Q.I have root rotting in my apple trees, I want to ask what ratio of water and hydrogen peroxide is needed to prevent root rotting?
and what concentration of hydrogen peroxide should be used (3% or 35%) along with water?? Root Rotting

Certified GKH Gardening Expert
I don't recommend it for preventing it, so much as I do correcting it. If you want rates for prevention, I would go with 1/8 peroxide to 7/8 water once per month. That should be sufficient without burning the plant.
Use only 3%, as 35% is very hard to get down to manageable levels in the amounts that you will need.
For treating it, you will use this 1 time at 1/4 peroxide and 3/4 water. Water in once, then once again after the soil dries completely or roughly a week later.
You can also use a combination of DOLOMITIC LIME and WETTABLE SULFUR once or twice per year to prevent and treat infections, and provide trace, and micronutrients to the soil.
This article will help you to care for apple trees: https://www.gardeningknowhow.com/edible/fruits/apples/apple-tree-planting.htm