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Nutsedge Identification (Feb. 22, 2012)

Identification is an important first step in weed management. Nutsedge is a difficult to control perennial weed throughout Arizona. There are two species of this weed that cause problems here and they are often misunderstood. Although it is often called nutgrass, nutsedge is neither a nut nor a grass. It is instead a member of the sedge family. Unlike grasses, sedges have solid triangular stems. Grasses commonly have round, flat or oval stems that are hollow. Sedge leaves are thick, stiff with a distinct midrib and are arranged in sets of three at their base. Although there are many sedges, only two are weeds here and these are among the most damaging and difficult to control. These are purple nutsedge (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus). Both are perennial weeds that are dormant during the winter. They produce seed although the seed is rarely viable and they spread vegetatively by below ground tubers (nutlets). These tubers are produced on rhizomes or below ground stems. Most of these tubers are within the top foot and a half although they can be found much deeper. Each tuber has up to seven buds from which new rhizomes and tubers grow. When shoots reach the surface they form basal bulbs and new leaves to keep this process fueled. In a single season one tuber can produce almost 2,000 new plants and 7,000 new tubers. These tubers can persist for several years and must be depleted to achieve complete control. Purple and yellow nutsedge respond differently to herbicides and it is important to make proper identification. Mixed populations can be found here and yellow nutsedge is, in general, easier to control. The following chart should help in properly identifying this weed.

Nutsedge Identification
  Purple Nutsedge Yellow Nutsedge
Distribution Mostly in the southern half of Arizona where it predominates. Does not tolerate soil temperatures much below freezing. Throughout Arizona. Less prevalent in the Southern half of Arizona than purple. Tolerates Soil temperatures below freezing.
Leaf Size and Shape Shorter leaf blade. Blunt tip. Darker green color. Shorter than yellow. 6-8" at maturity. Longer leaf blades. Tapered with pointed tip. Lighter green color. Generally taller, more upright and vegetative. 12-16" at maturity.
Inflorescence Reddish purple, loose seedhead. Yellow. Tighter seedhead in the shape of a Bottlebrush.
Tuber size And Shape Larger roughly one half to one inch in diameter. Scaly. Oblong. Smaller, roughly one quarter to one half inch In diameter. Smooth. Round.
Tuber Taste/Odor Bitter taste. Strong almond like odor. Sweeter, less bitter taste. No odor.
Tuber Growth Forms chains of tubers with several Interconnected on a single rhizome. Single tuber at the end of each rhizome

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College of Agriculture, The University of Arizona, Tucson, AZ.

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