The strange case of the rotting root

General Fruit Growing
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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!

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I saw this on another topic.

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Wow, that’s nasty - looks like someone took a torch to it!

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Google crown and collar rot and look at the images. Looks maybe like your tree.

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It is easy to find instructions on inarch grafting. Your best hope is to get a another apple tree on 111 rootsock, plant it as close to the tree as possible and graft the trees together by merging them a distance above the diseased rootstock. When I’ve done this, I’ve left a nurse branch on the new tree. If you could find a Cox on 111, or something as vigorous, say B118, you could leave the entire tree in case the trick fails and trees fail to merge. The new tree could replace the old and you save a season.

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Thanks to folks here for the advice; this evening I gave it a shot. I started by digging up a sprawling B118 rootstock that I had flopped over in some sawdust a year ago:

I excavated around the base of the afflicted tree a bit and buried the rootstock in several chunks around the root (the dog helped):

Then I sliced the scions diagonally with the cut faces inward, made two parallel cuts in the healthy bark above the rot, and lifted the bark from the bottom to make a flap. The bark wasn’t slipping yet so I excavated with a chisel down to what seemed like the usual rind graft layer, fit in the scion, and secured with a couple of staples.

On one of the larger stems I cut a tapered groove in the bark and a matching taper on the scion, and stapled it in instead of trying to make a single planar interface:

I left a couple of the twigs ungrafted per Alan’s advice, figuring if the tree dies (which seems likely) I can graft to them next year. I smeared the junctions with bowl ring wax, and soaked in the new roots with five gallons of water. At the end it looked like this:

I’ll post the results as things shape up this spring - thanks again!

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Ben, how did your tree and inarch graffs do? Any success? Sue

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Sue - thanks for asking. The arch grafts didn’t take, but the tree survived - so far. The rootstock leafed out, and the tree leafed out, but it became clear after a year or so that a couple residual threads of living tissue in the original trunk were carrying the life up into the branches. Over the next couple years the living part of the bark tried to wrap back around the trunk, which looked funny because it was well under 50% of the circumference.

Since then, branches have started dying off the tree, seemingly due to some kind of black mold or fungus attacking cut surfaces; I haven’t seen anything like it elsewhere but have it in at least two trees, one of which died completely. This one is down to two lower branches; I’m not sure whether it will survive.

All in all, apples and peaches seem much more susceptible here than on the island where I grew up, even though we’re only 10-20 miles away from the ocean. At some point if I have time maybe I’ll find our extension agent and ask about black mold on apple trees.

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