've seen this solution. I've tried the same slew of options trying to get rid of the larvae and nothing has worked effectively. Before I shell out the $$ to hire an old priest and a young priest, I'll give the hot water therapy a try.

If this works, you'll be my fnukcig hero! :)

@orangeuglad: I have a whopper of an infestation and I'm hesitant to try and grow anything indoors these days. I'm going to try your microwave method with my seed mix and use hot water on my existing plants.

If anyone else is reading this, I have to ask: will microwaving kill all the beneficial nutrients/bacteria that come with my seed starting mix? Even if it does I'll still try it. Last week, a batch of eggs hatched and I woke up to thousands of gnats taking over my kitchen. I had to call an exterminator! So my indoor herb garden had to be moved outdoors. My plan was to grow lettuce indoors this fall but the thought of those gnats is making me think twice...

Where are people buying seed starting mixes and potting soil mixes that harbor Fungus Gnats. If just once I had purchased that stuff and had an infestation of these buggers I would not purchase that product again, and would alert others to that problem.
Hot water is used to kill unwanted plant growth ("weeds") so whether pouring hot water on a potted plant would not harm that is highly debatable. Water hot enough to kill the Fungus Gnat larva would be hot enough to do serious harm to the plant. Water not hot enough to harm the plant will not harm those larva either.
Microwaving a seed starting or potting soil mix will not do anything to the non existent beneficial bacteria in those mixes.
Understanding something about Fungus Gnats can help in the management of them.

Here is a link that might be useful: Fungus Gnat Management

brand.. you really ought to have started your own post.

why in the world.. is someone in presumably.. z10 .. grow things indoors ...????

i always sterilize my indoor potting media ... see link

pouring water that is hot enough to kill the gnats.. will probably poach the roots ....

ken

Here is a link that might be useful: link

Quite a collection of solutions to the problem! However, we have a winner.

Go with RHIZO. You won't be sorry. And if you call any horticultural extension office to ask what to do about fungus gnats, they will tell you just what Rhizo posted.

Actually, control of fungus gnats is much simpler than even purchasing an insecticide - you are overwatering your plants!! Allowing the container to dry between watering and/or repotting with higher quality, better draining potting soil will generally eliminate the problem. Also a layer of coarse sand on the top of the potting soil will discourage any egg laying by the adults, who only have a lifespan of about 7 days.

Ken: Sometimes people live in these things called apartments, especially here in Los Angeles :-) Of those people, some are lucky to have a balcony or patio, but unfortunately all I have is a sunny window and some grow lights. It's certainly not ideal but my addiction to fresh lettuce and herbs is too strong!

Also, starting my own post would have meant getting "use the search tool" comments. I did that, and this post had exactly what I needed and my only question was about the method orangeuglad mentioned.

MulchMama: I ended up ordering Gnatrol and it should be here tomorrow. Fingers crossed!

Gardengal48: I let my plants dry out completely, even removing them from their pots to double check. Then I let them stay dry to the point of almost dying. Sure enough, the gnats came back. Originally, I made the mistake of purchasing Miracle-Gro Moisture Control and that was a big part of the problem. The plants I've repotted in a locally-sourced potting mix have been doing great.