How to Manage Pests
UC Pest Management Guidelines
Pathogen: Pseudomonas syringae
(Reviewed 5/06, updated 4/09)
In this Guideline:
Symptoms are most obvious in spring and include limb dieback with rough cankers and amber-colored gum. There may also be leaf spot or blast of flowers and young shoots. The sour sap phase of decline may not show gum and cankers, but the inner bark can be brown, fermented, and sour smelling. Flecks and pockets of bacterial invasion in bark occur outside canker margins. Frequently, infected trees sucker from near ground level; cankers do not extend belowground.
Pseudomonas syringae survives in or on plant surfaces, is spread by splashing rain, and is favored by high moisture and low temperatures in spring. The disease is worse in low or sandy spots in the orchard. Vigorous trees are less susceptible to bacterial canker. Young trees, 2 to 8 years old, are most affected. The disease rarely occurs in first year of planting and is uncommon in nurseries.
Planting trees that are budded or grafted about 32 inches above the root crown can help suppress bacterial canker infections. Bacterial canker tends to mostly affect weak trees, so any management practice that improves tree vigor (e.g., lighter, more frequent irrigation, improved tree nutrition, nematode management, etc.) will help to reduce the incidence of this disease. Trees on Lovell peach rootstock are more resistant than others; those on plum rootstocks are most susceptible. Delayed pruning may help.
In light sandy soils and some heavy soils, successful control has been achieved with preplant fumigation for nematodes. Application of copper during dormancy has not been shown to protect against bacterial canker.
UC IPM Pest Management Guidelines:
W. D. Gubler, Plant Pathology, UC Davis