Moth blight

SIR, - In reply to the letter "tree peril" (Herts Advertiser, August 21), many, if not all of the horse chestnut trees in the district are being affected by the horse chestnut leaf miner moth, Cameraria ohridella, which causes the leaves to turn brown and shrivel.

The moth's larvae mine within the leaves of horse chestnut and the damage caused by large numbers of larvae can be striking. Severely-damaged leaves shrivel and turn brown by late summer and fall early, well before normal leaf fall in the autumn.

The spread and establishment of C. ohridella is of particular concern because once established, the moth appears always to maintain exceptionally high rates of infestation without any evidence of decline. In European towns and cities there has been no decrease in populations even after many years, and severe damage to horse chestnuts has occurred on an annual basis, greatly impairing the visual appearance of the trees.

Despite the poor appearance of horse-chestnut trees infested with the moth, there is no evidence that damage by the moth leads to a decline in tree health or tree death. Trees survive repeated infestations and reflush normally in the following year. It appears that most of the damage caused by the moth occurs too late in the growing season to greatly affect tree performance. Consequently, there is no reason to fell and remove trees just because they are attacked by the moth.

Where the moth is established, the safest and most practical means of control is to remove fallen leaves during the autumn and winter. The moth over-winters as a pupa in the fallen leaves and commercial composting of leaves or burning them - if local regulations allow - destroys the pupae and reduces the moth population in the following spring.

Further information can be obtained from Forest Research, the research agency of the Forestry Commission, at www.forestresearch.gov.uk/leafminer

ANDREW BRANCH,

Trees and Woodlands Officer, St Albans District Council