Non-Peer ReviewedHexazinone is an effective weed control tool in alfalfa seed production. However, both researchers and producers have had variable success in Canada thistle control with hexazinone. The objective of this study was to determine the effects of hexazinone rates, application timing and residue management on Canada thistle control and alfalfa seed production. Two field trials were established with ‘Algonquin' alfalfa near Valparaiso, SK and Carrot River, SK in 1998. The Valparaiso trial was located on a fine-textured soil, high in soil organic matter. The Carrot River trial was located on a coarse-textured soil, low in soil organic matter. Three factors (three rates of hexazinone, three residue management treatments and two application dates) were tested in a randomized complete block design. Alfalfa seed yield and Canada thistle: density, dry matter and seed contamination, were determined in 1999. Alfalfa seed yield and Canada thistle control (density, dry matter and seed contamination) increased with increased rates of hexazinone at Carrot River but not at Valparaiso. No significant interactions between hexazinone rates, application timing and residue management for Canada thistle control were observed. However, residue management by application timing interaction was significant for alfalfa seed yield. Alfalfa seed yield was significantly higher following a spring burn at both sites
