Control of winter cereals in the spring with glyphosate

Poor survival of winter cereals due to winter conditions in Ontario can necessitate destruction of the stand in the spring to allow the subsequent seeding of an alternative crop. Winter cereals were seeded in the autumn of 2004 and 2005 at the Huron Research Station and at the University of Guelph Ridgetown Campus in Ontario to evaluate two formulations of glyphosate potassium (K) vs diammonium (DA) salt] at different doses (225, 450, 675, 900, or 1350 g a.e. ha⁻¹) for the burn-off of soft white winter wheat (SWW), soft red winter wheat (SRW), hard red winter wheat (HRW) and autumn rye (AR) in either late April or early May. There was no difference between the glyphosate formulations for the control of winter cereals at 1, 2, 3, and 4 weeks after treatment (WAT). There was generally improved control with glyphosate applications made in early May compared to late April however results were not always statistically significant. Generally, control of winter cereals increased as the glyphosate dose was increased from 225 to 1350 g a.e. ha⁻¹. The minimum dose of glyphosate required for providing 90% or greater control of SWW, SRW, HRW, and AR was 675 g a.e. ha⁻¹ at 4 WAT. Glyphosate applied at 675 g a.e. ha⁻¹ caused a 98, 97, 98, and 99% reduction in shoot dry weight of SWW, SRW, HRW, and AR, respectively. Based on this study glyphosate (K or DA) applied in late April or early May can be used at doses as low as 675 g a.e. ha⁻¹ to adequately control SWW, SRW, HRW, and AR in the spring.