Growing Degree-Days Optimize Trinexapac-Ethyl Reapplications On Ultradwarf Bermudagrass Putting Greens: Ii. Testing A Reapplication Schedule

Trinexapac-ethyl (TE) is commonly applied to ultradwarf bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy] putting greens for growth suppression and secondary benefits. Improperly timed reapplications will reduce the benefits of TE, but knowing when to reapply is difficult because suppression duration is affected by environmental conditions, especially temperature. In another experiment we determined that GDD with a base temperature of 0 degrees C (GDD(0)) was the most precise unit for predicting the maximum suppression point (MSP) after a TE application on a 'MiniVerde' ultradwarf bermudagrass putting green. The model suggested that the MSP occurred at 262 GDD(0) after the TE application. The objective of this second experiment was to test GDD(0) reapplication intervals for an extended period of time. We included four GDD(0) intervals (100, 200, 400, and 600) and two TE rates (0.022 and 0.044 kg a.i. ha(-1)). We hypothesized that reapplying TE before the MSP would result in a consistent suppression magnitude from day to day (i.e., consistent daily growth), which should be an ideal growth pattern for turfgrass managers. The 100- and 200-GDD(0) intervals yielded consistent suppression magnitude throughout the experiment, and suppression magnitude increased with the higher TE rate. In contrast, the 400- and 600-GDD(0) intervals allowed fluctuation in suppression magnitude from day to day. Discoloration occurred after initial applications and was more severe for the higher TE rate.