Revegetating Russian Knapweed (Acroptilon repens) Infestations Using Morphologically Diverse Species and Seedbed Preparation

Abstract

Highly degraded pastures and rangeland dominated by Russian knapweed (Acroptilon repens [L.] DC) are often devoid of desirable plants. Control efforts may be ephemeral because propagules of desirable species are not available to reoccupy niches made available by control procedures. Establishing desirable, competitive plants is essential for enduring management and restoration of Russian knapweed and other weed-infested plant communities. The objective of this study was to investigate the effectiveness of revegetating Russian knapweed-infested pastures with 3 nonnative, morphologically diverse species following 1 of 3 seedbed preparation treatments. In successive years, at 2 similar sites in southeastern Oregon, we sprayed Russian knapweed with glyphosate, then prepared the seedbed by burning, tilling, or leaving untreated. Following seedbed preparation, we seeded a perennial forb (alfalfa [Medicago sativa L.]), a bunchgrass (Siberian wheatgrass [Agropyron fragile {Roth} P. Candargy subsp. sibericum {Willd.} Melderis]), and a sod-forming grass (pubescent wheatgrass [Elytrigia intermedia {Host} Nevski subsp. trichophora {Link} Tvzel]) in monocultures and 2- and 3-species mixtures. We measured Russian knapweed and seeded-species density 1 and 2 years following seeding. The forb-seeding treatment decreased reinvasion of Russia knapweed by 50%-60% at 1 site, but otherwise, seeding treatment had little influence on total seeded-species density or Russian knapweed density. Tilling generally resulted in a 35%-40% reduction in Russian knapweed density compared with the control and resulted in the highest establishment of seeded species. Variability in annual precipitation appeared to influence seeded-species establishment between the sites. Our results suggest shallow tilling (10-15 cm) followed by drill-seeding desirable forbs and grasses may provide the best results when revegetating Russian knapweed infestations. Follow-up management should include strategies to enhance desirable species production while minimizing Russian knapweed reinvasion.