In Western Canada, the threat of herbicide resistance has grown like a weed in recent years. Behind the United States and Australia, Canada has the third greatest number of unique herbicide-resistant weed biotypes. The number of weed species in this country that have developed resistance has grown steadily since the 1970s and stands at about 80. No new meaningful modes of action have been introduced since the 1980s, and the selection pressure that produces resistance is expected to continue.