Key Takeaways

• False-green kyllinga is a troublesome weed on golf courses because of its aggressive and dense growth. Researchers explored various control strategies to see which ones provided the best long-term results.
• For postemergence control in cool-season turf, imazosulfuron (Celero) consistently provided the most effective control of false-green kyllinga.
• Early spring applications of pyrimisulfan (Arkon and Vexis) provided over 90% false-green kyllinga control, reduced large voids in turf cover that come with late-season applications, and can be added to existing preemergence applications.
• Combining late-summer herbicide applications with subsequent seeding of tall fescue dramatically improved control in golf course roughs, with imazosulfuron or halosulfuron (SedgeHammer) along with seeding resulting in better long-term control compared to herbicides alone.
   

As a warm-season perennial, false-green kyllinga emerges in late spring/early summer as the soil warms and grows rapidly throughout the summer months. The dense kyllinga mat expands as the rhizomes grow outwards. Dormancy occurs after the first frost in the fall.

Kyllinga may be indicative of chronically excessive soil moisture, which should be addressed as part of a management program. False-green kyllinga does not have tubers like yellow nutsedge, so physical removal with a sod cutter is an effective option if care is taken to remove the rhizomes, which in warm-season settings, are closer to the surface than bermudagrass rhizomes.

Investigating Selective Herbicide Options in Cool-Season Turfgrass

Methods
Our false-green kyllinga research has typically focused on postemergence herbicide options. We initially compared the effectiveness of herbicides commonly used to control sedge species (Elmore et al., 2019a). A preliminary experiment conducted in 2015 found that a single application of Celero (imazosulfuron) at 8.0 ounces per acre was more effective than SedgeHammer (halosulfuron) at 1.33 ounces per acre and Dismiss (sulfentrazone) at 8.0 fluid ounces per acre. These three herbicides were more effective than Tenacity (mesotrione) or synthetic auxin broadleaf herbicides that contain low rates of sulfentrazone (e.g., Speedzone EW).

Another set of experiments initiated in 2017 evaluated herbicide programs for control on golf courses in New Jersey and Indiana. Three experiments were conducted on creeping bentgrass golf course fairways or tees, and one was in golf course rough. These experiments evaluated single and sequential postemergence applications of Celero at 8.0 and 14.0 ounces per acre, SedgeHammer at 1.33 ounces per acre and Dismiss at 4.0 fluid ounces per acre. While Dismiss can be applied at up to 8.0 fluid ounces per acre in other cool-season grasses, 4.0 fluid ounces per acre is the maximum single application rate in creeping bentgrass. Applications were made after complete false-green kyllinga greenup in late May in Indiana and early June in New Jersey. The second herbicide application was made four weeks later. Celero and SedgeHammer were applied with a non-ionic surfactant at 0.25% volume/volume per the product label and all treatments were applied to the foliage at 44 gallons per acre carrier volume using standard flat-fan nozzles. False-green kyllinga control was evaluated at various times after application, with the most important evaluation occurring in September, 12 weeks after the initial application. Evaluating weed control at least two months after herbicide applications is important because many herbicides can suppress false-green kyllinga for a short period of time. Whether the herbicide provides lasting control should be determined several weeks after application.

Results
We found Celero was consistently the most effective herbicide across the four locations (Figure 1). In New Jersey, one Celero application was as effective as two applications, and the low label rate (8.0 ounces per acre) was as effective as the high label rate (14.0 ounces per acre). In Indiana, the low label rate applied once was less effective than the high label rate applied once, and if two applications were made, both rates were similarly effective. When Celero was applied twice it provided 100% false-green kyllinga control at all locations, at both rates. SedgeHammer was generally less effective than Celero. One application of SedgeHammer at the maximum label rate (1.33 ounces per acre) provided less than 60% control. Two applications of SedgeHammer were not more effective than one application in Indiana. In New Jersey, two applications of SedgeHammer provided 91% control which was similar to all Celero applications, but one application of SedgeHammer was much less effective than one application of Celero. Dismiss was less effective than SedgeHammer at all locations, with either one or two applications providing less than 50% control. Neither Celero nor SedgeHammer caused any turfgrass injury at any location. Dismiss caused minor transient injury (bronzing) to bentgrass, which is a typical response to the herbicide. 

Conclusions
Celero is a powerful tool to control false-green kyllinga. Yet, one of the weaknesses of this research is that controlling a severe infestation of false-green kyllinga in late spring or early summer is often not ideal from an agronomic or playability perspective, as you are eliminating much of your green cover just before summer. This approach is better suited for moderate infestations where the desirable turfgrass can reliably fill voids left behind as the weed dies. The next project we will discuss addresses a solution for severe infestations where little desirable turfgrass is present amongst the false-green kyllinga.

Late-Summer Herbicide Applications Combined With Seeding

Methods
To provide a solution for kyllinga control that better integrates with cool-season agronomy and promotes a strong stand of desirable turfgrass, we evaluated single postemergence applications in late summer combined with fall seeding. While late summer or early fall is typically an optimum time to make herbicide applications to control C4 perennial weeds (Brosnan et al., 2011; Elmore et al., 2013; Johnston & Henry, 2016), our preliminary research found early September applications were less effective than June applications (Elmore et al., 2019b). But this ignores the opportunity that autumn offers to integrate cultural practices like seeding that can complement herbicide applications. The objective of this study was to determine if combining late-summer herbicide applications with fall interseeding can improve false-green kyllinga control.

This research evaluated seven herbicide treatments alone and in combination with tall fescue interseeding, for a total of 14 treatments (Elmore & Tuck, 2022). It was repeated on adjacent sites in consecutive years in New Jersey at Rutgers Horticultural Research Farm No. 2 on a stand of false-green kyllinga harvested from a golf course where it was mowed at 2.5 inches. The seven herbicide treatments were sulfentrazone + carfentrazone (Dismiss NXT at 10.2 fluid ounces per acre), SedgeHammer at 1.33 ounces per acre, and Celero at 8.0 ounces per acre, applied either four weeks before seeding in mid-to-late August, or on the day of seeding in mid-to-late September. The final herbicide treatment was glyphosate (Credit 41 Extra at 32.0 fluid ounces per acre) applied on the day of seeding. Herbicides were applied as described in the previous experiment. While the labels of these herbicides indicate turfgrass cannot be seeded within four weeks of application, we wanted to test whether it was possible to spray and seed on the same day, especially since this is more practical in many lawn care settings.

To determine the influence of seeding, each plot was split in half and seeded or not seeded so the influence of seeding could be determined. Plots were core aerated and verticut to create a seedbed and turf-type tall fescue was seeded at 8.0 pounds per 1,000 square feet, followed by starter fertilizer at 1.0 pound of nitrogen (N) per 1,000 square feet. Two additional N applications were made the following spring at the same rate. False-green kyllinga control was evaluated in June, July and August the following summer. Turfgrass quality and tall fescue seedling injury were also evaluated.

Results
Celero, SedgeHammer, and Dismiss NXT applied on the day of tall fescue seeding caused severe tall fescue seedling injury and compromised tall fescue establishment. As expected, glyphosate applied on the day of seeding did not affect tall fescue establishment. However, when these herbicides were applied four weeks before seeding, they were much more effective when combined with tall fescue interseeding. Celero applied once provided 37% kyllinga control the following August (nearly one year after treatment) without seeding and 98% control with seeding (Figure 2). Without seeding, SedgeHammer was less effective than Celero. When combined with seeding, one application of SedgeHammer provided 90% control, which was statistically similar to Celero. Recall the previous study where one application of SedgeHammer provided poor kyllinga control while Celero was much more effective. Dismiss NXT combined with seeding was less effective than the other two herbicides, providing 56% control. Interseeding alone without herbicide treatment was not effective, providing only 23% control.

Conclusions
Combining seeding shortly after applications of Celero and SedgeHammer will increase competition from desirable turfgrass which can dramatically improve false-green kyllinga control from these herbicides. Just one application of Celero or SedgeHammer combined with seeding of tall fescue four weeks later led to nearly complete control of false-green kyllinga at golf course rough height. While we only evaluated seeding in this study, these results suggest that any cultural practice (e.g., N fertilization) that promotes turf growth to fill voids left by dead false-green kyllinga would probably be similarly effective. If kyllinga and turf are somewhat well mixed, seeding might not be needed, and increasing N fertilization for that fall season would probably be effective.

Getting Ahead of False-Green Kyllinga With Early Season Postemergence Applications

We know that postemergence herbicides applied in late spring or late summer can be effective. But what about applications in early spring at the same time we are applying preemergence herbicides for crabgrass and summer weed control? Conventional thinking was that postemergence herbicides should not be applied at this time because false-green kyllinga is not actively growing. But the advantage of this timing is that it allows you to assess whether you have enough turfgrass to produce a playable surface for the summer if the false-green kyllinga is eliminated. Also, from a logistics perspective, it can be tank-mixed with your preemergence herbicide for increased application efficiency – something that is especially useful on the lawn care side of the turfgrass industry. For many golf courses, mapping known problem areas and making spot applications rather than a blanket treatment may make more economic sense due to the much greater acreage compared to a home lawn. In both cases, the goal is to stay ahead and make sure infestations don’t reach the point that if killed by an herbicide, the fairway or rough would not be playable for the summer. Many infestations I have observed on golf courses are less severe and the early season postemergence strategy could be an effective option. This study sought to answer these questions.

Methods
We evaluated applications of pyrimisulfan (Arkon and Vexis) in mid-April followed by a second application six weeks later in both 2021 and 2022 (Aynardi et al., 2024). Arkon is a liquid formulation that was applied following label directions and granular Vexis was applied to dry turf using a shaker jar. Both treatments were irrigated into the soil. In both experiments, Arkon was applied at 1.2 fluid ounces per 1,000 square feet and Vexis was applied at 4.0 pounds per 1,000 square feet to a stand of cool-season turf infested with false-green kyllinga.

Results
Two applications of Arkon provided greater than 90% false-green kyllinga control in 2022 and over 75% control in the 2021 trial when cool-season turf plots were evaluated at the end of summer (Figure 3). A single application of Arkon in mid-April provided 30% to 60% control, which indicates two things. The first is that two applications must be made for this program to be effective. The second is that both the liquid and granular formulations of pyrimisulfan applied in April, just as false-green kyllinga emerges from dormancy, have substantial activity.

Conclusions
Pyrimisulfan is a relatively new herbicide in the market with the same mode of action as Celero and SedgeHammer. It can be an effective option for false-green kyllinga control and Vexis as a granular option offers more felxibility in when applications can be made. Notably, Arkon is the only postemergence sedge herbicide registered for use on putting greens and colonial bentgrass. We are currently evaluating whether this early season application strategy is also effective with Celero and SedgeHammer.

Final Thoughts

There has also been interest in whether preemergence applications can help to manage false-green kyllinga due to reports of it reappearing a few years after total control, presumably from the seed bank. However, evidence from recent research suggests this should not be a primary strategy because a lot remains unknown about false-green kyllinga seed viability and its seed emergence patterns, as well as how effective commonly used preemergence herbicides for other weeds would be on false-green kyllinga.

Early detection of small infestations and controlling them with postemergence herbicides is important for long-term management. In our experiments, minor infestations expanded rapidly after overwintering, likely through rhizome spread (Watson et al., 2025). This suggests that minor infestations may become much more problematic in subsequent seasons if they are not controlled early. Keeping a healthy and dense stand of turfgrass is also one of the best ways to control false-green kyllinga and weeds in general. Superintendents should also avoid unnecessarily wet soil conditions that favor false-green kyllinga. One of the key findings across our research has been that staying on top of the weed is essential. Once large mats of false-green kyllinga form in fairways or roughs, control becomes much more challenging and large voids will be left behind once you do kill the weed.

References

Aynardi, B.A., Elmore, M.T., McDonald, S.J., Reasor, E., Marvin, J.W., Williamson, R.C. & Segars, C.A. (2024). Application strategies using Arkon (pyrimisulfan) for control of false-green kyllinga and yellow nutsedge. Proceedings of the Northeastern Weed Science Society, Vol. 78 (p. 75).

Brosnan, J.T., Breeden, G.K., Elmore, M.T., & Zidek, J.M. (2011). Application timing affects bermudagrass suppression with mixtures of fluazifop and triclopyr. Weed Technology, 25, 591-597. doi:10.1614/WT-D-10-00165.1

Elmore, M.T., Brosnan, J.T., Mueller, T.C., Horvath, B.J., Kopsell, D.A., Breeden, G.K. (2013). Seasonal application timings affect dallisgrass (Paspalum dilatatum) control in tall fescue. Weed Technology, 27, 557-564.

Elmore, M.T., Patton, A.J., Tuck, D.P., Murphy, J.A., & Carleo, J. (2019a). False-green kyllinga control in cool-season turfgrass. Weed Technology, 33, 329-334. doi:10.1017/wet.2019.16

Elmore, M.T., Tuck, D.P., Diehl, K. (2019b). False-green kyllinga control with autumn herbicide applications. Proceedings of the Northeastern Weed Science Society, Vol. 73 (p. 44).

Elmore, M.T., & Tuck, D.P. (2022). Tall fescue interseeding and postemergence herbicides for false-green kyllinga (Kyllinga gracillima) control in turfgrass. Weed Technology, 36, 548-552. doi:10.1017/wet.2022.51

Johnston, C.R., & Henry, G.M. (2016). Dallisgrass (Paspalum dilatatum) control with thiencarbazone-methyl, foramsulfuron, and halosulfuron-methyl in bermudagrass turf. HortScience, 51, 754-756. https://doi.org/10.21273/HORTSCI.51.6.754

Watson, T.S., Elmore, M.T., Patton, A.J., & Tuck, D.P. (2025). False-green kyllinga
competitiveness from seed in turfgrass. Crop Science, 65(5), e70178. DOI:10.1002/csc2.70178.