VIEW ARTICLE

Disease Control and Pest Management

Effect of Soil Structure on Penetration by Metham-Sodium and of Temperature on Concentrations Required to Kill Soilborne Pathogens. Y. Ben- Yephet, Department of Plant Pathology, Agricultural Research Organization (ARO), The Volcani Center, Bet Dagan 50 250, Israel; Z. R. Frank, Department of Plant Pathology, Agricultural Research Organization (ARO), The Volcani Center, Bet Dagan 50 250, Israel. Phytopathology 75:403-406. Accepted for publication 16 October 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-403.

Penetration of metham-sodium and its efficacy against microsclerotia (MS) of Verticillium dahliae were evaluated in a loessial soil (20% clay content) with a single-grained structure and a clay soil (54% clay content) with well defined, aggregated structure. The chemical, applied in a dilute solution to 1 m² field microplots, killed the MS to a deeper level in the clay soil than in the loessial soil. To corroborate results obtained from field studies, penetration of metham-sodium was also tested in plastic columns filled with sieved or ground samples of soils. In the clay soil, the fungicide killed MS to a deeper level in the sieved samples with large (<6,000 μm) aggregates than in ground samples of the same soil containing smaller aggregates. In the loessial soil, however, the fungicide killed MS to the same depth in both the sieved and ground samples which had similar aggregate sizes. The toxicity of metham-sodium to resting structures of several pathogens was greatest at a high temperature (35 C). However, the temperature coefficient of the fungicide's activity was not constant. The fungicide dose required to kill 50% of the MS of V. dahliae at 15 C was 1.5, 3, and 6 times that required at 25, 30, and 35 C, respectively. The ED₅₀ for V. dahliae, Fusarium oxysporum f. sp. melonis, and Sclerotium rolfsii was half that for Sclerotinia sclerotiorum.