Optimizing ethephon application timing for ‘Meyer’ zoysiagrass seedhead suppression

Zoysiagrass ( Zoysia spp. Willd.) is a desirable, low‐input turfgrass species used on golf courses. However, prolific zoysiagrass seedhead production in the spring can increase golf course maintenance costs and reduce aesthetics. Previous research demonstrates that a single autumn ethephon application can suppress zoysiagrass seedhead production the following spring, but the optimum application timing is not well‐defined. The objective of this research was to determine the optimum window for an effective ethephon application for ‘Meyer’ zoysiagrass seedhead suppression. Small‐plot field research was conducted in Indiana, Kansas, Arkansas, and Tennessee. Seedheads were suppressed up to 99% depending on application timing. In Indiana, applications made on September 19 provided 99% seedhead suppression. In Kansas, applications between August 30 and September 18 yielded >64% seedhead suppression. In Arkansas, applications between October 3 and October 17 yielded >52% seedhead suppression. In Tennessee, applications between September 19 and October 23 provided >78% seedhead suppression. Applications made outside these windows resulted in more seedhead production at each respective location. Interestingly, optimum application timing was approximately 2 weeks later in Arkansas and Tennessee compared to Indiana and Kansas. Using growing degree days, a nonlinear Gaussian model was fit to predict the optimum ethephon application timing. In addition to data from this research, the proposed model accurately predicted observed zoysiagrass seedhead suppression in previously published research. This research better characterizes the optimum autumn application timing for Meyer zoysiagrass seedhead suppression across the transition zone. Autumn‐applied ethephon suppresses Meyer zoysiagrass seedhead production in spring. Seedhead suppression is diminished if ethephon applications are too early or too late in autumn. Growing degree days could be utilized to optimize ethephon application timings. Zoysiagrass produces seedheads in late spring and early summer. Seedheads are not wanted on golf courses fairways as they reduce looks and playability and also increase golf course maintenance costs. Ethephon is a plant growth regulator that can be applied to reduce these seedheads. The goal of this multi‐state research project was to determine the best time in autumn to apply ethephon to reduce the seedheads zoysiagrass produces in spring. Spring seedheads were reduced most in India