Just curious, why are you going crazy, i thought these bugs were harmless. Lol.

I've never had the problem, but if i did i would just bring in a couple of Drosera capensis from outside and put them with my Phals.

Fungus gnats thrive in a moist environment, so it's usually recommended that you allow the plants to dry out a bit more than you normally would... but that applies to most other types of houseplants, and I'm not so sure it's a good idea, depending on how you must water or mist your orchids.

I usually swat the adult gnats to get rid of them, and use Schultz's 3-in-1 spray to kill anything else. I haven't had a fungus gnat problem with my orchids yet, but I experienced a swarm of them last winter in my hippeastrum collection. I'm sure there are countless other sprays or homemade mixes that would work, and be more gentle, for orchids... anyone?

Yes, let them dry out and buy some yellow sticky tape which will catch them. It is safe for indoors and works well.

Arthur they can drive you nuts! They don't hurt the plants, but who wants these pests flying around in your face. One year I bought a few Venus fly traps hoping to catch them, but they died. Sticky paper works.

Jane

Arthur, they are harmless, but they are incredibly annoying. I've had to control massive outbreaks in office environments and let me tell ya, the people having to live with it loose their patience really quickly!

Ok, quick and easy gnat control 101:

1. Remove the top 2 inches of soil. This is where the gnats live and breed. Remove that and you are removing the pest.

2. As Jane and Jodik mentioned, let them dry out more than you normally would to dehydrate larvae.

3. Sticky yellow traps: These are primarily monitoring devices. IME, they can really actually CONTROL an outbreak only if two conditions are met: The outbreak is isolated to the plant the trap is in, AND the outbreak isnt that bad. In all my experiences with gnats and the traps, they aren't effective in eradicating the problem completely, just keep it down. Much like releasing beneficial insects. You cant rely on these as the only fix!

4. Most effective method: completely repot the plants into all new fresh potting media, removing all old media. Let the orchids sit unpotted for a while to allow it to dry out (i'd be generous and say a day).

5. Drench the potting media with a horticultural oil solution. Or in the alternative a solution of dish soap (Ivory, palmolive, etc...) There are also harder chems you can use. Merit(imidacloprid) immediately comes to mind. Gnatrol also works. Though I'm not sure if you need an applicators license for these. I get mine through my work.

6. larvae are feeding off of fungi in the soil. treat the potting media with a fungicide to kill of the food source.

Good luck!

Mosquito dunks contain BT, bacillus thuringus, which kills the larvae in the medium. Follow the directions for soaking the dunks. It takes a couple of weeks to get all the larvae and have the gnats disappear.

BT is not an insecticide and is not poisonous to animals or humans.

Gnats are too small to trigger a Venus fly trap, but as someone mentioned, the larger sundews (drosera) will catch a lot of them. Butterworts (pinguicula) are also good for this. You'd want to do a little reading up on carnivorous plant care.

I, too, have both heard and read that the mosquito dunks you buy to control the larvae in small ponds and water features work very well to eradicate fungus gnats in houseplants. I can't remember exactly what the mixture is, but I recall something about using approximately a quarter of one dunk dissolved in water and used on the plants when watering.

I would have used this method, myself, but I could only find the dunks in packages of more than one, and they were outrageously expensive! Since I don't have a pond or fountain to use the extras in, buying more than one dunk would be silly for me to do.

My point is... it's an easy and effective way to get rid of the gnats!

Cannot imagine clouds of the little flies, i've only ever seen a few around and in my Phal. collection and do not know how effective a sundew or two would be.

Here is a link to Petrichor's blog where he discusses an American sundew which he grows to perfection. That means absolutely no care!

I grow Drosera capensis which is supposed to be and is (in my conditions) the easiest one of all.

Here is a link that might be useful: Petrichor's blog (on sundews)

OMG Arthur, I've seen yellow sticky cards where you cant see anymore yellow, infestations can get so bad!! Be glad you haven't seen that cloud!

Ok, this weekend I'll go out to Home Depot in search of mosquito dunks! Seems like the best solution for me. Here's hoping!

Here is a link to Gnatrol giving the life cycle of the fungus gnat. Anytime you use a peat based mix for houseplants you are reintroducing fungus gnat eggs to your environment. Fungus gnat eggs survive eradication in the peat unless it is sterilized with heat or you use something like the Gnatrol.

You can also harvest fungus gnat larvae by inserting a raw potato, think French Fry, into the media. The larvae will swarm to eat the potato instead of the roots and you can scoop them out and toss them. Move the potato around the pot after each harvest.

You can also put a grit on the top of the media to keep the gnat from reentering to lay more eggs. If doing this, you need to bottom water the pot to keep the top dry.

I have never found larvae in bark or sphag but anything with peat they love. I use the fine coir if I have a terrestial and my house plants are potted in a fine pine bark.

My seed growing days taught me to hate fungus gnats and how to torture them to death.

Brooke

Here is a link that might be useful: fungus gnat control

Thank You, Brooke! That link is a keeper!!

--Stitz--

Mine came in when I brought the plants in for winter. The sticky traps worked to keep them in control. My plants are quite dry when the heat is turned on and they disappeared. I'm sure dryness works the best. I noticed a few this week flying around the Phals. Not enough to annoy me...yet.

Jane

Have had this problem - I tried a number of cures - for some reason the last few years they are a problem everywhere around here.

I have tried gnatrol, mosquito dunks in the water, mosquito bits in the top of pots ( did help ), yellow sticky tape, potatoes slices, and pouring hot water through the pots, all with limited success.

You are looking at a beast with a 7-8 day egg to gnat period. What you see is just what is flying. The person who suggests removing the top layer of soil is correct. I repotted everything. However I found the reinfestation was caused by one plant whose pot was alive with ugh -- getting that taken care of cured about 90% of the problem.
You seem to have identified the culprit, so brace yourself and completely repot it. In fact if you have a small collection you might want to repot them right now. Next mosquito bits in the top of every pot, this will eventually help. Finally evaluate your watering- no standing water, let the soil or mix dry out, especially the top. This gets rid of the fungus in the soil which they feed on. My plants are a lot drier now - but when I water - I really soak them. Now those bugs are living in your house drains - hate to tell you. Go buy a bottle of chlorox and pour about a cup down every drain then flush with hot water, cleans the pipes. Remember you need to be persistant repeat in a week. All of this should get it under control.

I did have some luck with potatoes, but again you are not killing the larvae. Same is true of the sticky traps. Mosquito bits were available here at Lowes and they have the bacteria which does in the larvae. What eventually worked for me was getting rid of the ones in the "source" plant, the mosquito bits (little pieces of mosquito dunks) and changing my watering practices. Now if I could just get rid of the critters outside.

Would you share your source of information about the fungus gnat larvae living in your drains please.

Brooke

The mosquito dunk method will get rid of them almost completely. I soak one overnight, use the water on the plants and within a couple of weeks they're gone. Repeat a few times. Been doing this for a couple of years now. In fact, they worked so effectively I didn't have any gnats to feed my CP's.

Brooke,

I don't know what Pamela can provide, and I can't provide actual literature, but i can tell you its common knowledge for those of use who deal with them on a regular basis. I don't know about drains, but they absolutely can live in places like HVAC ducts in your home/office where a/c condensation collects. As stated before they live and breed in wet environments, which HVAC vents easily provide. In office buildings, they can spread from plant to plant through the ventilation system. Actually, I think there was an airport in florida that was having a horrible infestation of fungus gnats in their ventilation system.

Terp I have dealt with fungus gnats and their larvae for many years and know how to get rid of them.

You can eradicate the eggs by sterilizing the peat based mix with heat, you can kill the larvae while in the juvenile stage before they leave the media and you can kill the adult before it reenters the media to lay eggs. The adult gnat does nothing harmful to the plants, their only purpose in life is to fly, have sex, reenter the media to lay their eggs and then die. Or fly up our nose.

If buildings in FL have fungus gnat larvae living in the HVAC systems, then the mold in the system is a health hazard to the human population. I would also be surprised if the larvae come equipped with waterwings.

Brooke

I swear, fungus gnats are born pregnant.

Wasn't trying to be condescending, brooke. i apologize if it came off that way. I put it the way I put it because I'm a trained horticulturist and I deal quite heavily with these pests on a daily basis in my job. Like you I know all about their life cycle, what damage they do/don't do, and how to eradicate them.

As for mold/fungus levels inside you mentioned, thats just not true. You'd be surprised at how low a level of food the larvae will survive on. One of my tips above was to treat with a fungicide to cut off their food source. But this alone won't fix the problem and must be used in conjunction with other eradication measures. I can't tell you how many time I've treated with Subdue, Cleary's, and Banrot (all fungicides) alone due to time constraints and still had the buggers live. Lowered the populations a bit but they were still a nuisance. So just a little bit of fungus in the ventilation system (not necessarily mold) will be more than enought to sustain a population breeding in a/c condensate.

Read this. Doesn't refer to breeding in ventilation but talks about spreading therethrough:
http://www.johnson-group.com.hk/eng/news.php?type=news&news_id=17

Regarding sterilizing the soil, you're right it can kill anything that is in the soil, and basically baking your soil is always a good practice. BUT from my own professional experience (and i'm not trying to trounce your own experience here...), it might stave off an infestation in the short term, but mycorrhizal fungus, their food source, will grow in the soil again...quickly...brought in by the plant itself and spores from the environment. If you have any residual gnats around, reinfestation can follow pretty quickly.

Have you learned enough yet, Deb? :)

I'm not a horticulturist but I play one on TV.

I'm not surprised a fungicide will not eliminate the problem. Fungicide will not kill the eggs even if it does kill the larvae.

The way to stave off infestation is to eliminate the problem and not reintroduce fungus gnats to the environment. Once eliminated, they don't come back unless you bring them back in.

I sterlized my potting media once in the microwave. The smell was so bad my husband suggested I not do that again. Thus my quest through the life and times of fungus gnats. If I couldn't have eliminated fungus gnats I would have given up on growing anything inside.

Brooke

"The smell was so bad my husband suggested I not do that again."

LOL! Is that the polite way of putting it?

One quick point: you'd be right about getting rid of them in the first place, but easier said than done. IPM 101: In most cases, you can never fully eradicate a pest, just control its population. Particularly when they are crawling around places other than the plants, like ventilation or benches.

Lets bring this thread back around, i think we're chasing our tails a little bit, and I kinda feel like you've gotten a little defensive over my answer to your question and now we're in an odd debate we're both right and yet somehow are disagreeing. I dont' even know what we're disagreeing on. So, lets start over: Yes, gnats can and do breed anywhere there's a moist environment, inlcuding ventilation and possibly drains. I'll leave it at that, and you can take from it what you will :)

kumbaya and so on and so forth :-D

hello, everyone, here is a link on gnats, drain flies etc which i found interesting http://www.pestproducts.com/fliesdrains.htm
i read somewhere (I tried to find the site but unsuccessful) about growing scented geranium to help control these flying gnats. anyways, i bought a scented geranium this summer and kept it in the sunroom. about a couple of weeks of having it, i had no more gnats. the other thing i found interesting was that a week ago i decided to cut down the scented geraniums to control its size and to get some cuttings to share, i found whiteflies all stuck to the fuzz on the leaves. they could not fly off. i was able to wash them off under the tap. i had not notice any white flies on any of my other plants (I have a non-orchid flowering plant which is very prone to getting whiteflies - very easy to tell when it gets it - the leaves all curl up and droop). in any case, no whiteflies on that plant. the scented geranium was quite unaffected by the whiteflies. i am quite surprised by how effective it was. the one i bought has a faint rose scent when the leaves are rubbed.
sue

Thats fascinating sue! Wish I coud say I had the same experience, though. We had a very minor fungus gnat outbreak in our greenhouse at work last winter, and a third of the greenhouse at the time was scented geraniums. Though to be fair the outbreak occured on the next bench over so the geraniums could possibly have had something to do with keeping the outbreak from getting worse than it did.

hello, terguy, my sunroom is not very big: 12'x14'. i still have a few gnats here and there in the house - i have plants in every room of the house. I have taken cuttings of the scented geranium and a citronella and put one in some of the rooms other than the sunroom. i am curious to see if i get less gnats.
sue

Update: well, things are a bit better (definitely not worse) I gave everything a liberal spraying of insecticidal soap and have since let everything dry out as much as I can without killing the plants. I've had a few days of seeing not many at all... then today I saw a few... I guess they hatched. I'm going to stick the potato slices in the dirt tonight (as recommended in this thread) and I'm going to spray them with insecticidal soap again. My local HD didnt' have the mosquito dunks so I may try another store this weekend if I think I may still need them. I'm interested in learning more about the scented geranium as mentioned above.

Thanks again all!

If you have any pet stores in the area that sell pond supplies they will probably have them.

Brooke

For me, sundews worked amazingly well. Don't know which species of Drosera I had, but got it at Home Depot. Was very easy to grow just by keeping it in a tray of distilled water and a light fertilizing once a month or two. Mine even bloomed. It was absolutely amazing at catching fungus gnats on my grow table of orchids. Every leaf was covered with 2 or three gnats in a few weeks.

BN

Just wanted to update all of you: Things have gotten much better. As suggested, a few weeks ago when it was still somewhat warmer out, I removed the top few inches of soil on my two indoor non-orchid plants and put fresh dry soil on top. Since then I've tried to give the soil time to dry out between waterings. The results have been good. I still see one or two gnats now and then, but its way more manageable. Thanks all for the wonderful help!

Glad it worked for you Deb! I'd give it a couple more drenches a week apart to help get rid of any larvae that might have hatched.

I don't know if "fruit" gnats are the same or not, but this summer I was over run with gnats. Now that the weather is cool, they are pretty much gone. But to handle this in the summer, I took pint water bottles, put in about 2 inches of water, 1 tbsp. of apple cider vinegar and and few drops of dish detergent. I then rolled a little piece of paper into a cone and placed it into the top of the bottle. The gnats went to the vinegar smell, went down and the soap grabbed them, they then drowned. I had these traps in several places around the kitchen. I still have one out, but now the problems seem over so I will dump it and throw out the bottle. Once all the adults are dead there shouldn't be more young.

If you put sand on top of the soil of regular house plants it will get rid of the gnats in a few days. You should use the decorative sand, the kind they use to put on top of cactus soil. Its basically beach sand without the salt in it. Works like a charm.

Purchase some Gnatol. Works all the time.

I'm surprised no one has mentioned using a fan.
Oscillating one is best.
Doesn't get rid of them completely but its so much easier that you can live with the few that may remain.
I hope some of you will try it.
Best wishes, Barbara.

You can also make a 3% hydrogen peroxide solution in water and pour into the soil of your plants. This is best done after you let the soil dry out I believe. Hydrogen peroxide kills the fungus gnat larvae in the soil, which is where they breed. This mixture does not harm your plants either, as long as you do not over do it. See this video: https://youtu.be/QI4p5T9n6Rw?t=29