|Botanical Name||Cyperus rotundus|
|Origin||India and Australia|
DescriptionPurple nutsedge has grass like, dark green glossy leaves to 200 mm long. Its flower head is reddish to purple brown on a three sided upright stem, 100-600 mm in height. Top growth is seasonal, becoming dormant over winter. Purple nutsedge is most easily identified by its extensive system of rhizomes and tubers. Tubers are 10-15 mm long and joined by fine rhizomes. Chains of up to 15 tubers may develop.
Where is it found?Purple nutsedge will invade most soil types on roadsides, waste areas, stream banks and cropping areas. It does not compete well in a good pasture sward or under shade from leafy crops.
Why is it a problem?It has been referred to as the world's worst weed. It is troublesome in 52 crop in 92 countries. Production of crops like potatoes and onions becomes practically impossible as the sharp shoots from nutsedge tubers penetrate the crop.
How does it spread?Flowering can produce seeds but seeds are rarely viable. This is not considered an important means of dispersal. In New Zealand purple nutsedge is mainly spread to new sites on cultivation equipment. It can also spread along streams, irrigation canals and by flood waters.
How do I get rid of it?
Deep and repeated cultivation to desiccate tubers that are brought to the surface can be a useful method of control overseas but is less reliable in New Zealand's temperate climate. Pigs to up-root and consume the starchy tubers may provide an organic method of control.
Glyphosate will give a good level of control but, being non selective, it is difficult to use in a cropping situation. Isolated patches can be pegged off and glyphosate applied 3 to 4 times over the growing season. In a lawn situation, weed wipe the longer, faster growing nutsedge leaves with 250-300 ml glyphosate plus penetrant in 10 litres water.
Halosulfuron-methyl (Sempra) can be applied over maize prior to canopy closure.
Clean all cultivation equipment prior to and after cultivation. Cultivate isolated patches last to prevent spread to the rest of the field.