Thorny problem for horse chestnuts

Nov 6 2008 Buckinghamshire Advertiser

People in the south of England have been shocked to see much-loved horse chestnut trees (Aesculus hippocastanum) with the shrivelled brown leaves this summer.

This devastation has been caused by the leaf miner Cameraria ohridello from central Europe, which was first noted in Wimbledon in 2002 and is now spreading rapidly.

Observations and studies have been made and, as we have informed our members, the best action is to disrupt the leaf miners' life cycles.

Gather up all fallen leaves and burn them to prevent moths emerging in April and flying on to the trunk of horse chestnuts where they mate before the female lays her eggs on the foliage. It is possible to compost the leaves, but only well away from horse chestnuts, to prevent any surviving moths flying or being wind blown to new host trees.

Repeated infestations of the leaf miner will render horse chestnut trees susceptible to diseases like bacterial bleeding canker,which can lead to death of the tree.

The red flowering horse chestnut (A. x carnea) is resistant to this leaf miner as it is a hybrid, and its American parent, A. pavia,produces an insecticidal chemical in its leaves.

MERELENE DAVIS

Honorary editor of The Dendrologist Chesham