The yellow-green flowers of leafy spurge were seemingly everywhere in late June on a pasture just northeast of Brandon.

The flowers swayed in the wind on a bright but very breezy morning as Jane Thornton spoke to about 75 people participating in a Manitoba Beef & Forage Initiatives (MBFI) field tour.

Leafy spurge was certainly the dominant weed in the area where Thornton was speaking, but it was less noticeable in other parts of the pasture.

Thornton, a Manitoba Agriculture pasture specialist, said there’s a reason for that. Predator insects, which feed on the weed, curbed the number and size of leafy spurge plants.

“For years, bio-controls (like the leafy spurge beetle) were released … but leafy spurge didn’t disappear,” said Thornton.

“Everybody sort of assumed that bio-controls weren’t doing their job. But I think they are working. The density of the stands are less than what they would have been (without bio-controls).”

Thornton is studying leafy spurge control with the MBFI, a research organization that is a collaboration between Manitoba Beef Producers, Ducks Unlimited, the Manitoba Forage and Grassland Association and Manitoba Agriculture.

MBFI staff and Thornton want to know if insect predators and grazing livestock can actually keep leafy spurge in check.

The question is relevant because the weed frustrates ranchers across the province.

“Leafy spurge is probably the most difficult noxious weed to control in Manitoba,” according to the Manitoba Agriculture website.

The researchers are employing the many little hammers model, often used in organic agriculture. In this case, they’re hoping beneficial insects damage leafy spurge and that grazing cattle will also have an effect.

“Eventually you get enough percentages, adding up, that you have an impact on it,” Thornton said.

Agriculture Canada scientists have studied such methods to control leafy spurge, but the MBFI team is hoping to quantify the benefits of bio-controls and grazing livestock.

Thornton and Mae Elsinger, an Agriculture Canada range management biologist, pointed out a few examples of natural predators, mostly beetles and larvae, feeding on leafy spurge.

Convincing insects to eat leafy spurge isn’t a problem, but getting cattle to eat the weed is another matter.

Goats like leafy spurge and sheep will eat it, but cows are less willing.

“Cattle have, basically, a total aversion to it,” Thornton said.

However, she is convinced they can be trained to eat leafy spurge, based on research from the United States.

Kathy Voth, a livestock grazing expert and author of Cows Eat Weeds, has demonstrated that cattle will eat undesirable plants.

Voth, who runs Livestock for Landscapes in Tucson, Arizona, has been teaching cattle to eat weeds such as Canada thistle, leafy spurge and knapweed since 2004.

“The steps I use are based on decades of research about how animals learn and how they choose what to eat,” Voth said in a Livestock for Landscapes document.

“I’ve learned what it takes to adapt the process so that anyone, anywhere can use it…. It’s now possible to teach a cow to eat a new weed in as little as eight to 10 hours spread over seven days.”

Voth’s one week method is straightforward:

• She feeds cattle morning and afternoon for four days. At each feeding they receive a different bag of feed, perhaps things such as oats, barley and soybean meal.
• On day five the cattle are fed in the afternoon. They are given a weed to eat, mixed with half a bag of feed that they ate in the first four days.
• On day six they receive the same weed mixed with a quarter bag of feed.
• On day seven they receive only the weed.

Thornton tried Voth’s strategy last year at the MBFI pasture and it was successful.

“Training cattle to eat leafy spurge is very cost effective,” she said. “It’s not an onerous training program.”

Thornton is now hoping to build on Voth’s research by determining if cattle will continue to eat it and if certain cows like leafy spurge more than others.

“I’m thinking within the population of cattle, there might be some that can metabolize it,” she said. “I want to go on and identify those cattle and … breed their offspring and see if they carry that trait…. Maybe we could build herds that are better at it.”

Thornton’s study will run for at least three years, but she hopes it goes longer.

For more information, visit www.mbfi.ca/index.php.