Green kyllinga in 1-inch bermudagrass turf (blue dye was used to mark green kyllinga patches).

Changes in environmental laws require golf course superintendents to find multiple strategies to combat weeds. In comparisons of mowing height and nitrogen use, higher mowing heights are more effective in fighting weeds, including kyllinga, in bermudagrass turf. Where mowing heights cannot be altered, providing adequate nitrogen will improve turfgrass competition over weed growth.

Environmental protection standards are increasing daily, and the turfgrass industry must discover alternative pest control measures.

Cultural practices cannot completely replace herbicides. Effective, long-term weed management requires an integrated approach that involves manipulating all facets of turfgrass management to favor turf growth over weed growth and applying herbicides as needed.

Mowing and fertilization, which are integral to providing good turfgrass quality on golf courses, also alter weed competition. Previous research has shown that:

	When mowing heights (1.3, 2.2 and 3.5 inches) and nitrogen rates (2 and 4 pounds per 1,000 square feet per year) were compared, high mowing height was the better cultural practice for reducing smooth crabgrass in tall fescue after 3 years (3).
	Bermudagrass invasion into tall fescue was reduced when mowing height was 2.2 inches compared with 0.75 inches (2).
	Indian mock strawberry survival in tall fescue was lowest when not mowed and highly fertilized and greatest when not fertilized and mowed at 2.4 inches (4).
	Yellow nutsedge populations in Kentucky bluegrass turf were reduced when mowed at 3.0 inches as compared with 1.5 and 0.9 inches (1).

Green kyllinga (Kyllinga brevifolia) is a perennial sedge that can establish in turfgrass through stolons and seeds and is becoming more common on golf courses in the southeastern United States. In favorable environments, green kyllinga forms thick mats that are especially prevalent on bermudagrass tees and fairways. Herbicides such as Manage (halosulfuron), Image (imazaquin), MSMA (monosodium methane arsenate) and Basagran (bentazon) are used to control green kyllinga on golf courses, but subsequent treatments are required to fully penetrate green kyllinga mats.

Little is known about green kyllinga biology within a turfgrass environment and how cultural practices influence its spread. The objective of the study was to determine whether mowing and nitrogen fertilization alter green kyllinga populations in bermudagrass turf.

Green kyllinga establishment
The two-year study was initiated in May 1997 in a mature Tifway bermudagrass turf. Plot size was 7 by 7 feet, and green kyllinga was either seeded or established by stolons in five small areas (subsamples) within each plot. Subsamples were measured periodically each year, and green kyllinga spread was recorded.

Green kyllinga in 2-inch bermudagrass turf.

Comparisons included kyllinga establishment (seed vs. stolon), two mowing heights (1 and 2 inches) and three nitrogen rates (zero, 0.5 and 1 pound per 1,000 square feet per month). Plots were mowed with a rotary mower two to three times each week, and nitrogen (ammonium nitrate) was applied every other week from May to October. Plots were watered as needed to maintain turfgrass quality.

Green kyllinga spread
Green kyllinga established in Tifway bermudagrass turf by both seeds and stolons. Green kyllinga populations established via stolons were larger than seeded populations in 1997; however, establishment method became less important the second year.

Mowing height influenced green kyllinga spread the most throughout the study. Low mowing (1 inch) favored green kyllinga growth, as weedy patches were more than twice as large in low-mowed turf compared with high-mowed turf (2 inches).

Previous research shows that green kyllinga competes poorly with bermudagrass when unmowed (5). In our study, low mowing favored green kyllinga competition in bermudagrass turf. This may explain why green kyllinga is found more often in closely mowed areas such as fairways, tees and greens and less often in roughs.

Plot area showing various examples of turfgrass quality (nitrogen fertility).

Nitrogen application favored bermudagrass competition. This was especially evident in seeded kyllinga infestations. In low-mowed turf, plots receiving 1 pound nitrogen per 1,000 square feet had half the amount of green kyllinga compared with plots not receiving nitrogen.

As expected, increasing nitrate levels improved bermudagrass quality and density. Previous research has shown that gaps in a fescue turfgrass stand have greater temperature fluctuations, and greater crabgrass infestation (6). Weed seeds often respond to temperature fluctuations and greater seed germination occurs in weakened turf because of favorable environmental factors. Therefore, weeds have a greater chance to establish and persist in weakened turfgrass stands, such as those receiving inadequate nitrogen.

Compared with nitrate fertilization, a higher mowing height is the better integrated approach to green kyllinga control in bermudagrass turf. Where mowing heights cannot be altered, providing adequate nitrogen for bermudagrass growth will improve turfgrass competition over weed growth. A dense, healthy turfgrass is the best deterrent to turfgrass weeds such as green kyllinga.

Literature cited

1. Black, D.W. 1975. Chemical and cultural control of yellow nutsedge in turf. M.S. thesis. University of Illinois, Champaign-Urbana.

2. Brede, A.D. 1992. Cultural factors for minimizing bermudagrass invasion into tall fescue turf. Agronomy Journal 84:919-922.

3. Dernoeden, P.H., M.J. Carroll, and J.M. Krouse. 1993. Weed management and tall fescue quality as influenced by mowing, nitrogen and herbicides. Crop Science 33:1055-1061.

4. Gray, E., and N.M. Call. 1993. Fertilization and mowing persistence of Indian mockstrawberry (Duchesnea indica) and common blue violet (Viola papilionacea) in a tall fescue (Festuca arundinacea) lawn. Weed Science 41:548-550.

5. Kawabata, O., R.K. Nishimoto, and C. Tang. 1994. Interference of two Kyllinga species (Kyllinga nemoralis and Kyllinga brevifolia) on bermudagrass growth. Weed Technology 8:83-86.

6. Rossi, F.S., T.J. Kim, and J.C. Neal. 1999. Ecological aspects of crabgrass infestations. Golf Course Management 67(1):53-56.

Todd Lowe is a turfgrass research assistant at Clemson (S.C.) University; Bert McCarty, Ph.D., and Ted Whitwell, Ph.D., are professors in the Clemson horticulture department.