Enhanced colonization by the blue stain fungus Ophiostomaclavigerum in glyphosate-treated sapwood of lodgepole pine

Abstract

The herbicide glyphosate was administered into the sapwood around the root collar of lodgepole pine trees, Pinuscontorta var. latifolia Engelm., to determine its effect on invasion by the blue stain fungus Ophiostomaclavigerum (Robinson-Jeffrey & R.W. Davidson) T.C. Harrington. In two experiments, lesions in the sapwood were longer and wider in trees treated with glyphosate before inoculation with O. clavigerum than in untreated, control trees. Ophiostomaclavigerum was recovered in a third experiment at seven times the distance from the point of inoculation in trees treated with glyphosate 3 weeks before inoculation as in untreated, control trees. We conclude that previously observed enhancement of brood development of the mountain pine beetle, Dendroctonusponderosae Hopk., was caused by glyphosate--induced inhibition of the trees' secondary defense response to invasion by the beetle's symbiotic fungi.