Spotted knapweed could do more harm than leafy spurge

The ISCM declared August Invasive Species Month and is highlighting the risks associated with the potential spread of spotted knapweed

The introduced invasive species spotted knapweed is easily identified once the plant produces its distinctive bright-pink flowers. But at this stage it is already well past the stage where controlling its spread is easy or feasible, warns the Invasive Species Council of Manitoba.

The Invasive Species Council of Manitoba wants all Manitobans to be on the lookout for an invasive plant species now spreading across Manitoba that has the potential to do as much or more damage as leafy spurge.

Spotted knapweed was first detected in southeastern Manitoba in 2009 but has more recently been found at sites across central and western sections of the province.

The highly competitive weed can quickly degrade native plant communities by reducing native plants required both by livestock and wildlife.

We need to control it now or face potential problems potentially even greater than those posed by spurge, warns the ISCM board, which declared August Invasive Species Month.

It’s highlighting this particular invasive weed because there’s still time to get on top of it, said Michelle Ammeter, with the Manitoba Weed Supervisors Association.

“By recognizing infestations early, and getting them under control, we have the potential of reducing the impact of spotted knapweed before it has the economic impact that leafy spurge does in Manitoba, or knapweeds do in other jurisdictions,” she said.

Big threat

Doug Cattani, a professor at the University of Manitoba and another ISCM board member said the highly invasive weed could potentially be even more problematic than leafy spurge.

A study released in 2010 showed what impact spurge had. That year it was determined it had spread over more than 1.2 million acres, affecting pastures, natural areas, hay and forage land, as well as roadsides, rail lines and utility corridors and having an economic impact of $40.2 million.

The main concern is that once it gets into native range it will quickly spread largely undetected, which is what happened with leafy spurge, Cattani said.

“Even with the activities and resources put into controlling leafy spurge I think between the 1999 and 2009 reports there was about a four times increase in area,” he said. “There were programs, but it was in areas that were hard to get at.”

Spotted knapweed has already caused significant damage to rangelands in both British Columbia and Alberta.

It’s on Manitoba’s Noxious Weeds Act and regulated under the federal Weed Seeds Order.

It was first detected in the southeastern corner of Manitoba in 2009 and before that thought to be an isolated incidence, say other ISCM board members. But new sites in recent years have been detected east of Winnipeg and north of the Trans-Canada Highway.

“Over the last couple of years we’ve been finding new sites east of Winnipeg and along Hwy. 1 towards Brandon and Deloraine and in the Sandilands area,” said Cory Lindgren, another ISCM member and Canadian Food Inspection Agency representative with the council. It’s also been found in a number of locations along Hwy. 12 near Steinbach.

It is believed that it has been spreading via rail lines and that plants are “hitchhiking on the rails” into Manitoba from northwestern Ontario, he said.

No competition

The problem with it is no animal will graze it and the biochemicals it produces alter surrounding soil, preventing growth of other plants around it and quickly allowing it to become a monoculture.

Spotted knapweed is identified by its distinctive bright-pink flowers and dark bracts on the flower which give it its spotted appearance.

In the first year of reproduction, the plant will bolt in mid- to late June and begin to flower in late June or early July. Flowering continues through August in most years. Seeds from one plant can produce well over 1,000 seeds which remain viable in the soil for five or more years.

The invader prefers dry or well-drained sites and can quickly invade ditches, roadsides, fields, rangelands, or gravel pits.

The ISCM board decided to declare an Invasive Species Month in August following suit with other programs across Canada now putting concerted effort into public education and awareness about the potential harm invasive species can cause, Cattani said.

Other invasive non-plant species have been attracting widespread attention, he noted.

“We’ve seen things like zebra mussels in the last few years really hit the forefront. It’s an invasive species. And I think we’re waiting with bated breath for the emerald ash borer to get into this jurisdiction,” he said.

“We’re trying to get on the side of ones that are just arriving or have imminent arrival and making the public aware so they can be the eyes in the landscape to let us know what’s happening,” he said.

Any sightings of spotted knapweed should be reported to a Manitoba Agriculture office and the Canadian Food Inspection Agency as they both have regulatory authority over weeds and invasive plants.

For more information on Invasive Species visit or email the group at [email protected].

About the author


Lorraine Stevenson

Lorraine Stevenson is a reporter and photographer for the Manitoba Co-operator with 25 years experience writing news and features. She was previously a reporter with the Farmers Independent Weekly and has also written for community newspapers in Winnipeg and Manitoba's Interlake.



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