Wild oat control is, like it or not, an increasingly costly issue in Western Canada. Not only is herbicide expensive (costing growers over $500 million annually), we are also seeing an increase in resistant wild oat populations. There are several fields with confirmed resistance to both Group 1 and Group 2 products. Farmers do and will need new methods of control. The good news is that in addition to using integrated weed management strategies for wild oats, farmers may have a new-to-us chemistry to look forward to.
Pyroxasulfone, not yet registered in Canada, but used widely in the United States (under the trade names Fierce, Piper, Zidua and Anthem), is a Group 15 herbicide. Its unique mode of action makes it an ideal candidate for herbicide group diversification and resistance management, according to Breanne Tidemann, a graduate student at the University of Alberta.
Tidemann has been involved in the operation of trials in 2011-2012 comparing fall and spring-applied pyroxasulfone in field peas at rates of 0. 50, 100, 150, 200, 300 and 400 grams of active ingredient per hectare. This trial was repeated at five locations: Edmonton and Kinsella, Alta., and Scott, Melfort and Kernan, Sask.
“The species that I’ve studied the most are cleavers and wild oats, and both are controlled by pyroxasulfone (environmental factors pending),” says Tidemann. “I’ve also seen excellent control of green foxtail.” Tidemann has also witnessed control-variability on kochia, which ranged anywhere from suppression to excellent control, and has heard reports of excellent control of downy and Japanese brome.
“Because pyroxasulfone is soil applied, organic matter of the soil and soil moisture are very important factors in the level of efficacy that we see,” says Tidemann. “We only saw injury at Scott and Kernan last year. Injury at these sites was severe (applied at high rates), however both had over 200% of their normal precipitation. In years prior to this no injury had been observed.
“The best weed control was happening at our lowest organic matter sties of Scott and Kernan and I would say the expected registration rate range between 100 and 150 g ai/ha would be adequate at those sites,” she says.
Pyroxasulfone is a wettable dry granule that is applied pre-seeding or early pre-emergence. It is currently under review by the Pest Management Regulatory Agency for registration on field corn in Canada.