DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY
Apple (Malus domestica 'Blenheim Orange') branch sawn through at the site of a cankerous outgrowth. The canker is the pale region, below and to left, permeated by branching brown areas of infected and dead wood. The original branch is above centre; with growth rings discernible around its paler circular core. Apple canker is a common disease of apples, caused by the fungus Neonectria ditissima (syn. Neonectria galligena, Nectria galligena). The fungus enters through wounds such as pruning cuts, sites of local damage or scars left by leaf fall. Here, the damage was caused by a persistent infestation of the woolly aphid, Eriosoma lanigerum. The aphid causes swellings to appear on infested twigs and branches; these in turn may develop surface cracking, allowing fungal access to the tissues beneath. This canker is about 10cm across; more than twice the diameter of the original branch.
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