1. Freeze Tolerance Freeze tolerance of each was determined on 15 Dec 2007, 15 Feb 2008, 15 Oct 2008, 15 Dec 2008, and 15 Feb 2009. Plugs 2.5-cm in diam. were placed in freezing chamber overnight at -3 o C and then subjected to temperatures of -6, -10, -14, -16 and -18 o C obtained by lowering temperature at a rate of 2 o C/hr. Tillers were counted after six weeks in the greenhouse and regression analysis was used to determine the temperature which was lethal to 50% of the tillers (LT 50 ). Correlation analysis was conducted to determine the relationships between spring and fall color and LT 50 s. Spring and Fall Color of Zoysiagrasses and Associated Freeze Tolerance David Okeyo, Jack Fry, Dale Bremer, and Channa Rajashekar, Kansas State Univ., Manhattan, KS 66506 Milton Engelke and Dennis Genovesi, Texas AgriLife Urban Solutions Center, Dallas, TX 75252 Introduction Extended fall color and early spring green up of zoysiagrass is preferable; however, promotion of color retention and growth in autumn with cultural practices has been associated with poorer freeze tolerance in warm season turfgrasses (Fry and Huang, 2004). K-State and Texas A&M have been cooperating since 2004 to develop improved, freeze-tolerant zoysiagrasses for the transition zone. Objectives Evaluate spring and fall color of zoysiagrass cultivars and progeny and determine if there is a relationship with freeze tolerance. Acknowledgements This research was supported, in part, by grants from the Heart of America Golf Course Superintendents Association, the Kansas Golf Course Superintendents Association, and the Kansas Turfgrass Foundation. Establishment and Maintenance Grasses were Meyer and DALZ 0102 (both Zoysia japonica), and 10 experimental progeny, most of which were crosses of Z. japonica x Z. matrella. All 12 grasses have demonstrated good winter survival in the field in Manhattan, KS since 2004. Plugs were planted in field plots measuring 0.6 m by 0.6 m in June, 2007. Plots were maintained using culture employed on golf course fairways and tees. Correlation Analysis Meyer was generally amongst the lowest in LT 50, lowest in green coverage in the fall, and highest in green coverage in the spring (Table 1). Significant negative correlations occurred between LT 50 on 15 Feb. 2008 and green coverage on 19 Oct. 2007 and 28 April 2008 (Table 2). In both cases, a greater percentage of green coverage was related to a lower LT 50 (i.e., better freeze tolerance). Although more green coverage in April may be expected to indicate better freeze tolerance, a similar observation in October is contrary to what would be expected. Range of green coverage on 19 Oct. 2007 was narrow (87 to 93%, Table 1), however, as the first freeze had not yet occurred. From field……to freezer… …to greenhouse. Conclusions Amongst this group of zoysia cultivars and progeny which have demonstrated good winter survival in the field over five years, percent green coverage in fall or spring was not consistently correlated with LT 50. Overview of LT 50 s and Green Coverage Digital Images Digital images to determine percentage green cover were taken weekly between 19 Oct and 27 Nov 2007, 17 Apr and 6 May 2008, 8 Oct and 2 Dec 2008, and 10 Apr and 18 May 2009. Images were analyzed using Sigma Scan Pro 5 under a hue threshold of 30 to 100, and saturation of 0 to 100. References Fry, J. and B. Huang. 2004. Applied turfgrass science and physiology. Wiley, Hoboken, NJ.