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Current level of impact
Known locations in RMNP: Moraine Park, 8500', infrequent in wet swails, montane.

Distribution
Origin: Introduced from Europe.
Geographic distribution: Locally frequent throughout northern U.S., becoming less frequent in south, central, and south western U.S. Scattered through Colorado from 5000 to 6000'. Grows in cultivated fields, meadows, along roadsides and in waste places. Common in gardens, ditch banks, and fertile waste areas where adequate water is available.
Soils: Mostly on rich soils. Adapted to a variety of soils, common on cultivated or non-compacted soils that are semi-moist to moist and fine textured. Found on soils with a pH range from 5.2-7.2.

Reproduction
Creeping perennial, reproduces by seeds and horizontal roots. Plant capable of producing roots from root buds nearly two feet deep, thus forming large colonies. Spreading rootstocks are the primary means of expansion and invasion into new areas. Flowers June to September.
Seed production: Seed production per plant may total 13,000. However some germination tests indicate that viability commonly be under 40%. A typical plant can produce 3000-10,000 achenes.
Seed longevity: Seeds may remain dormant for up to 6 years.
Seed dispersal: Medium potential for dispersal based on seed weight and seed size. Seeds possess simple hairs that may aid in dispersal.
Germination: Germination is higher under plant and litter cover. Nearly 80% of seeds germinate the first year. Optimal temperature for germination is between 25 and 30 C.

Control
Continuous removal of underground parts over a period of 80 days is necessary to exhaust underground food reserves in roots.
Mechanical: Frequent mowing can be used to reduce perennial sowthistle vigor and should be done at least two times a year to reduce seed production and reduce root reserves.
Chemical: Relatively resistant to many common broadleaf herbicides. Herbicides listed for control of perennial sowthistle include Banvel (dicamba), 2,4-D amine, or 2,4-D ester plus acid.

References

Bell, A.R., J.D. Nalewaja, and A.B. Schooner. 1973. Response of perennial sowthistle 
    selections to herbicides. Crop Science 13: 191 - 194.

Lemna, W.K. and C.G. Messersmith. 1990. The biology of Canadian weeds. 94. Sonchus 
    arvensis L. Canadian Journal of Plant Science 70:509-532.

Stubbendieck, J., C.H. Butterfield, and T.R. Flessner. 1992. Sonchus arvensis L. 
    pp. 125-131. In An Assessment of Exotic Plants of the Midwest Region. Final 
    Report. Department of Agronomy, University of Nebraska, Lincoln.