Control of Phytophthora Root and Crown Rot and Trunk Canker in Walnut with Metalaxyl and Fosetyl Al. M. E. Matheron, Former Graduate Student, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, University of California, Davis 95616. S. M. Mircetich, Professor, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 69:1042-1043. Accepted for publication 11 June 1985. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/PD-69-1042.

Monthly soil drenches with metalaxyl (36 mg a.i./plant) or fosetyl Al (1,800 mg a.i./plant) reduced root and crown rot in seedlings of Juglans hindsii and Paradox walnut rootstocks in soil artificially infested with Phytophthora citricola or P. cinnamomi and flooded for 48 hr every 2 wk. Metalaxyl was significantly more effective than fosetyl Al in reducing root and crown rot severity in seedlings of J. hindsii in soil infested with P. citricola. However, the fungicides provided similar disease control when applied to J. hindsii grown in soil infested with P. cinnamomi or to Paradox seedlings in soil infested with P. citricola or P. cinnamomi. Application of metalaxyl (270 mg a.i./plant) or fosetyl Al (900 mg a.i./plant) directly to stems of J. hindsii or J. regia significantly suppressed canker development when treated stems were subsequently inoculated with P. citricola or P. citrophthora. Both fungicides were active in the stems for at least 54 days after application.