Canker

Left unchecked, canker can gradually spread to affect whole branches and sections of trees. Severely-infected old trees may be beyond rescue, while young trees are vulnerable to infection, particularly where other susceptible trees are growing in close proximity. Where trees are suffering stress as a result of drought or waterlogging, they may be more liable to infection. Canker may also infect fruit, so they rot on the tree before harvesting or when in store. If your trees have suffered this in the past and you're considering replacing them, choose canker-resistant varieties such as the apples 'Grenadier', 'Laxton's Superb' and 'Newton Wonder', and the pear 'Concorde'.