Knapweed is highly competitive, capable of invading grassland sites to the exclusion of native vegetation. Domestic animals and wildlife such as elk rely on these range grasses and herbs for up to 80 per cent of their diet. Knapweed encroachment can destroy the forage base and would result in a significant decline in deer and elk numbers. If spread to its ecological limit, knapweed could infest up to 8 to 10 million hectares (20 to 26 million acres) in western Canada. - BC Ministry of Agriculture & Lands
Gerard Mulders has provided the folllowing photos to help identification of these plants.