Seed World

Rise Up Against Herbicide Resistance!


Growers are looking for new tools in their effort to stand up to herbicide resistant weeds.

Herbicide resistance continues to grow in both Western and Eastern Canada and is increasingly frustrating for growers, notes Graham Collier and James Ferrier, technical services managers for Nufarm.

According to Ferrier, four main weeds are rapidly developing resistance in the East (especially in Ontario): giant ragweed, common ragweed, common waterhemp and fleabane.

In the West, the culprits are kochia, wild oats, wild mustard and cleavers, Collier says.

Thankfully, there’s one weapon in the arsenal that is proving to be effective in both halves of the country: a pre-seed burndown of the fields by using a pre-emergent herbicide.

In recent years, pre-seed burndown has emerged as a hugely effective tool in the fight against herbicide resistance and weed control in general. According to Collier, it comes with a number of benefits:

  • It removes weed competition as early as possible — smaller weeds are easier to control, and gets rid of the competition for young crops, giving them a stronger start and better yields.
  • A pre-seed burndown application avoids the need to spray weeds when they are out of the ideal control stage later in the season, which can lead to sub-lethal herbicide doses and an increased risk of resistance development.
  • A pre-seed herbicide application can give better control and more complete control of weeds and limit weed seed production.
  • A pre-seed or pre-emergent herbicide application can allow growers to use herbicide modes of action that they can’t use in-crop. This increases the diversity of their herbicide rotation and slows resistance development.
James Ferrier

Despite its convenience, it’s crucial to understand that using a single mode of action is very unwise.

“There was a time when growers were happy putting glyphosate down alone, but it’s not as effective as it used to be considering the presence of glyphosate resistant weeds.  It’s a risk putting glyphosate down on its own without using another mode of action to protect,” Collier says.

Ferrier agrees.

“Growers have had to shift their thinking on weed control. We’ve gone from easily controlling weeds in-crop to now adding a pre-seed burndown application to the list. Farmers should strongly consider adding two other modes of action to the tank along with their glyphosate. That’s key.”

Why go to such lengths? Collier notes that weeds are actively developing resistance to more than just one group of herbicides, so using combinations of multiple products in addition to glyphosate gives you a much better chance of killing whatever weeds are predominant in a particular field and reducing their opportunity to develop resistance to individual herbicide groups.

“If you mix Group 2 and Group 9 herbicides in the tank, and you go and spray a field that already has Group 2 resistant weeds, you really are still only targeting those weeds using one mode of action,” Collier says.

Nufarm has employed a key chemistry to help provide growers with a powerful weapon against resistance. Pyraflufen is a novel new Group 14 active ingredient that is registered for pre-seed, non-residual control in many crops including pulses, cereals and soybeans.

Graham Collier

Recent federal approval of pyraflufen use on additional crops such as lentils, field peas and canola, as well as expanding the usage to a rate range, has allowed Nufarm to introduce two new products to enhance pre-seed burndown. Pyraflufen is now available in a pre-formulation with the new BlackHawk (cereals and soybeans) and GoldWing (pulses) herbicides in Western Canada.

In the East, BlackHawk is seeing success for use as a pre-seed burndown product for use on cereals, corn and soybean fields.

Nufarm’s other pre-seed weed control products include Valtera (based on the Group 14 flumioxazin a residual soil applied herbicide for use prior to pulses, soybeans, and wheat) and Conquer (with the Group 14 carfentrazone and Group 6 bromoxynil foruse before sensitive crops like canola).

“Ease-of-use for the grower is top-of-mind when we design these products. A product like BlackHawk has two modes of action in one jug so the grower doesn’t have to worry about adding in an additional one,” Ferrier adds. “We’re lucky at Nufarm to have talented chemists develop these products that are powerful, easy to use and also affordable.”