CHEMICAL AND BIOLOGICAL CONTROL OF PHYTOPHTHORA ROOT AND STALK ROT OF SOYBEAN

Abstract
Chemical and biological control of root and stalk rot of soybean (Glycine max (L.) Merr.) caused by Phytophthora megasperma Drechs. var. sojae Hildebr. (Pms) was attempted in greenhouse and field tests. In-furrow spray-drench and granular treatments of the experimental compound CGA 48988 (Ciba-Geigy), applied at planting time at rates ranging from 0.5 to 2.0 kg a.i./ha, greatly reduced loss of plants from the disease and doubled the yield of the cultivar Steele, which has a low degree of field tolerance to Pms race 6. An in-furrow spray-drench treatment with thiram at 1.0 kg a.i./ha significantly reduced loss of plants, but not as much as CGA 48988 and not sufficiently to increase yield. Captan and CGA 48988 applied to Harosoy 63 seeds (at 0.13 and 0.33 g a.i./kg of seed, respectively) by a pelleting technique gave short-term control in the greenhouse, but did not significantly increase plant survival and yield in the field. CGA 48988, which is systemic in soybeans, increased plant survival and. yield in the field at 1.65 g a.i./kg of seed in seed pellets. Inclusion of the fungal antagonist Gliocladium virens Miller, Giddens and Foster in seed pellets did not significantly control Pms either alone or in combination with a low rate of captan or CGA 48988.

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