The competitive ability of five cool-season grasses relative to Dalmatian toadflax, musk thistle, and downy brome was assessed in two field studies. In 1994, Bozoisky Russian wildrye and four wheatgrass varieties (Critana thickspike, Hycrest crested, Luna pubescent, and Sodar streambank wheatgrass) were seeded into populations of downy brome and musk thistle at Riverside, WY. The same grasses were seeded into populations of Dalmatian toadflax at Cheyenne, WY, in 1995. In 1997 and 1998, weed populations at both study sites were reduced in areas seeded with the five grasses relative to unseeded controls. Hycrest crested and Luna pubescent wheatgrasses were the most competitive against the three weed species. Bozoisky Russian wildrye was more competitive against Dalmatian toadflax than against the other weeds. Sodar streambank wheatgrass suppressed musk thistle and downy brome but was not competitive against Dalmatian toadflax. Seeded grasses, such as Hycrest crested and Luna pubescent wheatgrass, appeared to limit the re-establishment of these weeds. Economic model predictions of the net present values and the internal rates of return suggest that Hycrest crested and Luna pubescent wheatgrass can provide financially feasible long-term weed control only if desired grass yields are maintained for more than 15 yr.
Nomenclature: Crested wheatgrass, Agropyron cristatum (L.) Gaertn. × Agropyron desertorum Gaertn. var. ‘Hycrest’; Dalmatian toadflax, Linaria genistifolia spp. dalmatica (L.) Maire and Petitmengi #3 LINDA; downy brome, Bromus tectorum L. # BROTE; musk thistle, Carduus nutans L. # CRUNU; pubescent wheatgrass, Thinopyrum intermedium (Host. Barkworth & Dewey) Nevski var. ‘Luna’; Russian wildrye, Psathyrostachys juncea (Fisch) Nevski var. ‘Bozoisky’; streambank wheatgrass, Elymus lanceolatus (Scribn. & J. G. Smith) Gould var. ‘Sodar’; thickspike wheatgrass, Elymus macrourus (Turcz.) Tzvelev var. ‘Critana’.
Additional index words: Competition, economic analysis, integrated controls, perennial grass.
Abbreviations: ANOVA, analysis of variance; IRR, internal rate of return; LSD, least significant difference; NPV, net present value.
