Submitted to: Weed Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/30/1995
Publication Date: N/A
Citation: Interpretive Summary: Perennial weeds, such as Canada thistle, limit farmer adoption of reduced tillage cereal production systems for controlling wind erosion in the northern Great Plains. The extent to which Canada thistle reduces spring wheat yields in reduced and no till production systems has been described, but the mechanisms for competition are poorly characterized. The intent of fthis research was to determine when competition first occurs following cro emergence and to determine which spring wheat yield components are most reduced by competition with Canada thistle. This research establishes that even the first formed yield component, wheat stand, can be reduced by Canada thistle. This is noteworthy because most weeds do not reduce crop stand. This research suggests that Canada thistle, a highly competitive perennial weed, must be controlled in no till spring wheat either before or shortly after wheat emergence if Canada thistle's detrimental effects on wheat yield are to be minimized.
Technical Abstract: The objective of this research was to characterize Canada thistle's effects on spring wheat's major yield components using path coefficient analysis. This information provides insight concerning which yield components are reduced most by Canada thistle competition and when Canada thistle competition first occurs during spring wheat growth. Increasing Canada thistle density greatly decreased wheat stand in each of three years. Canada thistle also reduced spikes per plant and seeds per spike to varying extents depending on year, but Canada thistle had comparatively little effect on wheat seed weight. Path coefficient correlation analysis showed that Canada thistle reduced spring wheat yield chiefly by indirect effects via wheat stand. Indirect effects on wheat yield via later formed wheat yield components occurred chiefly via secondary indirect effects via wheat stand. These data suggest that Canada thistle must be controlled either before or shortly after wheat emergence if its detrimental effects on whea yield are to be minimized.