TDA 128 Plane Attack
Tree Damage Alert No 128
10th October 2008
Plane Attack - Major or Minor?
It is the unexpected incident that so often leads to a significant development. This has been the case from a recent telephone call from an Arboriculture Consultant. The question resulted from a casual observation he made while travelling, very slowly, from a site visit leading to the question "does Cameraria ohridella [Horse chestnut leaf miner] attack any species other than Horse chestnut?". The literature suggests a negative, but there are records of the leaf miner colonising the leaves of both Sycamore (Acer pseudoplatanus) and Norway maple (A. platanoides) where they have been growing very close to infested Horse chestnuts (Aesculus hippocastanum). However, it is not known if larvae on these hosts are able to pupate and emerge as adults to infect Horse chestnuts.
The question from the consultant, when pursued, related to London plane (Platanus acerifolia), and the answer was that Cameraria had not been recorded colonising that species. But, said the consultant, he had seen markings on the leaves of London plane that looked exactly like those of Cameraria on Horse chestnut leaves. Leaf and twig specimens, correctly packaged in a polythene bag, sent to us at Alice Holt Lodge confirmed this description, but no larvae were found.
Alford's 'A colour atlas of pests of ornamental trees, shrubs and flowers' (Manson Publishing Ltd, London) produced an illustration of Phyllonorycter platani, a dead ringer causing damage visually the same as the mines of Cameraria. However, the literature indicates Phyllonorycter platani, which is widely distributed in Mediteranean regions, has not been recorded in Britain, but the Forestry Commission's entomologists have records of the pest on other broadleaf species in Britain. The National Leaf Mining Scheme 2008 indicates pockets of the pest particularly in the south east of England, but also in the Manchester and Bristol areas. A fuller indication of the distribution is at http://www.leafmines.co.uk/html/Lepidoptera/P.platani.htm.
Adult Phyllonorycter platani are on the wing in late spring and lay eggs on the undersides of leaves, particularly those on lower branches. The larvae feed within the leaves forming broad, distinctive blotch mines, often several on a single leaf. Pupation occurs within the leaf and in suitable conditions adults may emerge in August leading to a second generation of larvae which pupate in the fallen leaves on the ground.
Larval feeding mines in leaves are disfiguring rather than debilitating - trees will not be killed by the insect attack, and so there is no need to consider felling or even pruning affected trees. However, we may have to learn to live with the leaves of London plane appearing discoloured and autumning early.
Control of the pest on landscape trees is not practical, but collection of fallen leaves and burning or thoroughly composting them should reduce the number of adults emerging in the spring.
Where is Phyllonorycter platani in Britain? If you see mines on the leaves of London planes please send to AAIS at Alice Holt Lodge specimens of damaged leaves, packaged in ploythene bags, giving details of the tree's location.
NOTE: Phyllonorycter species are common and occur on many hosts (12 species of Phyllonorycter are recorded on 17 genera of trees and shrubs grown in Britain). The insects have many predators present in Britain and so severity of an infestation may be controlled naturally. Cameraria ohridella differs in being the only species of the genus in Britain and so has no natural predators resulting in no control. Therefore, don't panic about the Planes as attacks by Phyllonorycter species are not necessarily likely to reach the same proportions as those of Cameraria!
Derek Patch and Brian Greig, AAIS, Farnham Surrey.
This is one of an occasional series of Tree Damage Alerts produced for the benefit of the arboricultural profession and issued by the Arboricultural Advisory and Information Service.