Outlaw ryegrass is refusing to release its grip on farmers’ land in other countries, and like a dimestore novel, the ending is predictable.
If it doesn’t die, it will take over the West.
Researchers fear that Canada may be involved in the shootout.
“As more and more livestock is grown on the Prairies, more forage will be needed. Part of that forage will be ryegrass and with it will come herbicide resistance,” said Hugh Beckie, a researcher with Agriculture Canada in Saskatoon.
Introduced as turf grass and annual pasture forage, ryegrass is among new forage crop choices for Canadian farmers. That concerns researchers because resistance to herbicides is one of the most famous features of the plant.
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While most Italian ryegrasses set seed only in their second year and tend to die during cold northern winters, Canadian farmers face a greater threat from the species Westerwold, which sets seed in its first season.
The Italian and Westerwold plants tend toward genetic mutations that make them resistant to some herbicide families, including Group One (ACCase grasskillers, especially those whose technical names end in “fop” such as Assure, Hoe-Grass and Horizon) and Group Nine (glyphosates such as Roundup, Laredo, Victor, Wrangler and Touchdown.)
In some parts of Australia, a cousin to the Italian and Westerwold ryegrasses called Rigid is a considered a weed. Researchers there fear that cereal crops may no longer be viable due to herbicide resistance in ryegrasses.
“We estimate that herbicide-resistant ryegrass costs Australian cereal growers ($97 million Cdn) a year,” said University of Adelaide researcher Rick Rousch.
Still some enemies
He said farmers in Australia have ryegrasses immune to various herbicide groups but so far no region has plants resistant to all products.
“Farmers are still having success with paraquat (Gramoxone) and trifluralin (Treflan, Bonanza, Rival, Edge, Advance and Fortress) and some have found control with pre-seeding burnoffs and delayed seeding,” said Rousch. “But that only works for those who do not have glyphosate resistance.”
Closer to home, farmers in Oregon’s Willamette Valley saw Group One herbicide resistance in Italian ryegrasses as early as 1987. In 1995 there were reports of Group Two (sulfometuron) resistance in Mississippi and in 1998 resistance to Group Nine (glyphosate) was found in California.
Ryegrass is a powerful competitor in cereal crops. A single plant per square metre has been shown in American tests to injure wheat crop yields by up to five percent.
Italian ryegrass infests 10 to 15 percent of winter wheat crops in the United Kingdom as short-term pasture and forage plantings come back to haunt producers in subsequent years.
In Ontario and Quebec, the grass has been grown as pasture and forage for more than 15 years and no herbicide resistance has been found. That is attributed to the grasses’ cold intolerance and limited popularity.
Nor is it resistant in continental Europe, partly because farmers there use only certified seed.
“With Westerwold there may be a problem in that it can become resistant and survive to set seed in Western Canada,” said Beckie.
To avoid herbicide tolerance:
- Use certified seed.
- Keep the plant from setting seed by grazing in mid-summer and again in fall.
- Use Italian ryegrass as forage and check that winterkill occurs.
- Promote fall germination through packing or harrowing.
- Avoid cultivation because seed may be buried.
- Use spring applications of glyphosates or other broad spectrum herbicides such as the mix of paraquat and diquat.
- Avoid growing a crop that might require any Type One herbicide in the year following the ryegrass.
- If a Type One herbicide is used, be sure it has a technical name ending in “dim” and not one ending in “fop.”
“Ryegrass has some very special properties to develop resistance. We have triazine (Group Five)-resistant canola grown in Western Australia. We have found ryegrass that has never seen this herbicide before and in one application and in one year, produce resistant seed. It is a weed problem you don’t want,” said Rousch.
