Of 54 isolates tested, 4 isolates of Phytophthora cactorum from udo and 10 isolates of unidentified Phytophthora species, each one from Rhoeo discolor and Brodiaea and 8 isolates from gerbera, showed distinct pathogenicity to udo by artificial inoculation test. Nine isolates of P. cactorum from six different crops except udo were clearly inferior to the isolates from udo in virulence to blanched stem of udo.