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 and/or total tree collapse. 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 occurs almost exclusively in orchards where almond or other Prunus spp. orchards previously existed. The disease is worse in low (cold) or sandy spots with high populations of ring nematode. Nitrogen deficient trees are most prone to bacterial canker as are young trees that are 2 to 8 years old. The disease rarely occurs in first year of planting and is uncommon in nurseries.

MANAGEMENT

The pathogen that causes bacterial canker is commonly present on the surfaces of many plants. Consequently, management of this disease should focus on preventing conditions that predispose trees to the disease.

• Before planting, properly sub-soil the orchard to break up hard-pan areas. When replanting an orchard, fumigate the soil before planting to reduce ring nematode populations.
• Trees planted on Marianna 2624 and peach-almond hybrid (Hansen) rootstocks are very susceptible to bacterial canker. Of the rootstock that are somewhat resistant to the disease, Lovell rootstock produces trees that are more tolerant than those growing on Nemaguard.
• Maintaining proper nutrition, particularly nitrogen, is important.
• Recent studies have shown that a foliar application of 100 lb/acre of low biuret urea before leaf drop significantly reduces canker size in infected trees.
• Annual nematicide treatments in October can help reduce disease severity.

PUBLICATION

UC IPM Pest Management Guidelines: Almond
UC ANR Publication 3431
Diseases
W. D. Gubler, Plant Pathology, UC Davis
J. E. Adaskaveg, Plant Pathology, UC Riverside
Roger Duncan, UC Cooperative Extension, Stanislaus County
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center
Acknowledgment for contributions to the disease section:
B. L. Teviotdale, Kearney Agricultural Center, Parlier

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