The Effect of Sustained Yield Suppression with Trinexapac-Ethyl On Nitrogen and Phosphorus Requirements of Creeping Bentgrass Golf Putting Greens.

The plant growth regulator trinexapac-ethyl (TE) is commonly applied to turfgrass to reduce clipping yield and enhance turfgrass color and visual quality.  These effects are sustained on creeping bentgrass (Agrostis stolonifera Hud.) putting greens when TE is re-applied every 200 growing degree days (base 0°C).  The purpose of this study was to evaluate the role of sustained yield suppression and quality enhancement, as a result of TE re-applications, on nitrogen and phosphorus requirements of golf course putting greens.  Two creeping bentgrass putting greens were constructed at the O.J. Noer Turfgrass Research Facility in Madison, WI.  Study #1 evaluated three biweekly nitrogen rates (5, 10, 20 kg N ha^-1) and two TE application rates (0 and 0.1 kg a.i. ha^-1) replicated four times in a randomized complete block design on clipping yield, visual quality, and color index on a peat-amended sand putting green. Data were collected biweekly during the summers of 2009-10.  The putting green in Study #2 was constructed with un-amended sand incorporated with four levels of phosphorus fertilizer (0, 8, 15, and 30 mg P kg^-1) with or without TE (0 and 0.1 kg a.i. ha^-1) in a randomized complete block design with four replications.  Clipping yield, visual quality, and color were paired with monthly Mehlich-3 soil test phosphorus (STP) levels during 2009-10.  Linear-linear plateau regression was used to calculate the critical STP level.  Results from Study #1 suggest that TE increased color and visual quality to a similar extent as increasing N fertilization rate by 25% while relative clipping yield is reduced 25% regardless of fertilization rate.  Critical STP level in Study #2 ranged from 6 to 10 mg P kg^-1.  Application of TE did not affect the STP critical level.  Re-application of TE every 200 GDD may allow for reduction in bentgrass putting green nitrogen application rate with no loss of turfgrass visual quality or color.