Evaluating cultural weed management techniques in soybean in Manitoba
Date
2020-03-30
Authors
Rosset, Jonathan DDJ
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Abstract
Soybean’s popularity as a rotational crop has increased in Manitoba and the Canadian Prairies due to its nitrogen-fixing capabilities and development of short-season cultivars genetically engineered to resist glyphosate. Appropriately designed cultural weed management techniques help mitigate the development of glyphosate resistant weed biotypes caused by excessive glyphosate applications. The cultural weed management techniques of row spacing, target density, and cultivar were evaluated to determine their effects on the critical weed free period in soybean and provide a framework for future regional recommendations. Three field experiments were implemented during the summers of 2016 and 2017 at three locations in southern Manitoba to examine the effects of (1) two row spacings, (2) three target densities, and (3) three soybean cultivars on the critical weed free period in soybean (chapter 3) and the structure of the associated resident weed community (chapter 4). Narrow row soybean shortened the critical weed free period by up to three development stages compared to wide rows. Soybean grown at a target density of 333,000 plants ha-1 lengthened the critical weed free period by up to two development stages compared to soybean grown at 666,000 plants ha-1. The effect of soybean cultivar was location dependent, however the cultivar with the shortest maturity and stature generally had the longest critical weed free period. A total of fourteen weed species were identified among field experiments, eight or less weed species occurred at individual site-years and these were dominated by fewer than three species. The structure and trajectories of the weed communities was affected overwhelmingly by the duration of the soybean weed free period. Soybean row spacing and target densities affected the trajectories of the weed community at the untreated and initial herbicide application stages. Further herbicide applications fully obscured the effects of the cultural techniques. Soybean cultivar did not influence the weed community. This research showed that soybean competitive ability can be improved by implementing specific cultural techniques that reduce the duration of time the crop must be kept weed free to minimize yield loss. Specific cultural techniques were also shown to influence the structure of the weed community.
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Keywords
Soybean, Weed management, Critical weed free period, Competitive ability, Row spacing, Stand density, Soybean cultivar, Weed community, Principal component analysis, Non-linear regression
Citation
Rosset JD, Gulden RH (2020). Cultural weed management practices shorten the critical weed-free period for soybean grown in the Northern Great Plains. Weed Sci 68:79–91. DOI: 10.1017/wsc.2019.60