Our results are consistent with the hypothesis that overexpression of the herbicide target gene ACCase confers resistance to the herbicide. This is the first reported case of target gene duplication conferring resistance to a herbicide other than glyphosate. © 2017 Society of Chemical Industry See related Article.

The popularity of grain amaranth and quinoa is growing in Ontario, increasing the interest in their cultivation. Two experiments were conducted in southern Ontario in 2013 and 2014 to evaluate optimal planting date (every two weeks from early May to late July), row width (38 or 75 cm), and critical weed-free period (the component of the critical period of weed control that defines the number of days that the crop must remain weed-free to prevent yield loss) in each crop. Grain amaranth and quinoa both reached physiological maturity and produced yields when planting dates ranged from mid-May to late-June. When either crop was seeded in July, yields decreased by more than 50% and the crop did not always reach maturity before the first frost. While row width did not have an impact on yield, it is advisable to grow the crops in wider rows (75 cm) to facilitate weed control early in the growing season (up to 30 d after emergence (DAE)). The critical weed-free period was 24 and 16 DAE for grain amaranth and quinoa, respectively, after which yields were maintained at 95% of the weed-free control. Based on these data, both crops could easily be integrated into the normal cropping rotations found in southern Ontario.Key words: critical weed-free period, row width, planting date, Amaranthus hypochondriacus L, Chenopodium quinoa Willd.Résumé : La popularité grandissante de l'amaranthe et du quinoa en Ontario accentue l'intérêt pour leur culture. En 2013 et 2014, les auteurs ont réalisé deux expériences dans le sud de la province en vue d'établir la meilleure date pour les semis (aux deux semaines, de mai à la fin de juillet), l'écartement idéal des rangs (38 ou 75 cm), et la période cruciale durant laquelle on doit combattre les mauvaises herbes (nombre de jours pendant lesquels la culture ne doit pas subir la concurrence des adventices afin qu'il n'y ait pas baisse du rendement) pour chacune des deux cultures. L'amaranthe et le quinoa parviennent à leur maturité physiologique et produisent des graines lorsqu'on les sème entre la mi-mai et la fin de juin. Des semis en juillet réduisent le rendement de moitié, et la culture ne parvient pas toujours à maturité avant les premières gelées. Bien que l'écartement des rangs n'ait aucun impact sur le rendement, on préconise des rangs plus distants (75 cm) pour faciliter le désherbage au début de la période végétative (jusqu'à 30 jours après la levée). La période cruciale durant laquelle on doit lutter contre les mauvaises herbes correspond à 24 jours après la levée pour l'amaranthe et à 16 jours pour le quinoa. Par la suite, le rendement demeure à 95 % de celui relevé pour la parcelle témoin désherbée. Selon ces résultats, on estime que les deux cultures pourraient facilement s'intégrer aux assolements usuels pratiqués dans le sud de l'Ontario. [Traduit par la Rédaction] Mots-clés : ériode de désherbage cruciale, écartement des rangs, date des semis, Amaranthus hypochondriacus L., Chenopodium quinoa Willd.

Palmer amaranth is one of the most economically important and widespread weeds of arable land in the United States. Although no populations are currently known to exist in Canada, its distribution has expanded northward such that it is present in many of the States bordering Canada and multiple pathways exist for its introduction. In this short communication we report on the transport of viable Palmer amaranth seed on imported sweet potato slips. A reproductive pair of Palmer amaranth seedlings were identified from soil accompanying imported sweet potato slips in 2018. Identification was confirmed using species specific single nucleotide polymorphisms.

The development of a linuron-free weed management strategy for carrot production is essential as a result of the herbicide reevaluation programs launched by the Pest Management Regulatory Agency in Canada for herbicides registered before 1995 and the discovery of linuron-resistant pigweed species in Ontario. Field trials were conducted in one of Ontario’s main carrot-growing regions on high organic soils in 2016 and 2017. Pigweed species seedlings were effectively controlled with PRE treatments of prometryn, pendimethalin, S-metolachlor, or glufosinate. POST treatments of pyroxasulfone and metribuzin followed by predetermined biologically effective dose (≥90% control of pigweed seedlings) of acifluorfen, oxyfluorfen, fluthiacet-methyl, and fomesafen achieved excellent crop selectivity and commercially acceptable pigweed species seedling control under field conditions. Carfentrazone-ethyl or fomesafen applied PRE severely reduced seedling emergence and yield in the wet growing season of 2017. This study demonstrated clearly that an alternative linuron-free strategy can be developed for carrots. The strategy of exploring the potential to use the biologically effective dose of selected herbicides to achieve crop selectivity and control of pigweed species seedlings was verified.

Frequent cultivation is often used to control weeds in crops such as lettuce. The efficacy of this technique on weed populations has been evaluated, but the effect on weed emergence and seedbanks is less documented. Studies in mineral soil indicate that soil disturbance can increase both weed emergence and seed persistence depending on where seeds are redistributed in the soil profile. Evaluations done in muck soil are scarce. This study evaluated the effect of two and four repetitive shallow (3.4 to 7.1 cm deep) cultivations on weed emergence and the weed seedbank in muck soil. Cultivation treatments (0, 2 and 4 cultivations using a inter-row rototiller) were done in lettuce plots from 2017 to 2019. Weed density was evaluated by species before each cultivation date and after crop harvest. Viable seedbanks were evaluated by collecting soil samples before and after each growing season and placing them in greenhouse flats. Statistical analyses were based on mixed models. Results showed that shallow cultivation modified the emergence patterns of weeds but did not reduce total emergence during the subsequent years or viable seedbanks. After two seasons without seed inputs, total emergence was reduced by 46.6% and the seedbank was reduced by 31.7% regardless of the cultivation treatment. However, the seedbank of the very abundant common purslane (<i>Portulaca oleracea</i>) remained high.