Chipmunks: pests and pleasures
The blues...

Our chestnuts are dying

Aesculus,hippocastanum,horse chestnut,leaf miner,Cameraria ohridella. Image l© (all rights reserved) As the plane from New York approaches Heathrow airport, look out of the window and the horse chestnut trees (Aesculus hippocastanum) are easy to spot. Not, as my mother insists, because they’re the first tree to develop autumn colour – although coming in to land in September that might at first seem to be the reason.

No. Just about every horse chestnut tree in the south of England has turned brown because it’s infested with a pest, the horse chestnut leaf miner (Cameraria ohridella). This little bug tunnels through the leaves causing translucent patches - in the same way as the leaf miners infesting chrysanthemums or aquilegias. But the tunnels soon merge, the leaf turns brown, the edges roll up, then the leaf drops off. By August, some trees have lost all their foliage. After a few years of losing all their leaves, trees die.

First noticed in south London in July 2002, trees across most of south and central England are now infested. It’s spread very rapidly and continues to spread. There is no effective control. Other species of Aesculus, plus Acer platanoides and A. pseudoplatanus, are also damaged.

Aesculus,hippocastanum,flowers,horse chestnut. Image licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.	
© Andrew Butko In Britain, the horse chestnut is an iconic tree. Its bold foliage opens from fat, sticky winter buds, then the dramatic spring flowers are followed by conkers, large shiny nuts used in kids games. The World Conker Championships are held, this year on 10 October, just a couple of miles away from where I’m writing this. Aesculus,hippocastanum,fruits,conkers. Image licensed under the Creative Commons Attribution-Share Alike 2.0 Generic license. Photograph © Andrew Dunn.

But – the horse chestnut is not a British native tree. It grows wild in Greece and Albania and was first brought to Britain in the early 1600s. It’s so common that some American observers would probably classify it as an alien invasive and would be delighted that the leaf miner is killing trees. By contrast, in Britain research is continuing to find a predator that will kill the leaf miner.

First it was the English elm, now the horse chestnut. But things change. Last year, in Northamptonshire a few miles from here, there were elm trees growing in the hedgerow that reached about 4.5m/15ft high. And on the south coast, there were many trees that were never infected. But things change again, and now those trees are again under threat.

Aesthetically and culturally the loss of so many of these trees is a disaster. But the horse chestnut has only been in this country for 400 years, the elm for 2000 years - not long, in the evolutionary life of a tree species. And things will continue changing.