Canopy height effects on vaseygrass and bermudagrass spread in limpograss pastures

Potential grass weeds in limpograss [Hemarthria altissima (Poir.) Stapf & Hubb.] pastures include vaseygrass (Paspalum urvillei Stead) and common bermudagrass [Cynodon dactylon (L.) Pers.]. Grazing management is critical to controlling spread of these grasses and maintaining productive limpograss swards, but competition dynamics among these species have not been evaluated under grazing. The objective of this experiment was to determine the effect of grazed canopy height (20, 40, and 60 cm) of continuously stocked limpograss pastures on changes in frequency of occurrence and ground cover of limpograss, vaseygrass, and common bermudagrass and plant density of vaseygrass. Experimental units were 0.5-ha pastures replicated four times in a completely randomized design. During the 2 yr of grazing, vaseygrass density decreased in all pastures, changing most for the 20-cm canopy height and least for the 60-cm canopy height (4.4 vs. 0.4 plants m(-2)). Changes in vaseygrass cover followed the same trend as density. In contrast, bermudagrass cover increased by seven percentage units if pastures were grazed to a 20-cm height, but the increase was less for 40- and 60-cm swards. These data show that continuous stocking of limpograss pastures decreased vaseygrass plant density, especially when canopy height was low; however, common bermudagrass invasion was favored by grazing to 20 cm, potentially compromising limpograss persistence. It is concluded that grazing continuously stocked limpograss pastures to approximately 40 cm is effective in decreasing existing populations of vaseygrass while minimizing invasion by common bermudagrass.