Biological weed control in temperate grasslands

Intensification of pastoral farming in the temperate world has seen a dramatic shift from the botanically diverse native grasslands (e.g. tussock grasslands of New Zealand, prairie and Pacific grasslands of North America, pampas of South America and steppes of Europe) where many grasses, forbs and shrubs coexisted to botanically depauperate systems. In the extreme, such as in high-intensity flatland dairy farming, high farm production targets may be achieved with a pasture composed of as few as two species such as Lolium perenne and Trifolium repens. In less-intensive farm systems, such as sheep or beef cattle grazing on hill lands, a botanically more diverse pasture is common and often acceptable. Weed control is central to the establishment, maintenance and sustained productivity of these managed pastures. In particular, it is necessary to control non-palatable, injurious and poisonous species that would otherwise reduce livestock carrying capacity or impose other costs on the farm system such as those associated with reduced animal product quality, health and welfare (Fig. 1). These costs can be substantial (Jones et al., 2000; Sinden et al., 2004; Bourdot et al., 2007a; Kaye-Blake et al., 2010).