Toxicity of methyl bromide to four pathogenic fungi in larch heartwood.

Toxicity of methyl bromide to representative pathogenic fungi was tested by exposing Armillaria ostoyae, Heterobasidion annosum, Lachnellula willkommii, and Leptographium wageneri grown in 1-cm media-amended Dahurian larch (Larix dahurica) wood cubes to initial concentrations of 0, 79, or 237 mg/L of methyl bromide for 8, 24, or 72 hours. All fumigations were performed at 18°C in sealed glass jars. Fumigant concentrations in the jars and sorption into the cubes were closely monitored. After fumigation, cubes were quartered and plated on selected media. The percentage of cube quarter sections with no visible growth after 2 weeks was used as a bioassay of fumigation efficacy. Survival was noted at concentration by time (C x T) values as high as 1270 mgh/L for Armillaria ostoyae, 3010 mgh/L for Heterobasidion annosum, 1230 mgh/L for Lachnellula willkommii, and 4750 mgh/L for Leptographium wageneri. Since previous studies have shown methyl bromide to diffuse slowly through wet wood, these values may be difficult to achieve in the center of logs using conventional tent fumigation techniques.