How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Symptoms are most obvious in spring and include limb dieback 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 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, 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

Problems with bacterial canker can be minimized at planting by carefully selecting the planting site, choosing the least susceptible rootstocks, and following recommended cultural practices regarding pruning and fertilizing. 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. Delayed pruning may help. Lovell nectarine rootstock is usually more tolerant than others.

In light, sandy soils and in some heavy soils, control has been achieved with preplant fumigation for nematodes. Application of copper during dormancy has not been shown to protect against bacterial canker.

Organically Acceptable Methods
Cultural controls are acceptable for use in an organically certified crop.

Chemical Control
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 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, apply nematicide around all trees in the affected area of the orchard on a yearly basis until the trees are 8 years old.

PUBLICATION

UC IPM Pest Management Guidelines: Nectarine
UC ANR Publication 3451
Diseases
W. D. Gubler, Plant Pathology, UC Davis
J. E. Adaskaveg, Plant Pathology, UC Riverside
Acknowledgment for contributions to the diseases section:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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