Cyperus rotundus Minimize

June 2001. A request was made from Fiji for information on nutgrass (Cyperus rotundus), also known as nutsedge and purple nutsedge/nutgrass, which is ranked as the most serious weed to agriculture in the Pacific (Waterhouse DF (1997) The Major Invertebrate Pests and Weeds of Agriculture and Plantation Forestry in the Southern and Western Pacific. Australian Centre for International Agricultural Research, Canberra, Australia). It also happens to be considered the world's worst weed.

The information obtained on the pest status and management of nutgrass in the Pacific
will be published under the title Prospects for integrated Nutgrass management in Pacific farming systems, available through SPC. A translation of the document in French is foreseen. The following was required:

1. Impact of nutgrass on farming systems/crops
2. Any cultural and mechanical control measures applied by farmers, whether recommended by Agriculture authorities or not
3. Herbicide recommendations for nutgrass control
4. Presence and effectiveness of biocontrol agents
5. Any research activities that include studies of nutgrass and its control
6. Any literature references (including annual departmental or research reports, memos, newsletters etc.).

Pigs were seen as part of a cultural control system. At least as early as 1968 this was suggested by John L. Hammerton, who was working in Panama. See Hammerton JO (1968) Nutgrass in Panama: first impression. PANS 14:339-345. Palau provided the following reference:

Mayton EL, Smith EV, King D (1945) Nutgrass eradication studies: IV. Use of chickens and geese in the control of nutgrass, Cyperus rotundus L. Journal of the American Society of Agronomy 37:785-791. 

Among their conclusions:

Geese effectively controlled nutgrass in 1/2-acre pens when the areas were cropped to cotton. In the pens grazed by the geese, very little cultivation of the cotton was required. Geese had to be given grain in the goose-cotton pens after nutgrass became scarce. Sale of geese and cotton largely defrayed the expenses involved in controlling nutgrass by the goose-cotton method.

The idea is to sub-divide the area into smaller plots and rotate the geese among them. There are good electric fences available now which are very easy to move around for rotational grazing.

In the 1940s, researchers in Mississippi, USA, showed that chickens could eradicate purple nutsedge from
small plots, and that geese could effectively control it in cotton fields. In Palau, chickens in small (about 15 x 15 m) plots control not only purple nutsedge, but almost all weeds. See photos.

CSIRO reported that, in cotton, glyphosate (Roundup) is applied
early in the season (Sept/Oct) with shielded hand sprayers so as to avoid drift. Next, nutgrass from the plant line is weeded by hand after rain (not a popular method). Once the cotton has grown, glyphosate is applied regularly with a large shielded sprayer behind a tractor. Problems arise when the weather turns wet and glyphosate cannot be applied in time and nutgrass outcompetes the cotton (Nov/Dec). Geese were considered, but a large number would be required. There is now a field management plan, including chemicals like Sempra (halosulfuron-methyl) and Zoliar (norflurazon).

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However, these chemicals limit what can be planted for a period of 2-3 years. Also, they have limited crop registration and there is no information regarding their effect on Pacific food crops.