Bacterial canker (Pseudomonas syringae pv. syringae) can affect all parts of stone fruit trees, with cherries and apricots the most susceptible.
Disease identification
Trees infected with bacterial canker will have dead bark and when the sunken surface bark is removed, the underlying tissue will be orange–brown (Figure 1).
Large amounts of gum can exude from the trunk and bark cankers (Figure 2).
The infection first appears on the leaves as water-soaked spots, which can turn brown and fall out as the leaves age (Figure 3). They can also have a yellowing, rolled appearance.
Bacterial canker can be identified on the fruit by sunken spots with dark centres and occasionally with underlying gum pockets.
Damage
Bacterial canker is favoured by wet, windy conditions in autumn and early winter, before and during leaf fall.
Damage to trees and limbs from pruning, hail or wind during early dormancy increases disease risk.
Rain during the growing season will encourage the disease to spread throughout the orchard.
Bacterial canker will cause economic loss through a reduced fruit yield and branches or whole trees dying.
Monitoring
Inspect orchard trees regularly throughout the growing season for signs of dieback and/or gum producing cankers. Mark severely infected trees for prompt removal.
Management
Cultural and physical
It is good practice to avoid pruning stone fruit trees in winter.
Prune soon after harvest or as close to bud burst as possible. Prune areas of the orchard with canker problems last and paint large pruning wounds with white acrylic paint or a proprietary tree wound dressing.
As canker can be particularly severe on young plantings, it is important to maintain a complete disease control schedule.
Avoid damage to trees, particularly during winter. Control wildlife such as rabbits, hares and macropods that will chew young green bark, creating disease entry sites.
Cherries and apricots are more susceptible than nectarines, peaches and plums. Therefore in orchards prone to bacterial canker infection, avoid planting cherries and apricots.
Biological
There are currently no biological controls available for controlling bacterial canker in stone fruit.
Chemical
There are registered chemical options available for the control of bacterial canker.
Download the Orchard plant protection guide
See this article in Tree Fruit Oct 2022
