Controlling False-green kyllinga in cool-season turf

False-green kyllinga (Kyllinga gracillima) is a warm-season perennial sedge (Cyperaceae) species that has become increasingly problematic in cool-season turfgrass. It has been reported as far north as Connecticut and south to the Carolinas. Green kyllinga (Kyllinga brevifolia) is another perennial sedge species that is nearly identical to false-green kyllinga but is found only in the Southern and Southwestern US.

False-green kyllinga is a rhizomatous mat-forming weed that resembles turfgrass except that it has a lighter green color. False-green kyllinga is especially competitive under low mowing heights common to athletic fields. It can often thrive undetected by the sports turf manager, particularly during periods of active growth as it forms a dense turf-like mat. False-green kyllinga is in the same plant family (sedges or Cyperaceae) as yellow nutsedge (Cyperus esculentus); both species have a triangular stem and three-ranked leaf arrangement. Yellow nutsedge is typically interspersed within the turfgrass canopy and has rapid vertical growth, making it very noticeable just a few days after mowing. Kyllinga is more noticeable in late August when it produces flowers (seedheads) that resemble small burs into the fall as growth slows and it goes off color. It becomes extremely noticeable during winter dormancy, which begins after the first frost.

As a warm-season perennial, false-green kyllinga emerges from rhizomes 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.

This section will discuss chemical, physical, and cultural considerations for false-green kyllinga control.

Physical removal

False-green kyllinga does not contain underground tubers like yellow nutsedge so physical removal using a sod cutter or fraze mowing is an effective option. It is important to make sure that you cut or fraze deep enough to remove the rhizomes. False-green kyllinga rhizomes are typically closer to the soil surface than those of bermudagrass, so removal is more practical. The advantage of physical removal is that seeding or sodding can be completed immediately after removal with no herbicide residual concerns. However, this strategy is expensive and can result in the field being unavailable during the renovation.

Selective herbicide options

False-green kyllinga is a perennial that emerges from rhizomes, therefore, pre-emergence herbicides used to control annual weeds are not effective. While pre-emergence herbicides can control kyllinga seed, the duration and timing of seedling emergence is not known.

There are several post-emergence herbicide options for false-green kyllinga. Herbicide applications should be made soon after kyllinga shoots fully emerge in late spring. This timing is essential to allow herbicide absorption by leaf tissue and limit the total number of follow-up applications. Make the first application in late May to mid-June. After re-growth is observed and sufficient shoot tissue is present for herbicide absorption make the second application. This is typically 3-6 weeks after the initial application.

Herbicides used for false-green kyllinga control/suppression will also provide yellow nutsedge control. However, many products registered for yellow nutsedge control will only suppress false-green kyllinga.

Herbicide options listed below are safe for use on most cool-season turfgrass species. Plan herbicide programs in advance of seeding to ensure that the herbicide will not reduce establishment. Refer to each product label for more information on use around seeding or sodding; most herbicides listed below can be used beyond 4 weeks of an application. Always refer to the label information on turfgrass safety and as the final authority for herbicide use. Additional options are available for use in warm-season turfgrass but are not discussed.

Imazosulfuron. Mode of action: ALS inhibitor (WSSA Group 2); trade name: Celero (8-14 oz/A). Celero is relatively new to the turfgrass market. Rutgers and Purdue research trials demonstrated that it provides excellent false-green kyllinga control. Two applications of Celero at 8 or 14 oz/A provided >95% control 12 weeks later in our trials. Single applications of Celero at either 8 or 14 oz/A provided were more effective than single applications of halosulfuron-methyl (Sedgehammer, Prosedge2) at 1.33 oz/A. Control may not be evident for up to 2 weeks after application. Apply with a non-ionic surfactant.

Halosulfuron-methyl. Mode of action: ALS inhibitor (WSSA Group 2); trade names: Sedgehammer (0.66 – 1.33 oz/A), Sedgehammer+, ProSedge 2, Manage (no longer sold), others. Rutgers and Purdue research trials demonstrated that two applications of halosulfuron-methyl at 1.33 oz/A provides good false-green kyllinga control in some locations but not others. Multiple applications at the high label rate (1.33 oz/A) will be required for long-term kyllinga control. Results may not be evident for up to 2 weeks after application. This herbicide should be applied with a suitable surfactant as indicated by the label except for the Sedgehammer+ formulation that already contains a non-ionic surfactant.

Sulfentrazone. Mode of action: PPO inhibitor (WSSA Group 14); trade names: Dismiss (4-8 fl oz/A); Echelon (prodiamine + sulfentrazone; 8-24 fl oz/A); Solitare WSL (quinclorac + sulfentrazone; 5.4-10.7 qts/A).

Note: Many combination products contain sulfentrazone but often at rates too low for kyllinga suppression.

Sulfentrazone is a resistance management alternative to ALS-inhibiting herbicides. Sequential applications will provide some kyllinga suppression; do not exceed 12 fl oz/A of Dismiss per year. Sequential applications of halosulfuron-methyl or single applications of imazosulfuron provided greater kyllinga control than sequential applications of sulfentrazone in Rutgers and Purdue research trials. Nutsedge or kyllingas treated with sulfentrazone will typically display injury symptoms within 48 hours after application. Good spray coverage is important for suppression with sulfentrazone. Dismiss can cause transient injury to cool-season turfgrass, particularly tall fescue in mid-summer.

Pyrimisulfan. Mode of action: ALS inhibitor (WSSA Group 2); trade name: Vexis.

Sequential applications of pyrimisulfan had efficacy against false-green kyllinga in preliminary Rutgers research trials. Pyrimisulfan was submitted for EPA registration but is not commercially available as of this writing. It will likely be first released as a granular formulation. It may be a resistance management option as it can control sedges that are resistant to other ALS-inhibitor herbicides.

Programs for control

Herbicide rotation is important to prevent herbicide resistance. Using herbicides with the same mode of action for several consecutive years can select for herbicide resistant weeds. While herbicide resistant kyllinga has not been reported, nutsedge resistant to the class of herbicides known as ALS-inhibitors has been found. Using herbicides currently available, a two-year program for resistance management could utilize imazosulfuron or halosulfuron along with cultural practices to improve turfgrass density in year 1 and spot treatment of escapes with sulfentrazone in year 2.

Much like nutsedge, kyllinga has competitive advantage over desirable turfgrass in areas with chronically high soil moisture. Especially in cases of severe infestation, consider modifying the irrigation regimen and/or drainage in conjunction with control programs. Seeding or sodding desirable turfgrass to fill voids of dead kyllinga should also be considered in conjunction with herbicide or physical removal programs.

Current research has evaluated the efficacy of herbicides applied in early June after kyllinga emergence. Where infestations are severe and kyllinga composes a significant amount of the turf sward, June might not be an ideal time for control in cool-season turfgrass due to the extensive loss of cover headed into summer. We are currently evaluating the efficacy of applications made in mid-September when it would be ideal to reestablish cool-season turfgrass into a dense mat of dead false-green kyllinga, but we do not have results as of this writing.

Matthew Elmore, PhD, is an Assistant Extension Specialist in Weed Science at Rutgers University; Aaron Patton, PhD, is a Professor and Turfgrass Extension Specialist at Purdue University; Bradley Park, MS, is a Sports Turf Research and Education Coordinator at Rutgers; and James Murphy, PhD, is an Extension Specialist in Turfgrass Management at Rutgers.