Does Miniverde Bermudagrass Respond Differently to Trinexapac-Ethyl Applications throughout the Season?.

Trinexapac-ethyl (TE) (Primo MAXX, Syngenta, Greensboro, NC) is a commonly applied plant growth regulator on well-maintained turfgrass. TE reapplications are difficult because TE is metabolized faster as temperatures increase, which renders a calendar-based reapplication schedule ineffective. Reapplication models based on growing degree day (GDD) accumulation is theorized as a possible solution. GDD reapplication models for creeping bentgrass (Agrostis stolonifera L.) putting greens have been developed. With these models, GDD accumulation (calculated in Celsius with a base temperature of zero) is monitored following a TE application and a repeat application is made after the predetermined threshold is reached. GDD accumulation is then reset to zero.

The objective of this trial was to develop a GDD model for TE reapplications on ultradwarf bermudagrass (Cynodon dactylon X C. transvaalensis Pers. L.) putting greens. A field trial was conducted on a MiniVerde putting green at the Sports Surface Field Laboratory in Auburn, AL during the summer of 2016 and repeated in 2017. This trial was designed to evaluate clipping yield following a single application of TE at 0.044 kg a.i. ha^-1. A single application was made on the first and fifteenth of May, June, July, and August to evaluate differences throughout the season. Clippings were collected three times per week, then dried for 48 hours before being weighed. Results indicate maximum clipping suppression occurred from 14 days after treatment (DAT) in May to 10 DAT in July; however, the GDDs to this point was relatively constant from 305 GDD in May to 314 GDD in July (daily GDD accumulation ranged from 15 GDD per day in May to 30 GDD in July). This trial indicates that reapplying TE at 0.044 kg a.i. ha^-1 before 300 GDD accumulate will provide consistent clipping suppression throughout the growing season.