Bacterial Canker

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 below ground.

Pseudomonas syringae survives in or on plant surfaces and is spread by splashing rain. It 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. Properly irrigate and fertilize young trees during the growing season. Trees on Lovell peach rootstock are more resistant than others; and 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 in California.

Bactericide applications have no reliable effect on bacterial canker and their use is not recommended. Preplant fumigation for nematode control reduces the severity of bacterial canker in newly planted orchards. Nematodes stress trees, which predisposes them to bacterial canker. The benefits of preplant soil fumigation for control of bacterial canker usually lasts only a few years; in some areas only limited improvements in disease control occur following soil fumigation. For additional information, see NEMATODES.