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This spring, Southeastern peach growers frequently noticed withered blossoms with an amber-colored gummy substance oozing from them, a condition known as blossom blast. Lab analysis showed that a strain of a bacterium, Pseudomonas syringae, caused this condition. This bacterium causes a disease in peach and other stone fruit known as bacterial canker. Bacterial canker can result in a reduction in fruit yield due to plant decline or loss of entire trees.

The bacterium is present inside or on the surface of plant tissue. Cool, wet weather occurring during our long bloom period predisposed trees to the disease. Poor soil conditions also favor disease development. Wind and rain help disperse the bacterium from tree-to-tree within an orchard.

Symptoms

In addition to blossom blast, other symptoms of bacterial canker include twig blight, dieback and leaf spots similar to bacterial leaf spot. Canker formation (dark areas) causes girdling and kills all plant material beyond the point of infection. Girdling of trunks and branches leaves a sunken area underneath the bark that elongates as the infection spreads upward or outward on the tree.  Removal of the bark will reveal a brownish streak in the vascular tissue. A  sour, fermenting odor often occurs from the infected tissue. You can detect this odor simply by walking through an orchard infected with the disease. Cankers formed on trunks can kill the entire portion of the tree above ground in a matter of weeks, but the root system will survive and produce suckers.

Disease cycle

The bacterium overwinters in cankers, buds, and other tissues of peach.  The bacterium also overwinters in weeds and other plant species near the orchard. Frequent rainfall, high humidity and cool temperatures in late winter and early spring favor growth of this pathogen. The bacterium enters leaves through stomata and begins to multiply. The bacterium then exits the leaf and moves to the shoot. Infection of trunks and branches occurs in fall and winter through wounds caused by pruning or freeze injury, or through natural openings. The bacterium can also be spread from tree to tree on pruning tools.  The bacterium infects fruit and seeds in cases where infected flowers survive.

Control

Follow sound cultural practices to improve overall tree health and minimize stress. Minimizing stress reduces the incidence of bacterial canker. Choose plant sites that are elevated to minimize freeze injury and occurrence of standing water. Reduce stress from nematodes by fumigating prior to orchard establishment. Copper products are not effective in controlling bacterial canker.

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