Why is it a problem?
- Spiny, aggressive invader that outcompetes native plants for nutrients and water, poisonous to grazing animals, and can increase forest fire severity.
- Roots grow 18 feet per year; spreads by seeds, stems and root fragments.
- Produces 40,000 seeds per plant; seeds viable for 20 yrs.
- Seeds dispersed by wind, water, animal droppings, on clothing and equipment, and in contaminated hay and crop seed.
- Allelopathic (produces chemicals that inhibit growth of other plants) and alters native pollinator habits.
How do I manage this plant?
- Avoid disturbing soil, which provides a foothold for establishment; where disturbance takes place, reseed with native species Avoid cultivation where Canada thistle is present, as this will stimulate production of horizontal stems and new shoots.
- Remove flowers before they produce seed.
- Extremely difficult to control once established, and requires a combination of mechanical, cultural, and chemical control.
- If discovered, recommend rapid response with chemical control.