Winter Pruning to Control Apple Canker

Apple ‘Lord Clyde’, before winter pruning to control canker

One of the trees on the Plot #79 allotment orchard – a Victorian-era heritage cooker from the Stockport area called ‘Lord Clyde‘ – has developed an unfortunate case of apple canker over the past growing season.

Although canker-infected trees can survive many years and still produce fruit, the canker will eventually kill off entire branches and in the meantime, those weakened branches can be prone to wind damage, possibly ripping off, or falling and damaging lower branches. Better to remove them and let the tree re-grow healthy stems to replace them. Apple canker can also spread from tree to tree if the fungal spores are carried between them, so again, it’s best to deal with the problem as early as possible.

As per the maintenance record for the tree, I first noticed the tell-tale symptoms of apple canker in June last year. I removed the infected material at the time, but it seems the infection had already spread to other parts of the tree. Only one thing for it now: major surgery. Winter is an ideal time to address this sort of issue – with the tree’s structure laid bare and every canker lesion clearly visible – by pruning out the affected areas.

Here are the pics of the apple canker lesions, showing typical symptoms: sunken, hollowed-out stems and that reddish-brown colouration of the infected material:

I’m not sure whether the fourth photo shows a wound that is definitely cankerous, or just a physiological problem caused by the tree guard having slipped over a pruned stem, trapping moisture around the cut end and causing some die-back. It doesn’t look great, either way.

Thinking about the position of the canker lesions on the tree, it was clear that I would have to prune out a significant part of the tree’s central structure. Generally speaking, pruning manuals advise you not to remove more than around 20% of a tree’s bulk in one season to avoid excessive re-growth, but that wasn’t going to be an option here. The question was, how much to remove?

I identified a choice of four cut-points, as shown:

(please excuse my camera’s decision to auto-focus on the background rather than the tree itself, as usual…)

From the top:

1) Removing the two main leaders, thereby taking out the worst-affected areas, but leaving a pair of strong horizontal branches, which hopefully aren’t infected.
2) Removing the four largest branches and leaving just three smaller ones to grow on.
3) Removing the area of trunk affected by the tree-tie damage, as well as the bulk of the tree.
4) Removing all but a half-metre section of the trunk, with the aim of rind-grafting either cuttings from the top growth (hoping they’re not infected) or another variety of apple.

In the end I decided to be cautious this year, and opted for the first cut. That way I could keep my options open: if the wood below the cut is clean then I could leave it there or, if there were signs of the canker spreading deeper into the tree, I could make another cut further down the trunk.

First I used loppers to take the branches back in sections, then took a good, sharp pruning saw to the trunk, making a slightly sloping cut to prevent water sitting on top of the wound. The result is quite a significant wound, but I won’t be applying any wound paste or pruning compound as there’s a risk that by doing so that I seal in canker spores or another bacterial infection. Trees have been healing themselves for many millennia, so I’m just going to leave this one to get on with it.

Those dark speckles on the wood – staining within the woody tissue of the tree – could be a sign of canker spreading down into the trunk. If the staining had been a lot more pronounced then I would definitely have made another, lower cut, but as they don’t look too drastic, I’ve decided to leave the pruning at that for now:

Apple ‘Lord Derby’, after winter pruning to control apple canker

I will be keeping a very close eye on his Lordship’s health this year, particularly the area of tree-tie related damage on the trunk. If there are any signs of incipient canker lesions breaking out on the remaining branches then they’ll be pruned out immediately. And if the damage on the trunk continues to spread then I’ll assume it is cankerous, and make another cut much further down the trunk.

In the meantime though, I’m hopeful that those horizontal branches might produce some fruit, so if I do have to take off most of the remaining wood later this year or next, then at least we’ll have something tasty to remember Lord Clyde by.

How about you? Have you had any apple canker issues to deal with? What’s your preferred method of addressing these sort of problems? Do let me know, via the comments.

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