MOVEMENT AND PERSISTENCE OF CHLOROPICRIN, VAPAM, AND METHYLISOTHIOCYANATE IN UNTREATED SOUTHERN PINE AND DOUGLAS-FIR TIMBERS

Untreated Douglas-fir and southern pine timbers were inoculated with brown-rot and white-rot fungi as vapor-sensing agents to evaluate the movement and distribution of fungitoxic concentrations of chloropicrin, Vapam, and methylisothiocyanate (MIT). Residual fumigant in timbers was determined by a bioassay with Gloeophyllum trabeum. The fumigants were introduced into 2.54-cm-diameter holes at timber midlength. Fumigants diffused throughout the cross-sectional area of both southern pine and Douglas-fir. The brown- and white-rot fungi generally showed similar tolerance to the fumigants. Chloropicrin killed most fungal cultures in both timbers 0.30 m from the treatment centerline (CL) within 1 week after treatment. Vapam and MIT were effective at 0.30 m from CL by 4 weeks. At 0.61 m from CL, the fumigants were ineffective in killing cultures implanted in southern pine. In Douglas-fir, Vapam was also ineffective at this distance, but chloropicrin and MIT were effective. In both southern pine and Douglas-fir, none of the fumigants killed cultures implanted at 1.22 m from CL. Bioassay of cores removed from fumigated southern pine timbers showed little residual fungistatic effect beyond 0.30 m. Residual fungistatic effect decreased in chloropicrin- and Vapam-treated southern pine 1 year after treatment and was not present in MIT-treated pine at 2 years after treatment. In Douglas-fir, all fumigants showed a residual fungistatic effect at 0.61 m from CL 2 years after treatment. In Vapam-and MIT-treated timbers, the residual fungistatic effect had decreased by 3 years after treatment. By contrast, a residual fungistatic effect was detected in chloropicrin-treated Douglas-fir at 1.22 m from CL at 3 years after treatment, and the effect was still present a year later.