Adapting your weed management plan in canola

Introduction

Weed management is essential for profitable canola production.¹ Yield loss from weed competition is highest in canola when weeds are growing prior to crop emergence or from weeds that emerge prior to the two-leaf canola growth stage. It is critical to get the canola off to a good start by controlling weed competition early in the season and do not delay herbicides application until all weeds have emerged. Weeds are highly competitive and can use important resources that include moisture, nutrients, and access to sunlight that would otherwise be available to the canola crop.¹ It is important to understand what the alternative weed control options and combinations are available with the potential for limited glyphosate and glufosinate supplies and as more weed species become resistant to these herbicides.

Preplant weed control options.

Burn-down herbicide weed control program

With the potential of a glyphosate shortage, the first important consideration is if there is enough availability for a single application this season and when would that application provide the most benefit? The most important glyphosate herbicide application is the first herbicide application that is planned.  This can be the burn-down pre-plant application or the first in crop herbicide application, utilizing a Roundup Ready^® tolerant canola product, depending on the production crop plan.

Multiple Effect Modes of Actions

When developing a herbicide plan, consider including multiple effective modes of action to help with weed control and managing weed resistance. One of the best opportunities to add another effective mode of action is in the burn-down or pre-emergent glyphosate application. Depending on your weed spectrum, the following active ingredients are some options for pre-emergence/burndown tank mix partner with glyphosate:

Group 4 – halauxifen

Group 6 – bromoxynil

Group 13 – clomazone

Group 14 – carfentrazone

Group 27 – topramezone

All these active ingredients can be tank mixed with glyphosate and many are found in combination with glyphosate as a premixed herbicide.

In crop, post emerge, herbicide options

Weeds are likely to be smaller and easier to control early in the season. If possible, plan to apply a first application of postemergence herbicide between the cotyledon and two-leaf stage to help maximize yield potential. If available, this allows for the opportunity to make a follow-up application with a second in-crop application to control the next flush of annual weeds and/or perennials weeds before the canopy closes. There are several in crop herbicide options available, but it is important to understand the weed species that these other herbicide options control, but also understand any pH, soil type, re-cropping intervals, preharvest intervals, or any other crop production considerations (Figure 1).  

Figure 1. Post-emergent herbicide options for Canada (conventional and herbicide tolerant products).¹ Figure courtesy of the Canola Council of Canada. Reprinted with permission.

TruFlex™ canola with Roundup Ready^® and LibertyLink^® Technologies

Growers using TruFlex™ canola with Roundup Ready^® and LibertyLink^® Technologies can choose between application combinations with either Roundup^® brand herbicide or Liberty^® brand herbicide for weed spectrum control that exist in their field. In Canada, only Roundup WeatherMAX^® with Transorb^® II Technology herbicide and Roundup Transorb^® HC Herbicide are registered for over-the-top application in TruFlex™ canola or Roundup Ready^® canola. Depending on the problem weeds in the field and focusing on early herbicide application, using these herbicides in different combinations can help. For example, if wild oats or cleavers are the concern, starting with Roundup^® brand herbicide first at a rate to control the weed size present will be the most beneficial. An application of Liberty^® brand herbicide can help manage glyphosate-resistant kochia when the kochia is smaller than four inches. A follow-up application of herbicide can be utilized as needed depending on weed pressure and herbicide availability.

There are tank mix options that can add another effective mode of action:

Group 1 – clethodim, quizalofop

Group 4 – clopyralid, quinclorac

Always follow-up with your local representative on local fit and weeds in your field to determine the best tank mix partner. Always read and follow label recommendations with all these products.

For more weed resistance management information, please visit https://www.mixitup.ca/.

Considerations when changing a canola herbicide program

When considering an herbicide change for any reason think about the following:

1. Assess fields for weed species present and weed density to understand the effectiveness of available herbicide program options.  
2.  Consider how soil pH, soil type, harvest restrictions, weed size limitations, minimum rotational interval and how precipitation may affect the timing and application rates for herbicide programs and following crop rotations.
3. Understand the tank mix restrictions with any combination of herbicides, insecticides and fungicides.
4. Understand the cost of an alternate herbicide program.
5. Cool temperatures can affect weed control efficacy and depends on the type of herbicide application, the rate applied, and the physiological status of the target weed.
6. Watch in-season availability and cost of any herbicide when replacing a glyphosate or glufosinate herbicide program or adding an additional mode of action to a herbicide tank mix, as there may be a domino effect creating supply issues for alternative herbicide programs.

Conclusion

Early weed control that consists of a burn-down herbicide application or preplant tillage followed by an in-crop herbicide application, before the four-leaf stage of the crop, is often enough weed control needed, depending on the weed species.¹ Whenever considering any herbicide program consult your local agronomist or ag chemical supplier to identify your soil types, weed species and environmental conditions. Always read and follow the most recent chemical label.