Effects of soil water content and soil temperature on efficacy of metham-sodium against Verticillium dahliae

Soil column studies were conducted to investigate the influence of soil water content and soil temperature on the efficacy of metham-sodium and its degradation product methyl isothiocyanate against Verticillium dahliae. The viability of the microsclerotia (MS) of the fungus in the top 30 cm of fumigated and control columns was measured. Temperatures for studies were 2 or 22°C, and the soil water content, expressed as soil matric potential, varied from -23 (wet), -113 (moist), to -2485 J/kg (dry). There was a significant interaction of soil water content and temperature on the efficacy of metham-sodium against V. dahliae MS. For the low soil temperature (2°C) the fumigant was more effective against MS of the fungus in wet than in moist or dry soil. Soil water content did not affect fungicidal activity of metham-sodium when the soil columns were maintained at 22°C. These results suggest that the fumigant has a greater efficacy against dahliae in wet/cold soil conditions compared to the other conditions tested. Consequently, it was recommended that metham-sodium be applied to fields by chemigation in late fall or early spring to obtain efficacious results.