Candidate Tools for Integrated Weed Management in Soybean at the Northern Frontier of Production

Abstract

The development of early-maturing soybean [Glycine max(L.) Merr.] varieties has led to an increase in soybean production in canola (Brassica napusL.)-dominant crop rotations in western Canada. Herbicide-resistant (HR) volunteerB. napuscan be difficult to manage in HR soybean using herbicides alone. In 2013 and 2014, four field experiments were conducted in Manitoba, Canada, to evaluate soybean row spacing, seeding density, nitrogen supply, and interrow tillage as candidate nonchemical weed management tools for an integrated program to manage volunteerB. napusin soybean. Among treatments and sites, volunteerB. napusproduced about 830 seeds plant−1and resulted in large seedbank inputs (averaging about 20,300 seeds m−2). VolunteerB. napusseedling recruitment differed among sites, and resulted in two distinct classes of sites based on average seedling densities of 39 and 89 plants m−2. Weed management tools were more effective at the sites with higher volunteerB. napusdensities. At these sites, soybean yield was greater when using an increased soybean-seeding density (44% greater yield using a seeding density of 682,500 vs. 455,000 seeds ha−1) or interrow tillage (36% greater yield with vs. without using interrow tillage). Soybean row spacing (19 vs. 38 vs. 76 cm) did not affect soybean yield, unless the reduction in row spacing was combined with an increased seeding density (65% greater yield with narrow-row soybean seeded at 682,500 vs. wide-row soybean seeded at 455,000 seeds ha−1). At the sites with higher volunteerB. napusdensities, seed production of canola volunteerB. napuswas greater when nitrogen fertilizer was applied to simulate an environment with greater nitrogen supply (77% greater number of volunteerB. napusseeds produced with vs. without broadcast application of 23 kg N ha−1urea). In northern climates, seeding soybean at increased densities using narrow-row spacing in fields with limited soil inorganic nitrogen and using interrow tillage in wide-row production systems are effective strategies that could augment chemical weed management in an integrated program for management of volunteerB. napus, and perhaps also other competitive early-season weeds.

Interference and management of herbicide-resistant crop volunteers

“…Management of HR canola volunteers is most challenging in broadleaf crops. For example, limited herbicide options to control HR canola volunteers in pulse crops, sugarbeet, and soybean (Stachler and Luecke 2009) increases the necessity of optimizing crop competitiveness to mitigate yield loss (Geddes and Gulden 2018;Mierau et al 2019). Pollen-mediated gene flow from adjacent GR canola fields or admixtures in planted seed lots can result in trait stacking in volunteers, even if the cultivar grown in a field is not GR (Beckie et al 2003;Friesen et al 2003;Hall et al 2000; Figure 1), which the grower may not anticipate.…”

Minimizing competition between glyphosate-resistant volunteer canola (Brassica napus) and glyphosate-resistant soybean: impact of soybean planting date and rate

“…There is potential for integrated weed management in soybean crops to better manage volunteer GR canola, for which herbicide options are limited (Geddes and Gulden 2018). Geddes and Gulden (2018) found a positive response of soybean to integrated weed management practices, although they did not look at the impact of planting rate and date combined. It is not known whether these two cultural control methods can affect competition between volunteer GR canola and GR soybean.…”

Exploiting the resource-ratio (R*) hypothesis for weed management in legume crops: An example of volunteer Brassica napus in soybean

“…While the persistence of volunteer canola in the soil seedbank depends upon environmental and edaphic factors (Geddes, 2021), timely soil disturbance can contribute to a reduction of volunteer canola populations prior to soybean production (Geddes and Gulden, 2017). However, limitation of volunteer canola seed production in crops grown subsequent to canola is imperative to limiting persistence of this weed (Geddes and Gulden, 2018;Geddes and Gulden, 2021). Soybean and canola have similar herbicide resistance traits (Mierau et al, 2020).…”