Purple Nutsedge Control in Turf and Ornamentals

P nutsedge (Cyperus rotundus), commonly known as nutgrass in Hawai‘i, is a common weed in both turf and ornamental areas. The plant is found in locations receiving full sunlight that provide enough water and nutrients to sustain its growth. Its growth is severely restricted by shade. The plant has slender leaves that are connected to a network of underground stems (rhizomes), roots, and tubers. Although purple nutsedge flowers profusely if not mowed, very few seeds are formed, and few of them can reproduce. Thus seeds are not often the source of new purple nutsedge plants. The underground tubers and corms (the “nuts” or “nutlets”) are the primary source of purple nutsedge infestations. Some tubers are linked to aboveground growth, but other tubers may not be connected to leaves aboveground (Photo 1). Left undis­ turbed, purple nutsedge will spread by growing laterally underground, spreading several yards each year. Some other weedy plants can be mistaken for purple nutsedge, including yellow nutsedge (Cyperus esculentus L.), green kyllinga (Kyllinga brevifolia), and white kyl­ linga (Kyllinga nemoralis) (Photo 2), which have leaves resembling those of purple nutsedge. Purple nutsedge has brownish flowers, and its tubers occur in chains. Yel­ low nutsedge, which is primarily found in the Hāmākua coast region of the island of Hawai‘i, has straw-yellow flowers, and its tubers occur at the end of rhizomes. The kyllingas have no tubers, and their round flower heads have a green or white globe-shaped structure. New infestations of purple nutsedge occur when tu­ bers are moved from one area to another in soil, plant containers, or on equipment. Under optimum conditions, a network of nutsedge plants arising from one tuber can produce 100 or more tubers in about 100 days. About 1. Purple nutsedge plant with multiple stems (connected by rhizomes), leaves, seeds, roots, and tubers; the ruler is 6 inches long.