ENHANCED COLONIZATION BY THE BLUE STAIN FUNGUS OPHIOSTOMA-CLAVIGERUM IN GLYPHOSATE-TREATED SAPWOOD OF LODGEPOLE PINE

The herbicide glyphosate was administered into the sapwood around the root collar of lodgepole pine trees, Pinus contorta var. latifolia Eng elm., to determine its effect on invasion by the blue stain fungus Oph iostoma clavigerum (Robinson-Jeffrey & R.W. Davidson) T.C. Harrington. In two experiments, lesions in the sapwood were longer and wider in t rees treated with glyphosate before inoculation with O. clavigerum tha n in untreated, control trees. Ophiostoma clavigerum was recovered in a third experiment at seven times the distance from the point of inocu lation in trees treated with glyphosate 3 weeks before inoculation as in untreated, control trees. We conclude that previously observed enha ncement of brood development of the mountain pine beetle, Dendroctonus ponderosae Hopk., was caused by glyphosate-induced inhibition of the trees' secondary defense response to invasion by the beetle's symbioti c fungi.