Horse chestnuts under threat

Conkers under threat by pests and diseases, reports Matt Appleby.

horse chestnut
Horse chestnuts are under treat from leaf miner and bleeding canker.
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Pests or diseases have damaged most of Britain’s 470,000 horse chestnut trees and there are just five years left to find a solution, experts warn. Dr Glynn Percival, manager of the Bartlett Tree Research Laboratory at the University of Reading, said: “I don’t think the prognosis is good at all, unless we find something to control the leaf miner. In trees that have leaf miner we do get an increase in the severity of bleeding canker because they have so little energy to defend themselves.”

He continues: “Our research shows trees without leaf miner produce conkers twice the weight of those with – 8g against 4g, which is a 50 per cent drop. We planted them out and the 4g conker germination rate is lower and the vigour is lower. There’s a definite knock-on effect, our data shows. The affected trees’ conkers are smaller and they have less vigour when germinating because of leaf miner.”

“Horse chestnuts have got maybe another five years unless we get these issues under control. The trees are living off their own natural resources. They’re brown and crispy when everything else is green. No energy is being produced.” He said his research shows that honey fungus is also attacking stressed trees, killing them off quicker.

Pests and disease

In lowland England the “vast majority of places have leaf miner and it is here to stay”, said Dr Michael Pocock, organiser of the Conker Tree Science project and an ecologist at the UK’s Centre for Ecology & Hydrology. “The project has been running for a few years and is coming to an end in terms of tracking the main thrust of the spreading of horse chestnut leaf miner.” He added: “In the long term, I don’t think it’s looking good for horse chestnuts. While horse chestnut leaf miner causes premature leaf loss, it is horse chestnut bleeding canker that is likely to cause the demise of the tree in England,” he added. “Bleeding canker is a much more serious problem because it can cause tree death. Once it enters the tree, it has basically got it for life and can hasten death.

“A particular problem is that it can cause limbs to die and drop, and that causes issues with health and safety and trees need much more attention with management and felling. The canker causes trees to be felled and no one wants to replant horse chestnuts because they look so scrappy because of leaf miner, these two working together mean there’s not a great prognosis for our wonderful big horse chestnut trees. Over the next two or three decades it could be the case that horse chestnuts are scarcer in parks and gardens.”

Matt Appleby

About Matt Appleby

Matt is a former teacher turned journalist. He took up writing while in New Zealand and trained as a journalist there. He has since written five books (three on cricket and two on gardening) with The Children's Garden due out in spring 2016 published by Frances Lincoln. He writes for Horticulture Week and other publications. Married with two boys, aged 3 and 6 he lives in London.
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