Integrated Management of Leafy Spurge-Infested Rangeland

Abstract

Leafy spurge is an invasive Eurasian weed on pastures and rangeland in North America where it reduces grass forage production. Our objective was to determine the effects of multispecies grazing combined with Aphthona flea beetles on leafy spurge-infested rangeland. On two western North Dakota sites divided into four 25- to 79-ha pastures, two grazing duration treatments were applied: season-long with 7 to 10 cow pairs and 20 to 25 sheep from late May through mid-September, and rotation with 18 to 21 cow calf pairs and 45 to 60 sheep for 3 weeks twice per year. Grazing treatments started in 1998 and continued through 2002. Aphthona spp. were released beginning 1991 and were widespread in both pastures by 1998. Four grazing enclosures were randomly located in each pasture in the spring of 1998. Cover of leafy spurge, grass, and forbs, as well as density of vegetative and flowering leafy spurge stems were measured in July 1998 through 2002. Aphthona densities were counted July 1999 through 2002. Grazing initially increased leafy spurge vegetative stem density, but grazing decreased vegetative stem density from 104 in 1999 to 20 stems m-2 in 2002. Season-long grazing reduced vegetative stem density by over 30 stems m-2 compared to rotation grazing. Leafy spurge flowering stems decreased from 80 stems m-2 to 4 stems m-2 in 2002 in all treatments. The decrease was more rapid when grazing was combined with Aphthona. Initially, Aphthona densities were greater in the grazed areas than the exclosures, but by 2002 more Aphthona were found in the exclosures than the grazed areas. Grazing reduced grass cover and increased forb cover. Results suggest combining multispecies grazing and Aphthona when restoring spurge-infested grasslands produces a synergistic effect.