Evaluation of soil fumigants on soilborne fungal pathogens in a controlled-environment system and in soil

A controlled-environment system was developed for determining the effects o n fungal pathogens of fumigants such as methyl bromide (MB) for various com binations of doses (C) and exposure time (T). In this system, sclerotia of Sclerotium rolfsii, added to a sandy soil, were most sensitive to MB when s oil moisture was 20% of its water-holding capacity. Extension of the exposu re time (T) to MB enabled a reduction in the dose needed to kill 50% (CT50) of S. rolfsii sclerotia or macroconidia of Fusarium oxysporum f. sp. basil ici. However, killing of S. rolfsii sclerotia was more effective at high do ses of MB for short exposures (4-48 h) than at a low dose for longer period s (48-96 h) with the same C x T value. Killing of macroconidia of F. oxyspo rum f sp. basilici at high concentrations and short exposures was similar t o that at longer exposure to low concentrations, with the same C x T values . Sclerotium rolfsii sclerotia were the least sensitive to MB, relative to chlamydospores off. oxysporum f. sp. radicis-lycopersici and F. oxysporum f . sp. basilici macroconidia and chlamydospores, the latter being the most s ensitive. In field plots, the incidence of propagule mortality was correlat ed with C x T values. (C) 1999 Published by Elsevier Science Ltd. All right s reserved.