Operation Cordon Rescue: Remedial Action vs Apple Canker

Last week I posted details of the state of play of the various cordon apple trees that I’m growing down on the allotment, and mentioned three trees that are suffering from bad apple canker infections.

I headed down to the plot again earlier this week to take another look at them, and quickly realised that my original plan – to leave them alone until winter pruning season – wasn’t going to cut the mustard. Instead, urgent remedial action was needed, and so that’s what I carried out.

This certainly isn’t the first time that I’ve encountered and dealt with apple canker – it’s one of the common perils of growing apple trees on an allotment site with a lot of other apple trees around – but I thought it might be helpful if I talked through my decision-making process one more time.

Striped Beefing

As you can see from the photo above, this tree’s leader has almost been entirely girdled by the canker lesion. Here’s a close-up that demonstrates how the infection has completely destroyed the phloem – the region of cells just below the bark that transports essential nutrients around the plant – and thereby cut off nutrient supply to the top part of the tree.

This next photo shows the effect on the section of the tree above the canker lesion: darkening leaves, with patches of damage and die-back, suggesting that nutrient deficiencies are already starting to cause problems:

Contrast those leaves with the still-healthy, green-leafed side-shoot that has sprouted from below the canker lesion.

Often the best remedial action for a canker-infected tree is to remove the affected area with a clean, sharp pruning saw. The first cut I made was to remove the top-growth:

This was mainly to reduce the weight of the stem, so that the next, most important cut, would be easier to manage. That second cut was below the infection, just above the point of origin of the new stem. That looks like a nice, clean cut…

…but I am slightly concerned by that brown splodge in the middle of the xylem tissue – the woody core of the main stem – which could indicate that the canker infection has spread further down the tree. If that’s the case, and if a new lesion breaks out below this cut, then I might lose the tree. Otherwise, if that cut heals nicely, the infection doesn’t spread, and that new shoot develops into a useful replacement leader, then the tree will have been saved and will hopefully go one to be a strong and productive ‘Striped Beefing’ for years to come.

‘Egremont Russet’ x2

Rather sadly, both of the ‘Egremont Russet’ cordon trees that I planted on our plot have been infected by apple canker, and I don’t have any immediate replacements waiting in the wings, although I can get access to more grafting material for next winter. Still, if I could save one or both of these trees that would be a definite bonus, as they’re my wife’s favourite russet variety.

Here’s the first tree, and immediately we can see that once again the main leader is in imminent danger of being girdled by the canker lesion, but there are two new shoots growing out from beneath the point of infection.

One of the shoots is far too close to the lesion to be worth keeping…

so the cut had to be made lower down the stem, just above the other new shoot. The good news is that the xylem tissue looks clean, so it’s unlikely that the canker will have progressed this far down. I’m hopeful that this tree will make a good recovery, and the new stem, which is quite a bit longer than the photo suggests, will go on to form a useful replacement leader.

Alas, it doesn’t look so promising for the other tree. As I mentioned in my round-up post, this tree has two canker lesions and isn’t showing much sign of regrowth. The first lesion is part-way up the main stem, and looks bad enough already:

But the killer is the second lesion, on the rootstock itself. With this degree of damage occurring this close to the ground, there’s really no point trying to save the tree, so the next time I’m down at the plot, it will be removed and destroyed.

I’ll plant up a replacement tree in the spring, and hopefully the new one won’t fall victim to the dreaded apple canker.

How about you? Do you struggle with apple canker in your trees? Do you ignore it, or try to treat it – I’ve been told before that crushed garlic packed into the lesion is a worthwhile remedy, but I haven’t gotten around to trying that one yet – or just prune it out as I have done? Do please let me know, via the comments.