Population Dynamics of Phytophthora parasitica, the Cause of Root and Crown Rot of Catharanthus roseus, in Relation to Fungicide Use. D. M. Ferrin, Assistant Professor, Department of Plant Pathology, University of California, Riverside 92521. R. G. Rohde, Former Staff Research Associate, Department of Plant Pathology, University of California, Riverside 92521. Plant Dis. 76:60-63. Accepted for publication 23 June 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0060.

Populations of Phytophthora parasitica from the root zones of container-grown Catharanthus roseus treated with fosetyl-Al applied as foliar sprays or soil drenches and metalaxyl applied as soil drenches were determined 3, 5, 7, 9, and 11 wk after transplanting. Fosetyl-Al had no effect on pathogen populations when applied every 4 wk as foliar sprays at either 2.4 or 4.8 g a.i./L. Pathogen populations were affected more when fosetyl-Al was applied every 4 wk as soil drenches at 1.92 than at 0.96 g a.i./L. Fresh root and shoot weights of plants treated with fosetyl-Al were not significantly different than those of nontreated plants in infested soil and were significantly less than those of nontreated plants in noninfested soil. Metalaxyl delayed the increase of pathogen populations at all concentrations tested but was most effective when applied every 4 wk at 37.4 mg a.i./L. Fresh root and shoot weights of plants treated with metalaxyl were significantly greater than those of nontreated plants in infested soil and were not significantly different than those of nontreated plants in noninfested soil.

Keyword(s): Aliette, Subdue.