Apple Canker, Canker, Apple and Pear Canker, Fungal Canker
Fungal canker is the most widespread and serious of the fungal cankers. Although it can be referred to as Apple and pear canker, it has a wide host range of woody plants. Damage from this fungus is relatively slow but can result in the complete death of trees if the cankers are in vital areas. Fortunately, the damage caused is localised to the area of the cankers and so by removing branches that have the cankers is a valid treatment. However, if the material is being removed while the canker is producing pustules then these will release spores into the air which can reinfect the tree through wounds.
Elongated sunken lesions in the branches appear on branches, often around a leaf scar, side branch or bud. At the centre of the lesion, the bark dies and may fall away. The lesions also can cause girdling of the plant or the branch to die past the lesion. Sometimes, during the Spring and Summer, small cream pustules can appear on the cankers. However, more often only small red pustules appear during the Autumn and Winter. The fungus can also infect the fruits while they're still on the tree and cause a brown rot and for them to stay on the tree over Winter.
Having multiple wounds on the tree open it up to easily get infected. Sites with poor drainage. Over-fertilizing.
Lesions around wounds.
White or red pustules forming round the edges of lesions.
Girdling of stems.
Dieback of branches.
Growing resistant varieties of plants. Cutting out and burning infected branches. Completly removing badly diseased trees and burning them.
There are no chemical treatments.
The spores from the pustules (white or red) are carried on the wind or splashed by the rain onto an open wound on the tree. The fungus infects the bark and develops inside the branch. As it grows it kills off the cambium layer inside the branch which causes it to drop and show the lesions. The fungus then produces pustules of spores. The white pustules in the spring are asexual and the red autumn pustules are sexual.
Minimising wounds caused to trees. Keeping good airflow through and around plants. Keeping good hygiene around plant eg. cleaning tools after pruning an infected plant, removing and burning infected material. Having good drainage. Not over fertilizing plants.