Bio-herbicide hammers broadleaf weeds

After nearly two decades of research and development, a made-in-Canada bio-herbicide may soon hit the market.

The product doesn’t have a brand name but scientists refer to it as Phoma macrostoma, a fungus found on Canada thistle that can control a range of broadleaf weeds, such as dandelions, wild mustard and Canada thistle.

“Monocot crops like wheat, oats, barley are all tolerant, meaning Phoma can be applied to them and they won’t be harmed,” said Michelle Hubbard, an Agriculture Canada pulse crop pathologist in Swift Current, Sask., who worked on Phoma macrostoma for about four years as a post-doctoral researcher.

Hubbard was in southeastern Saskatchewan in early March, where she spoke at the Weyburn Farm Update meeting about Phoma macrostoma and its potential uses in Canadian agriculture.

Ag Canada researchers discovered the fungus in the 1990s, learning that it grows naturally on Canada thistle and causes the weed to turn white and die.

A team of Agriculture Canada scientists, including Karen Bailey and Russell Hynes of Saskatoon, isolated the fungus and developed a granule that can be applied to the soil.

“When applied … before weed emergence the fungus causes the emerging thistles to come up white,” states an Ag Canada document on the bio-herbicide. “The fungus produces phytotoxins during its growth phase, which are taken up by the susceptible plants.”

Testing has shown that the bio-herbicide can control dandelions, annual sow thistle, Canada thistle and wild mustard at levels between 60 to 100 percent.

“There’s some other weeds like … ragweed that are affected but they (require) a bit of a higher dose to be killed off,” Hubbard said.

Ag Canada has patented the technology in more than a dozen countries and in 2017, Quebec company, Premier Tech, bought the licensing rights for the granular bio-herbicide.

“The next challenge lies in reducing production costs so we can bring it to its full market potential,” Pierre Talbot of Premier Tech said in a statement released in 2017.

“It is now up to us to move forward, in collaboration with AAFC, and make this a large-scale commercial success.”

The Western Producer asked Premier Tech to comment for this story, but it didn’t respond by press time.

Phoma macrostoma is not listed as a product on the company’s website so its official launch may be a year or two away.

Premier Tech hasn’t revealed its marketing strategy but the cost of the bio-herbicide will likely be higher than established synthetic products.

“The first, most likely application would be turf or horticulture because people are more likely be willing to pay what it costs,” Hubbard said.

The U.S. pesticide market for home and garden use is worth more than $2 billion annually so that could be a logical place to start, especially since Phoma macrostoma is effective against dandelions.

“Then I would think organic (agriculture) after that. And then conventional,” Hubbard added.

One opportunity within conventional agriculture could be management of herbicide-resistant weeds. Many weeds have become harder to kill as they evolve resistance to commonly used herbicides like glyphosate.

Hubbard studied how Phoma macrostoma killed broadleaf weeds and learned that the biological process is complex.

“Phoma’s mode of action is more complicated. That’s exciting because it implies, to me, that (weed) resistance is less likely to develop,” she said. “The fungus biologically colonizes the host, as well. So, there’s at least three or more different modes of action.”

It’s possible that the bio-herbicide, when it comes to market, could be too pricey for use on broad-acre crops. However, it might make sense to use it in a portion of a barley or wheat crop, Hubbard said.

“It could also be applied as a spot treatment if there was a really difficult-to-manage Canada thistle area in field.”

The granular bio-herbicide persists in the soil only for a relatively short time — for months, not years, as is the case for some other herbicides.

That means oilseed crops like canola and pulses can be grown the following growing season, the year after Phoma macrostoma is applied to the soil.

“You might expect to see some yellowing or bleaching of the subsequent pulse or oilseed,” Hubbard said. “But no difference in biomass or yield.”

For more information on the bio-herbicide, visit

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