Fungicides for Control of Phytophthora Root Rot of Azalea in Landscape Beds. D. M. Benson, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Plant Dis. 69:697-699. Accepted for publication 21 February 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-697.

Ethazol, fosetyl Al, and metalaxyl at rates of 0.025, 0.044, or 0.0014 kg a.i./5.5 m² of soil surface were applied to landscape beds of azalea cultivar Hinodegiri that were naturally infested with Phytophthora cinnamomi. The fungicides were applied at 30- or 60-day intervals during the growing season for 2 yr. No foliar symptoms developed on plants during the first growing season, and disease incidence based on root isolations of P. cinnamomi was low to nil. Dramatic symptom development was observed in some plots during the second growing season where P. cinnamomi was not controlled. Fungicide efficacy in decreasing order of protection was metalaxyl, fosetyl Al, and ethazol. In general, no differences in rates of symptom development regardless of fungicide were associated with 30- or 60-day intervals of application. Mortality after two growing seasons was greatest in untreated, infested plots and ethazol-treated plots, lower in fosetyl Al-treated plots, and nil in metalaxyl-treated plots. Inoculum density of P. cinnamomi was highest in the root zones of plants in untreated, infested plots and ethazol-treated plots (range 1.0–3.8 propagules per gram [p/g] of soil), intermediate in fosetyl Al-treated plots (range 0.1–2.2 p/g of soil), and lowest in metalaxyl-treated plots (range nil to 0.07 p/g of soil) over a 2 yr period. At the rates tested, only metalaxyl gave satisfactory control of Phytophthora root rot of azalea in landscape beds.