1483 HORTSCIENCE VOL. 39(6) OCTOBER 2004 Renovating Golf Course Fairways with Zoysiagrass Seed Aaron J. Patton 1 Department of Agronomy, Purdue University, 915 West State Street, West Lafayette, IN 47907-2054 David W. Williams 2 Department of Agronomy, University of Kentucky, Room N-222J Agricultural Science Building, Lexington, KY 40546-0091 Zachary J. Reicher 2 Department of Agronomy, Purdue University, 915 West State Street, West Lafayette, IN 47907-2054 Additional index words. Zoysia japonica, MSMA, dithiopyr, glyphosate, herbicide, conversion, interseeding Abstract. Zoysiagrass (Zoysia japonica Steud.) requires few inputs and provides high-qual- ity turf in the transition zone, but is expensive to sprig or sod. Establishment by seed is less expensive than vegetative establishment, but little is known about renovation of existing turf to zoysiagrass using seed. Two experiments were performed to determine effects of herbicides and seeding rates on establishment of zoysiagrass in Indiana and Kentucky. In the first experiment, interseeding zoysiagrass into existing perennial ryegrass (Lolium perenne L.) without the use of glyphosate before seeding resulted in 2% zoysiagrass coverage 120 days after seeding (DAS). In plots receiving glyphosate before seeding, zoysiagrass coverage reached 100% by 120 DAS. In the second experiment, MSMA + dithiopyr applied 14 days after emergence (DAE) or MSMA applied at 14+28+42 DAE provided the best control of annual grassy weeds and the greatest amount of zoysiagrass establishment. Applying MSMA + dithiopyr 14 DAE provided 7% less zoysiagrass coverage compared to MSMA applied 14 DAE at one of the four locations. Increasing the seeding rate from 49 kg·ha –1 to 98 kg·ha –1 provided 3% to 11% more zoysiagrass coverage by the end of the growing season at 3 of 4 locations. Successful zoysiagrass establishment in the transition zone is most dependent on adequate control of existing turf using glyphosate before seeding and applications of MSMA at 14+28+42 DAE, but establishment is only marginally dependent on seeding rates greater than 49 kg·ha –1 . Chemical names used: N-(phosphonomethyl) glycine (glyphosate); monosodium methanearsenate (MSMA); S,S-dimethyl 2-(difluoromethyl)-4-(2-methylpro- pyl)-6-(triflurormethyl)-3,5-pyridinedicarbothioate (dithiopyr). Zoysiagrass (Zoysia japonica Steud.) is a warm-season turfgrass well-suited for golf course fairways, tees, and bunker faces in the transition zone of the U.S. Once established, zoysiagrass creates a dense, high-quality turf that is relatively inexpensive to maintain. Zoysiagrass is tradition- ally established through plugging, sprigging, strip-sodding, or sodding (Portz et al., 1981). However, because of the high cost of vegetative establishment, less well-adapted species such as bermudagrass (Cynodon spp. Rich.) or perennial ryegrass (Lolium perenne L.) are often used in- stead of zoysiagrass in transition zone fairways. Improved zoysiagrass cultivars established by seed were recently developed and commercially released (NTEP, 2001). Zoysiagrass establish- ment by seed is desirable because it is less expensive than vegetative establishment. Successful fairway renovation depends on conversion from one species to another as quickly as possible. If renovation disturbs golf- ers or closes fairways for an extended time, golf courses lose revenue. Interseeding a new species directly into existing turf does not disrupt golfers, but may not be successful because of competi- tion from existing grasses (Eggens, 1979). In- terseeding creeping bentgrass (Agrostis palustris Huds.) or kentucky bluegrass (Poa pratensis L.) into highly competitive annual bluegrass (Poa annua L.) is only marginally successful (Eggens, 1979; Gaussoin and Branham, 1989; Reicher and Hardebeck, 2002a). Interseeding a species or cultivar into another similar species or cultivar is unsuccessful because the new seedlings have little or no competitive edge over the existing established grass (Kendrick and Danneberger, 2002). However, seeding a warm-season grass into a cool-season grass may be successful because of their distinctly different seasonal growth cycles. Little infor- mation exists on interseeding a warm-season grass into an existing stand of a cool-season grass. Zoysiagrass interseeded into perennial ryegrass produced only 5% coverage after one growing season in Kansas (Zuk and Fry, 2002). However, only one seeding rate (49 kg·ha –1 ) was used in their study in spite of suggested seeding rates of 38 to 98 kg ha –1 (Portz et al., 1981; Landry and Choi, 1995). Additionally, Madison (1966) reported higher seeding rates of cool-season grasses increased seedling num- ber shortly after emergence. Therefore, higher seeding rates may give zoysiagrass seedlings a competitive advantage when interseeding cool-season turf. Weed control is often necessary after seed- ing to optimize establishment (Johnson, 1976). Fast-growing weeds will out-compete slow germinating and slow growing zoysiagrass during renovation. Competitive annual grassy weeds such as crabgrass (Digitaria spp.) and goosegrass (Eleusine indica L.) germinate in late spring and early summer and reduce zoysiagrass establishment (Carroll et al., 1996). There are several herbicides labeled for the control of crabgrass and goosegrass in established zoy- siagrass, but none are labeled for use on zoy- siagrass seedlings. Portz et al. (1981) found the preemergence herbicide siduron [1-(2-methyl- cyclohexyl)-3-phenylurea] applied before seed- ing produced the highest zoysiagrass coverage, but two postemergence applications of MSMA plus 2,4-D [(2,4-dichlorophenoxy) acetic acid]/ dicamba (3,6-dichlor-2-methoxybenzoic acid) also provided acceptable zoysiagrass coverage. Siduron can be used on seedling turfgrass to control crabgrass, but it provides poor residual control in the transition zone (Dernoeden, 1984). Dithiopyr, a preemergence herbicide with early postemergence activity, has longer residual activity than siduron and provides better weed control for cool-season turf renovations (Reicher et al., 1999). Preliminary field work showed that MSMA, dithiopyr, and MSMA + dithiopyr are safe on zoysiagrass seedlings 1 week after emergence or later (Hardebeck and Reicher, 2003; Reicher and Hardebeck, 2002b). We initiated research to determine 1) effect of seeding rate and nonselective herbicides on zoysiagrass establishment when interseeding into perennial ryegrass, and 2) effect of seeding rate and postemergence weed control during zoysiagrass renovation on four golf courses in the transition zone. Materials and Methods Interseeding zoysiagrass into perennial ryegrass. Research was conducted at the W.H. Daniel Turfgrass Research and Diagnostic Center, West Lafayette, Ind. Soil type was a Stark silt loam (fine-silty mixed mesic Aeric Ochraqualfs) with a pH of 5.9, 224 kg·ha –1 P, 1044 kg·ha –1 K and 7.3% organic matter. Ex- periments were initiated on 23 May 2001, 30 May 2002 and 15 June 2002 on an established perennial ryegrass stand with a mowing height of 1.9 cm. Experimental design was a 2 × 3 factorial with two herbicide treatments and three seeding rates. Herbicide treatments were glyphosate before interseeding or no glyphosate. Glyphosate was applied in 815 L·ha –1 of water with a 1.5-m boom with three flat fan nozzles at 1.7 kg·ha –1 in 2001 and 5.9 kg·ha –1 in 2002 to 1.5 × 1.5-m plots with a CO 2 pressurized sprayer at 207 kPa. Seeding rates were 49, 98 and 146 kg·ha –1 pure live seed (PLS) ‘Zenith’ HORTSCIENCE 39(6):1483–1486. 2004. Received for publication 25 Oct. 2003. Accepted for publication 17 Feb. 2004. Purdue University Agricultural Experiment Station journal 17281.The authors thank Judy Santini for help with statistical analysis and the Midwest Regional Turf Foundation for partial support of this project. 1 Graduate research assistant, to whom correspon- dence should be sent; e-mail ajpatton@purdue. edu. 2 Associate professor.