The biology of Canadian weeds .106. Linaria dalmatica (L.) Mill.

Dalmatian Toadflax, Linaria dalmatica (L.) Mill. (Scrophulariaceae), is an important weed of rangelands, agricultural crops and waste areas in North America. The literature is less extensive than for the closely related yellow toadflax (Linaria vulgaris Mill.). Introduced from Eurasia as an ornamental plant into North,America by 1894, it became naturalized in seven Canadian provinces and all of the United States of America west of the 100th meridian except for New Mexico. In North America it ranges from ca. 35 degrees to 56 degrees N latitude and it grows from near sea level to altitudes up to ca. 2800 m. Production of up to one-half million seeds per plant and its long-lived perennial nature make the species highly competitive and able to invade cropland and even stands of native ungrazed vegetation. Linaria dalmatica is a hemicryptophyte with strong vegetative reproduction and dormant seeds. Growth of creeping roots after removal of aboveground plant parts limits the effectiveness of control treatments such as grazing, clipping, mowing or burning. Several herbicides control the species for the short term; the smooth and waxy leaf surfaces may hinder herbicide uptake. Experimental biological control with insects since the 1960s shows promise.