The family Cyperaceae includes approximately 3,000 different species, of which over 200 are recognized as weeds and nearly 42% of these weeds are of the genus Cyperus. Purple nutsedge (Cyperus rotundus) and Yellow nutsedge (Cyperus esculentus) are the most widespread weed species of this genus. Purple nutsedge, a paticularly invasive and aggressive weed, has been classified as the world's worst, but its cousin Yellow nutsedge can be found on five different continents- South America, North America (the US and Canada), Australia, Asia, and Africa and causes widespread damage to a variety of crops and also unsightly discoloration in lawns.

Yellow nutsedge is a perennial plant whose leaves and flowering stalks will usually die in the Autumn as temperatures begin to drop, but its roots- in the form of tubers, survive in the soil and will sprout when soil temperatures reach 43°F or above. The tubers can usually be found in the top 6 inches of soil where they will complete a life cycle of around 3 years. In crops, most plants sprout from tubers and the seeds contribute little to the the plant's spread.

The weed is easily identified by a triangular shaped stem and yellow leaves, 3 to 4 inches above the ground, that appear slick or waxy. During the start of Spring and the end of Autumn, when conditions are cool and the weed's growth is slower, the leaves are not usually present making Yellow nutsedge difficult to recognize.

The tubers that the perennial Yellow nutsedge sprout from are the weed's key to survival and therefore its weak point. Limiting the production of the tubers by identifying and removing small nutsedge plants before they can develop more than six leaves will facilitate the control and eventually the demise of the weed. By removing the sprout when it is still very young, the tuber is forced to produce a new plant in its place, depleting nutrient reserves from the tuber to produce fresh leaves. The new stalk will be weaker than the previous stalk, but if allowed to continue to derive energy from the sun through new leaves, the tuber will gradually regain its previous strength. Mature tubers may sprout as many as 12 times before its reserves are drained.

Digging at least 14 inches into affected turf by hand is the ideal way to remove smaller plants, as tilling with a machine will result in the spread of the nutsedge tuber which can regrow and sprout anew even after it has been broken up into several pieces, although repeated tilling of small areas before the plant can produce more than six leaves will inhibit its population. Herbicides applied to the leaves have little effect on mature tubers as there is minimal translocation of fluid from the leaves to the tuber itself.

Polyethylene ground covers will not control the Yellow nutsedge, as the spines at the ends of its leaves are extremely stiff and sharp resulting in tears in the cover that allow moisture and sunlight in. Fabrics made of more durable Polypropylene polymers though, are highly effective in the supression of nutsedge growth despite being water and air permeable, allowing drainage if the fabric is used beneath fresh topsoil.




http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-204X2001000100025
http://www.ppws.vt.edu/scott/weed_id/cypes.htm
www.agry.purdue.edu/turf/pubs/agry9804.htm
www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7432.html

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