Suppressing Innovation zoysiagrass seedheads with ethephon

A plot of Innovation zoysiagrass that received a Proxy application at 5 fluid ounces per 1,000 square feet on Sept. 4, 2019. Photo taken on May 31, 2020. Photo by Manoj Chhetri

Innovation zoysiagrass (Zoysia matrella Cavalier × Z. japonica Anderson 1 cv. KSUZ 0802), a recently introduced cultivar, boasts a higher density and finer texture than Meyer zoysiagrass (Z. japonica Steud.), but equivalent cold tolerance (2, 9). Innovation has a potential to provide high-quality turf and playing surfaces for use on golf course fairways and tees in the U.S. transition zone. Despite its favorable attributes, it experiences an issue with the development of stiff, stalky seedheads during late spring, impacting both the playability and visual appeal of the turf. Seedheads cause fairways and tees on golf courses to have a visual color change (i.e., purple cast) when they emerge, and after mowing, seed stalks that remain leave a white cast on these areas. This concern is particularly troubling for golf course superintendents and players (5) and the resulting increased mowing requirements, which incur greater fuel, labor and equipment maintenance costs (1). To address this issue, there is interest in exploring the efficacy of ethephon on Innovation zoysiagrass, a standard industry solution for seedhead suppression in annual bluegrass (Poa annua).

Previous research on ethephon has demonstrated its effectiveness in suppressing seedheads in Meyer zoysiagrass, with minimal damage following applications, particularly during autumn. Nonetheless, there remains a gap in understanding how Innovation responds to ethephon treatment. Given the cultivar's potential for use in golf course settings, it is imperative to investigate the efficacy of ethephon for effective seedhead management.

Consequently, the study seeks to accomplish three primary objectives: firstly, to assess the efficacy of ethephon in suppressing seedheads in Innovation zoysiagrass; secondly, to determine the most suitable application timing based on weather conditions; and thirdly, to evaluate any potential phytotoxicity after ethephon application. This research aims to provide insights into the applicability of ethephon for managing seedheads in Innovation zoysiagrass, offering potential benefits for the golf course industry.

Table 1. Effect of ethephon application timing on Innovation zoysiagrass seedhead suppression in Manhattan, Kan.

Materials and methods

The study was conducted at the Rocky Ford Turfgrass Research Center in Manhattan, Kan., over two growing seasons from August 2019 to May 2020 and August 2020 to May 2021. The soil type was a Chase silty clay loam, with a pH level of 7.3. The turf was maintained at a height of 0.625 inches (1.6 centimeters), mowed three times weekly using a walk-behind reel mower, and clippings were returned. Nitrogen, supplied in the form of urea (46% nitrogen-0% phosphorus-0% potassium, Lesco Professional Turf Fertilizer), was applied on June 3 and July 1 in 2019, and on May 26 and July 2 in 2020, at a rate of 1 pound nitrogen per 1,000 square feet (48.8 kilograms per hectare). Adequate irrigation was provided to prevent visible wilting, and dithiopyr (Dimension 2EW, Dow AgroSciences) was applied at 1 pound active ingredient per acre (1.12 kilograms per hectare) on April 19, 2019, and April 24, 2020, to prevent crabgrass emergence. A herbicide mixture (Speedzone, PBI-Gordon Corporation) was applied on April 19 and June 20, 2019, and May 10, 2020, to manage broadleaf weeds. Additionally, flutolanil (ProStar 70 WG, Bayer Environmental Science) was applied on Sept. 4, 2019, and Sept. 10, 2020, at a rate of 8.6 pounds active ingredient per acre (9.6 kilograms per hectare) to prevent large patch.

The experiment was arranged in a randomized complete block design with four replicates. Each plot, measuring 4 feet by 4 feet (1.22 meters by 1.22 meters), received one of 11 ethephon (Proxy 2L, Bayer Environmental Science) application timings, from late August through early November, along with a control group. In the second experiment, an additional early application timing was introduced. Proxy was applied at 5 fluid ounces per 1,000 square feet (15.9 liters per hectare) with a CO2-pressurized sprayer, and irrigation and mowing were withheld for at least two days after each ethephon treatment. Seedhead counts were conducted using a 20-inch-by-20-inch (51-centimeter-by-51-centimeter) template, with percent seedhead suppression (PSS) calculated using this equation]:

Seedhead suppression (PSS, %) = (1-(number of seedheads in treated plot)/(number of seedheads in control plot)) x 100

Phytotoxicity from ethephon was assessed through visual determination of turf color on a scale of 1 to 9, and spring green-up and mowing quality were also visually rated.

Data analysis involved one-way analysis of variance (ANOVA), treating block as a random effect. Significant F-test results prompted the separation of treatment means using Tukey's Honestly Significant Difference (HSD) test. As the application timing dates differed between Experiments 1 and 2, data were analyzed and presented separately for each experiment.

Table 2. Effect of ethephon application timing on Innovation zoysiagrass injury as determined by turf color ratings after treatment in 2019 (Experiment 1).

Results

Seedhead suppression

The timing of ethephon application significantly influenced percent seedhead suppression in Experiment 1 (P < 0.0001) and Experiment 2 (P < 0.0001)  (Table 1). In Experiment 1, PSS varied from 15% to 82%, with the highest suppression (82%) observed for ethephon applied on Sept. 4 and the lowest (15%) for the Nov. 1 application. An optimal application window between Sept. 4 and Oct. 23 resulted in at least 50% PSS, with the peak efficacy occurring between Sept. 4 and Oct. 3. In Experiment 2, PSS ranged from 5% to 85%, with the highest suppression (85%) observed for ethephon applied on Sept. 3 and the lowest (5%) for the Oct. 29 application. The optimal application window in Experiment 2 fell between Aug. 20 and Sept. 24, providing statistically similar seedhead suppression ranging from 68% to 85%.

The study revealed considerable variation in ethephon efficacy on Innovation zoysiagrass across the two experimental seasons. Inconsistencies from year to year have been previously reported, emphasizing the need to understand these variations. Previous studies on Meyer zoysiagrass have shown that ethephon efficacy depends on environmental conditions and varies by location (1, 6, 7). The study’s two-year data suggested that achieving at least 70% seedhead suppression is possible by correctly timing ethephon application. Results from our and Patton et al. (2018) studies suggest that ethephon applied early in the autumn when temperature begins to cool down would more effectively suppress seedheads in zoysiagrass than that in late autumn or late summer in the transition zone. 

Table 3. Effect of ethephon application timing on Innovation zoysiagrass injury as determined by turf color ratings after treatment in 2020 (Experiment 2).

Phytotoxicity

Several studies have documented turf injury, particularly a decline in turf quality, following the application of ethephon across various turfgrass species (3, 10). Conversely, some studies have reported minimal or no injury associated with ethephon application (1, 4, 8). Discrepancies in findings may be attributed to differences in factors such as turfgrass age, mowing heights, cultivars, application timing and intervals across these studies (4). In our study, we assessed phytotoxicity by quantifying browning of leaves, which manifested as a decline in turf color. Ethephon application timing influenced the extent of injury in Experiments 1 and 2.

In Experiment 1, Innovation experienced injury below commercially acceptable levels for at least four weeks following treatment when ethephon was applied on Aug. 28 (Table 2). In Experiment 2, only the first two applications (Aug. 20 and 27) led to Innovation injury causing quality to fall below acceptable levels for four and three weeks, respectively (Table 3). In our study, canopy discoloration on Innovation was transient and more pronounced only with late-summer application timings. Future research exploring the effects of tank-mixing ethephon with trinexapac-ethyl or iron on Innovation could provide valuable insights.

Turf quality post-mowing in spring

Ethephon application timing significantly influenced mowing quality in Experiment 1 (P < 0.0001) and Experiment 2 (P < 0.0001) (Table 4). Dates of ethephon application leading to higher seedhead suppression correlated with improved mowing quality. The presence of tough seedhead stalks post-mowing affected quality. For instance, Innovation treated on Sept. 4, 2019, with 82% PSS, exhibited a mowing quality of 8.3 on June 8, 2020, whereas those treated on Nov. 1, 2019, with 15% PSS, had a mowing quality of 6.0 on the same date. Additionally, spring green-up in April and May following ethephon application showed no significant difference from the non-treated plots, suggesting that autumn ethephon application may not impact winter injury or survival of Innovation zoysiagrass.

Table 4. Effect of ethephon application timing in 2019 and 2020 on Innovation zoysiagrass mowing quality in 2020, 2021.

Summary

A single ethephon application on Sept. 4, 2019, or Sept. 3, 2020, achieved over 82% seedhead suppression, but the window for such effectiveness was limited. Overall, applying ethephon in September consistently suppressed at least 60% of Innovation seedheads over two years, except for Sept. 10, 2020, likely due to rainfall. Applications from Aug. 20 to 28 effectively suppressed seedheads but led to undesirable turf discoloration for four weeks. Late-summer timings resulted in inconsistent suppression, suggesting ethephon’s efficacy on Innovation depends on environmental conditions, necessitating further research on parameter-based applications. In Kansas, our two-year data revealed that at least 70% seedhead suppression could be achieved with ethephon application. The most consistent and reliable suppression occurred when ethephon was applied in early autumn (September). These results align with prior findings in Meyer zoysiagrass, defining the optimal application window for suppressing Innovation zoysiagrass seedheads in the U.S. transition zone.

The research says

• Ethephon effectively suppresses Innovation zoysiagrass seedheads. 
• Ethephon efficacy varies with application dates when applied in autumn.
• Ethephon application in late summer caused unacceptable discoloration.

Acknowledgements

We appreciate the funding provided by GCSAA, Heart of America GCSA and Kansas Turfgrass Foundation.

Literature cited

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Manoj Chhetri (mkc6518@psu.edu) is an assistant professor in turfgrass science at Pennsylvania State University, University Park; Jack D. Fry is a professor and turfgrass Extension specialist at the Olathe Horticulture Research and Extension Center, Kansas State University, Manhattan; and Megan M. Kennelly is a professor and department head in the Department of Plant Pathology at Kansas State University, Manhattan.

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