Weeds

Quizalofop alone or in combination with imazamox, imazamox + bentazon, or imazamox/imazethapyr, and glufosinate mixed with clethodim resulted in more than 80% visible control, plant mortality, and reduction in biomass of glyphosate-resistant downy brome 21 days after treatment. Glyphosate-resistant downy brome was confirmed in a…

Growing soybean on high soil mineral nitrogen (N) fields, or when N fertilizer was applied in increasing rates, resulted in an increase in volunteer canola competition and a corresponding linear decrease in soybean yield. Research was conducted in Manitoba looking at the resource-ratio (R*) hypothesis….

Kochia with resistance to glyphosate was found at 78% of sites sampled, with 44% of sites exhibiting fluroxypyr resistance, and 28% with dicamba resistance. Triple resistance to Group 2 ALS inhibitors, Group 9 glyphosate, and one of the Group 4 synthetic auxins was found at…

Fall applications of flumioxazin, pyroxasulfone, and combinations of flumioxazin and pyroxasulfone to manage weeds emerging the following spring is a safe and effective weed management program in ultra-early seeded wheat. Ultra-early planting of wheat with a soil temperature trigger of 0-2.5 C has been shown…

Yield losses caused by kochia competition are high, with mean losses reported to be 68% in grain corn, 62% in sorghum, 52% in soybean, 46% in sugar beet, 40% in silage corn, 23% in sunflower, 20% in spring wheat, 13% in canola and field pea,…

Layering Group 14 herbicides saflufenacil or carfentrazone + sulfentrazone pre-plant with a Group 2/6 imazamox/bentazon post-emergent treatment can effectively control glyphosate- and ALS inhibitor-resistant (Group 2 + 6) kochia in field pea. Layering will also help to reduce herbicide selection pressure through the use of…

A flax rotation that included 3 years of alfalfa with reduced herbicide applications provided similar wild oat and cleaver control as a flax-barley-flax-oat rotation with recommended herbicide applications. Including 2 successive winter cereal crops in a 5 year rotation also improved wild oat control. Wild…

Weed control has typically focussed on preventing yield loss with the side benefit of controlling weed seed return to the seedbank. This research proposes to turn that approach on its head by developing an understanding of when weed control is critical to prevent the return…

Early  crop topping treatment with a systemic herbicide targeted at panicle emergence had the largest impact on wild oat density, dockage, seedbank, and crop yield in the following year. An early, or a combination of early and late crop topping (at initiation of seed shed),…

A randomized-stratified survey of 315 sites in Manitoba found that, overall, 58% of the kochia populations tested were glyphosate-resistant, while 1% were dicamba-resistant. There was a rapid increase in glyphosate-resistant kochia over a five-year time frame, and the survey also confirms the first cases of…

Action and economic thresholds for volunteer Roundup Ready canola in Roundup Ready soybean were determined. Economic thresholds of less than 0.5 plants/ft2 (<5 plants/m2) highlight the highly competitive nature of volunteer canola in soybean crops. Volunteer glyphosate-resistant (GR) canola is a challenge for Roundup Ready…

A 2018 survey found that Russian thistle populations collected in Manitoba did not exhibit resistance to acetolactate synthase inhibitors (tribenuron/thifensulfuron; Group 2), synthetic auxins (2,4-D ester or fluroxypyr; Group 4), or glyphosate (Group 9). The status of herbicide-resistant Russian thistle in Manitoba was unknown, so…

In a 2017 Alberta survey, 13% of the kochia populations sampled were fluroxypyr-resistant. Only 4% of the populations were both fluroxypyr- and dicamba-resistant, indicating that different mechanisms may confer resistance to these herbicides. When combined with estimates of dicamba resistance, about 28% of kochia populations…

Combining a post-emergent herbicide application with a subsequent pre-harvest glyphosate application resulted in the best dandelion control. Growers should consult with their oat buyer to ensure that they will accept oats treated with pre-harvest glyphosate. The objective of this study was to determine if cultural…

Weed surveys show that the incidence of herbicide-resistant grassy and broadleaf weeds continues to increase across the Prairies during the survey periods of 2014 through 2017. The perceived cost of herbicide resistance was estimated at $13.36 per acre. Regular surveillance for herbicide-resistant (HR) weeds has…

Control of glyphosate-resistant kochia was achieved with the use of effective tank-mixtures utilizing Group 4, 14 or 4+19 herbicide groups. But the confirmation of Group 4 resistance in kochia highlights the need for careful herbicide stewardship to prevent further selection of multiple herbicide-resistant kochia. In…

The most effective and consistent treatments for glyphosate-resistant (GR) kochia management included Authority (sulfentrazone) applied pre-emergence, post-emergent Enforcer D (fluroxypyr/bromoxynil/2,4-D) at the high label rate, and post-emergent Infinity (pyrasulfotole/bromoxynil). Glyphosate-resistant (Group 9) kochia has rapidly spread across Alberta since it was first discovered in 2011…

All 15 PRE followed by POST herbicide combinations provided better control of volunteer canola compared with the glyphosate-only control, but tribenuron (i.e. Express SG) followed by bentazon, and tribenuron followed by imazamox plus bentazon (i.e. Viper ADV) provided solutions that were low cost, registered in…

Effective pre-emergent or pre-emergent followed by post-emergent (two-pass) programs tested in this research on the U.S Great Plains should be proactively utilized by growers to manage glyphosate/dicamba resistant kochia in Roundup Ready 2 Xtend (glyphosate/dicamba-resistant) soybean. A similar approach may prove useful for western Canadian…

Redekop Seed Control Unit, an integrated reversible cage mill with blade system that provides Harvest Weed Seed Control, was assessed for volunteer canola control. Blade configuration in combination with chaff feeding rate did not affect volunteer canola control, which remained above 99%. Harvest Weed Seed…

Based on wild oat seed viability, early clipping of wild oat panicles before seeds are viable, in short-statured crops, may become a valuable tool for integrated wild oat management. Wild oat is one of the most problematic weed species in western Canada due to widespread…

Cleavers can germinate very early in the spring, making pre-seed burnoff a good way to control 
the weeds when they’re small and limit cleavers 
seed in harvested canola. Pre-harvest saflufenacil plus glyphosate may also provide short- and long-term management. This study shows that cleavers populations…

Fluazifop, quizalofop, clethodim, sethoxydim, and glyphosate can all reduce downy brome and Japanese brome biomass, especially when applied shortly after germination to plants less than 4.3 inches tall —with a tendency for fluazifop and quizalofop to be most effective. Research evaluated the efficacy of glyphosate…

Soybean grown in narrow rows shortened the critical weed-free period (CWFP) by up to three soybean developmental stages at site-years with increased weed pressure. Low-density soybean stands lengthened the CWFP by one soybean developmental stage compared with higher-density soybean stands. Generally, the cultivar with the…

Seeding a tall cultivar at 80 seeds/ft2 in early May along with the application of an in-crop wild oat herbicide resulted in the greatest stand establishment and crop biomass, as well as the lowest weed biomass in flax. Flax is a poor competitor with weeds,…

Model predictions suggest that farming can remain profitable without glyphosate by consistently utilizing key non-herbicidal weed management practices combined with robust pre-emergence soil residual herbicide treatments. However, maintaining low weed seed banks will be challenging. The possibility of farming without glyphosate is an important issue…

Trends in herbicide resistance management over the past decade were identified and include renewed efforts by the agrichemical industry in herbicide discovery, cultivation of crops with combined (stacked) HR traits, increasing reliance on pre-emergence vs. post-emergence herbicides, breeding for weed-competitive crop cultivars, expansion of harvest…

Target a soybean seeding rate of 4 to 6 plants per square foot for optimum net return and improved crop competition against volunteer glyphosate-resistant canola. Pre- and post-emergent herbicides were also assessed for control of volunteer glyphosate-resistant canola in soybean. Limited information exists for the…

Time to 90% loss of glyphosate-resistant kochia seed viability averaged less than 8 months. Short seedbank longevity, delayed and reduced germination, and delayed time to first leaf of glyphosate-resistant kochia can be used to develop weed control strategies. Kochia herbicide resistance continues to spread across…

A kochia survey in southern Alberta in 2017 found that all kochia populations were resistant to Group 2 ALS inhibitors, 50% of populations were resistant to Group 9 glyphosate, and 18% of populations resistant to Group 4 (dicamba) herbicides. Kochia populations with triple resistance to…

Where the saline forage site contained root zone salinity approaching severe, the best forage control treatments were AC Saltlander green wheatgrass seeded on 15 or 30.5 cm row spacing. The next best option was alternating rows of AC Saltlander green wheatgrass with slender wheatgrass seeded…

Of the seven unregistered herbicides assessed, flax has excellent crop tolerance to fluthiacet-methyl, pyroxasulfone, and topramezone. Flumioxazin caused severe crop damage in high moisture situations and is not recommended for further trials. Field experiments were conducted in 2015 and 2016 at the Kernen Research Farm…

Of 45 Russian thistle populations tested from central and southern Alberta in 2017, 31 (62%) were Group 2 (ALS inhibitor) resistant. No populations exhibited resistance to Group 9 (glyphosate). A random survey of Russian thistle was conducted post-harvest in fall, 2017. A total of 45…

Field trials found pyroxasulfone (Focus), pyroxasulfone + flumioxazin (Fierce), and pyroxsulam (Simplicity) provided effective control of Japanese and downy brome in winter wheat. Trials were established at Lethbridge and Kipp, Alberta, and Scott, Saskatchewan, over three growing seasons to compare herbicides for control of downy…

Wild oat resistance has increased over three surveys conducted since 2001. In surveyed fields where wild oats were found, Group 1 wild oat resistance increased in Alberta from 11% in 2001 to 58% in 2017. In 2017, 247 fields were randomly surveyed across Alberta prior…

Herbicide screening studies on triallate-resistant (Group 8) wild oats found cross-resistance to Group 1 and Group 2 herbicides. Additionally, unexpected resistance to Group 14 and Group 15 herbicides was found even though the wild oats had never been previously exposed to these herbicides. Two relatively…

The critical weed free period for lentil starts at the five-node stage and lasts until the 10-node stage. Research found that applying Clearfield herbicides to lentils at the five- to six-node stage provided the best weed control and highest yield. Two research studies conducted at…

Seed 35 seeds per square foot and apply at least 13.4 lbs. P205 per acre to improve wild oat competitiveness and increase tame oat yield. A three-year study was conducted at Agriculture and Agri-Food Canada Indian Head to determine if side-banded phosphorus (P) in combination…

Diverse crop rotations had similar net returns to canola-wheat rotations one-half the time and up to $45 per acre more the rest of the time. Adding integrated weed management practices without relying on wild oat herbicides resulted in similar wild oat pressure as canola-wheat rotations….

Agriculture and Agri-Food Canada research scientists Hugh J. Beckie and K Neil Harker identified herbicide-resistant weed management practices that have the most impact on managing herbicide selection pressure. Their top 10 management practices are based on research and growers’ experiences over the last 30 years.