Cirsium arvense

Scientific Name Cirsium arvense (L.)
Common Names English: Canada thistle; German: Ackerkratzdistel; French: Chardon des champs; Spanish: Cardo blanco
Description 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.

Descriptions

Characteristic Features

Prickly leaves, lilac florets.

Cotyledons

Wide oval, fleshy, dark green, entire, hardly petiolate, prostrate.

Stems

Erect, ramified, spineless, nearly hairless, angularly furrowed, up to 150 cm (59.05 inch) high.

Leaves

First leaves inverse-ovate, following leaves lanceolate, simple to pinnatifid, wavy-ruffled, sessile.
Leaf margin with soft to hard spines.

Propagatio Organs

Flowers

Capitulum small, spherical, with lilac florets, usually loosely clustered in an inflorescence.
Dioecious.

Flowering Period

Summer.

Fruit

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.

Seeds

Germination usually in spring.

Viability Of Seeds

20 years.

Propagation

By seed.
Shallow germinator (0.5-2 cm, 0.19 - 0.78 inch) depth.
3,000-5,000 seeds/plant.

Occurrence

Habitat

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.

Soil

Loam soils, loam indicator.

Additional Crop Information

Also watershore and waysides.

Agricultural Importance

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. Canada Thistle greatly reduces yield and quality.

Control

Integrated Crop Management

Hand-cutting, mowing and controlled burning can reduce the weed. 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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