Survey of glyphosate- and dicamba-resistant kochia

Kochia (Bassia scoparia (L.) A.J. Scott) is a problematic tumbleweed, which infests row crops and ruderal areas within western Canada. Herbicide resistance makes kochia management challenging for producers. Widespread resistance to acetolactate synthase-inhibitors, evolution and spread of glyphosate resistance, and the occurrence of dicamba resistance has been previously noted in Saskatchewan. This study's objective was to evaluate the occurrence and distribution of glyphosate- and dicamba-resistant kochia in central and southern Saskatchewan. A randomized, stratified survey was conducted in the fall of 2019 at 303 sites. Rotational history was obtained using the Agriculture and Agri-Food Canada Annual Crop Inventory. Kochia samples were collected from cropped fields (78%), ditches (17%), oil well sites (2%), and railway grades (3%). Glyphosate resistance was detected in 87% of samples (n = 275) within 137 Rural Municipalities (RMs). Dicamba resistance was detected in 45% of kochia samples (n = 255) in 87 RMs. Crops infested with herbicide-resistant kochia included wheat (Triticum aestivum L. and T. durum Desf.), canola (Brassica napus L.), lentils (Lens culinaris Medik.), barley (Hordeum vulgare L.), flax (Linum usitatissimum L.), and peas (Pisum sativum L.). Reducing the soil seedbank and preventing dispersal will be critical to mitigating resistance. Good herbicide stewardship including mixing multiple modes of action is paramount. Cultural strategies to increase canopy closure and crop competitiveness to limit biomass and seed production are recommended. Kochia occupies many environments outside of cropped fields, and a community-wide management approach may be necessary to reduce dispersal potential of tumbling plants that disperse seed.