What’s Happening to Our Horse Chestnuts?

Horse Chestnut Tree (Sannse at the English language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons)

Horse Chestnut Tree (Sannse at the English language Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)%5D, via Wikimedia Commons)

When I was a little girl, we used to go to visit my Auntie Mary, who lived in a Home in Chingford. Auntie Mary had a learning disability, which my great-grandmother always swore was the result of Mary hitting her head on a kerbstone when she was a child, but by the time that I knew her, she was in her seventies.  The Home was a grand house in its own grounds, but the huge, high-ceilinged rooms always had a faint whiff of boiled cabbage and urine about them. Auntie Mary was a cheerful soul, who loved nothing better than playing ‘Banker’, a card game which involved cutting the pack into piles, and betting on which one would  reveal the highest card when turned over. It could go on for hours.  We would play for pennies, and she almost always won, because in spite of her challenges, Auntie Mary always knew exactly how many coins she had, and had an unerring instinct for which was the winning pile. When she was a young girl and was sent out to do the errands, she always knew when people were trying to cheat her, even though she was able to do little about it.

Conkers (By Solipsist (Own work) [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons)

Conkers (By Solipsist (Own work) [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)%5D, via Wikimedia Commons)

My younger brother and I loved Auntie Mary, with her institutional hair cut and toothless grin, but the place itself scared us. We didn’t understand why someone was always screaming, or why there was an old lady sitting in an armchair, a white strand of spittle dangling from the corner of her mouth. And when things got too much, Dad would take us outside. In the grounds was the most magnificent Horse Chestnut tree. In the winter, there would be conkers. In the summer, the tree would be full of blossom, looking like a Christmas tree covered in candles.

Horse Chestnut blossom 'Candles' - via Wiki, attribution uncertain.

Horse Chestnut blossom ‘Candles’ – by Karel Jakubec.

Horse Chestnut blossom (By William N. Beckon (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons)

Horse Chestnut blossom (By William N. Beckon (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)%5D, via Wikimedia Commons)

Poor Auntie Mary, who never asked for a single thing out of life except for the occasional card game and a hug from my father (who she doted on), died unexpectedly following complications from a cataract operation. I never see a Horse Chestnut tree without thinking of her, and so I have been horrified at the state of many of the Horse Chestnut trees that I’ve observed over the past few years. Here, for example, is one that grows just inside Coldfall Wood in East Finchley.

Horse Chestnut in Coldfall Wood

Horse Chestnut in Coldfall Wood

The leaves of the tree have not just turned brown, they have turned to a crisp. Furthermore, although we are now in November, this has been happening for months. Let’s have a closer look at the leaves of another Horse Chestnut that I found further into the wood:

Horse Chestnut Ivy 005Horse Chestnut trees are under siege from several directions. The first is via a fungus called Guignardia aesculi, which was first reported in 1935. It first appears in June, and causes blotches which are often outlined in yellow, as in the leaves above. However, the trees have largely learned to live with this fungus. The real problem is a more recent invader.

Leaf showing infestation by Horse Chestnut Leaf Miner

Leaf showing infestation by Horse Chestnut Leaf Miner

Horse Chestnut Leaf-miner, Cameraria ohridella, first arrived in the UK in 2002. It is a micro-moth, and its caterpillars burrow between the layers of the leaf, usually between the veins – in the photo above, you can see that the leaves have become transparent, with a little black blob indicating a pupa. The new moths emerge in May. The infestation starts at the bottom of the tree and spreads up, causing the leaves to shrivel and turn brown. This leads to early leaf fall. Although this is not fatal, it makes the trees unsightly, and greatly shortens their period of leaf growth. As if this was not enough, the size of the nuts is also reduced, disappointing any children old-fashioned enough to like a game of conkers alongside their online activities.

Adult of Cameraria ohridella. Taken by Soebe in Northern Germany and released under GNU FDL.

Adult Horse Chestnut Leaf Miner. Taken by Soebe in Northern Germany and released under GNU FDL.

Horse Chestnut Leaf Miner pupa 9By Varel from czech wikipedia (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons)

Horse Chestnut Leaf Miner pupa 9By Varel from czech wikipedia (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/3.0)%5D, via Wikimedia Commons)

Horse Chestnut Leaf Miner Caterpillar (By Claude Debrauer (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons)

Horse Chestnut Leaf Miner Caterpillar (By Claude Debrauer (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)%5D, via Wikimedia Commons)

So, what can be done? One thing that many local councils are doing is to gather up the fallen leaves and burn them – this will reduce the number of moth pupae that hatch and produce new moths. Birds, especially tits, have been seen eating the caterpillars, and may be responsible for munching up between two and four percent of the insects.

Blue Tit feeding on Horse Chestnut Leaf Miner caterpillars (By Rafał Konieczny (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons)

Blue Tit feeding on Horse Chestnut Leaf Miner caterpillars (By Rafał Konieczny (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-3.0 (http://creativecommons.org/licenses/by/3.0)%5D, via Wikimedia Commons)

However, the final answer may come from a much smaller predator. There are hopes that parasitoid wasps may find the Horse Chestnut Leaf Miner to their liking, and that they will start to increase their numbers as they discover how much tasty protein is lurking between the layers of the leaves. There is also evidence that some trees have immunity to the Leaf Miner, and suffer to a much lesser extent.

Eulophid (parasitic) wasp attacking a caterpillar (not a Leaf Miner in this case) via Stephen Ausmus at United States Dept of Agriculture.

Eulophid (parasitic) wasp attacking a caterpillar (not a Leaf Miner in this case) via Stephen Ausmus at United States Dept of Agriculture.

The Forestry Commission emphasise that there is no reason to destroy a tree with a Horse Chestnut Leaf Miner infestation – although unsightly, the hope is that gradually a balance between predator, prey and natural immunity will develop. There is some evidence that the degree of parasitism is increasing in areas like London, where the Leaf Miner has been present for the longest time.  In the meantime, we will have to wait, and hope that our Horse Chestnut trees are soon healthy and magnificent again, as they were in the days when Auntie Mary was alive.

Lone Horse Chestnut Tree on the Ashridge Estate  © Copyright Paul Buckingham and licensed for reuse under this Creative Commons Licence

Lone Horse Chestnut Tree on the Ashridge Estate © Copyright Paul Buckingham and licensed for reuse under this Creative Commons Licence

 

 

One thought on “What’s Happening to Our Horse Chestnuts?

  1. Pingback: Ordinary Plants | Bug Woman – Adventures in London

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