The main problem with peroxide is that it is not specific in its action. It
will oxidize whatever susceptible matter that it touches. That can be a
fungus body, a bacterium, or plant tissue. The concentration we buy at
retail here in the US is 3% active peroxide. It is probably useful as a
disinfectant down to about 1%, but the effectiveness will decrease
proportionally as it becomes more dilute.
If you are targetting a pathogen, you run the risk of using up all the
oxidizing power on extraneous organic material surrounding the target.
Peroxide does have the advantage of decomposing into water. But I think for
horticultural purposes, killing the target pathogen is the primary intent.