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Current level of impact
Known locations in RMNP: Distribution mostly restricted to areas where orchard grass was planted.
Assessment: An intermediate number of patchy distributed populations. When added together, populations would cover an estimated area less than 5 hectares. Found in sites disturbed in the last 10 years. Does not appear to be aggressive in areas where plant is located in RMNP. However, has potential for invading and modifying existing communities.

Distribution
Origin: Eurasia, introduced as a hay and pasture grass that has escaped from cultivation.
Geographic distribution: Throughout most of U.S. except desert or arctic regions. Scattered throughout Colorado, especially in cultivated areas, from 4000-8000'.
Ecological distribution: Sagebrush, pinyon juniper, cottonwood, mountain brush, aspen, ponderosa pine, spruce fir communities and occasionally desert shrub communities. Often in the wake of disturbance. Roadsides, lawns, fields, ditch banks. May be injured in areas with dry, cold winters and no snow cover, or if subjected to warm temperatures in January or February followed by a period of extreme cold temperatures. Relatively drought tolerant but does not tolerate extended periods of drought.
Soils: Does well in most soil types and will persist in shallow, infertile, and poorly drained soils. Adapted to a variety of sandy and loamy soils. Fine or coarse soils.

Reproduction
Perennial, reproduces by seeds and tillers. Flowers May to September, one of first grasses to grow in spring. Seed reach maturity in spring.
Seed longevity: Potential to remain viable for 2-3 years, some studies show viability as long as 12-14 years.
Germination: Some studies show that germination is enhanced by alternating temperatures.

Competition
Orchard grass aggressively spreads. When nutrients are available, will out compete many weedy species.
Response to shade: Highly shade tolerant. Also grows well in open areas.

Control
Tolerates close mowing and may become a problem in lawns. Since its rootstocks do not spread, pulling out young plants can be an effective small scale method of control.
Mechanical: Generally, mechanical methods will not control orchard grass because it has evolved under repeated cultivated conditions. In some cases, repeated mowing may stimulate tillering.
Chemical: Numerous herbicides are active on orchard grass (but not specific to orchard grass) including: Direx (diuron), Kerb (pronaminde), Arsenal (imazapyr), Bromax (bromacil), Aatrex (atrazine), and Proncep or Caliber (simazine).

Notes: Good to excellent forage for livestock and wildlife, especially liked by deer.

References

Casler, M.D. 1988. Performance of orchard grass, smooth brome, and ryegrass in 
    binary mixtures with alfalfa. Agronomy Journal 82: 1093- 1098.

Jung, G.A. and B.S. Baker. 1973. Orchard Grass. Pages 285-296. In Heath, M.E., 
    D.S. Metcalfe, and R.F. Barnes (eds.). Forages: The science of grassland 
    agriculture. 3rd edition. Iowa State University Press, Ames. 755 pp.

Mortimer, A.M. 1976. Aspects of the seed population dynamics of Dactylis glomerata 
    L., Holcus lanata L., Plantago lanceolata L., and Poa annua L. Proceedings 
    of the 1976 British Crop Protection Conference 2:687-694.]

Stubbendieck, J., C.H. Butterfield, and T.R. Flessner. 1992. Dactylis glomerata 
    L. pp. 192-197. In An Assessment of Exotic Plants of the Midwest Region. 
    Final Report. Department of Agronomy, University of Nebraska, Lincoln.