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Fungitoxicity of Metalaxyl against Phytophthora parasitica var. nicotianae. T. H. Staub, CIBA-GEIGY Limited, Agricultural Division, 4002 Basle, Switzerland; T. R. Young, CIBA-GEIGY Corporation, Agricultural Division, Vero Beach, FL 32960. Phytopathology 70:797-801 . Accepted for publication 26 November 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-797.

The biological mode of action of metalaxyl (CGA-48988) against Phytophthora parasitica var. nicotianae was investigated on agar and on tobacco seedlings in petri dishes. The ED50 for mycelial growth on V8-juice agar was 0.2 μg/ml. On water agar the formation of sporangia from chlamydospores was completely blocked by a concentration of 1 μg/ml. In the petri dish-tobacco seedling system, 0.2 μg/ml CGA-48988 prevented the formation of sporangia both from chlamydospores and on infected tobacco roots. When sporangia or zoospores were used as inoculum for tobacco seedlings, CGA-48988 did not inhibit germination or penetration processes; however, fungus development within treated roots was completely blocked by a concentration of 1 μg/ml. Protective and therapeutic action against black shank in tobacco seedlings was exhibited at 1.0 μg/ml of CGA-48988.

Additional keywords: CGA-48988, Nicotiana tabacum, Phytophthora nicotianae var. nicotianae.