Easier transportation worsens weed problem

MEDICINE HAT, Alta. — COVID-19, the virus that caused a global pandemic, is spread by one of the same things that allow invasive weeds to spread: ease of transportation in modern society.

“We have this amazing, fantastic global transportation system that didn’t exist for almost all of history,” said invasive species expert Kelly Cooley.

“We’ve never been able to move plants, animals, diseases around the world so quickly from every continent on earth, just in a matter of hours. And that’s why we have some of the challenges we have, but it is also the reason we have some of the amazing standards of living that we have now…. It is definitely a mixed blessing.”

Cooley, owner and operator of CoolPro Solutions, said many invasive weeds can easily travel with or on people, as a virus can, and once here those weeds can ride on water, animals and in some cases, wind to take over native plant species.

He listed some of the more troublesome invasive weeds in Alberta during the Farming Smarter Cypress Conference held last month.

Flowering rush

Cooley said this creeping perennial spread in southern Alberta after the 2013 flood washed it downstream from Calgary, where it had been innocently planted in a city park back in the 1980s.

“Now we have flowering rush all the way down the Bow (River), all the way into the South Saskatchewan River and I don’t know how far it goes after you get into Saskatchewan.”

Now anyone irrigating from the South Saskatchewan River system could be getting weed seeds along with water.

It is also a major problem in British Columbia’s East Kootenay region.

“The invaders take advantage of disturbance and they move very quickly and they colonize very quickly,” said Cooley. “It’s a very difficult plant to get under control.”

It can be killed with glyphosate but often the location of the weed colonies near water prevents chemical use. Other control methods such as pulling and cutting are problematic because flowering rush can regenerate from root fragments.

Phragmites australis

This water-loving creeping perennial, which came from overseas, is well established in the eastern part of North America and is making steady inroads in the West.

“This is one that can transform your ecosystem,” said Cooley. “It can colonize, it can completely take over landscapes and choke out anything that wants to get to and from the water system it surrounds. It likes water. It likes to have its feet wet. Nothing can get through it.”

Thick growth and sharp leaves in healthy stands prevent penetration. Mechanical control has been tried but because it can spread by root pieces as well as seeds, that control method is ineffective.

In Alberta, and possibly elsewhere, phragmites have been spread along railways where they grab hold in wet areas along the tracks. Cooley estimated the weed is now in about 15 sites around Alberta. One patch on the north side of Medicine Hat was quickly attacked by county and city personnel, who report no regrowth in the past three years.

Another phragmites discovery in the County of Newell, near Brooks, was also identified early and attacked by mechanical means, then kept under control with targeted herbicide spraying.

“It underlines the importance of using all your tools,” said Cooley.


Farmers are well acquainted with kochia, a summer annual that thrives with lots of sunlight and heat. Its taproot can be up to four metres long, combined with many short lateral roots.

It likes disturbed areas and salinity. It spreads by seed, often via tumbleweed action, but those seeds last only one to two years near the soil surface. The weed has become tolerant to glyphosate. It can be controlled by hand pulling or digging, but its populations make that impractical in many cases.

It can be controlled through grazing when plants are immature but nitrates can be a problem. Planting competitive vegetation such as perennial grasses can help control kochia.

Downy brome

Topping the problem list among winter annuals is downy brome. It germinates in fall or grows from a taproot and then flowers in summer. Downy brome is thought to have arrived in Alberta in about 1898 from Washington state, said Cooley.

There are now more than 100 million acres of downy brome in the United States and Canada.

“This would be the coronavirus of the plant world.”

Downy brome is well adapted to take over landscapes after fire. In small patches it can be controlled by hand pulling. Glyphosate also works and a new herbicide developed by Bayer, called Esplanade, also shows promise, Cooley said.


This winter annual has not been found in Alberta but is spreading into the western U.S. where it is a serious issue and is on Montana’s noxious weed list. It can choke out native grasses and is a concern even in no-till fields.

Medusa head

Another winter annual not yet found in Alberta, medusa head has spread from the western U.S. over the continental divide. It is a noted problem in Washington state. Medusa head, so named for its multiple heads, looks somewhat like green foxtail, but can grow up to two feet tall. There is no herbicide registered to control it.


A pest among biennial weeds, burdock completes its life cycle over two years, starting out with a taproot and basal leaves in the first year, followed by bolting, flowering and spreading seeds in its second year.

Best control results are achieved in its first year of growth, said Cooley. Broadleaf herbicides are an effective control.

Spotted knapweed

This simple perennial has invaded millions of acres in the U.S. and Canada. Its growth inhibits the growth of other plants nearby. It is easily spread in contaminated hay.

“Don’t let knapweed get a hold on your farm please. If you have a little bit, treat it with the highest respect,” said Cooley. There are several effective herbicides but small patches are best managed by digging or hand pulling, bagging and burning.

Diffuse knapweed

A cousin to spotted knapweed and similar to kochia in its tumbleweed capacity, diffuse knapweed is a very aggressive species that can survive fire and sometimes even herbicide applications.

“If you do have these knapweeds, don’t assume you’ve got them even if you’ve put a couple years work into it because they will persist,” said Cooley.

Invasive weeds can easily travel with or on people and then ride on water, animals and wind to take over native species

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