Impact of Fall Applications of trinexapac-ethyl…

By Jordan Booth, David McCall, Ph.D., Mike Goatley, Ph.D., Shawn Askew, Ph.D.

Research continues at Independence Golf Club on winter management of ultradwarf bermudagrass (UDB) putting greens. For the last three years, research has been conducted to evaluate the impact of fall and winter applications of trinexapac-ethyl (Primo Maxx, Syngenta) on cold tolerance of UDB. Primo Maxx is traditionally used in the summer to reduce vertical growth, improve the quality of cut and provide consistent putting green playability. The rationale of this research is that Primo Maxx may improve cold tolerance by reducing unnecessary fall growth and allow for plants to reserve energy (carbohydrates) heading into winter dormancy. Dormancy is UDB’s greatest defense against cold winter damage. Previous field research in 2017/ 18 and 2018/19 showed that fall and winter applications of Primo Maxx did have a positive impact on spring UDB turfgrass quality and reduced fluctuations in growth during the fall and winter months.

A study in 2020 was designed to evaluate the impact of fall Primo Maxx treatments on the cold tolerance of UDB in an early-winter freeze situation. Twenty-four ‘Champion’ UDB plugs were planted in February 2020 in 6" pots. The UDB pots were maintained in a greenhouse at 65– 85°F, receiving 3oz/A of Primo Maxx every 14 days. In July the UDB pots were randomized and placed into a modified chest freezer where light and temperature were regulated to mimic fall growing conditions. Nighttime temperatures were dropped 5°F every two weeks until pots were exposed to 35°F at night to replicate fall nighttime temperatures. During this time, twelve pots received 3oz/A of Primo Maxx every 14 days while 12 did not. After 12 weeks of ‘fall’, replications of three untreated UDB pots and three TE UDB pots were exposed to 15°F for 4, 6, 8, and 10 hours respectively. Pots were analyzed for percent green cover using digital image analysis software to evaluate cold-exposure damage. Nonlinear regression analysis predicted a 50% mortality exposure point for ‘Champion’ UDB under Primo Maxx treatments of 9.84 hours at 15°F (r 2 =0.836) compared to 11.38 hours at 15°F (r 2 =0.671) for non-treated ‘Champion’ UDB pots. Contrary to field evaluations, these data suggest that fall applications of Primo Maxx reduce cold tolerance of ultradwarf bermudagrass. However, more research is needed to validate these findings.

This trial is currently being repeated at two different locations. Future research will evaluate the impact of Primo Maxx on cold tolerance of UDB during mid-winter and early spring below-freezing scenarios. This research is being supported by a grant from the United States Golf Association.