Bleeding canker disease hitting beloved ‘conker’ tree hard

Bleeding canker disease hitting beloved ‘conker’ tree hard

A reader from Ovens recently got in touch to voice concern about the dead horse chestnut trees he sees along the N22 on the outskirts of Cork city, and the death of magnificent, old specimen trees all over Ireland.

Many readers will remember the schoolbook poem:

‘Under the spreading chestnut tree/The village smithy stands;/ The smith, a mighty man is he,/ With large and sinewy hands/ And the muscles of his brawny arms/Are strong as iron bands’ (‘rubber bands’, we said, delighting in making a joke of Longfellow’s lapidary line.)

It is, indeed, to be regretted that the chestnut tree may shortly go the way of the village blacksmith, and schoolboys may no longer be able to play ‘conkers’ — but the game, in any case, seems to be out of fashion and no self-respecting young fella over 10 years old would be seen dead swinging a chestnut at the end of a string and issuing challenges to  classmates to engage his chimney-corner-smoke-hardened, vinegar-dipped, wizened warrior in a battle royal to be crowned champion conker of the school.

However, it seems that older boy hobbyists continue the tradition at the annual Northamptonshire World Conker Championships, where conkers must exceed 1.25 inches to compete, and winning nuts are often over 2 inches in diameter.

Now, our familiar white-flowering Irish horse chestnuts are succumbing to bacterial Bleeding Canker Disease, dramatically increasing all over Europe since the early 2000s. 

The first official reports in Ireland were in 2010, based on trees infected in Phoenix Park. 

Shortly afterwards, park authorities began felling these trees — 90% of total — and replacing them with London plane trees.

London planes are resistant to most diseases and to air pollution — in fact, they efficiently remove pollutants from the air. 

Fast-growing to 20m-30m, they are wildlife friendly and conducive to pruning and pollarding. 

While not entirely invulnerable to blights, they present a robust alternative to the stricken chestnuts.

First hybridised in Spain or, possibly, in London’s Vauxhall Gardens (hence the London label) by John Tradescant the Younger, they are maple-like in appearance. 

Tradescant made many journey to Virginia in America, collecting plants (and also, incidentally, the ceremonial cloak of Chief Powhatan, paramount chief of the Algonquian people, numbering 20,000 when the English colonised Virginia in c1600.)

In the event of all our local village and countryside horse chestnuts succumbing to the disease, London planes, with their ‘urban’ roots, might seem unsuitable replacements but they quickly become quite ‘wild’ and look not unlike our familiar sycamores; the five-lobed leaves are similar, and turn a bright orange colour in autumn. 

Bleeding canker disease hitting beloved ‘conker’ tree hard

The seeds, bumpy or spikey 2cm-diameter globes, hang between the leaves like pendant earrings. 

They are eye-catching, although not as pretty as the twin-winged samaras of the sycamores which rotate as they fall, slowing as they catch on the wind, and drifting widely to disperse their seeds beyond the parent tree.

While the canker is almost always deadly to infected trees, the arrival, across Europe, of a micro-moth, seemingly no bigger than of a grain of rice, prematurely puts paid to the foliage but does not kill. 

In recent years, I annually see the twin trees standing either side of the entrance to a picturesque old house devastated by Horse Chestnut Leaf Miner caterpillars that have tunnelled through the leaves, causing them to prematurely turn brown and die.

Dead leaves carpet the earth below, while above, those leaves that are still green hang in tatters, holed and filigreed, the edges eaten away, curling and withering on the stem. 

It’s a sad sight. Early September and defoliation is already advanced.

The moth was first recognised as a new species in Macedonia (where, apparently, horse chestnuts are used to relieve coughing in horses) in 1986. 

Travelling 60 km per year, it reached Britain in 2002 and then Ireland in 2013, possibly windborne or on imported plants. 

The beauty of the foliage is short-lived and the chestnuts small, affecting regeneration (perhaps saddening the Northamptonshire conker men). 

Also, if the moth attacks victims of bleeding canker disease, it may spread the infection to others.

Can nothing be done to combat the moth? Would installing peanut feeders and nest boxes induce blue tits, great tits and coal tits to settle in the infected trees and cull the caterpillars? 

One warm summer night, some years ago, I watched blue tits harvesting tree caterpillars to feed their chicks — at 10.30pm, in half-dark, they were still carrying beakfuls to their nest every three minutes, a constant shuttle; blue tit clutches average 10 chicks.

Regarding the fatal canker disease, Czech scientists offer hope that by inoculating trees with the pathogen, identifying resistant trees and using their seeds, they may establish resistant populations.

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