Tim R. Murphy

Extension Weed Scientist, The University of Georgia

You know you can call a weed any name you wish. And, as long as the management strategy controls the weed then there is no problem. However, sometimes an improper common name can lead to a control failure. Consider this - the Cyperaceae, the sedge family, has about 4000 species found across the world (Correll and Johnston 1979). Numerous members of this family are found in turfgrasses, and many of these species look like a grass. But after repeated attempts to control these grass "look-alikes" with the postemergence gramincides used for turfgrass weed control such as sethoxydim (Vantage), fenoxaprop (Acclaim Extra) and fenoxaprop (Fusilade II) some of us may begin to realize "maybe this ain't a grass after all."

Sedges are not grasses and respond differently to most herbicides. In general, sedges are yellow-green to dark-green, with triangular stems and three-ranked leaves, unlike the two-ranked leaves of the grass family (Table 1). The leaf sheath of sedges is closed and encircles the stem.

Several sedges (Cyperus spp.) are major problem weeds in turfgrasses. Of these species, only two, purple (C. rotundus) and yellow nutsedge (C. esculentus), form tubers. Other problem species of the Cyperaceae family include annual or water sedge (C. compressus), green (Kyllinga brevifolia) and fragrant kyllinga (Kyllinga sesquiflorus), globe sedge (C. croceus), Texas sedge (C. polystachyos) and cylindric sedge (C. retrorsus).

Yellow and purple nutsedge are low-growing perennials which at first glance resemble a grass. In fact, some people call these species "nut-grass." Seedhead color is often used to distinguish between the two major nutsedges. Yellow nutsedge has a yellowish- to straw-colored inflorescence, while purple nutsedge has a reddish- to purplish-colored inflorescence. Leaf tip shape is another distinguishing characteristic, but is difficult to see in turfgrasses that are regularly mowed. Leaf tips of purple nutsedge are generally wider and gradually taper to a sharp point. Conversely, yellow nutsedge leaves become constricted near the narrow, needle-like tip. Yellow and purple nutsedge are not believed to produce viable seed but due to their underground tubers and rhizomes, these species have tremendous reproductive capacity. Excellent color photographs and descriptions of these and other sedges may be found in Weeds of Southern Turfgrasses (Murphy et al. 1992), Color Atlas of Turfgrass Weeds (McCarty et al. 2001), and at the UGA Turfgrass website (www.georgiaturf.com).

Most sedges thrive in soils that remain wet for extended periods of time. The first control step is to correct the cause of continuously wet soils. Do not over-irrigate an area, and if necessary, provide surface and subsurface drainage.

The overwhelming majority of turfgrass preemergence herbicides do not control sedges. Triazine herbicides (e.g., atrazine, simazine) provide fair preemergence control of some annual sedges, but generally are ineffective on perennial species. Metolachlor (Pennant) provides preemergence control of most annual sedges and yellow nutsedge. However, purple nutsedge is not controlled by metolachlor. Preemergence control of purple nutsedge is currently unavailable.

Historically, postemergence chemical control of most sedges was attempted with repeat applications of 2,4-D, the organic arsenicals (MSMA, DSMA), or a combination of the two. Although the organic arsenicals were effective, numerous applications over a period of years generally were necessary. Also, extensive damage resulted with certain turf species, such as centipedegrass and St. Augustinegrass.

In the past 10 to 15 years several postemergence herbicides have been registered for sedge control in turfgrasses (Table 2). Bentazon (Basagran T/O) will control yellow nutsedges and several annual sedges in all species of turfgrass. Two applications, at an interval of 10 to 14 days, are necessary for control with bentazon. Purple and yellow nutsedge, annual sedges and kyllinga species can be controlled with imazaquin (Image). Tank-mixing recommended rates of MSMA with imazaquin in MSMA-tolerant turfgrasses generally increases sedge control. For optimum results with imazaquin, apply two treatments during the late spring and summer months. The first application should be made after full spring green-up of warm-season turfgrasses and when sedges are visible in the turfgrass canopy. Apply the second treatment 6 to 8 weeks later when sedges re-emerge. Image is not labeled for use in cool-season turfgrasses. Another excellent herbicide for sedge control is halosulfuron (Manage). This herbicide provides good to excellent control of both purple and yellow nutsedge, annual sedges and fair control of the kyllinga species. Similar to imazaquin, a repeat application 6 to 8 weeks after the initial application will be necessary for season-long sedge control. The various turfgrass species have excellent tolerance to halosulfuron. The key factor to sedge control is persistence. We do not have a herbicide that can be applied one time and eradicate nutsedge. Repeat applications at prescribed intervals shown on the herbicide label will be required for acceptable control within a given year. And, it will be necessary to think of nutsedge control as a multi-year project. Research conducted in Georgia showed that imazaquin + MSMA applied for three consecutive years totally eliminated purple nutsedge from a turfgrass site (Johnson and Murphy 1992). A South Carolina study investigated the effect of multi-year herbicide applications on yellow nutsedge control and tuber populations (Lowe et al. 2000). Control was > 90% and tuber populations were reduced 92% for the best herbicide combination at the end of this 4-year study. However, 200,000 tubers per acre were present after 4 years of > 90% yellow nutsedge control.

Nutsedge is indeed a formidable weed in turfgrasses. While new chemistry has been registered to control nutsedge, control programs will still need to be an annual event. Another factor is getting good control with nutsedge herbicides is to treat when nutsedge is actively-growing and there is good soil moisture. Nutsedge, annual sedges and kyllinga species are aggravating turfgrass weeds. But we have made progress, and we can effectively manage nutsedge and related sedge species if we properly maintain turfgrasses and stay on a dedicated control program for several years.

REFERENCES

1. Correll, D. S. and M. C. Johnston. 1979. Manual of the Vascular Plants of Texas. The University of Texas at Dallas, Richardson, TX.

2. Johnson, B. J. and T. R. Murphy. 1992. Purple nutsedge control with imazaquin in bermudagrass turf. UGA-CAES Res. Bull. 408, Athens, GA.

3. Lowe, D. B., T. Whitwell, S. B. Martin and L. B. McCarty. 2000. Yellow nutsedge (Cyperus esculentus) management and tuber reduction in bermudagrass (Cynodon dactylon X C. transvaalensis) turf with selected herbicide programs. Weed Tech.14:72-76.

4. McCarty, L.B., J.W. Everest, D. W. Hall, T. R. Murphy, and F. H. Yelverton. 2001. Color Atlas of Turfgrass Weeds. Ann Arbor Press, Chelsea, MI.

5. Murphy, T. R., D. L. Colvin, R. Dickens, J. Everest, D. Hall and L. B. McCarty. 1992. Weeds of Southern Turfgrasses. The Univ. of Georgia Cooperative Extension Service, Athens, GA.

Table 1. Distinguishing characteristics of grasses and sedges.

Table 2. Sedge control ratings for selected turfgrass herbicides¹.

¹From McCarty, L. B. 2000 Pest control recommendations for professional turfgrass managers. Clemson University EC 699.

²Follow directions on herbicide label for repeat applications.