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Using fall-applied residual herbicides can save you time in the spring

Read Time: 5 minutes

By Trish Mead August 29, 2023

Considering post-harvest herbicide applications can help your operation in the long run

I’m sure you can all agree when I say this growing season has been anything but ordinary. We had severe drought conditions in many parts of the country persisting through the first part of summer. This led to unusually low weed populations at both pre-seed and early in-crop herbicide timing. Then came the rain later in the season which led to immense weed growth. Unfortunately, these weather conditions resulted in particularly high late-season weed populations that ended up being beyond the scope of chemical control. What are some ways that you can avoid situations where weed management can easily get out of control?

Fall-applied residual herbicide applications can benefit your weed management plan in many ways

Harvest passes give you an excellent opportunity to assess the efficacy of your seasonal weed control activities and plan your post-harvest herbicide application. The top four benefits of fall-applying residual herbicides include:

  1. Optimization of your spring workload when it comes to weed control.
  2. Reduction in the time that weeds use up crucial nutrients and moisture in your soil
    Since herbicides are already in place, weeds are already being managed.      
  3. Prevention of applying herbicides in sub-optimal spring conditions when weeds may not even be present.
  4. Enhanced management of herbicide-resistant species and control of flushing weeds.

Additionally, for liquid products that can be mixed with glyphosate, fall applications are more optimal for winter annual, and perennial weed control. This practice does, however, require an adequate fall application window as well as a confident crop plan.

Consider using granular fall-applied herbicides

Granular applications are a tried-and-true way to manage resistant weeds. Products such as Edge® MicroActiv®, Avadex® MicroActiv, Treflan® MicroActiv, and Fortress® MicroActiv (see table below) can offer unique groups of action for herbicide-resistant kochia and wild oat control in a variety of crops. These products are best-applied post-harvest to ensure adequate activation time and allowance for snowpack to maximize soil contact. Six to eight weeks of residual weed control is provided with these products.

There are liquid formulations of these granular options such as Avadex® Liquid EC and Treflan® Liquid EC that can offer improved convenience of application; however, these should be reserved for soils free of residue.

A table breaking down herbicide usage

**Pre-emergent control only

Liquid herbicides make a convenient approach to fall applications

Liquid applications can be applied with ground sprayers making them much more accessible for most operations. With liquid, you can tank mix with glyphosate to control emerged weeds in a single pass. Flumioxazin, a liquid ingredient, can provide up to four weeks of residual activity, while pyroxasulfone can work for up to eight weeks.

A table breaking down herbicide usage

Always refer to product labels for specifics.

Fall-applied residual herbicides help weed control in the following situations:

  • You are rotating a low-competing crop such as flax.
  • You are rotating a crop with limited in-crop herbicide options such as field peas.
  • You have herbicide-resistant weed populations in the crop you are already rotating to.
    • Group 1 resistant wild oats in barley.
    • Kochia in Roundup Ready® canola.
  • You have weed populations difficult to control in the crop you are rotating to.
    • Cleavers in LibertyLink® canola.
  • You have difficulty keeping up with herbicide applications in the spring.

If you’re wondering what fall residual herbicides are best for your farm situation, contact your local Cargill rep to discuss your options this fall.



Edge® MicroActiv®, Avadex® MicroActiv, Treflan® MicroActiv, Fortress® MicroActiv, Avadex® Liquid EC and Treflan® Liquid EC are products of Gowan Company LLC. Fierce®WG/EZ and Valtera™WG/EZ are products of Nufarm. Focus® is a product of FMC Corporation.

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Trisha Mead

Trisha is the Market Development Agronomist for Northeast Alberta, covering Vermilion, Vegreville, and Viking. She studied crop science at the University of Alberta and started her agronomy career in soil science and nutrient management, gaining valuable expertise in soil health. She enjoys working alongside the amazing growers in her community and supporting them in their farm practices.