pretty much anything will kill fungus gnat larvae. My weapon of choice is Orange Plus household cleaner solution. Smells good, biodegradle. For me, it is available at my closest store (Wholefoods), but it may not be so easy to find depending on where you are. I dilute it down so the water is only just orange-colored. (no, no precise measurements....) I've also used knock out gnats. But like I said, pretty much anything will kill those things. Just repeat regularly for a few weeks.

I'm not sure if you can find it right now but if you can locate BT(Bacillus thuringiensis ) for mosquito larve you can soak the duks or pellets in lukwarm water for awhile then water your Orchids with it. This will kill the knat larva and it won't hurt your pets or children at all.

As for your Phal, sounds like your having trouble getting water into your plant. Either your not watering enough or something has happened to your roots to cause them to die off. I don't know what your growing conditions are but I have my phal in a mix of Sphag and lava rock in a plastic pot. With near 80% humidity and good air circulation I have to water every 3 to 4 days. You have good temps for spiking a phal and if its getting enough light it might need more water than 7 to 10 days. Your medium should get close to drying out but don't let it dry completely. If you think it's getting plenty of water then unpot your phal and check the roots for rot. If your roots are white and firm then think about increasing the watering. If you are growing in straight sphag and it is packed tightly then it may have been staying wet in the center and is now rotting your roots. If your roots are brown and mushy then you need to trim them off and search on here for info on saving rootless phals ( I like the s/h method myself). Then when you get new roots and you go to repot you should think about trying an airier potting medium or at least keep the sphag looser in the pot.

I agree with the BT advice. Discovered those last year. I put one in a pail of water, let it soak overnight and then used that water on the orchids. Within a few weeks, my gnats were TOTALLY gone. You can dry out the dunks and reuse over and over .

Kevin

Dittoes on Salvia's and Kevin's advice about BT. I got fungus gnats last fall when we had a week of rain everyday.

Fungus gnats eggs hatch in wet medium. The gnats are a sign that the medium is too wet.

Reading on the forum, I read about mosquito dunks (they were still in all the stores then).

Everything Salvia & Kevin said was true: soak, use dunks-water for watering, and in a couple of weeks, gone.

i have had good results using Physan 20 - my understanding is that gnats feed on algae and the physan kills the algae in the medium so the bugs have nothing to feed on. in a couple weeks they are all gone. also, i've read that the gnats do not harm the plant at all since they eat algae, they are just a nusance to have flying around your house.

Thanks all, for the advise! And Salvialvr, you were right-- I did have a root rot problem!! There still are several healthy ones (looks like enough that I shouldn't need to go the spag and bag route or anything like that) but I'm glad I caught it now before it got too bad! Hopefully things will start to improve now.

Happy HOlidays!!

Interesting, now know why I don't have gnats in the summer I keep dunks in the rainwater I use . Also Sundew CP work good,They take a little extra care but worth it .. Gin

I made another discovery this winter. I haven't used the dunks this year and have only noticed a few gnats. I think the Bug Geta Plus granules I've been using for my Bush Snail problem have also killed the gnat larva. At least that's the only thing I can think of that may be keeping them at bay.

Have you ever seen a gnat larva? They're really quite disgusting and quite large in comparison to the adult gnats. The first time I saw some they reminded me of maggots.

Here's a pic I found.

Here is a link that might be useful: {{gwi:209289}}

Yes, Kevin they are ugly! Have you ever seen the fungus gnat in the mix just before it emerges into the black adult? They are stark white - crawling through the mix - really creepy.

If anyone has house plant type plants and have fungus gnats annoying you, here is a fun way to harvest the larvae before they emerge to fly up your nose. Take a french fry shaped piece of raw potato, insert it into the potting mix. 24 hours later, remove the ff and you will see the larvae congragated around the fry. Spoon the live, wiggling larvae and pitch outside. It is really fun to toss them out when the temps are zero. Call me perverse! Reinsert the ff in a different area and in a few days, the larvae will be gone. The larvae prefer the ff to your roots.

Brooke

Sounds like you have a few good suggestions, Blossomgirl. One option that I haven't heard floating around is to simply repot. No chemicals needed. The larvae live in the medium. No medium, no larvae. You can also use a horticultural oil or insecticidal soap as a drench, and that should kill larvae and adults in the medium alike. The key is also to run your plants drier so you kill off the larvae that thrive in moist environments.

I would also like to correct a couple misconceptions I have read in this thread:
1) the larvae do NOT eat orchid roots or algae. They eat the fungus in the soil, nothing more. hence their name Fungus gnats. Proper treatments for commercial production always include a fungicide.

2) the presence of gnats does NOT necessarily indicate that the medium is too wet. Gnats are resilient little buggers and survive on less moisture than you think. I've had plants stay bone dry for a couple weeks, only to water and have them still be there. They can be pretty difficult to get rid of. The "too wet" mantra is a bit outdated, especially when you consider there are a lot of plants , like spathiphyllums and caladiums, whose preferred moisture level is definitely on par with ecology of gnat larvae. It makes sense if you have gnats on a cactus or other dry-thriving plants, but not with the majority of other plants we have in our collection

I'm not sure if they are as harmless as stated. I've read quite a few articles like the following. I'm not sure if I would worry if I only had big plants with big roots, but with seedlings it might be another story.

Here is a link that might be useful: Larva chomping roots

I wouldn't worry about big roots because the larvae have tiny mouths :>) I would worry about an orchid with tiny, thin roots. Thankfully, I've never experienced it with orchids.

If you have ever grown seeds and then the seedlings, inside, they can eat the roots off of seedlings. When you find a tiny plant, flopped over with zero roots, you can thank the larvae.

The eggs of fungus gnats can survive all forms of abuse and still survive. Bone dry doesn't bother them, they just wait for the media to become wet and warm enough to hatch. Freezing the media doesn't kill the eggs. Again, moisture and warmth and they hatch.

To sterilize a peat based media, you can either bake it, microwave it or use boiling water. That will kill eggs and give you an egg free media. My husband didn't take kindly to my baking and microwaving the mix - it stinks to high heaven.

Brooke

I micrwaved some medium once also and it took several washings to get rid of the stench afterwards! yuk!
sue

It was a great way to get my husband to take me out to eat - smell the kitchen up soooo bad it is nauseating.

Boiling water works but it takes a lot of water and is very time consuming for large amounts of media. The smell wasn't bad enough to get me a night out though.

Brooke

Hey, Brooke. I think termites have tiny mouths, too, don't they? :)

Interesting information about the gnats, Terpguy.

I just this minute discover gnats in my orchids! I am trying cider vinegar, ( about a half inch in plastic cup), with a few drops of dish soap, covered with plastic wrap secured with an elastic. I cut a 1/2 inch hole in the top and hope to catch some. Also, I’ve read that potato pieces, cut to 1/2 inch pieces and placed on top of my bark medium, so my orchids now have potatoes on them! Will post results in 48 hours.