THIS WAS originally imported as an ornamental reed to make a striking addition to the garden but it quickly escaped. Giant reed, also known as elephant grass, forms a large, 5-8m-high clump of bamboo-like canes clothed in long, thin, grey-green leaves. A variegated form with cream and green leaves ( Arundo donax var. versicolor) is also a popular garden specimen. Outer stems tend to droop at the edge of clumps where they are not supported by the mass of canes, while the woody stems start out erect, then become semi-lax over time. Attractive, fluffy terminal flowerheads appear in autumn.
Giant reed forms dense thickets that slowly crowd and shade out other more desirable plants. It spreads from root fragments, either through soil movement or dumping of garden waste, and although it rarely sets seed at present, there is concern that this may change in future. Giant reed is a potential wetland weed and can affect aquatic native fauna. It is also capable of blocking drains and streams and causing pipe damage and flooding.
HOW TO GET RID OF IT
Cut it down close to the ground and spray the regrowth with 10 ml/l Amitrole + 10 ml/l Gallant + penetrant before it reaches 60cm. Continue respraying when it’s under 60cm until regrowth ceases (normally 4–6 treatments). Minimise herbicide contact with the soil and other vegetation as Amitrole is non-selective, residual and corrosive. Stray emergent shoots can be cut at ground level and injected with 10ml of undiluted Amitrole into each stem. Smaller clumps can be dug out by hand and disposed of at a refuse transfer station or burnt. Follow up frequently to check for regrowth.
MILTON MUNRO is a soil and plant scientist for rural supply company PGG Wrightson. He looks at common pasture weeds you’ll find on your block and how to deal with them.