Survey of glyphosate and dicamba resistant kochia in Saskatchewan
Sharpe SM, Leeson J, Geddes C, Beckie H, Willenborg C (2022) Survey of Glyphosate- and Dicamba-Resistant Kochia in Saskatchewan. Annual meeting of the Canadian Weed Science Society in Halifax, NS. November 14, 2022.
Kochia [Bassia scoparia (L.) A.J. Scott] is an halophytic, invasive tumbleweed and a troublesome weed for Western Canadian agronomy. Kochia has evolved resistance to several herbicide modes of action including Group 2 (several), Group 4 (dicamba, fluroxypyr), and Group 9 (glyphosate) with multiple-resistant biotypes present in Saskatchewan. Previous surveillance activities for Saskatchewan in 2011/2012 identified the presence of glyphosate-resistant kochia in nine municipalities. The study objective was to determine the current occurrence of glyphosate-, and dicamba-resistant kochia at 300 sites within central and southern Saskatchewan. A post-harvest stratified-random survey was conducted in the fall of 2019 with site selection stratified by proportional cultivated land area per ecodistrict. A composite sample were gathered from twelve plants at each location. Seed was threshed and screened in the greenhouse with glyphosate (900 g ae ha-1) and dicamba (280 g ae ha-1). Screening occurred in cycles between October 28, 2020 to September 30, 2022 in a greenhouse in Saskatoon, SK. Of the screened populations, 87% demonstrated some degree of glyphosate resistance (n=275) while 45% demonstrated some degree of dicamba resistance (n=255) with 103 populations demonstrating resistance to both herbicides. For glyphosate resistance, 22% demonstrated a high level of resistance (>60% survival), 86% demonstrated moderate glyphosate resistance (21 to 60% survival), and 33% demonstrate low level resistance (1 to 20% survival). For dicamba-resistant kochia, only 1 population (0.4%) demonstrated high resistance while 1% demonstrated moderate resistance and 44% low level resistance. Substantial increases in glyphosate-resistant kochia populations were detected across the agronomic production region of central and southern Saskatchewan. Adoption of integrated kochia patch management strategies and monitoring ditches and field margins is advisable. Good herbicide stewardship practices including applying chemistry at proper staging, using full label rates, and rotating modes of action will be critical to mitigate ongoing resistance evolution.