VIEW ARTICLE

Comparative Efficacy of 2-Chloro-6-Methoxy-4(Trichloromethyl) Pyridine and Ethazole for Control of Phytophthora Root Rot of Rhododendron and Soybean. H. A. J. Hoitink, Associate Professor, Department of Plant Pathology, Ohio Agricultural Research and Development Center, Wooster 44691; A. F. Schmitthenner, Professor, Department of Plant Pathology, Ohio Agricultural Research and Development Center, Wooster 44691. Phytopathology 65:69-73. Accepted for publication 30 July 1974. DOI: 10.1094/Phyto-65-69.

Dowco 269 [2-chloro-6-methoxy-4-(trichloromethyl) pyridine] effectively controlled Phytophthora cinnamomi on rhododendron. Soil drenches (300 µg/ml) before inoculation prevented root rot, whereas drenches applied after inoculation did not. Dexon drenches were ineffective. Ethazole was less effective than Dowco 269, but a 375-µg/ml drench prevented root rot. In greenhouse tests, a 100-µg/ml drench or 1.12 kg/hectare(ha) furrow treatment of Dowco 269 effectively controlled soybean root rot caused by Phytophthora megasperma var. sojae. Furrow treatment with ethazole (1.12 kg/ha) was equally effective, but phytotoxic. Slight stunting was caused by 2.24 kg/ha Dowco 269. Foliar sprays with Dowco 269 delayed appearance of rhododendron and soybean root rot symptoms, indicating that systemic uptake of Dowco 269 by leaves and stems, and movement into roots may occur. Dowco 269 does not eradicate P. cinnamomi or P. megasperma var. sojae, race 1, from infected rhododendron or soybean plants.