Conker Canker

Warning. This could get nerdy, folks…

Sarah’s worried. She asks:

“Say, you don’t know about this thing with the chestnut blight? I’m really worried about the trees in the park, a lot of them seem to be hit by it. Do any scientist types know if it’s something that will move on, or will it kill the trees?”

The Phantom replies:

You alarmed me there, Sarah. So much so that I went out yesterday to check every chestnut tree I could find in the park. Of course it had nothing whatsoever to do with the lovely sunshine or the threat of cold-and-nasty for the next few days. This was Science. Obviously.

According to the BBC website, the alarming-looking ‘bleeding canker’ which is a nasty bark fungus, and the leaf-miner moth which make the leaves wizen and drop off, only seem to affect Horse Chestnut trees* but given the close proximity of horse chestnuts to the historic sweet chestnut trees* I wanted to make sure. I don’t think they’re connected genetically (I believe that the edible ones are more closely related to beech trees) but I’m no expert.

The blighted trees had reached Chatham and the Medway by 2006 which is when the BBC site’s dated, so I checked the RHS for symptoms to look out for. There are icky pictures of particularly bad cases on the BBC site.

As far as I can tell, the leaf miner just saps the trees, and makes them sick, but they can recover. And as it’s been a wet summer, they may have gone away anyway. The bark blight is the real baddie – and some forestry types seem to think it could be the next Dutch Elm Disease. There’s a rather alarming – if short on detail – map here that shows instances of the disease.

Obviously the leaves are mostly all dropped just now, so it was hard to tell whether they’d died because they’d been chomped or because it was winter. I could only look out for the nasty Bleeding Canker. I must have looked like some loony, staring up into trees, peering closely at the bark and muttering to myself but I couldn’t see anything that didn’t look like it shouldn’t be there (save the odd parrot…)

So yes – I think that it’s something to be on the lookout for – but personally I couldn’t see any problems up there yesterday. And because it only affects Horse Chestnuts (as far as I can find out) I don’t think it’s an immediate danger to the 300-year old Sweet Chestnuts.

*The Phantom’s Scientific Chestnut Identification Field Guide:

  • Horse Chestnuts (Aesculus hippocastanum, if you want to get down, dirty and latin…)

    The classic conker trees – you can tell the difference by looking at the leaves – they’re much bigger and look sort-of hand-like (to me, anyway…) They have ‘candles’ in the spring – pink and white, and they come up with big shiny, inedible conkers in autumn, in little hard green spiky cases. They’re the ones you bake in vinegar and tie on bits of hairy string then smash into other kids’ vinegar-baked arsenals (though you’re probably not allowed to do that kind of thing any more due to H&S regs…)

    They’re nothing to do with:

  • Sweet chestnuts (Castanea sativa)

    Those big, gnarled-trunk jobbies that are getting in the way of an easy Olympics. The leaves are more spindly with crinkly edges, and even youngish trees look knobbly. But the big difference is in the nuts – they’re edible for humans. The cases are much spikier and look softer.When they’re on the tree, they look almost ‘fluffy’ from a distance. Don’t be fooled. Wear gloves to pick them up – they’re buggers for ripping your hands to shrebbons trying to open them.

    If you can get there before the hoardes of Chinese grannies who suddenly appear out of nowhere armed with giant carrier bags every autumn, you can gather them and roast them on the obigatory ‘open fire…’ (make a cross in the bottom with a knife first or they explode.)


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