Dr. Merrill Ross, Professor of Weed Science at Purdue, is well-known for many things, among these are his Canada thistle boxes. This box (approximately 4 ft tall by 2 ft wide by 8 ft long) was filled with soil, planted with one 12-inch long Canada thistle root, then received natural rainfall for the period of 4 months.
Every few inches on the root system of Canada thistle is a node that can give rise to a new plant. So, to control this weed one must kill the root system, which is usually very difficult to achieve and may take several years to accomplish.
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Last updated: 3 May 2001/tlm.
The Plant & Pest Diagnostic Laboratory at Purdue University.