Wound-inoculated stems of potted 5 yr old Colorado blue spruce transplants subjected to drought stress became predisposed to attack by a conidial isolate of C. kunzei. Bark cankers appeared on stems with a plant water potential of -20 and -30 bars. No cankers formed on unstressed stems or on stems of plants subjected to freezing stresses of -20.degree. and -30.degree. C. The pathogen colonized wood tissues of stressed and unstressed stems to the same extent but formed necrotic cankers only on the bark of drought-stressed plants. Drought stress apparently is the main factor in the predisposition of spruce to Cytospora canker. A selective medium was developed for isolation of C. kunzei.