Yellow nutsedge (Cyperus esculentus) is a member of the Cyperaceae (or sedge) family, along with closely related “cousins” of green kyllinga (Kyllinga brevifolia) and false-green kyllinga (Kyllinga gracillima). All three of these grass-like
weeds have a distinguishable triangular stem and three-ranked leaf arrangement, and all three are C4 or warm-season species with a perennial life cycle.
In the U.S., false-green kyllinga has become an unwelcome invasive weed problem in turfgrass sites in the northern and transition zones from Connecticut to the Carolinas and west into Arkansas. Green kyllinga is perhaps less cold tolerant and therefore
prefers the coastal Carolinas down to Florida and westward into Texas and Arizona.
Green kyllinga and false-green kyllinga look practically identical, and it is therefore difficult to tell them apart. A good botanist is needed to determine that green kyllinga seeds have a toothed keel, but false-green kyllinga seeds are smooth. Incidentally,
the genus Kyllinga is named after Danish botanist Peder Lauridsen Kylling (1640-1696) and was actually named in his honor by another botanist, C.F. Rottbøll (1727-1797).
False-green kyllinga spreads by rhizomes and forms a dense mat that can easily dominate a closely mowed turfgrass stand. False-green kyllinga is often observed in golf course fairways at 0.5-inch (1.3-centimeter) mowing heights and in putting greens mowed
at 0.125 inch (3.2 millimeters).
With false-green kyllinga becoming problematic in cool-season turfgrasses, researchers at Rutgers University and Purdue University collaborated to evaluate three commonly utilized herbicides for control of this weed. These field studies were located
at two sites in New Jersey and two sites in Indiana under standard test plot methods with replicated treatments and uniformly populated with false-green kyllinga. The sites in New Jersey were a creeping bentgrass fairway and cool-season mixed-species
rough, and the sites in Indiana were a creeping bentgrass fairway and tee.
All herbicide treatments were delivered as a single application in late May/early June and also as two sequential applications also starting in late May/early June and applied again 28 days later. The herbicide active ingredients and application rates
were as follows: imazosulfuron (0.375 pounds active ingredient per acre [420 grams active ingredient per hectare]), imazosulfuron (0.66 pounds a.i./acre [740 grams a.i./hectare]), halosulfuron (0.06 pounds a.i./acre [70 grams a.i./hectare]), and sulfentrazone
(0.125 pounds a.i./acre [140 grams a.i./hectare]). Test plots were evaluated for percent weed control both visually and from ecological grid counts per plot.
At 12 weeks after those treatments were first applied, 100% false-green kyllinga control was observed in those plots that received imazosulfuron in two sequential applications at either 0.375 pounds active ingredient per acre or 0.66 pounds active ingredient
per acre. A single application of imazosulfuron at 0.375 pounds active ingredient per acre or 0.66 pounds active ingredient per acre resulted in a range of 78%-99% control. A single application of halosulfuron had 36%-59% control, and two applications
had 35%-92% control. A single application of sulfentrazone resulted in 14%-31% control, and two applications yielded 17%-35% control.
These collaborative field studies showed that imazosulfuron and halosulfuron could be utilized in an integrated false-green kyllinga control program. Keep in mind, sulfentrazone also may be an option to include in an acetolactate synthase (ALS) herbicide
resistance management program, because imazosulfuron and halosulfuron are both ALS inhibitors (i.e., ALS is the enzyme involved in biosynthesis of amino acids). Of note, these treatments were applied in a late May/early June timeframe shortly after
false-green kyllinga emergence was visually observed; therefore the summer may not be the ideal time to interseed cool-season turfgrass into voids created by dead false-green kyllinga.
False-green kyllinga is often found in sites with excessive soil moisture due to poor drainage or other reasons, and these environmental conditions give this weed a competitive advantage over desirable turfgrasses. A herbicide program in conjunction with
cultural practices can help prevent this unwelcome weed from overstaying its welcome.
Source: Elmore, M.T., A.J. Patton, D.P. Tuck, J.A. Murphy and J. Carleo. 2019. False-green kyllinga (Kyllinga gracillima) control in cool-season turfgrass. Weed Technology 33:329-334.
Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 21-year member of GCSAA.