Where have all the conkers gone?
19 October 2010
The British conker is under siege from a pest that is infesting horse chestnut trees and spreading across the country at a rate of 40 miles a year.
Many gardeners will have noticed the premature browning and shedding of the leaves on horse chestnuts, Aesculus hippocastaneum, which then can eventually be killed off.
The problem stems from a moth, Cameraria ohridelle, first detected by the RHS Entomology Service from a sample of leaves sent into our Advisory Service, which is spreading across the country at about 40 miles a year. The original sample was sent in from the London Borough of Wimbledon in 2002. Within the eight years since detection the pest has reached Wales and Scotland is now under threat.
Double whammy of infection
It is the moth’s larvae that cause the problem. They burrow within the leaf structure which then turns the foliage brown, leaving trees weak as they have less time to make and store food. This can also mean that the conkers produced are much smaller.
Unfortunately at the same time a bacterium, Pseudomonas syringae pv. aesculi, first detected in the 1970s, has re-awoken in the last four years, possibly because the trees are weak and unable to offer resistance, and is causing bleeding cankers. This combination of early leaf fall and bleeding can kill the tree off.