Kitchen Garden Blog

You know how as you get older bits of you start to crinkle and crease and pucker until you’re beginning to bear more than a passing resemblance to the surface of the moon? Well – thank your lucky stars you’re not an apple tree.

Because if you are, then all those lunar crinkles get deeper and longer and almost inevitably turn into entire craters. These get wider and wider till they’re suppurating sores, and eventually your arm drops off.

See? It’s not as much fun as you’d think, being an apple tree.

Of course, canker isn’t really an ageing disease, although it does appear more frequently on older trees. These days, what with warm, wet summers – much loved by fungal diseases everywhere – it is as inevitable as the moon rising in the evening. If you grow apples (or pears, of course) you will, almost inevitably, spot a tell-tale callous one day.

So I wasn’t altogether surprised when I was trimming the excess growth off my apples this week – a little late in the day, but I got sidetracked by sowing lettuces and such – to discover my trees, too, are starting to succumb.

The symptoms, once you’ve seen them once, are easy to spot. The bark starts to pucker and peel – in a previously unaffected tree you may not spot this, as it’s similar to other types of damage such as squirrel damage, but then it starts to affect larger branches. At this point the puckering gets more damaging to the bark which becomes sunken and separates, revealing dead inner wood; the tree then tries to heal itself with callouses, and that forms the classic canker welt. This spreads and bites deeper until it girdles the branch and any growth above it dies.

The fungus attacks not just apples but also Sorbus (mountain ash), ash and beech: but I’ve only seen it on fruit trees. There’s another – worse – type of canker, bacterial canker, but that’s mainly confined to cherries, plums and peaches – none of which I grow (yet).

It’s supposed to be worse on acid soils – but my soil’s pH is 7.5, which is very alkaline. I think in my case it’s more because the soil is pretty much permanently damp in Somerset, another environment the fungus adores. I’m afraid no amount of drainage is going to counteract West Country rain so this is something I just have to live with.

Your main line of defence is to cut out as many of the cankers as you find, making sure you go back right into clean, healthy wood. This is, of course, rather a radical solution if the canker is on a major branch: but if you go back to the nearest side branch the new growth quickly takes over. As long as you can keep the canker out of the main trunk, an apple tree can live with the occasional callous and still remain productive for many, many years.

But just a word about hygiene. I’m usually quite lackadaisical about hygiene in the garden, on the possibly woolly theory that if there are fungi and bacteria and viruses and such like flitting about the place on the backs of aphids and floating around in the soil and drifting about in the air, then an over-zealous attention to disinfecting things on my part isn’t going to make a blind bit of difference since they’ll all just move back in and do their dirty work the moment the top is back on the Dettol.

But in this case, you can save yourself – and the tree – a lot of grief in years to come by keeping things disinfected as you’re pruning. Think of it as surgery: you wouldn’t expect a surgeon snipping out some diseased bit of you to do it without at least giving a good scrub to the knife he used on that bloke with the lump on his leg half an hour ago, so it’s the least you can do for your apple trees.

I disinfect the blades of my secateurs (a quick wipe with kitchen towel soaked in Jeyes Fluid or Dettol does the trick) every time I know I’ve pruned back cankered wood, and certainly when I move on to another tree.

Another precaution you can take is to prevent the canker fungus re-entering via your pruning wounds. I have a pot of Arbrex handy for badly-affected trees so that I can paint the cuts: it does takes longer, but I balance that out by thinking of all that pruning time I’m saving next year.

You’ll never rid a tree of canker once it’s got it: but with a little care and attention, like the signs of ageing, you can keep it at bay with a reasonable hope of success for many, many years before terminal decline sets in. And at that point, you can always trade it in for a younger model. I think perhaps now is a tactful point to let the comparison between apple trees and old people drop. Sorry.

Tags: apple diseases, apples, canker, plant diseases