Seasonal Chemical Management Practices for Aging Ultradwarf Greens in South Florida.

Recently, new bermudagrass cultivars [Cynodon transvaalensis (L.) Pers. X Cynodon dactylon (Burtt-Davy)] with more decumbent growth habits coined as "ultradwarfs" have been released for use on golf course greens and tees as an alternative to standard varieties that have been used for over 40 years. However, little research information is available on ultradwarf management requirements. To address this, a four-year experiment was conducted in South Florida on a United States Golf Association specified green to examine nitrogen (N) fertility, and N to potassium (K) ratios, on the quality, growth, and performance of three commercially-released ultradwarfs (Champion, TifEagle, and FloraDwarf). This research documented the need for adjusting fertilization as the green ages and for the ultradwarf in cultivation.  Fertilizing at the 879 kg N ha^-1 yr^-1 resulted in quality grass with minimal disease presence, and with mean tissue-N and K concentrations of 3.1 and 1.4 % respectively. For each of the tissue sampling dates, tissue-N and K were present approximately as a 2:1 ratio, regardless of N rate and N:K ratio applied. As the green aged, fertilizing with 586 kg N ha^-1 yr^-1 was adequate. It appears that Champion and TifEagle have different mechanisms for increasing aboveground growth and had better turf quality and growth characteristics than FloraDwarf. Consequently, N rates will differ among grass cultivars and grass expectations, with the latter needing to be maintained at a minimum of 586 kg N ha^-1 yr^-1.