The Horse Chesnuts are already producing an abundant crop of nuts. You will have seen the leaves beginning to turn, and in some cases with well-developed Autumn colours. Or have they?
We have heard much of the diseases attacking our trees. The Ash Dieback has been in the news lately, but a number of tree species are under attack. Oak, Pine, Sweet Chesnut amongst the most well known. The Horse Chesnut needs to be included in that list as the leaf miner (Cameraria ohridella) lives in these trees. It was first reported in the UK in 2002, in the London Borough of Wimbledon, and has since spread north, south and west to most of England and parts of Wales, and there has been one confirmed sighting in Scotland
Its larvae (caterpillars) mine within the leaves, and at high population densities, they can destroy most of the leaf tissues. Although it can cause severe damage to horse chestnut leaves on an annual basis, hence the early ‘browning’ of the leaves in addition to the normal autumn shading.
While the tree seems to be able to deal with the invasion, coming up clean in spring, it is possible that differences in climate, or interactions with other pests and diseases, might lead to greater impact in the UK. Consequently, the effects of the moth and its interaction with other pests and diseases, especially bleeding canker of horse chestnut, is being studied through the long-term monitoring of more than 300 chestnut trees at several sites in southern England. These trees are assessed twice each year for infestation, disease crown condition, growth and signs of dieback.