Stopping the spread of wild oats

There’s a fresh focus on the decades-old problem of herbicide-resistant wild oats

Stopping the spread of wild oats

There are a number of things from the 1970s few people wish to see return: leisure suits, avocado-coloured bathroom fixtures and platform shoes may come to mind. But if you’re a crop farmer, there’s a more serious threat from that era making a comeback — wild oats.

Eric Johnson. photo: Supplied

Sixty-nine per cent of wild oats across the Canadian Prairies show herbicide resistance, said University of Saskatchewan plant scientist Eric Johnson, with 27 per cent resistant to both Groups 1 and 2 herbicides — the products most commonly used to control them.

“From the ’70s up until the mid-’90s, the industry introduced a number of very effective wild oat herbicides,” said Johnson, speaking at the Lethbridge, Alberta-based Farming Smarter conference in December.

Why it matters: Once wild oats develop resistance to Groups 1 and 2 herbicides, you are mostly limited to granular, soil-applied, pre-emergent herbicides — and resistance to those have already been found in all three Prairie provinces.

“The thought was there would be a never-ending pipeline of new herbicides available to growers to control wild oats. That didn’t materialize and we haven’t seen any new modes of action since the mid-’90s or early 2000s.”

Once wild oats develop resistance to Groups 1 and 2 herbicides, growers are mostly limited to granular, soil-applied, pre-emergent herbicides such as Avadex or Fortress (both of which contain the Group 8 active ingredient triallate). Group 3 herbicides such as Edge are also recommended for suppression of wild oats when applied in fall.

However, resistance in wild oats is an ever-moving target. Resistance to triallate, for example, has been found in all three Prairie provinces, said Johnson.

In a nod to an earlier era, the Wild Oat Action Committee of the ’70s and ’80s has been rebranded as the Resistant Wild Oat Action Committee (RWOAC). In partnership with the Canadian Weed Science Society (CWSS), its goal is to educate and engage farmers to develop and adopt diverse approaches to managing wild oats.

Although RWOAC has had a rocky start due to COVID-19, Johnson, the committee chair, says the organization — comprised of researchers, producers and other ag stakeholders — has already outlined some key things farmers can do. Some of these include identifying both old and new management methods, lab testing for herbicide resistance and preventing spread of the weed.

Scout, sample and send

Scouting is a commonly encouraged practice for identifying both ailments and opportunities in farm fields. When it comes to herbicide resistance in wild oats, the RWOAC recommends looking for patches of the same weed type — including dead weeds of the same type. Producers should also be on the lookout for irregularly shaped weed patches as well as patches with no clear boundaries.

Keep in mind that what might appear to be resistance may not be, necessarily. RWOAC suggests ruling out field-scale weed patterns from a host of other potential causes, including plugged nozzles, misses or overlaps, tank cleaning or mixing, turning, drift, soil residue and herbicide underdosing.

Eric Johnson, chair of the Resistant Wild Oat Action Committee, says farmers can learn how to manage herbicide-resistant wild oats from efforts made in the past as well as new innovations from Australia. photo: Supplied

There are some dos and don’ts to keep in mind when collecting wild oats for resistance testing. RWOAC recommends gathering at least 2,000 (one to two litres of seed per subgroup) clean and mature seeds. Indicate on your packaging the herbicide or herbicide subgroup you would like tested for resistance. Avoid collecting dirty, diseased or green seeds or pre-harvest herbicide-treated seed. Don’t include stems and debris.

When it comes to packaging, be sure to pack dry seeds and complete the request form available from the lab. Avoid using plastic bags for shipping; opt for a paper bag instead.

RWOAC offers examples of labs throughout the Prairie provinces that test for herbicide resistance in wild oats. These can be found on the Herbicide Resistance Testing infographic on the RWOAC website at weedscience.ca/wild-oat-action-committee (CWSS hosts the RWOAC site on its page).

Stop the spread

If there’s a bright side to wild oats, it’s that their seeds tend to stay in patches and don’t stray far from home unless moved by human activity. That’s why it’s crucial — especially at harvest time — to make sure they’re not unintentionally spread by combines and other equipment moving in and out of fields.

Practices suggested by RWOAC to minimize the spread of wild oats include the following:

  • Contain the patch because a small area is easier to manage than an entire field. Consider using the patch for livestock feed if practical.
  • Mow the patch before seedset, if possible.
  • Disconnect the straw chopper on your combine before harvesting these patches.
  • Bale and/or burn the straw in the patches themselves.
  • Manage wild oat seeds in chaff by using chaff collectors, chaff lining or impact mills.

See what’s out there, get involved

Many of the wild oat management strategies identified in the ’70s and ’80s are still useful, said Johnson. There is a publication from that era located online. He urges producers struggling with wild oats to check it out.

“It’s called Growth Habit and Control of Wild Oats and it summarizes all that was learned about the ecology and biology of wild oats,” he said.

There has also been research in other countries — notably Australia — on the leading edge of fighting herbicide resistance in wild oats. Although wild oat is present in Australia, most of the focus has been on resistant ryegrass. Despite this, many of the principles and innovations they have developed have applications in managing wild oat.

“Australia has a huge herbicide-resistance problem but they’ve made great strides with producers working hand in hand with researchers. You can learn more about these innovations on weedsmart.org.au.”

Johnson would like to see producers share their own success stories related to fighting wild oat and herbicide resistance.

“I think we need to do a better job of engaging producers in developing solutions,” he said. “If you’ve made changes and they’re working, we would really like to document them and see what we can do in terms of getting other growers to adopt those changes.”

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