Effect on tree health
Despite the poor appearance of horse-chestnut trees infested with C. ohridella, there is no evidence that damage by the moth leads to a decline in tree health, the development of dieback, or tree death. Trees survive repeated infestations and re-flush 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 C. ohridella.
Significant dieback of branches in the canopy, or death of horse-chestnut trees, is caused by other factors, e.g. bleeding canker of horse chestnut, or a combination of factors. Trees showing these symptoms need to be checked by a qualified arboriculturist so that appropriate management can be undertaken.
See also Management of Cameraria ohridella
Horse chestnut trees on the south side of Wimbledon Common, London, in September 2003, severely infested with Cameraria ohridella
The same trees in May 2007. The trees have flushed normally and there is no sign of dieback in the canopy or any other evidence of a decline in tree health, despite five years of heavy infestation by Cameraria ohridella. (A small sycamore has been removed to the left of the first horse chestnut)
Horse-chestnut flowering in the autumn in 2006 following defoliation by C. ohridella
(Photo: Andy West)
During the autumn of 2006, there were a number of reports of horse-chestnut trees, which had been defoliated by C. ohridella, re-flushing and flowering again late in the season. The same phenomenon has been observed in other European cities, e.g. in Berlin.
The long-term effects of re-flushing in the autumn on tree vitality are not clear. At present, there are no reports of any detrimental effect on subsequent tree performance. However, in central Europe, shoots which re-flush in the autumn and which do not harden sufficiently before the winter, are sensitive to frost damage, and this can lead dieback of twigs and small branches in the following year. Such damage is probably less likely in the UK where severe autumn frosts are less common.
See also Host plants of Cameraria ohridella