NEWS for North Dakotans
Agriculture Communication, North Dakota State
University
7 Morrill Hall, Fargo, ND 58105-5665
July 23, 1998
Spraying wheat with Roundup herbicide just before harvest may be the best way to kill Canada thistle in many areas of North Dakota, research shows.
"When wheat is mature, at 25- to 28- percent moisture, an application of Roundup controls thistle and evenly ripens the crop," says Kent McKay, a North Dakota State University crops specialist at the NDSU North Central Research Extension Center near Minot. Field trials indicate that approach will typically kill 75 percent or more of the thistles.
McKay explains that herbicide applications in the fall are typically most effective against Canada thistle because the plant is moving nutrients to the root system.
Weed specialists say that, ideally, Canada thistle is best controlled by a herbicide application three weeks after harvest when the thistles begin growing again. "In central and western North Dakota we face the question of whether that regrowth is going to occur," McKay says. "It's about a 50-percent chance that they'll go dormant and we won't see growth again until next spring. That means we've missed a window of opportunity for controlling them."
McKay says Canada thistle is the top weed problem for many producers in north central North Dakota. And this year's wet conditions have been ideal for thistle growth and spread while hampering producer's weed control efforts. The perennial thistle spreads by its roots and by seed. "It's spreading like wildfire in some areas of the state," McKay says.
McKay and Brian Jenks, a weed scientist at the North Central Research Extension Center, are studying other options for controlling Canada thistle, and have found that Roundup is consistently effective before harvest. Roundup has no carryover so there are no crop rotation concerns. McKay says many growers use an application of Roundup before wheat harvest to get thistle infestations under control before the field is planted to crops like sunflowers, lentils, canola or peas. All of which might be injured by carryover from other herbicides. Also, there are few labeled herbicides for controlling Canada thistle in those crops.
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Source: Kent McKay (701) 231-7682
Editor: Tom Jirik (701) 231-9629