VIEW ARTICLE

Disease Control and Pest Management

Efficacy and in vitro Activity of Two Systemic Acylalanines and Ethazole for Control of Phytophthora cinnamomi Root Rot of Azalea. D. M. Benson, Assistant professor, Department of Plant Pathology, North Carolina State University, Raleigh 27650; Phytopathology 69:174-178. Accepted for publication 30 August 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-174.

One drench of the acylalanines CGA-38140 (72 μg/ml) or CGA-48988 (18 μg/ml) applied 3 days before inoculation controlled Phytophthora root rot of azalea for 24 wk. Rates of 72 and 144 μg/ml of CGA-48988 were phytotoxic to Hershey Red azalea if applied more frequently than three times in 24 wk. Lower rates of CGA-48988 (18 μg/ml) were not phytotoxic. Ethazole (222 μg/ml) was as effective as the acylalanines in control of root rot only if applied at least four times in 28 wk. Systemic activity of CGA-48988 was demonstrated 6 days after drenching azaleas at rates 12–36 times the rate that effectively controlled root rot (18 μg/ml). After 5 days, ED₅₀ for linear extension of Phytophthora cinnamomi in vitro was 0.11, 0.16, and 0.32 μg/ml for CGA-48988, CGA-38140, and ethazole, respectively. Inhibition of sporangial formation was similar for all three compounds with ED₅₀ values ranging between 0.11 and 0.17 μg/ml. The ED₅₀ values for inhibition of chlamydospore formation were 0.01, 0.04, and 1.4 μg/ml for CGA-38140, CGA-48988, and ethazole, respectively. When the compounds were drenched on 6-cm soil columns containing an agar disk of P. cinnamomi at 2 cm, ED₅₀ values for subsequent growth on cornmeal agar were 1.9, 2.2, and 320.0 μg/ml for CGA-48988, CGA-38140, and ethazole, respectively. Ethazole mobility in soil columns was not enhanced by additional water. At the concentration of the acylalanines and ethazole effectively controlling root rot, these materials acted like fungistats rather than fungitoxicants.