Using Ethephon for Seedhead Suppression of ‘Innovation’ Using Ethephon for Seedhead Suppression of ‘Innovation’ Zoysiagrass Zoysiagrass

Abstract The performance of ethephon (Proxy) on seedhead suppression of ‘Innovation’ zoysiagrass was evaluated during the 2019–2020 growing season in Manhattan, KS. Treatments evaluated Proxy applied in a single autumn application at 5 fl. oz./1,000 ft 2 on multiple dates between August 28 and November 26, 2019. Seedhead suppression ranged from 15% (application on November 1) to 82% (applied on September 4). Dates between September 4 and October 3 were the optimum application window for ethephon application on Innovation zoysiagrass as seedhead suppression was at least 62% with minimal turf injury occurring. Summary The performance of ethephon (Proxy) on seedhead suppression of ‘Innovation’ zoysiagrass was evaluated during the 2019–2020 growing season in Manhattan, KS. Treatments evaluated Proxy applied in a single autumn application at 5 fl. oz./1,000 ft 2 on multiple dates between August 28 and November 26, 2019. Seedhead suppression ranged from 15% (application on November 1) to 82% (applied on September 4). Dates between September 4 and October 3 were the optimum application window for ethephon application on Innovation zoysiagrass as seedhead suppression was at least 62% with minimal turf injury occurring. golf


Summary
The performance of ethephon (Proxy) on seedhead suppression of 'Innovation' zoysiagrass was evaluated during the 2019-2020 growing season in Manhattan, KS. Treatments evaluated Proxy applied in a single autumn application at 5 fl. oz./1,000 ft 2 on multiple dates between August 28 and November 26, 2019. Seedhead suppression ranged from 15% (application on November 1) to 82% (applied on September 4). Dates between September 4 and October 3 were the optimum application window for ethephon application on Innovation zoysiagrass as seedhead suppression was at least 62% with minimal turf injury occurring.

Rationale
Zoysiagrass (Zoysia spp. Willd.) provides high-quality turf and playing surfaces for golf fairways and tees throughout the transition zone of the United States (Lyman et al., 2007). Innovation zoysiagrass, evaluated experimentally as 'KSUZ 0802' (Zoysia matrella 'Cavalier' × Z. japonica 'Anderson 1'), is a fairly new cultivar that has cold tolerance equivalent to 'Meyer', but also enhanced density and a finer leaf texture (Chandra et al., 2017;Patton et al., 2017). However, Innovation produces seedheads in late spring that impact the playing surface and aesthetics. Seedheads appear to leave a purple cast across fairways and tees on golf courses when they emerge, and after mowing seed stalks that remain leave a white cast to these areas. Playability is also affected, and ball roll distance is reduced due to lingering seedheads on playing surfaces. This is concerning to golf course superintendents and golfers (Kane and Miller, 2003 Patton et al. (2018) on Meyer zoysiagrass showed that the use of ethephon, a plant growth regulator, has been effective in seedhead suppression with negligible injury when applied in autumn. The efficacy of ethephon on suppressing Innovation zoysiagrass seedheads has not been evaluated. We hypothesized that ethephon, when applied on Innovation zoysiagrass in autumn, works similarly on Meyer as both cultivars produce seedheads in late spring in the transition zone.

Objective
To determine the efficacy of ethephon in suppressing seedheads on Innovation zoysiagrass and determine the optimum application window.

Study Description
The experiment was conducted at the Rocky Ford Turfgrass Research Center in Manhattan, KS. The study area was sprigged with Innovation zoysiagrass in June 2017. The soil type was a Chase silty clay loam (fine, smectitic, mesic Aquertic Argiudolls) with a pH of 7.3. The site was mowed at 0.625 inches three times weekly with a walk-behind reel mower and clippings were returned. Nitrogen was applied on June 3 and July 1 to provide 1 lb/1,000 ft 2 at each application. The area was sufficiently irrigated to prevent visible wilting.
The experiment was arranged in a randomized complete block design with four replicates. Each plot measured 4 × 4 ft. The treatments consisted of 11 application timings of ethephon (Proxy 2L, Bayer Environmental Science) applied from late August through early November, and a nontreated control (Table 1). Proxy was applied at 5 fl. oz./1,000 ft 2 with a CO 2 -pressurized sprayer equipped with TP8006EVS flat-fan nozzles (TeeJet Technologies, Glendale Heights, IL) calibrated to deliver 2 gallons/1,000 ft 2 at 40 psi. The irrigation and mowing were withheld for at least 2 days after ethephon treatment application throughout the study period.
Dithiopyr (Dimension 2EW, Dow AgroSciences) was applied to prevent crabgrass on April 19, 2019. Speedzone was applied on April 19 and June 20, 2019, to control broadleaf weeds. ProStar 70 WG was applied on September 7, 2019, to prevent large patch infection.
Seedhead data were collected in the following spring in 2020. Once formation of seedheads was visible in the canopy, mowing was ceased until the peak inflorescence development was observed (determined through visual inspection). A 20-× 20-inch template was randomly placed in each experimental plot and visible seedheads were counted once the peak inflorescence stage was determined on May 31, 2020. Percent seedhead suppression (PSS) was determined as: PSS = 100 × [1-(seedheads count on treated plot) / (seedheads count on nontreated plot)] Kansas State University Agricultural Experiment Station and Cooperative Extension Service Phytotoxicity was measured as change in turf color determined visually on a scale of 1-9 in which 9 = dark green turf with no discoloration; 6 = minimally acceptable discoloration with some browning; and 1 = completely bleached white leaf. Turf injury was rated weekly starting one week after initial treatment (WAIT) until the first frost occurred. Also, spring green up was rated visually on a scale of 1-9 in which 1 = brown turf and 9 = fully green turf on April 8 and 21, and May 5, 2020.

Results
Ethephon application timing affected Innovation seedhead suppression and the results ranged from 15 to 82% (Figure 1). The treatment applied on September 4 had the greatest suppression (82%) and was statistically similar to the treatments applied on September 11, 18, and 25; and October 3. The applications made between September 4 and October 23 had at least 62% suppression. However, the 62% suppression result may not be commercially acceptable in all instances. This suggests that the optimum application window for effective seedhead suppression in Innovation zoysiagrass is rather narrow. Furthermore, the large variation observed between replications, as indicated by the error bars in Figure 1, raises questions on the consistency of seedhead suppression. For example, the treatment applied on September 25 had large variability. Treatments applied after the first frost on November 1 and 6 had the lowest suppression and revealed the poor efficacy of ethephon when applied late in the season.