Creeping thistle (Cirsium arvense)

Introduction:

Cirsium arvense is an herbaceous perennial in the Aster family. It occurs in nearly every upland herbaceous community within its range, and is a particular threat in grassland communities and riparian habitats. C. arvense is shade intolerant and can tolerate soils with up to 2% salt content. It grows on all but waterlogged, poorly aerated soils, including clay, clay loam, silt loam, sandy loam, sandy clay, sand dunes, gravel, limestone, and chalk, but not peat. It spreads primarily by vegetative means, and secondarily by seed. The seeds spread as a contaminant in agricultural seeds in hay and in cattle and horse droppings and on farm machinery. It produces an abundance of bristly-plumed seeds that are easily dispersed by the wind and they may also be transported by water.

Description:

C. arvense is a herbaceous perennial of the aster family with erect stems 0.5 - 1.0m tall, prickly leaves, and an extensive creeping rootstock. Stems are branched, often slightly hairy, and ridged. Leaves are lance-shaped, irregularly lobed with spiny, toothed margins and are borne singly and alternately along the stem. Rose-purple, lavender, or sometimes white flower heads appear from June through October, generally, and occur in rounded, umbrella-shaped clusters. The small, dry, single-seeded fruits, called achenes, are 0.3 - 0.5m long and have a feathery structure attached to the seed base. The plant is usually dioecious, with male and female flowers produced on separate plants. Female (pistillate) flowers can be readily distinguished from male (staminate) flowers by the absence of pollen (abundant in male flowers) and presence of a distinct vanilla-like fragrance.

Occurs in:

Agricultural areas, riparian zones, ruderal/disturbed, urban areas, wetlands.

Habitat description:

C. arvense occurs in nearly every upland herbaceous community within its range, and is a particular threat in prairie communities and riparian habitats. Throughout its range it is common on roadsides, in oldfields, croplands, and pastures, in deep, well-aerated, mesic soils. In eastern North America, it occasionally occurs in relatively dry habitats, including sand dunes and sandy fields, as well as on the edges of wet habitat, including stream banks, lakeshores, cleared swamps, muskegs and ditches. It is shade intolerant. It grows on all but waterlogged, poorly aerated soils, including clay, clay loam, silt loam, sandy loam, sandy clay, sand dunes, gravel, limestone, and chalk, but not peat. It can tolerate soils with up to 2% salt content. It grows best between 0 - 32 °Celsius. It tolerates annual precipitation ranging from 305-1015mm per year and grows best with 400-750mm of precipitation per year.

General impacts:

C. arvense threatens natural communities by directly competing with and displacing native vegetation, decreasing species diversity, and changing the structure and composition of some habitats. Species diversity in an “undisturbed” Colorado grassland was inversely proportional to the relative frequency of C. arvense. It presents an economic threat to farmers and ranchers. Infestations reduce crop yield through competition for water, nutrients and minerals, and through interference with harvest. In Canada, the major impact of C. arvense is in agricultural land, and in natural areas that have been disturbed or are undergoing restoration. In the United States, it is a host for bean aphid and stalk borer, insects that affect corn and tomatoes, and for sod-web worm, which damages corn. In Bulgaria, C. arvense is a host for the cucumber mosaic virus. In addition to reducing forage and pasture production, it may scratch grazing animals, resulting in small infections. It has been identified as a management problem in many national parks and on TNC (The Nature Conservancy) preserves in the upper Midwest, the Great Plains states, and the Pacific Northwest. Infestations of C. arvense may contribute to the elimination of endangered and/or endemic plant species, such as the Colorado butterfly plant in Wyoming.

Geographical range:

Native range: It is native to southeastern Europe, the eastern Mediterranean, and possibly northern Europe, western Asia, and northern Africa.

Known introduced range:It now has a near global distribution between 37 and 58-59 degrees N in the northern hemisphere, and at latitudes greater than 37 degrees S in the southern hemisphere, exclusive of Antarctica. It occurs throughout Europe, northern Africa, western and central Asia, northern India, Japan, China, northern North America, South Africa, New Zealand, Tasmania, and southeastern Australia.

Management information:

C. arvense should be removed from high quality natural areas when it is first observed. The plant is very tenacious and difficult to control once established. In lower quality areas, management effort should be influenced by the extent of invasion; greater effort is warranted in areas that have new and/or small invasions, which are more likely to be eliminated or contained. Management programs should be designed to kill established clones since the species spreads primarily by vegetative expansion of the root system. It takes at least two growing seasons to determine whether a particular control method is effective. At this time, there are no control methods suitable for wide-spread use in natural areas that eradicate, rather than reduce C. arvense. Control efforts may be more successful when the plant is under environmental stress. The plant is drought and flood sensitive, and its roots are cold-sensitive. Cutting or applying herbicide to shoots after a very severe winter may add sufficient stress to kill plants.

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