Control of Medusahead (Taeniatherum caput-medusae) Using Timely Sheep Grazing

Abstract

Medusahead is among the most invasive grasses in the western United States. Selective control of this noxious winter annual grass is difficult in California grasslands, as many other desirable annual grasses and both native and nonnative broadleaf forbs are also important components of the rangeland system. Intensive grazing management using sheep is one control option. This study was designed to determine the optimal timing for sheep grazing on heavily infested medusahead sites, and to evaluate the changes in species composition with different grazing regimes. Midspring (April/May) grazing reduced medusahead cover by 86 to 100% relative to ungrazed plots, regardless of whether it was used in combination with early spring or fall grazing. Early spring (March) or fall (October to November) grazing, alone or in combination, was ineffective for control of medusahead. In addition, midspring grazing increased forb cover, native forb species richness, and overall plant diversity. At the midspring grazing timing, medusahead was in the “boot” stage, just prior to exposure of the inflorescences. The success of this timely grazing system required high animal densities for short periods. Although this approach may be effective in some areas, the timing window is fairly narrow and the animal stocking rates are high. Thus, sheep grazing is unlikely to be a practical solution for management of large medusahead infestations

Introducing cattle grazing to a noxious weed-dominated rangeland shifts plant communities

“…These studies have consistently demonstrated that properly timed (late-spring, post-bolting/preflowering phenological stages -that is, immediately prior to seed head production) and intensive (high animal density resulting in high pressure on vegetation) grazing can reduce medusahead cover by 30% to 100% and yellow starthistle flower heads by 75% to 90% (DiTomaso et al 2008;Thomsen et al 1993). Experimentally manipulated livestock grazing has also been shown to enhance herbaceous diversity and native plant richness in vernal pools, interior annual grasslands and coastal grassland sites (DiTomaso et al 2008;Hayes and Holl 2003;Marty et al 2005). However, there is little published work examining pasture-scale (greater than 80 acres) implementation of prescribed grazing to manage invasive weeds.…”

“…Although germination timing is similar to that of the surrounding grassland community, medusahead does not produce seed heads until late April or May, after most naturalized annuals have completed their life cycle (Dahl and Tisdale 1975;DiTomaso et al 2008;Young et al 1970). Yellow starthistle commonly produces seed heads in May and June; it begins flowering in June and can continue beyond October (DiTomaso et al 2000;DiTomaso et al 2008). In fact, many of yellow starthistle's developmental stages (seedling, vegetative, flowering, seed formation and maturation) generally extend well into the summer dormant period distinctive to Mediterranean climates (Maddox 1981).…”

“…Together, these rapidly expanding species cover more than 15 million acres throughout California (DiTomaso and Healy 2007;DiTomaso et al 2008;Pitcairn et al 1998;Young 1992).…”

“…These species germinate after the first fall rains, with smaller germination events sometimes occurring later in the wet season (Benefield et al 2001). Although germination timing is similar to that of the surrounding grassland community, medusahead does not produce seed heads until late April or May, after most naturalized annuals have completed their life cycle (Dahl and Tisdale 1975;DiTomaso et al 2008;Young et al 1970). Yellow starthistle commonly produces seed heads in May and June; it begins flowering in June and can continue beyond October (DiTomaso et al 2000;DiTomaso et al 2008).…”

“…Prescribed grazing is the controlled implementation of the timing, frequency and intensity of grazing to achieve specific goal(s), such as weed control. Small-scale grazing studies (5 acres or fewer) have examined the effects of livestock type (cattle, sheep, goats), grazing intensity (animals per acre) and grazing season (winter, early spring, late spring) on individual weed species (e.g., DiTomaso et al 2007;DiTomaso et. al 2008;George et al 1989, Lusk et al 1961Thomsen et al 1993).…”