I’m hoping folks can help me with advice on if/how to execute an inarch graft to try to save a ~5 year old apple tree.
The tree is Cox Orange Pippin on Antonovka from Fedco. The location is southern Maine (z5a), in a site that I would say gets at least 75% sun on average. The tree grew well from the start, fruited 2 years ago despite its youth in the really good apple season two years ago, and put on around 18" of new tip growth last year.
As I was putting on the spiral wrap last fall I probed for roundheaded apple borers, which are very common here. I found no sign of them, but I found that the bark was dead nearly all the way around. After the snow melted I pulled off the wrap and found the dead zone had extended surprisingly far up the trunk:
There is only one small area on the circumference where there appears to be any life in the bark extending down to the root, on the left side of this image (where I nicked it in a couple places with my knife:
It’s not slimy, moldy, blackened, or otherwise unusual in appearance; it just looks like ordinary fungal decay, as if it were a piece of firewood I stuck in the soil. There is no obvious sign of the graft union, so I can’t tell if the rot is confined to the root or otherwise related to the graft. Of the 40 or so apple trees I have planted, this is the first time I have seen an apple tree root rot without any obvious injury - usually they are amazingly resilient; they can be chewed up by borers except in a couple narrow strips and in a few years they overcome it entirely, but in this case it’s as if whatever immune system the tree has just wasn’t functioning. The only possible connection I can make is that the soil isn’t great; it’s a few inches of contractor’s loam over heavy blue marine clay, but it’s on a pretty good slope so it’s never soggy or in standing water, and I have other trees growing nearby that don’t seem affected. Plus, last summer was extremely dry so it seems a strange time to get a moisture-related rot issue.
Is this spontaneous overwhelming rot of an apple tree root a known problem in the Northeast?
As to a possible rescue, I have a spare B118 rootstock that I flopped down in sawdust last spring to stool some additional roots from; I’m contemplating whether I should dig it up, curve the root around the base of the tree, and graft in the multiple small stems above the rot line:
Unfortunately the sawdust insulated the soil beneath, and the root is still firmly frozen into the ground. However it’s supposed to break 80F for the first time tomorrow, so it should melt out soon. But my instinct is that this tree is probably toast, since I don’t see what would keep the rot from continuing to overwhelm the living tissue.
I would very much appreciate anyone’s advice on what type of grafts to use for the inarches, or whether I should save the trouble - thanks!