Picture 1. Untreated Champion bermudagrass vs. Champion bermudagrass treated with Primo at 1.5 ounces per acre every 10 days.

Successful course management is based on turfgrass quality and not total yield. Turf managers fertilize putting greens to promote color and plant health. However, luxuriant growth often disrupts surface uniformity and decreases green speeds. Inhibiting undesirable shoot growth with plant growth regulators (PGRs) provides more consistent putting surfaces and may further enhance turfgrass color and quality.

Currently, trinexapac-ethyl (TE) is the most popular PGR in the turfgrass industry. TE (Primo Maxx) represents a newer generation of gibberellic acid (GA) inhibitors that interferes with the 3b-hydroxylase conversion of GA20 to GA1, inhibiting cellular elongation in turfgrass leaves (Rademacher, 2000). Sequential applications of TE on Tifway bermudagrass provide consistent growth suppression, avoidance of post inhibition growth enhancement and improvements in turf quality (Fagerness and Yelverton 2000). Multiple applications of TE to bermudagrass may also delay fall dormancy and promote spring greenup (Fagerness and Yelverton, 2000; Richardson, 2002).

Research demonstrates TE improves turf grown under stressful conditions that would otherwise result in poor turf quality and substandard rooting. Diamond zoysiagrass (Zoysia matrella (L.) Merr) receiving monthly and bimonthly TE applications displayed higher root mass, higher root viability and improved photosynthesis under reduced light conditions (Qian and Engelke, 1999). Applications of TE on creeping bentgrass (Agrostis palustris Huds.) greens under low light intensities did not affect root mass but did increase turf cover from 6 percent to 33 percent (Goss et al., 2002). Monthly applications of TE in a two-year field study were safe on rooting of Penncross creeping bentgrass (Fagerness and Yelverton, 2001). Research is currently lacking, however, on the safety of TE applications to dwarf bermudagrass putting greens.

Recently introduced dwarf bermudagrass varieties provide Southern golf courses with a putting- green quality that is comparable to creeping bentgrass (McCarty and Miller, 2002). However, with potentially reduced photosynthetic capacity from closer mowing heights, dwarf bermudagrass turf maintained as close as one-eighth-of-an-inch may have depletion of carbohydrates available for root growth. Low cutting height and frequent mowing are directly correlated with decreases in root growth and carbohydrate reserves (Beard, 1973; Hull, 1992). Translocation of reserve carbohydrates in roots occurs after mowing for utilization in the production of new leaf tissue (Younger, 1969). Therefore, balancing photosynthate allocation away from shoot growth with TE may provide more favorable growing conditions for dwarf bermudagrass root systems. Research at Clemson University investigated effects of TE with various nitrogen (N) levels and PGR combinations on ultradwarf bermudagrass growth.

Picture 2. TifEagle bermudagrass treated weekly with 0.5 pounds of nitrogen per 1,000 square feet vs. 0.25 pounds of nitrogen per 1,000 square feet with trinexapac-ethyl every three weeks.

Materials and methods Experiments were conducted at the Clemson (S.C.) University Greenhouse from September 2002 to May 2003. Experimental designs were randomized, complete blocks with four replications.