A friend just lost a beautiful five year old Goldrush apple on M 26 to collar rot. Can he plant another apple, say on M111, in that same spot or would the phytophthora (collar rot) stay in the soil and kill the next one too? Many thanks for advice. Perimeter deer fence rules out other planting spots.
No expert here but after I read this article, I think it could be done. Your friend should improve soil structure and choose highly resistance rootstock like G 41 or G 935. Not M111.
If it were I, I would plant a new tre on a raised bed or a mound. G41 is a semi dwarf, a bit taller than B9. I like it. I heard good thing about G935, too.
I agree with @mamuang.
The mound is important.
At a large orchard where I once worked ,we had a low laying block of trees on 106 that had heavy losses from apparent collar rot. We made wheel barrow size mounds and replanted with m111 ,… Most of the replants grew well. Maybe 5% died again. We eventually got a good stand.
M111 is listed as “moderately resistant” to collar rot.
It is tolerant of poorly drained soil.
And just as importantly, it is widely available.