NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665
August 24, 2000
With Canada thistle rapidly becoming North Dakota’s number one noxious weed, late summer and fall provide an opportunity for effective control. Using the right combination of tillage and herbicide improves control and may reduce the amount of herbicide required, according to a North Dakota State University weed scientist.
Richard Zollinger, extension weed specialist at NDSU, says a key to successful control of Canada thistle is to understand how it grows and use that knowledge to advantage.
Over 90 percent of Canada thistle’s root system is below cultivation depth. The only way to effectively control the root system to apply herbicides when maximum translocation of the chemical to the underground roots will occur. This happens in late summer or fall after day length is less than 14 hours, says Zollinger.
Long summer days with over 16 hours of daylight induce Canada thistle plants in the rosette stage to bolt and produce flowers. Thistle plants that emerge after there is less than 14 hours of sunlight will not bolt but stay in the rosette stage.
At this stage the plants pump more food reserves down to the root system. Applying mobile herbicides like 2,4-D, Banvel, Tordon, Roundup and Curtail/Stinger at this time also results in greater translocation of herbicide to the roots and subsequently greater root kill, Zollinger says.
Research in Canada showed that thistle treated at the rosette stage had 88 percent fewer shoots present a year after treatment as plants treated in the bud stage with twice as much herbicide.
Roundup applied to Canada thistle in the rosette state at half the rate recommended for the bud stage resulted in 98 percent control for two years after treatment, Zollinger says.
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Source: Richard Zollinger, (701) 231-8157
Editor: Gary Moran, (701) 231-7865