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 on fungal pathogens of fumigants such as methyl bromide (MB) for various combinations 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 soil moisture was 20% of its water-holding capacity. Extension of the exposure 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. basilici. However, killing of S. rolfsii sclerotia was more effective at high doses of MB for short exposures (4-48 h) than at a low dose for longer periods (48-96 h) with the same C x T value. Killing of macroconidia of F. oxysporum f sp. basilici at high concentrations and short exposures was similar to 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 sensitive. In field plots, the incidence of propagule mortality was correlated with C x T values. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.