How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Symptoms are most obvious in spring, and include limb die back with rough cankers and amber colored gum. There may also be leaf spot and blast of young flowers and shoots. The sour sap phase of bacterial canker may not show gum and cankers, but the inner bark is brown, fermented, and sour smelling. Flecks and pockets of bacterial invasion in bark occur outside canker margins. Frequently, trees sucker from near ground level; cankers do not extend below ground.

COMMENTS ON THE DISEASE

Pseudomonas syringae survives 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, while young trees, 2 to 8 years old, are most affected. The disease rarely occurs in first year of planting, and is uncommon in nurseries.

MANAGEMENT

Delayed pruning may help. Of the rootstocks commonly used for cherries in California, Mahaleb is the most tolerant of bacterial canker, Colt is moderately susceptible, and Mazzard is susceptible. Copper sprays applied at the beginning and end of leaf fall have given variable control.

Treatment Decisions
In light, sandy soils and in some heavy soils, control has been achieved with preplant fumigation for nematodes. Nematodes stress trees, which predisposes them to bacterial canker. The benefits of preplant soil fumigation for control of bacterial canker usually last only a few years; in some areas only limited improvements in disease control occur following soil fumigation.

Following planting, if bacterial canker occurs in an orchard, treat all trees with fenamiphos in that area of the orchard on a yearly basis until the trees are 8 years old.

PUBLICATION

UC IPM Pest Management Guidelines: Cherry
UC ANR Publication 3440
Diseases
J. E. Adaskaveg, Plant Pathology, UC Riverside
W. D. Gubler, Plant Pathology, UC Davis
Acknowledgment for contributions to the diseases section:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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