Glyphosate Timing and Tillage System Effects on Glyphosate-Resistant Canola (Brassica napus)1

摘要

Glyphosate-resistant canola has been widely adopted in western Canada. This has prompted producer interest in the timing of glyphosate application, particularly under zero tillage, where glyphosate is often applied preseeding. Field experiments were conducted at Lacombe, Edmonton, and Beaverlodge in Alberta in 1997, 1998, and 1999 to determine the importance of preseeding glyphosate and the most effective growth stage to apply glyphosate to canola to optimize yield and weed management. Treatments consisted of zero-tillage systems, with and without preseeding glyphosate, and a conventional-tillage system involving preseeding tillage operations. Glyphosate was applied at the one- to two-, three- to four-, or five- to six-leaf stages of canola in each tillage system. Canola yield and weed dry weight were largely unaffected by the tillage system. In most instances, the highest canola yields occurred when glyphosate was applied early to the crop. The opposite occurred at Lacombe and Edmonton in 1999, however, where canola yield increased as glyphosate was applied at later crop growth stages. This yield benefit likely resulted from the control of late-emerging weeds that exerted competitive pressure on canola. Early glyphosate timing in glyphosate-resistant canola may eliminate the need for preseeding glyphosate in zero-tillage systems, and optimize yield and weed control.