Seems I have a light infestation of fungus gnats on my arundinacaea. Nothing major at all, but being in a small closet grow space (above the wife’s clothes haha) I’d like to handle them as fast as possible…

I’ve read up on them and it seems a solution of water and hydrogen peroxide kills the larvae instantly.
(I plan on repotting with small pebbles to help drainage and perhaps a casing layer of sand/pebbles on top to keep moisture down)

is peroxide phalaris safe ?

It should be OK, if there's no detail in the source of the peroxide treatment idea you can refer to hydroponics guides for appropriate concentrations. Diatomaceous earth can be added to the soil as well. F*** those little blighters!

What is the temperature range like where you are? Can't you grow P. arundinacea outdoors? (Maybe you posted something about your indoor grow decision, but I certainly forgot the exact details rn )

My phalaris plants had a horrible issue with fungus gnats a while back as well. They were originally outside, but I brought them in and noticed gnats everywhere shortly after.

At first I tried watering with neem oil, and it worked a little, but the gnats were still around. So then I added some yellow sticky traps, which caught dozens of gnats, but this too did not get rid of them completely.

So I decided I needed to go all out.

To finally get rid of the gnats I watered with hydrogen peroxide (1 part 3% hydrogen peroxide and 4 parts water), added several yellow sticky traps to each plant, and added a 1-2cm layer of fine sand to the top of the soil. After adding the sand I dusted each plant with some diatomaceous earth. Then I would water with neem oil weekly. After about 2 months I stopped seeing gnats everywhere.

Once the gnats left I stopped watering with neem oil and added some mycorrhizal fungi to the plants. They are all looking good now and doing fine.

Best of luck with getting rid of those gnats

I will likely hit it with a 1:4 peroxide:water solution first, maybe a few times and see what happens.
It is going to be an outdoor grow but this was just a test tbh.
If the peroxide doesn’t work then I am just going to clip all the material and put it back into dormancy/outside.
Braindrops I would go that route if it were going to be an indoor grow but, I want to put as little effort indoors as possible right now.
Might even clip it regardless as I could definitely use the space ..

"1:4 peroxide:water" is ambiguous without stating the starting concentration of the peroxide (because there's no way you'll get hold of 100% hydrogen peroxide!) Anything above 29.9% is impossible for the general public to get hold of in EU countries nowadays but hydroponic suppliers used to carry 35% stuff routinely (from what I saw in the UK); I don't know what the rules are on the other side of the Atlantic - and the impression I get from Australia is that strong peroxide isn't going to be readily available there either.

That said, whether you're using a 29.9% or a 35% solution won't really make that much of a difference. Using something weaker would entail diluting it less. (Obviously)

Good point downwardsfromzero. The hydrogen peroxide I had used was 3%. I will edit my post to include that info

I actually had no idea of that side of hydrogen peroxide. That’s really interesting. Definitely deserves more research.

After looking into it a little more, I used a 1:2 ratio with a 3% hydrogen peroxide.