According to crop protection industry experts, the arrival of a new herbicide mechanism of action (MOA) within the next 15 years is unlikely. Similarly, a report commissioned by CropLife indicates that it now takes over 10 years to bring a new herbicide product to market.

 

However, this does not mean that new weed management solutions aren’t on the horizon. Research on the use of mechanical weed control on the Prairies is thriving, driven by demand in organic production, increasing herbicide-resistant weed populations, and the need for more weed management tools in special crops like hemp, sunflowers and pulses.

 

Research from the University of Saskatchewan has determined that pulse crop producers can achieve weed control similar to hand weeding or using herbicide by using a combination of a rotary hoe or tine harrows and inter-row cultivation. When used individually, each piece of equipment contributed to weed biomass reduction, with the rotary hoe generally giving the best weed control and inter-row tillage giving the least. However, weed control – and crop yield – were maximized when an early pass with the rotary hoe or harrows was followed with inter-row cultivation (Table 1). This highlights the importance of early weed control and of managing weeds both within and between crop rows.

 

Although not included in this study, the results suggest that a single method of mechanical weed control paired with other weed management tools, such as herbicides, could also effectively target weeds at different timings.

 

Table 1: Weed Control with Combined Mechanical Weed Equipment

 (Alba & Shirtliffe, University of Saskatchewan)

 

Weed Species

Weed Control (%)

Harrows + Inter-row Cultivator

Rotary Hoe + Inter-row Cultivator

Green foxtail

76 – 94

33 – 92

Lamb’s-quarters

83 – 98

74 – 89

Pigweeds

90 – 98

71 – 91

Wild buckwheat

64 – 95

64 – 95

Wild mustard

95

95

 

Like herbicides, correct timing of mechanical weed control is critical to maximize weed control while limiting crop injury. The harrows and rotary hoe can be used prior to crop emergence, or provide selective weed control in-crop. The rotary hoe is limited to the cotyledon stage of peas and lentils, while harrows can be used up to the 5 node stage. Inter-row cultivation is non-selective in its weed control, but may be safely used until much later crop stages (e.g. 10 node).  In all cases, higher seeding rates are recommended to offset potential crop injury.

 

Although still recommended, higher seeding rates may not be as necessary when using European designed inter-row cultivators capable of accurately targeting weeds between crop rows as narrow as six inches. Camera-guided row sensing technology coupled with a cultivator that moves independently from the tractor are the keys to this precision.  Crop Systems researchers at the University of Manitoba have been impressed with the accuracy of their unit across a range of crops from early emergence to just prior to canopy closure – even at speeds of up to 10 miles per hour and using a tractor without GPS guidance. Surprisingly, depending on the shank, these cultivators can also be used to manage weeds in minimum till cropping systems.

 

Unfortunately, mechanical weed control this accurate comes with a relatively hefty price tag, but researchers hope costs will decrease as this technology becomes more mainstream. For example, University of Saskatchewan weed researchers are using the same guidance system on an inter-row sprayer.

 

The CombCut, also of European descent, may be the most unique piece of mechanical weed control equipment to hit Canada. Picture a cutter bar of X-ACTO® knives that can be angled and pitched to cut rigid stemmed weeds while allowing flexible young cereal crops to pass through unscathed (or so the theory, and You-Tube video, goes). Recently acquired CombCuts have been put to the test by Alberta Agriculture and Agri-Food Canada and University of Manitoba researchers, who will continue to experiment with the units in 2018. Lessons from the 2017 growing season highlighted the importance of adjusting the equipment for individual crops, crop stages and field conditions.

 

New equipment for mechanical weed control may not be a fit for every farmer. Fortunately, weed researchers from the University of Manitoba have identified a simple tillage tweak to indirectly help manage volunteer canola. A fall tillage pass within three weeks of canola harvest was found to double volunteer canola germination, allowing greater seed bank depletion prior to fall frost (Figure 1). Spring tillage also caused an increase in volunteer canola germination, but to a lesser extent than the fall. The icing on the cake is that this effect was seen regardless of the tillage implement used, including a light pass with harrows.

 

Figure 1: Effect of Tillage on Volunteer Canola Seedbank Depletion

(Geddes & Gulden, University of Manitoba)

 

 

 

Mechanical control as a tool for weed management was largely abandoned in the 1980s when many prairie farmers adopted conservation tillage practices. In some cases, advances in mechanical weed control technology may allow for its integration back into these systems as a more targeted, less intensive approach. It’s worth keeping tabs on as we’ve only just begun to scratch the surface in this area of research on the Prairies.

 

By: Jeanette Gaultier

 

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Jeanette Gaultier, Ph.D., P.Ag., CCA.
Jeanette completed her B.Sc. in Agronomy at the University of Manitoba and continued her studies at the Universities of Manitoba and Saskatchewan to earn her Ph.D. in Soils & Pesticide Science. She has worked for Manitoba Agriculture since 2008, first as Pesticide Specialist and more recently as the provincial Weed Specialist. Jeanette lives with her husband and three children near Notre-Dame-de-Lourdes, Manitoba, where they operate a U-pick strawberry farm.

Herbicide-resistant weeds are nothing new to prairie farmers. Since the late 1980s, 20 different weed species in Alberta, Saskatchewan and Manitoba have developed resistance to one or more herbicide groups (Table 1). Yet until recently – and despite the variety of weed species and herbicide groups involved – resistance has ‘looked’ the same.

Herbicide-resistance is the result of a genetic change in a weed species, one that can be passed down from generation to generation. A chance mutation in an individual weed allows it to survive a herbicide application while the rest of its species die off, leaving it and only it to set seed that also carries the herbicide-resistant trait. Repeated use of the same herbicide or herbicide group continues to select for weeds with this trait allowing the resistant population to grow relative to the susceptible population. Research has shown that it can take as little as four years to go from five per cent herbicide-resistance to over 80 per cent herbicide-resistance in a weed species population when the same herbicide mode of action is used year after year.

Best management practices to delay herbicide resistance In addition to a robust crop rotation:

  • Use an integrated approach to weed management that uses cultural, mechanical or biological controls in addition to herbicides
  • Tank mix or sequentially apply herbicides with different modes of actions effective on target weeds
  • Scout fields two to three weeks after a herbicide application to determine if it performed as expected

The evolution of herbicide-resistance in weeds can be broadly classified as either “target” site or “non-target” site resistance. Within each of these broad classifications are a number of specific resistance mechanisms used by weed populations to survive herbicide application. The risk of developing one or more of these resistance mechanisms depends mainly on the weed species and on the herbicide mode of action and use pattern.

In the early days, herbicide-resistance in prairie weeds was largely attributed to target site resistance, a mechanism that causes the weed’s target site to change ‘shape’ and no longer bind with the herbicide. Currently, there are over ten known mutations that alter the Group 1 target site (ACCase) and over twenty mutations that alter the Group 2 target site (ALS). Changes to the target site usually confer a high level of resistance to a particular herbicide(s) at field application rates and may also allow cross resistance to other herbicides in the same herbicide group.

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Eric Johnson, M.Sc., P.Ag.
Eric Johnson is a Research Assistant with the Weed Management Research Lab at the University of Saskatchewan. He has over 30 years of diverse experience in weed management research and extension. His research interests include chemical, cultural, and mechanical weed control.
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Tom Wolf, Ph.D, P.Ag.
Tom Wolf grew up on a grain farm in southern Manitoba. He obtained his BSA and M.Sc. (Plant Science) at the University of Manitoba and his Ph.D. (Agronomy) at the Ohio State University. Tom was a research scientist with Agriculture & Agri-Food Canada for 17 years before forming AgriMetrix, an agricultural research company that he now operates in Saskatoon. He specializes in spray drift, pesticide efficacy, and sprayer tank cleanout, and conducts research and training on these topics throughout Canada. Tom sits on the Board of the Saskatchewan Soil Conservation Association, is an active member of the American Society of Agricultural and Biological Engineers and is a member and past president of the Canadian Weed Science Society. Twitter: @nozzle_guy

1. Agronomy gives us tools for endless creativity. TW: Canadian agriculture has benefitted tremendously from a well-funded and effective plant breeding program that advances the quality and yields of our crops. We also have access to a large selection of fertilizers that address soil fertility shortcomings, and pesticides that protect yield potential. But these tools don’t address all of the challenges facing our producers, and might simply be band-aids that conceal the real problems. How do we solve the big issues such as pesticide resistance? We can’t spray ourselves out of that problem. At the International Weed Science Congress held in Prague recently, one of the industry speakers stated that a new herbicide mode of action was unlikely before 2025. Soil degradation and erosion? No fertilizer can reverse those processes, even if they contribute to vigorous plant growth. Plant health and vigour?