Pseudomonas Canker of Pear Trees in Oregon, Cultivar Resistance, and Effect of Trunk Guards on Canker Incidence and Bacteria Survival on Bark. R. A. SPOTTS, Mid-Columbia Agricultural Research and Extension Center, Oregon State University, Hood River 97031. L. A. CERVANTES, Mid-Columbia Agricultural Research and Extension Center, Oregon State University, Hood River 97031. Plant Dis. 78:907-910. Accepted for publication 20 June 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0907.

Extensive cankers caused by Pseudomonas syringae pv. syringae were observed on young pear trees in early spring 1991 following low-temperature injury in December 1990. The majority of cankers were on the trunk and lower scaffold limbs, usually close to or extending into the trunk. Canker incidence was greater on trees with trunks enclosed in corrugated, white plastic guards than on trees without guards. Survival of P. s. syringae inoculated on the surface of the bark of Bartlett trees was significantly greater when tree trunks were covered with guards than when guards were not used. P. s. syringae was isolated from all canker margins in spring 1991, but incidence decreased to 30-50% of the cankers after two growing seasons. The cultivars Bosc and Cornice were rated as susceptible to Pseudomonas canker. Red strains of d'Anjou and Bartlett were considered resistant in both field evaluations and a detached shoot test.