Phytophthora Root Rot of Banksia: Host Range and Chemical Control. J. J. Cho, Associate Researcher, Department of Plant Pathology, University of Hawaii, HITAHR, Maui Branch, Kula 96790. Plant Dis. 65:830-833. Accepted for publication 19 January 1981. Copyright 1981 American Phytopathological Society. DOI: 10.1094/PD-65-830.

Phytophthora cinnamomi was isolated from blackened roots of 2-yr-old Banksia speciosa plants grown on the island of Maui, Hawaii. Infected plants wilted rapidly, and one side or all of the plant died; other symptoms were collapse of the bark and dark brown discoloration of xylem tissue. B. prionotes and B. occidentalis were also affected. Inoculation of 20 1-yr-old B. speciosa plants with a mycelial homogenate confirmed pathogenicity. Inoculation studies with 0, 1 × 10¹, 1 × 10², 1 × 10³, or 1 × 10⁴ zoospores per plant indicated that B. occidentalis, B. prionotes, B. burdettii, and Protea cynaroides were highly susceptible; B. menziesii was moderately susceptible; B. caleyi was moderately tolerant; and B. integrifolia and B. collina were highly resistant to P. cinnamomi. Susceptibility among species differed at inoculum levels of 1 × 102 and 1 × 10³ zoospores per plant. Soil drenches of metalaxyl protected plants against P. cinnamomi better than did ethazole and fenaminosulf.