Mullumbimby couch and other sedges
Common names are often misleading. Mullumbimby couch (Cyperus brevifolius) is not a couch, and other members of the Cyperus genus commonly called nut-grasses are neither grasses nor nut-bearing plants. In fact, all these plants are sedges, which invade stealthily because their fine foliage makes it hard for gardeners to detect them until they have gained a major foothold.
Most other lawn weeds are annuals and therefore appear as seasonal problems, but Cyperus species are perennial. They are so vigorous that they can rob the lawn of water and nutrients, and eventually they will take over completely. Being prolific seed producers, they also spread quickly to other areas of the garden and travel using underground rhizomes.
Once Mullumbimby couch and other sedges are well established they are difficult to eradicate. Hand-weeding or spot-painting with certain systemic herbicides can halt a small invasion — but it is important to note that not all herbicides are compatible with all lawn types
Suitable herbicides contain bentazone, halosulfuron and MSMA but check with garden centre staff as the wrong chemical can seriously harm a lawn. Always read the product label and apply as directed.
Prevention is better than a cure and a robust lawn is less susceptible to invasion by any weed, including Cyperus species.