below). Even if this does not occur, the poor appearance of affected horse chestnuts may lead to a change in perception of their value as amenity trees.
Control
Certain insecticides will have activity against the pest but widespread and routine use of these would be costly, time- consuming, in many cases impractical and certainly not environmentally friendly. There is a hope that natural enemies (such as parasitic wasps) may build up and reduce moth numbers, but this is only happening on a small scale at present. As the pest overwinters in fallen leaves then burning, burying or composting will help, at least where affected trees are geographically isolated from other horse chestnuts. The common white horse chestnut, Aesculus hippocastanum, is very susceptible to attack, but other species vary in susceptibility and the red- flowered hybrid A. x carnea is highly resistant.
Bleeding Canker Bleeding Canker
affected, leaves held up to the light will be translucent, and it may be possible to see the larva or pupa within them. Similar blotch symptoms may be caused by a fungal disease called Guignardia leaf blotch (see below). The moth produces a number of generations during the year, and finally overwinters as pupae within the fallen leaves.
The Threat
The potential damage that the moth may cause to horse chestnuts in the UK is still a matter for conjecture. The overwintering pupae are very frost-tolerant, so a hard British winter (now more of a rarity anyway) will not kill them. Our increasingly hot, dry summers are also ideal for the moth. In parts of Europe, where the moth has been a problem for a number of years, repeated early defoliation has not killed trees. However, there is a worry that this may lead to a reduction in the vigour of the trees, making them more susceptible to other problems such as drought and attack by other pests and diseases (such as bleeding canker, described
A disease called bleeding canker of horse chestnut has been known in the UK since the 1970’s. At this time the cause was found to be a microscopic, fungus-like organism called
Phytophthora. The disease was not particularly common, and confined to south-east England. In recent years, however, the number of cases of bleeding canker has increased rapidly, and the problem is now found throughout England, with cases also recorded in Wales and Scotland. There has been a similar dramatic increase in disease levels in Holland, France and Germany. In most of the ‘new’ cases it has not been possible to identify Phytophthora as the cause.
Symptoms
Affected trees have areas of dead bark, which produce a red, brown or blackish ooze. If this bark death results in the girdling of branches or trunks, then death of the limb or the entire tree can result. If the outer bark is removed from affected areas, the inner bark will often be found to have a mottled,
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