Reduction of Phellinus weirii Inoculum in Douglas-Fir Stumps by the Fumigants Chloropicrin, Vorlex, or Methylisothiocyanate

Abstract

Abstract Three dosages of chloropicrin and Vodex, with and without sealing, and one dosage of methylisothiocyanate (MIT) in capsules or open glass tubes were applied to Douglas-fir stumps to reduce Phellinus weirii (Mutt.) Gilb. inoculum. After 2 years, all fumigants had reduced the amount of inoculum, but MIT was less effective than chloropicrin or Vorlex. Neither higher levels of fumigant nor sealing the stump tops resulted in further reduction of inoculum. Inoculum in dead stumps was not further reduced by covering stumps with a plastic tarp. Presence of advanced decay did not seem to be advantageous for movement of the fumigant in stumps and roots. Assessment of inoculum survival by using either aseptic isolation techniques or observations of fungal regrowth on the cut surfaces of incubated root disks were comparable for detecting viable P. weirii in root disks from untreated stumps. As a percentage of prefumigation inoculum volume, isolations from fumigated stumps, indicated more viable P. weirii in roots (22%) than did fungal regrowth (7%). Most root disks contained viable P. weirii where residual fumigant was not detected in bioassays, whereas viable P. weirii was not found in 26 of 27 root disks where fumigant was detected. For. Sci. 33(2):316-329.