Pasture Watch
The weeds in the wet
IT'S during the wetter months that umbrella sedges (Cyperus eragrostis, Cyperus congestus) get ready to take over.
They prefer to grow in waterlogged areas, places too wet for desirable pasture species to grow. They’re not palatable to stock, so they colonise bare soil, replace pasture, compete with crops, and clog drains.
Umbrella sedges produce large amounts of seed. They die back in winter, but thanks to a large swollen rhizome, they take off during summer and outcompete other pasture species and crops that struggle in dry soil and heat. While they’re actually perennials, they can grow like an annual, depending on soil conditions.
When you see them in spring, umbrella sedges look grass-like. However the leaves are slightly wider than ryegrass, shinier, and v-shaped. In late spring to early summer, they grow multiple seed heads on top of a triangular stem.
Cyperus eragrostis is spread throughout
New Zealand, except for Westland, Otago, and Southland. Cyperus congestus is found in the northern regions of both islands, Gisborne, and Canterbury.
How to control umbrella sedges Improving drainage in wet areas of pasture and growing healthy, strong pasture plants helps to prevent them from spreading.
You can mow umbrella sedges just before they go to seed, which helps with control and will sometimes kill them.
Discing and chopping the roots during cultivation also helps.
Very few selective herbicides are effective. Even glyphosate requires a high rate or an additional companion herbicide.
Always read the label and consult a professional before using chemical
• controls.