Win the war on weeds

Written by Cassandre Cusack on May 23 2018

Category: Grow Grain

Action today will pay off this season and beyond.

You face highly competitive weeds throughout the year. They may have overwintered, established early in the spring, or they may be tough to control in-season. Rather than contemplating whether it’s economical to take action on a given weed in any single year, think about the effect that weed can have on the seedbank for subsequent years and take the necessary control measures before it has a chance to become a long-term problem.


Start by scouting fields in the fall before the next season begins. For example, if you have a spring wheat field with Canada thistle, consider a pre- or post-harvest herbicide application to get weeds under control, especially if you are planning a crop such as field peas the following season. There are limited chemical options for Canada thistle and this will help eliminate a more costly than necessary in-crop application that may not be as effective at that time of year.

Start with a clean field in the spring, and seed early (if possible) at the optimum rate. Wheat plants having a 2-3 leaf head start on wild oats will out-yield wheat establishing at or later than wild oats. A crop can outcompete weeds for soil moisture and nutrients to a certain extent if given the leg up. Seeding at an optimum rate helps with competitiveness.


Scout for weeds early in the season. If highly competitive weeds establish early on, act fast. I like to see wild oats controlled before the 3 leaf stage to minimize the amount of moisture and nutrients they steal from the crop. I have also found that a yield-robbing weed like wild buckwheat is relatively easy to kill with the right chemical at earlier growth stages. However, once these plants have wrapped themselves around the crop they are much harder to kill. Eliminating wild buckwheat early will also alleviate any headaches at harvest time - their vine-like stems that stay green in the fall can cause trouble with your equipment.

When it comes to winning the war on weeds – not just one battle – good crop rotation will help you avoid build-up of high populations of competitive weeds. A longer crop rotation will also provide more chemical options.

You don’t have to rely solely on chemical solutions for tough to control weeds, but when using herbicides, keep these basics in mind:

  • Ensure you use the right product for the weed spectrum, and always use the label rate.
  • Light or heavy weed infestation? This may affect the rate of product you use when the label rate varies.
  • Spray for weeds at the right time to avoid yield loss.
  • Use proper water volumes and travel speeds to ensure adequate coverage to minimize weed escapes.

Managing highly competitive weeds before they become a big problem will ultimately save you money in control measures and prevent yield loss.
If you’ve got questions about how to handle your worst weeds, contact a Cargill location near you.

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