THE OCCURRENCE OF PHYTOPHTHORA SPP. IN IRRIGATION SYSTEMS IN BRITISH COLUMBIA

Twenty-seven of 31 irrigation sources serving the Okanagan and Similkameen valleys of British Columbia were contaminated with Phytophthora. P. cactorum, the cause of collar rot of fruit trees in this region, was recovered from 15 sources; P. cambivora and P. citricola from 1 each; P.. megasperma from 4 sources. Many isolates of uncertain identity also were recovered. P. cactorum, P. cambivora, and P. citricola were pathogenic to rootlets of young apple seedlings in laboratory tests, but only P. cactorum is considered an important pathogen in this region.