The stem nematode Ditylenchus weischeri was recently reported on creeping thistle (Cirsium arvense) in Canada. Two greenhouse studies examined host suitability of crops commonly grown in the Canadian Prairies for D. weischeri and the closely related parasite of many crops, D. dipsaci. In the first study, common pulse crops (yellow pea, chickpea, common bean, and lentil), spring wheat, canola, creeping thistle, and garlic were evaluated. Plant biomass and reproductive factor (R_f = nematode recovered/inoculated) 8 weeks postinoculation were used to determine host suitability. Creeping thistle biomass was reduced by D. weischeri whereas D. dipsaci reduced biomass of four of five pea and two of three bean varieties. Two pea varieties were weak hosts for D. weischeri, with R_f slightly >1. D. weischeri aggressively reproduced on creeping thistle (R_f = 5.4). D. dipsaci reproduced aggressively on garlic (R_f = 6.4; a known host), moderately on pea varieties (R_f > 2), and weakly on chickpea and bean (R_f > 1). In the second study, using creeping thistle and yellow pea, D. weischeri was recovered from aboveground parts of the plants and seed of the former and D. dipsaci from the later. The results show that D. weischeri parasitizes creeping thistle but not other crops and that D. weischeri host preference is different from that of D. dipsaci.

Soybean [Glycine max (L.) Merr.] has recently become a popular rotational crop in the Canadian Northern Great Plains where herbicide-resistant (HR) soybean cultivars have been widely adopted. Intense reliance on herbicides has contributed to the development of HR weeds in soybean and other crops. Cultural weed management practices reduce the need for herbicides and lower the selection pressure for HR weed biotypes by improving the competitiveness of the crop. The effects of two row spacings, three target densities, and three cultivars on the critical weed-free period (CWFP) in soybean were evaluated as three separate experiments in southern Manitoba. In the row-spacing experiment, soybean grown in narrow rows shortened the CWFP by up to three soybean developmental stages at site-years with increased weed pressure. In the target density experiment, low-density soybean stands lengthened the CWFP by one soybean developmental stage compared with higher-density soybean stands. The effect of soybean cultivar varied among locations, yet tended to be consistent within location over the 2-yr study, suggesting that competitive ability in these soybean cultivars was linked to edaphic and/or environmental factors. Generally, the cultivar with the shortest days to maturity, which also had the shortest stature, consistently had a longer CWFP. Each of these cultural practices were effective at reducing the need for in-crop herbicide applications.

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.