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An Assessment of Exotic Plant Species of Rocky Mountain National Park

Agropyron repens (L.) Beauv. (Elytrigia repens var. repens)
Quackgrass, couchgrass (Poaceae)


Current level of impact
Known locations in RMNP: Alluvial fan, Horseshoe Park.
Assessment: Few scattered populations in park. When added together, all populations would cover an estimate area less than 5 hectares. Found in areas disturbed in the last 11-50 years. Generally does not appear to be affecting native plant communities or secondary succession processes.

Distribution
Origin: Mediterranean region, introduced from Europe.
Geographic distribution: Generally distributed throughout U.S. except in the south. In Colorado found from 4500 to 9000'.
Ecological distribution: Waste places, most cropped areas, pastures, and grasslands on gravely and sandy soils. Chiefly in disturbed or mesic to moist sites. Often as a weed of cultivated lands, along waterways and in meadows, occasionally in mountain brush and conifer communities.
Soils: Adapted to moist soils in cool temperate climates. Does best on mostly moist or fertile soils. Roots can penetrate hard soils. Tolerates pH ranges from 4.5-8.0 and grows vigorously on alkaline soils.

Reproduction
Perennial grass, reproduces by seeds or rhizomes. Plants can reproduce from reserves of dormant buds (as high as 1200 buds per plant). Flowers late May to September. Seeds germinate in fall or spring. Capable of producing viable seed more than once per season. Quackgrass is self-sterile which results in reduced amounts of viable seed. However, this does not affect local abundance due to ability to reproduce vegetatively.
Seed production: Produces abundant seed; however, generally less than 1000 seeds/plant.
Seed longevity: Grains can retain their viability for up to 5 years, possible up to 10 years.
Seed dispersal: Seed may be spread in crop seed, straw, and manure.

Competition
Following disturbance, an abundance of shoots are reproduced from root fragments. An aggressive weed that quickly crowds out desirable plants. Initially forms a dense clump through extensive tillering. The following season plants expand and form patchy stands and may form pure stands if undisturbed.
Level of impact: Quackgrass reduces productivity in crops and pasture. Aggressively grows in spring and fall. Has the potential to retard natural succession.
Response to shading: Only moderately shade tolerant, overall vigor decreases when shading exceeds 50%.

Control:
Because seeds can remain viable in soil for up to 10 years, and its ability to reproduce from rhizomes, quackgrass is extremely difficult to control mechanically. Buds are commonly held in a dormant state until separation from the parent plant occurs, so mechanical control efforts may only stimulate bud production.
Chemical: May be controlled with AAtrex (atrazine). Roundup may be applied to actively growing quackgrass. Other herbicides that also may be used to control quackgrass include: Arsenal (imazapyr), bromax (bromacil), Fuldilade 2000 (fluzifop-P-butyl), Hyvar (bromacil), Pramitol (pramitol), Princep (simazine), and Velpar (haxazone).
Other: Prescribed burning and grazing may reduce the vigor and abundance of quackgrass. Quackgrass may also be gradually replaced by other species through natural succession processes.

Notes
Is a rapid invader, and quickly stabilizes moist eroding soils. Considered noxious in cultivated soils.

References

Kells, J., and G. Wanamarta. 1987. Agropyron repens control with selective 
    herbicides. Weed Technology 2:129-132.

Werner, P.A., and R. Rioux. 1977. The biology of Canadian weeds. 24. Agropyron 
    repens (L.) Beauv. Canadian Journal of Plant Science 57:905-919.

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