Combined soil treatments and sequence of application in improving the control of soilborne pathogens

The effects of reduced doses of methyl bromide (MB) or metham sodium, heati ng, short solarization, and soil microbial activity, alone or in combinatio n, on survival of soilborne fungal pathogens were tested in a controlled-en vironment system and field plots. Sublethal doses of heating or MB delayed germination of Sclerotium rolfsii sclerotia. Combining MB and heating treat ments was more effective than either treatment alone in controlling S. rolf sii and Fusarium oxysporum f. sp. basilici. The application healing followe d by fumigation with MB, was significantly more effective in delaying and r educing germination of S. rolfsii sclerotia and in controlling F. oxysporum f, sp. basilici than the opposite sequence. Further, incubation in soil an d exposure to microbial activity of previously heated or MB-treated sclerot ia increased the mortality rate, indicating a weakening effect. Similarly, incubation of chlamydospores of F. oxysporum f. sp. melonis and F. oxysporu m f. sp. radicis-lycopersici in soil in the field after fumigation further reduced their survival, confirming the laboratory results. In field tests, combining MB or metham sodium at reduced doses with short solarization was more effective in controlling fungal pathogens than either treatment alone. Treatment sequence significantly affected pathogen control in the field, s imilar to its effect under controlled conditions. This study demonstrates a frequent synergistic effect of combining soil treatments and its potential for improving pathogen control and reducing pesticide dose, especially whe n an appropriate sequence was followed.