PSEUDOMONAS CANKER OF PEAR TREES IN OREGON, CULTIVAR RESISTANCE, AND EFFECT OF TRUNK GUARDS ON CANKER INCIDENCE AND BACTERIA SURVIVAL ON BARK

Extensive cankers caused by Pseudomonas syringae pv. syringae were obs erved on young pear trees in early spring 1991 following low-temperatu re 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 corrug ated, 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 th an when guards were not used. P. s. syringae was isolated from all can ker margins in spring 1991, but incidence decreased to 30-50% of the c ankers after two growing seasons. The cultivars Bose and Comice were r ated as susceptible to Pseudomonas canker. Red strains of d'Anjou and Bartlett were considered resistant in both field evaluations and a det ached shoot test.