THE BIOLOGY OF CANADIAN WEEDS .105. LINARIA-VULGARIS MILL

Yellow toadflax, Linaria vulgaris Mill. (Scrophulariaceae), is a weed of rangelands and agricultural crops. Introduced from Eurasia into Nor th America more than 300 yr ago, it is now naturalized in all province s and territories up to 60 degrees northern latitude and beyond 2000 m altitude. It became a concern in the middle of this century when it i nvaded the prairies. Its seriousness as a weed declined in the late 19 50s, possibly as a result of biological control. Concern has been rene wed recently because the adoption of minimum tillage techniques could lead to greater abundance. Reproduction is vigourous by means of adven titious root buds and by high seed production. Growth forms, vegetativ e reproduction, flower phenology, and germination are variable. The ca pability for regrowth from root parts makes L. vulgaris a difficult we ed to eradicate and limits the efficacy of cultural control methods. T he possibilities for chemical control are limited due to resistance to common herbicides. Biological control projects conducted during the p ast 50 yr have been partly successful and are on-going.