Hydrogen Peroxide in Water

[Undergrounder]

I find it really hard to time the watering of all my plants, since this summer has been the coolest, wettest for decades. In short, im having general problems with root rot and until i get the watering right, i want to help the plants out with some kind of 'edge', a fungacide or preventative to help me out a bit

I tried a systemic fungacide recently, but that's super expensive and i want to save the bulk of it for the true winter.

I have tonnes of Mancozeb, but that's more for leaf spot as i understand - but would this work for root rot as an additive to general watering?

Also i have tonnes of Hydrogen peroxide, which is cheap, so could i add a very dilute amount to each watering to help? Although i've never heard of anyone trying this before.

P.S I did a quick search and apparently people DO use it, although more commonly in hydro setups.

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