It’s time to talk about resistance management, again

January 24, 2019

Graham Collier doesn’t mince words when he talks about herbicide resistance. “We have a serious problem in Western Canada,” says the technical services manager for the Western Prairies with Nufarm Agriculture Inc.

“If you are going to use herbicides on your farm, you have to expect that you will be selecting for resistance to those herbicides,” he says. “Over time, you remove the highly susceptible individual weeds and select for the ones that are tolerant for some reason, whether those weeds are truly resistant because of a physiological change or resistant in another manner.”

Collier gives the example of weeds that germinate later, after a herbicide application. “The weed population isn’t physiologically resistant to the herbicide, but when you make an application at the same time each year you select for later germinating individuals, which over time makes up the bulk of the population,” he says.

Proactive is the way to go

Weeds are tricky, and the best way to manage resistance development is with a proactive approach. The message is the same if you farm in Eastern Canada.

Canada unfortunately ranks third in the world for the cases of herbicide resistance. We’re behind Australia and the United States, but in many cases, Canada is building new cases of herbicide resistance faster than other countries.

Collier is autely aware that academics and agronomists talk about the importance of managing herbicide use to reduce the development of resistance.

“In Western Canada, we have more species and more populations within species that are developing herbicide resistance,” says Collier. “From rapid resistance to Group 2, glyphosate-resistant kochia, and several other weed species at risk of developing resistance to glyphosate including wild oats, cleavers, Russian thistle, and green foxtail.”

It’s important to remember that weeds are mobile, they don’t have to respect borders. “Weeds are good at reproducing and distributing seed,” says Collier. “For example, some weeds produce very few, large seeds with high survivability, while others produce thousands of small seeds that may not be viable for very long, and only a small percentage need to be viable for success.”

The trouble with kochia

Kochia is an example of a weed that seems to have adapted well to the environment. It produces thousands of seeds per plant, can move via tumbling to distribute seeds, and will change its growth pattern depending on competition, moisture, heat and other available resources. “A weed like kochia can distribute seed from field to field with assistance from the wind. It can also distribute genetic traits from field to field, being a cross-pollinated species,” says Collier. “We can’t stop pollen moving in the wind, but we can limit the spread of resistant weeds and the development of new resistant biotypes by following a few simple steps.”

So what can farmers do in their fields to slow the risk of resistant weed development?

  1. Change up your farm practices. Do something different every year to throw weeds off their game. Weeds are smart but they thrive on routine so change it up and mess them up. Alter herbicide application timings or include an application timing you haven’t before.
  2. Rotate crops. Plant different crops and change up growing habits and competition levels in your fields.
  3. Rotate herbicide mixtures. Use different modes of action and products with multiple modes of action. Rotate your tank mixes and change application timing.
  4. Scout for survivors. After spraying get out in the field and see if you can find patches or individuals that were not controlled – testing for resistance to most modes of action is available in Canada. Finding and managing those patches/fields early can save money and time in the long run.
  5. Keep records. Knowledge is power. Keep track of what you’ve done in the past and keep it easily accessible for planning next year.

Don’t wait to start

From his perspective, James Ferrier says some growers are receptive to the resistance management message, but most growers wait until they see a resistant weed problem on their farm before they act. And by then, it’s too late. As the technical services manager in Eastern Canada for Nufarm, Ferrier sees part of his role is to find technical and agronomic fits for Nufarm’s products – especially as part of a strong resistance management plan.

“We focus on products with multiple modes of action and multiple actives that have little or no known resistance in the key segments where we are marketing,” says Ferrier. “Across Canada, we are encouraging growers to rotate modes of action, rotate actives and rotate crops. Looking at the whole agronomic approach will help us delay herbicide resistance.”

Want to find out more about your weed control options as part of a sound resistance management plan? Ask A Nufarmer at 1.800.686.5444, visit Nufarm.ca and follow us @NufarmCA.