Risk Associated with the Weed Seeds in Imported Grain

Abstract

The risk of introducing weeds to new areas through grain (cereals, oilseeds and pulses) intended for processing or consumption is 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. There is a need to examine the association of weed seeds with grain commodities throughout the production process from field to final end use, and inspection of representative samples for grain crops commonly imported to India. In the field, weed seed contamination of grain crops is affected by factors such as country of origin, climate, biogeography, production and harvesting practices. As it moves toward export, grain is 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 India, inspection data show that grain shipments contain a variety of weed seeds including seeds of regulated weeds. However, grain cleaning and processing methods tailored to end use at destination also affect the presence and viability of weed seeds. For example, grains that are milled or crushed for human use present a lower risk of introducing weed seeds than grains that undergo minimal or no processing. Risk analysis allows each of these stages to be evaluated in order to characterize the overall risk of introducing weeds with particular commodities, and guide regulatory decisions about trade and plant health.