Chemical Control of Phytophthora cinnamomi on Avocado Rootstocks. M. D. Coffey, Professor, Department of Plant Pathology, University of California, Riverside 92521. H. D. Ohr, Extension Plant Pathologist, S. D. Campbell, Staff Research Associate, and F. B. Guillemet, Staff Research Associate, Department of Plant Pathology, University of California, Riverside 92521. Plant Dis. 68:956-958. Accepted for publication 24 April 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-956.

Good control of Phytophthora cinnamomi was achieved with 2-yr-old Hass avocado nursery trees grafted on Duke 7 clonal rootstocks by using fosetyl-Al as a 3-L preplant application (500 μg a.i./ml) 48 hr before planting and as a postplant soil treatment at either 70 or 35 g a.i./m², two or four times per year, respectively. Similar disease control was obtained using a mixture of metalaxyl and etridiazole (ethazol) in which the preplant dosages were 25 and 200 μg a.i./ml and the postplant rates, applied twice per year, were 2 and 10 g a.i./m² of metalaxyl and etridiazole, respectively. Twenty-year-old Fuerte avocados on Phytophthora-susceptible rootstocks severely infected with P. cinnamomi were pruned back to their scaffold limbs and treated with either metalaxyl or fosetyl-Al. Both fungicides restored fruit production within 2 yr. The most cost-effective treatment was a foliar spray (3 g a.i./L) of fosetyl-Al applied three to five times per year.