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In Vivo Expression of Resistance to Metalaxyl by a Nursery Isolate of Phytophthora parasitica from Catharanthus roseus. 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. 76:82-84. Accepted for publication 1 August 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0082.

Populations of a metalaxyl-insensitive isolate of Phytophthora parasitica from a nursery in southern California were determined every 2 wk for 10 wk from the root zones of container-grown Catharanthus roseus either treated or not treated with metalaxyl or fosetyl-Al. When compared with no treatment, metalaxyl applied every 4 wk as soil drenches at 18.8 or 37.4 mg a.i./L and fosetyl-Al applied every 4 wk as foliar sprays at 4.8 g a.i./L had no effect on populations of the isolate. However, increase of the pathogen population was delayed and the population was significantly less (P < 0.05) than that of the nontreated control at 6 and 10 wk when fosetyl-Al soil drenches at 1.92 g a.i./L were applied every 4 wk. Based on determinations of fresh shoot and root weights, metalaxyl failed to control disease and fosetyl-Al provided acceptable control.

Keyword(s): Aliette, Subdue.