How to Manage Pests

Pests in Gardens and Landscapes

Bacterial canker and blast—Pseudomonas syringae

Symptoms of bacterial canker and blast are most obvious in spring and include limb dieback with rough cankers. Cankers are irregularly shaped, brown, water-soaked areas that develop in the bark and outer sapwood of spurs, branches, and the tree trunk. Small cankers can develop on twigs at the base of infected buds. Amber-colored gum may exude from the margins of cankers. In cold, wet weather, blossoms may turn brown, shrivel, and cling to the tree. Leaves also may develop dark spots that later drop out. Sunken spots may develop on young fruit. A more severe form of the disease, the sour sap phase, generally occurs in younger trees. This phase may not show gum and cankers, but the inner bark is brown, fermented, and sour smelling. Reddish flecks and pockets of bacterial invasion in bark occur outside canker margins. Trees frequently sucker from near ground level. Cankers do not extend below ground.

Identification | Life cycle

Solutions

Avoid planting on shallow soils. Plant less susceptible rootstocks. Choice of rootstock and varieties can influence the susceptibility of plums, prunes, and cherries to bacterial canker and blast. Generally, vigorous trees have less trouble with bacterial canker Practice measures, such as adequate fertilizer and irrigation that encourage good plant growth. If trees have been infected, remove entire affected branches in the summer, being sure to eliminate the entire canker and a few inches below. If freezing conditions occur during bloom or early fruit growth, cover them or use protective shelters.

Gumming on branches
Gumming on branches
Water-soaked areas
Water-soaked areas
Affected blossoms
Affected blossoms


Statewide IPM Program, Agriculture and Natural Resources, University of California
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Agriculture and Natural Resources, University of California

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