Impact of shading and defoliation on Vulpia spp.
Vulpia species (Vulpia bromoides, Vulpia myuros) are annual grass weeds prevalent in southern Australian, dryland pastures. Vulpia provides poor quality forage and its seeds damage hides, carcasses and skins. Knowledge on how shading affects Vulpia growth and survival can be used to develop grazing strategies aimed at Vulpia suppression. A pot experiment was established to assess the impact of shading on Vulpia growth by adjusting sward height. The swards (phalaris (Phalaris aquatica) and Vulpia) were maintained at 3, 6, 12 or 24 cm to simulate continuous grazing at different grazing pressures, or defoliated to 2 cm once the sward reached 30 cm, to simulate rotational grazing. All treatments were compared to the control (Vulpia without any shading/surrounding sward). Solar radiation and temperature at the soil surface, plus Vulpia tiller numbers, panicle numbers and biomass were measured. There was a decline in solar radiation as sward height increased. Mean radiation levels in the simulated rotation were intermediate to the 12 and 24 cm treatments. However, the increase in shading in these treatments did not reduce Vulpia panicle production. In contrast, Vulpia panicles per plant were lower in 3 cm and 6 cm swards than in the control (16, 19 and 77 panicles per plant respectively). The most effective treatment was the rotation, or simulated grazing, which reduced tiller and biomass per plant when compared to the shorter swards (3 and 6 cm) and panicles per plant when compared to the control. A rotationally grazed system, with a combination of severe shading and defoliation, could suppress Vulpia to a greater extent than in continuously grazed pastures, where solar radiation levels are higher and defoliation is less severe.