Seeding cool-season grasses to suppress white locoweed (Oxytropis sericea) reestablishment and increase forage production

Livestock poisoning can occur on short-grass prairies when locoweeds are actively growing in spring before warm-season grasses begin growth. White locoweed grows in early spring, completes flowering and seed production by early summer, and goes dormant. Perennial cool-season grasses may provide competition to suppress locoweed or reduce its reestablishment following control. Furthermore, these grasses may provide alternative palatable forage to livestock early in the spring. The objective of this study was to suppress white locoweed reinvasion by seeding cool-season grasses at two mixed-grass and two short-grass prairie sites. White locoweed and associated species were controlled with glyphosate (1.1 kg ai/ha) and picloram (0.38 kg ae/ha) in 3 by 15 in plots. The plots were seeded to 'CDII' crested wheatgrass, 'Vavilov' Siberian wheatgrass, 'Luna' pubescent wheatgrass, 'Bozoisky' Russian wildrye, smooth brome, 'NewHy' wheatgrass, sideoats grama, and 'Immigrant' forage kochia. In addition, a native grass plot, treated with picloram to control locoweed without harming the native grasses, and a nontreated control plot, were established in each replication. Establishment of crested wheatgrass, Siberian wheatgrass, and Russian wildrye averaged 60% over all sites. The other treatments had establishment rates < 30% and were considered unsuccessful. Forage production of Russian wildrye was 2,962 kg/ha, Siberian wheatgrass was 2,736 kg/ha, and crested wheatgrass was 2,339 kg/ha, compared with 1,051 kg/ha for the nontreated control. Mortality of locoweed seedlings was greatest in the pubescent wheatgrass seeding. All seeded species suppressed reestablishment of indigenous locoweed plants.