SUPPRESSION OF KNAPWEED INVASION BY CRESTED WHEATGRASS IN THE DRY INTERIOR OF BRITISH-COLUMBIA

An experimental plot established 11 yr previously in the dry interior of British Columbia was resampled to test the ability of crested wheatgrass and Russian wild rye [Elymus-junceus] to suppress the invasion of diffuse knapweed. Knapweed density was high in non-seeded plots, moderate in Russian wild rye plots and very low in crested wheatgrass plots. Watering experiments indicated that lack of soil moisture resulted in high seedling mortality and prevented knapweed invasion into crested wheatgrass plots. Diffuse knapweed reinvaded a similar experimental area in a higher rainfall region of British Columbia, which shows that the same cultural practices will have different effects on knapweed suppression under different climatic regimes.