Herbicide tolerant canola systems and their impact on winter crop rotations

Canola is widely grown in Australia to provide diversity within winter crop rotations. Its production is heavily reliant on triazine tolerant varieties but Clearfield^® and conventional varieties are also significant components of the industry. Glyphosate tolerant varieties have been introduced, thereby providing an alternative technology to be incorporated into the farming systems. To evaluate the potential impact of the relative herbicide technologies, a comparison of herbicide tolerant canola weed management systems was undertaken at Wagga Wagga, Australia over a 5-year rotation. Near isogenic lines of conventional, glyphosate tolerant and triazine tolerant varieties were evaluated for their abilities to control annual ryegrass (Lolium rigidum), the most challenging weed of temperate crops in Australia. Glyphosate tolerant and triazine tolerant canola achieved high levels of ryegrass control and attained higher yields than the conventional system. Glyphosate tolerant canola provided extra control of broadleaf weeds and also achieved better seed oil levels when compared with the other canola systems. There were positive flow-on weed management benefits for the remainder of the crop sequence from the weed control achieved in the initial crop, particularly following glyphosate tolerant canola. Subsequent control of volunteer canola in all treatments was readily achieved by using paraquat/diquat. The glyphosate tolerant weed management system was more profitable than the triazine tolerant system, although no allowance was made for technology costs as they were not known at the time of study. These outcomes demonstrate the potential value of herbicide tolerant canola to Australian farmers.