Fungus gnats infestation
 

For many years I never had any other plants but orchids, and mostly Phalaenopsis, simply because they were the only ones that survived :biggrin:

So this year I decided that I'm going to learn about plants and really do an effort. I started by buying one plant (I thought let me not do more than one at the time) last May and I got a dieffenbachia. I thought it handy to get one of these self-watering things (it's like a see-through ball with a stick that goes into the soil) especially for the extremely hot summer that we just had. Anyway that ball kept getting empty quickly and I figured this must be because of the extreme heat. So at one point during the summer I got all these little annoying fruit-flies in my house. They were constantly flying in circles around my face and just really annoying. I realized that they were in the 100's if not 1000's around the dieffenbachia. :((

By searching online I learned that they were not fruit-flies but fungus gnats. I was told that I should separate the plant from other plants, which I did. I also repotted it, got rid of all the soil and just put new fresh soil in it. I stopped the self-watering thing, I just try to keep it dry as much as possible. Oh I also put out fruit-fly traps, they caught a good amount of them.

Although there are not so many of these fungus gnats as there used to be, definitely a lot less, but they're still there. I also just realized that when I picked up the dieffenbachia from it's outside pot, it was full with flies on the inside of the outside pot (hmm, hope you understand what I mean). See I had put a layer of LECA on the bottom of the outside pot, simply because otherwise the inside pot (the one the plant is actually in) would sink down too deep, so to sort of make it come up a big higher. So around the Leca beads.... and all around the side of the pot it was just full with flies. I immediately put the outside pot out of doors (it's really cold outside 9C = 48.2F), and now the plant is just sitting on a plate.

The thing is...I suppose I'll still have to repot this plant again? I probably have to anyway as last time I used garden soil (which was the only one I had) and later I've learned this type of soil is not suitable for house plants. So I guess I better get the right type of soil this time. (I realize this has nothing to do with orchids, but if anyone has a tip, it's always welcome :D )

The other thing is: I did separate the Dieffenbachia from my other plants (orchids) last summer, but I think I was too late. See I've still got these annoying little fungus gnats flying around my orchids now... and I mean we're in October now. It's not a huge amount of gnats, but there's definitely a few. It's just annoying when I'm sitting at the table in the kitchen about to eat and then one is right in my face. Or when I'm watching TV in the living room. :(

Should I do something about them or would you say don't bother since it's not a huge amount of gnats anymore?

Mosquito dunks!! You let them soak in the water overnight then water the plant with it ..bye bye to fungus gnats. I buy the granules...I find them to be easier to use for this purpose. They are a beneficial bacteria so not harmful...unless you are a mosquito or fungus gnat. Water with solution a few times and they'll be gone.

One little caution...use the solution within a week because it does stink really bad if left sitting too long.

I buy my granules on amazon.

The organism in mosquito dunks is known as Bacillus thuringiensis israeliensis and is normally available in several forms at any garden center.

the gnats don't do much damage but just like butterflies and moths start off as caterpillars, fungus gnats start off as larvae living in damp soil. It's these larvae that are nibbling away at your roots and will do damage which you cannot see. The biggest concern is them spreading disease amongst your plants while damaging the roots.

Correct. They live off fungi growing on decomposing organic matter. when they have stripped that clean, they go after roots.

I just ordered some through ebay. Looks like they don't sell them in Australia. Sounds like it not only works for mosquitos but also works on fungus gnats.

Thanks for the tips about using the solution within some amount of time. I think that I'll cut up a piece ----- ie. divide it bit, and put pieces in a spray-wand container, and then spray the media with it --- letting the solution seep into the media.

I've searched online for these mosquito dunks and it seems like they don't sell them here in the Netherlands, or the "Bacillus thuringiensis israeliensis." It seems like I can only get it if I order it from Amazon from the States. I'm going to ask a friend who has more experience ordering from Amazon. I've never done this before.

---------- Post added at 04:21 AM ---------- Previous post was at 04:19 AM ----------

Hmmm, yeah that's the part I'm worried about. :hmm

---------- Post added at 04:41 AM ---------- Previous post was at 04:21 AM ----------

Thanks everyone for your replies.

The good news is that I just repotted the Dieffenbachia for the 2nd time. I realized that I made a mistake last time, I didn't use the right kind of soil. I used garden soil (I didn't know there was a difference but someone then told me that this is too acid) rather than soil for house plants. I flushed the roots out and sprayed them with hydrogen peroxide (I don't know if that helps but I just happened to have that at hand) and I repotted it. The Dieffenbachia is good now, as far as I know no more fungus gnats. The problem was this plant, this is where it all started. Unfortunately I learned too late that I should have separated it from the orchids, in order to avoid spreading.

OK..so the greatest news is that the fungus gnats are down to a minium. There really aren't that many left. But I know they are still there because there is always at least one flying around my head and up in my face. It must come from the orchids, as I said the other plant is good now. Plus I've kept it separate recently.

1) Switch to a less organic mix - Well, I've had this suggestion before, to use Leca balls. I think it might be something for the Phalaenopsis orchids that I've got. The thing is that I repotted all my orchids not too long ago, last summer, now the temperatures are less warm and I'm thinking if I would repot again wouldn't that put them through a more stress again? On the other hand I think maybe my mistake was that I added some spaghnum moss through the bark, maybe I should better have stayed off the spaghnum? At least in regards to the Phals.

But then I've got the other type of orchids that you don't want to let dry out completely, I've heard, like the Paphiopedilum. Not to mention the Macodes Petola that I just got... that one is sitting in spaghnum moss.

5) Get some carnivorous plants. - This one is interesting because I tried that last summer and the Sarracenia that bought died within a few weeks. I don't know what I did wrong, I tried to do exactly as I was suggested when I searched for the care online.

I'm glad at least it's just down to a few of these little gnats... but I'll definitely look into the Dunks thing, even if I have to order it from abroad.

Sarracenia are not well suited for growing indoors for a couple reasons, regardless of what any care instructions may say. If you want a carnivorous plant for indoor conditions, get something more forgiving that doesn't require a hard winter dormancy, such as Drosera capensis.