|Scientific Name||Cirsium arvense (L.)|
|Common Names||English: Canada thistle; German: Ackerkratzdistel; French: Chardon des champs; Spanish: Cardo blanco|
Perennial weed with deep taproot and deep-set, initially perpendicularly-running root stolons that later bend downward geniculately, non-lacteal.
C. arvense likes nitrogen and has a very high phenotypic variability with different subspecies.
Prickly leaves, lilac florets.
Wide oval, fleshy, dark green, entire, hardly petiolate, prostrate.
Erect, ramified, spineless, nearly hairless, angularly furrowed, up to 150 cm (59.05 inch) high.
First leaves inverse-ovate, following leaves lanceolate, simple to pinnatifid, wavy-ruffled, sessile.
Leaf margin with soft to hard spines.
Capitulum small, spherical, with lilac florets, usually loosely clustered in an inflorescence.
One-seeded indehiscent fruit, 1.7-3.9 mm (0.067 - 0.15 inch) oblong, slightly crooked, yellow-gray to olive-green, pappus up to 20 mm (0.78 inch) long.
Germination usually in spring.
Viability of Seeds
Shallow germinator (0.5-2 cm, 0.19 - 0.78 inch) depth.
Open, mesophytic areas, with optimal growth between 50 and 75 cm (19.68 - 29.52 inch) annual rainfall, agricultural land, roadsides, ditch spoil banks, gopher mounds and overgrazed pastures.
Loam soils, loam indicator.
Additional Crop Information
Also watershore and waysides.
C. arvense is a tenacious and economically important agricultural weed. It has a fibrous taproot and is capable of sending out lateral roots as deep as 90 cm (35.43 inch) below ground, from which shoots sprout up at frequent intervals. It also readily regenerates from root fragments less than 2.5 cm (0.98 inch) in length. This vegetative way of propagation results in the formation of “hot spots” in infested fields which rapidly expand, if not adequately controlled. Canada thistle greatly reduces yield and quality.
Useful non-chemical contribution to Integrated Weed Management
Hand-cutting and mowing can reduce the weed stand. Due to its perennial nature, entire plants must be killed in order to prevent regrowth from rootstock. Hand-cutting of individual plants or mowing of larger infestations should be conducted prior to seed set and must be repeated until the starch reserves in the roots are exhausted.
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