Pathway risk analysis of weed seeds in imported grain: A Canadian perspective

Abstract

The risk of introducing weeds to new areas through grain (cereals, oilseeds and pulses) intended for process ing or consumption is typically considered less than that from seed or plants for planting. However, within the range of end uses for grain, weed risk varies significantly and should not be ignored. In this paper, we discuss pathway risk analysis as a framework to examine the association of weed seeds with grain commodities throughout the production process from field to final end use, and present inspection sampling data for grain crops commonly imported to Canada. In the field, weed seed contamination of grain crops is affected by factors such as country of origin, climate, biogeography and production and harvesting practices. As it moves toward export, grain is typically cleaned at a series of elevators and the effectiveness and degree of cleaning are influenced by grain size, shape and density as well as by grade requirements. In cases where different grain lots are blended, uncertainty may be introduced with respect to the species and numbers of weed seed contaminants. During transport and storage, accidental spills and cross-contamination among conveyances may occur. At the point of import to Canada, inspection sampling data show that grain shipments contain a variety of contaminants including seeds of regulated weeds and species that represent new