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North Dakota Tourism

Bowman County Courthouse
104 1st St NW
Bowman, ND 58623

Eliminating Canada thistle crucial, weed board says

September 19, 2014


By BRYCE MARTIN | Pioneer Editor |

Bowman County experienced an extremely large amount of moisture this year that caused an abundant growth of Canada thistle, a noxious weed.

Whether landowners and operators find uncontrolled mature Canada thistle plants or new rosettes, early fall applications are very effective at controlling even the worst Canada thistle infestations, according to the Bowman County Weed Board.

On Oct. 2, 2013, the weed office sprayed Milestone herbicide on a dense infestation of mature Canada thistle around a slough.

“Recently, a producer who farms near there asked me what we used and what time of year it was,” said Randy Gaebe, Bowman County weed officer.

Gaebe’s method of spraying proved effective.

While there are a few small patches of Canada thistle still present at that area, upon Gaebe’s visit to the site this week, it was 95 percent controlled compared to last year.

“We will do follow up work to hopefully give it the final knockout punch,” Gaebe said.

Canada thistle is the only thistle in North Dakota that has become a cropland pest.

The best approach to Canada thistle control in cropland should include an in-crop herbicide treatment to suppress Canada thistle growth, minimize crop yield losses, and prepare the thistle for a fall post-harvest treatment. Preharvest and fall-applied treatments provide the most effective long-term control. The best herbicide to use will vary depending on crop rotation.

For non-cropland, Gaebe suggested spraying five to seven ounces per acre of Milestone herbicide with a non-ionic surfactant.

Canada thistle usually grows two to three feet tall with alternate, dark green leaves that vary in size. The leaves are generally oblong, the length three to five times the width, usually deeply lobed, and have spiny toothed edges. The thistle’s leaf edge spines vary in size and number according to variety.

The weed is a perennial that spreads both by seed and underground rhizomes. However, Canada thistle is not very competitive in healthy turf.

The flowers produce from 40 to 80 seeds per head. Seeds mature rapidly, spread with pappus on the wind, and are able to germinate within 8 to 10 days after pollination.

Canada thistle has an extensive underground root system that may penetrate the soil to a depth of 10 feet or more and grow laterally 12 to 15 feet per year.

“If we are going to rid our county of Canada thistle, we need to all do our part and persistently go after any Canada thistle plants we know of,” Gaebe said.