Fungus gnats -- some good inexpensive ways to dispense with them - Orchid Board

cythaenopsis · #1 09-12-2011, 01:53 PM

I've got a fungus gnat problem. They were pretty much isolated to one room. My orchids were doing fine, showing no gnat habitation for many months... until now.

Apparently the gnats finally found the nice moist moss bedding of my phals and are having a party. My phals were just recently repotted, so I don't think there's any fungus growth. I had thought they only appear where fungus exists, but apparently they can do well in moist areas and even encourage the growth of fungus.

I've read up on a number of treatments. The two prominent ones are neem oil and GoGnats. I don't have a lot of plants to treat, just a half-dozen. I suspect neem is the more natural way to go about it, although I understand that it stinks pretty badly. Is GoGnats the better choice? Does this stuff last a long time? The smallest package of GoGnats I could find is rather large 16oz and is $25 shipped. With neem, it was 8oz for about $12. Recommendations?

RosieC · #2 09-12-2011, 01:57 PM

I like using Butterwort carnivorous plants. I've also tried Pitchers and Sundew but the Butterwort seems the best. Venus doesn't work on these tiny ones.

They don't get rid of them completely but I not only notice a couple when I water rather than them being anoying in the house.

I've not tried any chemicals because most of the advised ones don't seem available in the UK. I've heard that Mosquito dunks that you can buy in the USA for ponds are good. You put them in the watering water and it kills the gnats. I can't get them here though.

cythaenopsis · #3 09-12-2011, 02:05 PM

Thanks Rosie. I'd forgotten to mention that I'd seen mosquito dunks referenced before, but didn't see any details about how to put them to use. They're meant for applications to ponds and other large waters, so I'm not sure about how one would use them for plants. I'll have to do some further searching.

Bud · #4 09-12-2011, 04:26 PM

oils also attract fungus...
I found several good gnat killer from RepotMe.com...and I dealt with fungus by repotting and spraying the roots with physan20

Ray · #5 09-12-2011, 05:42 PM

If you focus on just killing the gnats, you're fooling yourself.

Where there are fungus gnats, there are both fungus and gnat larvae. It's a good indicator that you need to repot, as the medium is decomposing rapidly.

RosieC · #6 09-13-2011, 07:08 AM

Quote:

Originally Posted by Ray

It's a good indicator that you need to repot, as the medium is decomposing rapidly.

However once you've got them, and unless you kill all the larvae then you will probably have them even in fresh medium. They are in all of mine including the recently repotted (into very fresh medium) but I know that unless I get rid of them in all plants at once they will just settle back into the repotted ones soon after the repotting.

Before I had the carnivorous plants even my ones in Lecca would have them coming up out the pot when I watered.

As Ray has said the only way to completely get rid of them is to kill the Larvae as well as the flies. If I could find a good method of that in the UK I would, for now I control the numbers rather than irradiate them.

Paul Mc · #7 09-13-2011, 08:34 AM

I used the mosquito dunks/bits and while it seemed to make quiet a dent last winter, it never fully solved the issue. I think Rosie is right in that if you see an issue then you need to repot all of your orchids to get rid of the infestation. Repotting only one or two will do you no good if they are swarming your entire collection. Luckily, this was the spring that I repotted all of my orchids. So we'll see if they come back or not.

Eyebabe · #8 09-13-2011, 08:49 AM

I put the dunk bits in the media AND you can also put them in your water prior to watering. Helps kill the larva.

Neem oil will kill the flying ones.

They are a pain tho

cythaenopsis · #9 09-13-2011, 11:53 AM

Tenacious little buggers aren't they. My phals were perfectly free of them since last October when I first started my collection. I'd spotted a few flying around a couple of plants I had in another room, and I didn't think they'd migrate. But these adults are pretty fast. I've discovered them exploring other parts of my apartment. They eventually found my orchids and decided to start a small colony there.

Well, one phal seems unaffected right now; it's just the two older ones, which I recently repotted. The roots had a little bit of rot on them (black segments), and so I cut back most of it (not all, as I didn't want to take out long healthy root segments). That must have allowed for enough fungal growth to support the gnats. I'll have to get that Physan 20, apply it to the roots, re-pot and apply it to the moss.

Is the main problem the moss being damp for long periods, providing an ideal environment for fungal growth? If so, I can see why some folks are eager to switch off the moss to bark potting mix.

silken · #10 09-13-2011, 12:34 PM

My friend used a shot of Malathion (mixed in water of course) flushed thru her media and it pretty much did it. It was on Phals and the plants are fine. I know some prefer a less chemical approach, but if you want to eradicate, rather than just reduce them, it worked well to kill the larvae. Then a mist of it will kill the parents, or you can try yellow sticky paper. However, the parents will continue to lay eggs in the media and you may have to flush with Malathion again. It stinks terribly, but works. If it was me, I would leave the media well soaked with Malathion for an hour, then flush with clear water. It should kill the larvae pretty much on contact.