WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Bacterial Blight/Canker

(Pseudomonas syringae)

Diseases

 

Symptoms

Bacterial blight can be a serious blueberry disease in Northwestern Washington during wet springs, and especially when associated with frost damage. Only previous season canes are affected. Cankers range in size from less than an inch to the whole length of the cane; tissue turns reddish brown to black when infected. Buds in the infected region will die. If the stem is girdled with the canker, buds above the infection will die. Loss is due to reduction in plant vigor and yield due to dead tissue.

 

Life History

Pseudomonas syringae is a naturally present environmental bacterium that can survive on the surface of the stem; it only infects the plant if it enters the stem through wounds, such as from frost damage, or through natural openings, such as leaf scars. A protein produced by the bacteria allows ice-nucleation during low-temperature periods causing winter-injury to the plant; hence the disease association with frost-damage. P. syringae is more often a problem during early to late spring, especially if late frosts are prevalent.

 

Monitoring

Begin monitoring in dormancy before pruning, looking for blighted tips or cankered twigs. Symptoms are similar to Blueberry scorch virus and Botrytis blight, and can easily be confused. Send in samples to a diagnostic lab for verification if unsure of pathogen.  In machine harvested fields, also scout post-harvest for infection in harvester wounds.

 

Thresholds and Management

Threshold depends on market, weather, and variety grown.  Atlantic, Burlington, Coville, Chandler, Darrow, and Patriot are very susceptible; Elliott, Rancocas, and Weymouth are more resistant.  In a mature planting, consider treatment when more than 10% of plants are infected or any infection is detected on basal whips.

Prune out diseased wood as soon as it is noticed, and especially before autumn rains, to prevent spread of the bacteria.

Chemical control should begin at the start of the dormant period in October, with sprays to reduce bacterial levels on the plants. Apply sprays before autumn rains, and maybe again in the spring starting at bud-break. Although copper was considered effective, some increasingly resistant bacterial strains have been found in British Columbia.

Initial trials with two biological control products have shown promising results. Serenade (Bacilllus subtilis strain QST713) and BlightBan (Pseudomonas fluorescens strain A506) have been tested for several years in British Columbia. Both products have shown to reduce disease incidence, especially in fields with high disease pressure. The timing of application of these products is crucial; they should be applied early in the spring, before the damaging frost periods. The proposed method of control of these products is by replacing the harmful bacteria with the non-ice-nucleating strains of bacteria which will reduce frost injury. Both Serenade and BlightBan may also have some control on Botrtyis and Mummyberry infections.

 

References

Michigan State University, Michigan Blueberry Facts, Bacterial Canker
http://www.blueberries.msu.edu/bacterialcanker.htm

Oregon State University Extension, An Online Guide to Plant Disease Control, Blueberry-Bacterial Canker
http://plant-disease.ippc.orst.edu/ShowDisease.aspx?RecordID=176

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WSU Whatcom County Extension • 1000 N. Forest St., Bellingham, WA 98225 • (360) 778-5800 • whatcom@wsu.edu