DISTRIBUTION AND IMPORTANCE IN NORTHWESTERN ALBERTA OF TOADFLAX AND ITS INSECT ENEMIES

Abstract

A survey was conducted during 1971–73 to determine the distribution of toadflax (Linaria vulgaris Mill.) in the Peace River region of northwestern Alberta. A total of 4,189 ha were found to be moderately or heavily infested. Approximately 47% of the infested land was used for perennial forage crops and 45% for annual crops and summer fallow. The remainder occurred on abandoned lands or in farmyards and woodland. Comparison with estimates of toadflax distribution made in 1956 indicates that the weed may be decreasing in a large portion of the survey areas, although increases are apparent on a few farms. Two biological control agents, the flower-feeding beetle, Brachypterolus pulicarius L., and the seed-eating weevil, Gymnaetron antirrhini Payk., accompanied by improved tillage practices appear to be the major factors restricting the spread of toadflax. The weed is not considered a serious problem in cereal crops but is troublesome in forage crops such as creeping red fescue (Festuca rubra L.) where high densities reduce seed yields.