Effect of Density and Control of Canada Thistle on Production and Utilization of Alfalfa Pasture

A 4-year field study was conducted to determine losses and gains in alfalfa production and utilization due to direct competition of various densities of Canada thistle (Cirsium arvense (L.) Scop.) and their control. Regardless of initial Canada thistle density, within 4 years all stands under no control approached one plant/sq ft. Mowing after each grazing period for 4 years almost eliminated Canada thistle. Throughout the study, the rate of alfalfa stand reduction was the same under mowing treatment regardless of Canada thistle density. Mowing increased alfalfa production 6.2 T/A in 4 years over no control in plots having initial Canada thistle stands of two plants/sq ft. The production loss due to Canada thistle stands of two plants/sq ft was 7.4 T of alfalfa for a 4-year period. Alfalfa consumption was reduced 4.5 T/A.