Management of Navua sedge (Cyperus aromaticus): a role of competition using two pasture species

Abstract

Navua sedge (Cyperus aromaticus (Ridley) Mattf. & Kük.), is a grass-like perennial weed and is native to equatorial Africa and islands in the Indian Ocean, off the coast of southeast Africa. It was accidentally introduced to Northern Queensland, Australia where it has invaded rangelands and cropping [e.g. sugarcane (Saccharum officinarum L.)] areas. Currently, the weed is causing a significant loss to agricultural productivity by smothering pasture, crops, and native plants due to its fast growth rate as well as the absence of sustainable weed control methods. Therefore, it is essential to find a weed control method which can suppress Navua sedge growth to prevent further spread and to control the weed’s invasiveness. The hypothesis that vigorously growing grasses can outcompete and suppress the growth of this invasive weed was tested.

A replacement series competition study using five density ratios, at two soil moisture levels of 50 and 100% of field capacity, was established to determine the intraspecific and interspecific competition effect of two fodder grass; Rhodes grass (Chloris gayana Kunth) and humidicola (Brachiaria humidicola (Rendle) Schweick). on the growth of Navua sedge. At all density ratios and for all three species, there were minimal growth differences in response to soil moisture level. Navua sedge managed to produce more tillers and leaves under all moisture levels as well as at all intraspecific and interspecific competition levels than Rhodes grass and humidicola. However, Rhodes grass produced 4.2 times more biomass in mixtures with Navua sedge than when with humidicola. The results indicate that Rhodes grass had a greater competitive ability than Navua sedge or humidicola, and hence a good candidate to compete with Navua sedge in the field.