Core Ideas Current weed management strategies in flax are limited.A multi‐factor weed management system is needed to control herbicide‐resistant weeds.Combining several factors has a greater impact on crop‐weed competition than any factor alone.The best combination is a competitive cultivar, seed early, high seeding rate, and use an in‐crop herbicide. Flax (Linum usitatissimum L.) is an important crop with value in both food and industrial markets. However, flax competes poorly with weeds and as a result, flax yield can be severely inhibited by weed competition. Factors that favor crop competitive ability will have great value in improving weed management in flax. This research sought to identify different combinations of seeding date (early vs. late May), seeding rate (400 vs. 800 seeds m−2), cultivar height (short vs. tall), and herbicide (present vs. absent) that could improve the competitive ability of flax. Field studies were conducted across western Canada over 3 yr from 2014 to 2016. Results showed that seeding a tall cultivar at a high seeding rate in early May combined with an in‐crop herbicide application increased crop establishment by 210 plants m−2. This in turn increased aboveground crop biomass and seed yield by as much as 549 and 617 kg ha−1, respectively. This combination of factors significantly reduced aboveground weed biomass by 50 kg ha−1, although no single factor or combination of factors affected weed seed fecundity. By seeding competitive flax cultivars at higher rates earlier in the growing season, and by combining this with an in‐crop herbicide, producers can develop sound cropping systems that provide more competitive flax crops and another profitable cropping option.

Flax yield can be severely reduced by weeds. The combination of limited herbicide options and the spread of herbicide-resistant weeds across the prairies has resulted in a need for more weed control options for flax producers. The objective of this research was to evaluate the tolerance of flax to topramezone, pyroxasulfone, flumioxazin, and fluthiacet-methyl applied alone as well as in a mix with currently registered herbicides. These herbicides were applied alone and in mixtures at the 1X and 2X rates and compared with three industry standards and one nontreated control. This experiment was conducted at Carman, MB, and Saskatoon, SK, as a randomized complete block with four replications. Data were collected for crop population, crop height, yield, and thousand-seed weight. Ratings for crop damage (phytotoxicity) were also taken at three separate time intervals: 7 to 14, 21 to 28, and 56+ d after treatment. Crop tolerance to these herbicides varied between site-years. This was largely attributed to differences in spring moisture conditions and the differences in soil characteristics between sites. Herbicide injury was transient. Hence, no herbicide or combination of herbicides significantly impacted crop yield consistently. Flumioxazin was the least promising herbicide evaluated, as it caused severe crop damage (>90%) when conditions were conducive. Overall, flax had excellent tolerance to fluthiacet-methyl, pyroxasulfone, and topramezone. Flax had excellent crop safety to the combination of pyroxasulfone + sulfentrazone. However, mixing fluthiacet-methyl and topramezone with MCPA and bromoxynil, respectively, increased crop damage and would not be recommended.

Glyphosate-resistant (GR) canola is a widely grown crop across western Canada and has quickly become a prolific volunteer weed. Glyphosate-resistant soybean is rapidly gaining acreage in western Canada. Thus, there is a need to evaluate herbicide options to manage volunteer GR canola in GR soybean crops. We conducted an experiment to evaluate the efficacy of various PRE and POST herbicides applied sequentially to volunteer GR canola and to evaluate soybean injury caused by these herbicides. Trials were conducted across Saskatchewan and Manitoba in 2014 and 2015. All treatments provided a range of suppression (>70%) to control (>80%) of volunteer canola. All treatments with the exception of the glyphosate-treated control reduced aboveground canola biomass by an average of 96%. As well, canola seed contamination was reduced from 36% to less than 5% when a PRE and POST herbicide were both used. Moreover, all combinations of herbicides used had excellent crop safety (<10%). All PRE and POST herbicide combinations provided better control of volunteer canola compared with the glyphosate-only control, but tribenuron followed by bentazon and tribenuron followed by imazamox plus bentazon provided solutions that were low cost, currently available (registered in western Canada), and had the potential to minimize development of herbicide resistance in other weeds.