Scalping and Creeping Bentgrass Quality As Influenced By Ethephon and Trinexapac-ethyl

Scalping and Creeping Bentgrass Quality as Influenced by Ethephon and Trinexapac-ethyl

Peter H. Dernoeden and Raymond L. Pigati, Department of Plant Science and Landscape Architecture, University of Maryland, College Park, MD 20742

Corresponding author: Peter H. Dernoeden. pd@umd.edu

Abstract

Ethephon is commonly tank-mixed with trinexapac-ethyl (TE) and applied to putting greens in spring to manage annual bluegrass (Poa annua L.) seedheads. Previous research indicated that ethephon can predispose fairway-height creeping bentgrass (Agrostis stolonifera L.) to scalping. It would be prudent to determine if ethephon has similar effects on creeping bentgrass maintained as a putting green. This study was conducted on a mature stand of ‘Providence’ creeping bentgrass grown on a sand-based rootzone and maintained as a putting green. In 2007 and 2008, ethephon (3.8 kg ai/ha) and TE (0.045 kg ai/ha) were applied alone or in tank-mix combination either once or twice beginning in April. Scalping first became evident on a consistent basis in early June about 38 days following the second ethephon application in each year. Two applications of ethephon alone or tank-mixed with TE resulted in significant scalping that persisted from 35 to 56 days. Plots treated twice with ethephon exhibited reduced quality for 28 to 84 days. Golf course superintendents should be made aware of the potential level and time period that ethephon can predispose putting green height creeping bentgrass to scalping.

Introduction

Plant growth regulators (PGRs) were first evaluated in turfgrasses for the purpose of suppressing foliar growth in low maintenance or roadside situations to reduce mowing and thus inputs of fuel and labor (3,11). Over the years, PGRs have gained widespread usage on golf courses to reduce clippings, improve green speed, to suppress annual bluegrass (Poa annua L.) seedheads, and for other purposes (4,11). The use of ethephon for the purpose of controlling annual bluegrass seedheads in creeping bentgrass (Agrostis stolonifera L.) greens and its effect on turf quality and other factors has received a considerable amount of attention in recent years (7,8,12,13,15). Ethephon effectively controls annual bluegrass seedheads, but can reduce the color and quality of creeping bentgrass (7,8,12). The objectionable effects of ethephon use in creeping bentgrass have been described as eliciting a lighter green canopy color, leaf chlorosis or yellowing, and thinning of the turf (7,12,15). The discoloration of turf induced by ethephon has been attributed to leaf senescence and chlorophyll breakdown, which occurs when ethephon reacts with water to produce the hormone ethylene (8,10). Additionally, ethephon was reported to reduce rooting in creeping bentgrass and bermudagrass [Cynodon dactylon (L.) Pers. var. dactylon × Cynodon transvaalensis Burtt-Davy] (14). Tank-mixing ethephon with trinexapac-ethyl (TE), however, can darken leaves and improve quality in both creeping bentgrass and bermudagrass (7,14,15).

In Kentucky bluegrass (Poa pratensis L.), two applications of ethephon (4.5 and 6.7 kg ai/ha) in late April and early June were reported to cause stem elongation, which resulted in turf scalping (3). Scalping was caused by the elevation of crowns induced by ethephon, but this adverse effect was not detected until autumn (3). The elongation of Kentucky bluegrass stem internodes in response to ethephon was observed by others, but there was no mention of scalping in those reports (2,5,10,17). Diesburg and Christians (5), however, did report that ethephon (4.48 kg ai/ha) caused slight phytotoxicity to Kentucky bluegrass, which was observed 32 to 47 days after treatment. Eggens et al. (6) applied ethephon at rates ranging from 0.5 to 8.0 kg ai/ha one, two and three times on a three-week interval between July 1981 and May 1982 to mixed fairway stands of creeping bentgrass and annual bluegrass. They observed a decline in turf quality due to annual bluegrass injury, but did not observe any injury to the creeping bentgrass. Stier et al. (16) evaluated ethephon at various rates in creeping bentgrass maintained as a fairway in Indiana and Wisconsin. They reported that ethephon use was associated with scalping and a temporary reduction in creeping bentgrass quality in Indiana, but scalping was not observed in Wisconsin. Unpublished field research also indicated that two applications of ethephon (3.4 kg ai/ha) predisposed fairway height creeping bentgrass to scalping, but one application did not (P. H. Dernoeden, unpublished data). It is stated on the manufacturers’ label that scalping may occur in some creeping bentgrass cultivars after more than two ethephon applications (1). Generally, two or more applications of ethephon may be recommended to provide a high level of annual bluegrass seedhead control (1,7).

Ethephon has become an important tool to golf course managers, and it would be prudent to assess the potential of this PGR to predispose putting green height creeping bentgrass to scalping. Since TE has been shown to mitigate some of the discoloration effects of ethephon it also should be evaluated in combination with ethephon (7,13). Hence, the objectives of this field study were to assess the potential for scalping elicited by ethephon alone or tank-mixed with TE and applied to creeping bentgrass maintained as a putting green.

Study Site, Treatments, and Data Collection and Analysis

This study was conducted at the University of Maryland Turfgrass Research Facility in College Park, MD. Turf was a mature stand of ‘Providence’ creeping bentgrass grown on a sand-based rootzone built according to USGA recommendations (9). The 2007 and 2008 studies were conducted on different areas of the same research green. Soil was a modified sand mix (97% sand, 2% silt, and 2% clay) with a pH of 6.5 and 10 g/kg of organic matter. The study area had no history of PGR treatment. In 2007 and 2008, ethephon 2S (3.8 kg ai/ha) and TE 1ME (0.045 kg ai/ha) were applied alone or in tank-mix combination (hereafter ethephon + TE). The rates and sequential treatment application interval were made according to label directions (1). Each PGR alone or in tank-mix combination was applied once or twice. In the Baltimore-Washington DC corridor, ethephon applications would likely begin mid to late March when targeting P. annua seedhead suppression. There was no P. annua in the study site, and applications were initiated between 18 and 20 April of each year to coincide with the third spring mowing and 100% green-up of turf in the study site. In 2008, an additional treatment was assessed to determine if multiple applications of TE would mitigate scalping induced by ethephon. The new treatment was ethephon + TE applied twice on 18 April and 7 May, and an additional three applications of TE were applied to these plots on 25 May and 5 and 18 June (hereafter ethephon + TE 5×). Trinexapac-ethyl was applied twice in 2007 and five times to the same plots in 2008. Turf was mowed five times weekly with a triplex mower to a height of 4 mm and clippings were removed. The site received N at between 75 and 88 kg/ha between early April and late May in 2007 and 2008, and an additional 12.5 kg N per ha on 6 August 2008 from water soluble N sources. The site was irrigated to prevent wilt. Dollar spot (Sclerotinia homoeocarpa F.T. Bennett) and brown patch (Rhizoctonia solani Kuhn) were controlled with preventive applications of iprodione (14.7 kg ai/ha) applied on a two week interval beginning in early June of each year. Iprodione was chosen because it has no known PGR effects. The PGRs were applied in 467 liters/ha of water with a CO₂ pressurized (262 kPa) backpack sprayer equipped with an 8004 flat fan nozzle. Plots were 1.5 × 1.5 m and arranged in a randomized complete block with four replications. Turfgrass quality was evaluated visually using a 0 to 10 scale where 0 = entire plot area brown or dead; 7.0 = minimum acceptable quality; and 10 = optimum greenness, uniformity and cover. Injury from scalping was visually assessed using a 0 to 5 scale where 0 = entire plot area green and healthy; 1.5 = moderately severe scalping; 2.5 = objectionable and unacceptable injury from scalping and 5.0 = over 50% of the plot area brown or dead from scalping. Scalping and quality ratings were obtained weekly after scalping became evident. Data were subjected to the analysis of variance using SAS General Linear Model procedure (SAS Institute Inc., Cary, NC) and significantly different means were separated by Fisher’s protected least significant difference test at P ≤ 0.05. References to data not shown generally apply to ratings on dates when there were no significant treatment differences compared to the control.

Scalping and Turf Quality, 2007

The PGRs were applied initially on 20 April and sequential applications were made on 7 May 2007. Scalping did not appear until 14 June, or 53 days after the study was initiated and 38 days following the sequential application (Table 1). On 14 June, plots treated twice with either ethephon or ethephon + TE had equally severe levels of scalping (Fig. 1). Significant levels of objectionable scalping injury persisted as late as 12 July (i.e., for 28 days), which was 81 days following the initial application of PGRs. Scalp ratings were statistically similar among plots treated once with ethephon, once with ethephon + TE and the control on all rating dates. Plots treated twice with TE alone exhibited little or no scalping on all rating dates.

Table 1. Scalping in a ‘Providence’ creeping bentgrass research putting green in response to ethephon and trinexapac-ethyl (TE), 2007.

Treatment	No. of applica- tions^x	Scalping (0-5; ≥ 2.5 unacceptable)
Treatment	No. of applica- tions^x	14 Jun	21 Jun	28 Jun	5 Jul	12 Jul	19 Jul	26 Jul
Ethephon TE Ethephon + TE Ethephon Ethephon + TE Untreated	1 2 1 2 2 —	2.0 b^y 0.3 c 1.7 b 4.0 a 3.6 a 1.9 bc	1.8 bc 0.5 c 1.8 bc 3.8 a 3.5 ab 1.3 c	2.1 abc 0.4 c 1.4 bc 3.3 a 3.1 ab 1.3 c	2.5 ab 1.0 b 1.4 b 3.4 a 3.2 a 1.3 b	2.1 ab 0.3 c 1.1 bc 2.3 ab 2.9 a 0.9 bc	0.6 ab 0.0 b 0.1 ab 0.9 a 0.6 ab 0.0 b	0.0 a 0.3 a 0.0 a 0.4 a 0.3 a 0.0 a

^x Treatments were applied initially on 20 April and sequential treatments (2×) were applied 7 May 2007.

^y Means in a column followed by the same letter are not significantly different based on Fisher’s protected least significant difference (P ≤ 0.05) test.

Fig. 1. The scalped plot in the foreground was treated twice with ethephon on 20 April and 7 May 2007 and the photo was taken on 16 June 2007. The darker green, background plot was an untreated control.

Turf quality ratings primarily reflect scalping injury rather than turf color. Between 14 June and 12 July, plots treated twice with ethephon or twice with ethephon + TE exhibited a significant reduction in quality compared to the control, which was judged to be unacceptable (< 7.0) (Table 2). Plots treated once with ethephon or ethephon + TE had quality equivalent to the control on all rating dates. Plots treated with TE appeared darker green and this resulted in very good quality ratings (> 8.5) on most dates. However, quality of plots treated with TE was equivalent to the control on all dates. Ethephon-treated bentgrass appeared lime or yellow-green, when compared to TE-treated and untreated bentgrass.

Table 2. Turf quality of a ‘Providence’ creeping bentgrass research putting green as influenced by ethephon and trinexapac-ethyl (TE), 2007.

Treatment	No. of applica- tions^x	Quality (0-10; ≥ 7.0 acceptable)
Treatment	No. of applica- tions^x	14 Jun	21 Jun	28 Jun	5 Jul	12 Jul	19 Jul	26 Jul
Ethephon TE Ethephon + TE Ethephon Ethephon + TE Untreated	1 2 1 2 2 —	6.6 b^y 8.5 a 7.4 ab 5.3 c 5.4 c 7.7 ab	7.1 a 8.3 a 7.5 a 5.9 b 5.9 b 7.9 a	7.1 abc 8.1 a 7.9 a 6.0 c 6.4 bc 7.7 ab	7.5 ab 8.5 a 8.3 a 6.5 b 6.6 b 8.2 a	7.6 ab 8.5 a 8.5 a 7.1 b 7.1 b 8.5 a	8.3 b 9.3 a 9.0 ab 8.1 b 8.3 b 9.1 ab	9.0 ab 9.3 a 9.4 a 8.9 ab 8.5 b 9.2 a

^x Treatments were applied initially on 20 April and sequential treatments (2×) were applied 7 May 2007.

^y Means in a column followed by the same letter are not significantly different based on Fisher’s protected least significant difference (P ≤ 0.05) test.

Scalping and Turf Quality, 2008

In 2008, the ethephon + TE 5× treatment was added to determine if the additional TE applications would mitigate the scalping effect associated with ethephon in 2007. Significant levels of scalp injury were observed in plots treated twice with ethephon alone on 25 May and 6 and 13 June (Table 3; some data not shown). Consistent levels of severe scalp ratings began 20 June, about 44 days after the second application of ethephon. Plots treated once with ethephon exhibited significant levels of scalping compared to the control between 20 June and 11 July, which was judged to be low to moderately severe (ratings = 1.0 to 2.0). Scalping in plots receiving two applications of ethephon alone remained evident until 8 August, a duration of 56 days between 13 June and 8 August. From 20 June to 25 July, significant and objectionable levels (≥ 2.5) of scalp injury were observed in plots treated twice with ethephon alone or twice with ethephon + TE. Plots treated with ethephon + TE 5× were scalped less versus plots treated twice with ethephon alone or plots treated twice with ethephon + TE on 27 June, and 4, 11, and 18 July. While multiple TE applications reduced scalping, a higher level of scalp injury was observed in plots treated with ethephon + TE 5× versus the control on all dates between 20 June and 25 July. Although scalp injury had dissipated greatly by 8 August, all plots treated twice with ethephon, regardless of being mixed with TE, had scalp ratings greater than were observed in untreated plots on the final rating date (i.e., 8 August).

Table 3. Scalping in a ‘Providence’ creeping bentgrass research putting green in response to ethephon and trinexapac-ethyl (TE), 2008.

Treatment	No. of applica- tions^x	Scalping (0-5; ≥ 2.5 unacceptable)
Treatment	No. of applica- tions^x	25 May	6 Jun	13 Jun	20 Jun	27 Jun	4 Jul
Ethephon TE Ethephon + TE Ethephon Ethephon + TE Ethephon + TE Untreated	1 5 1 2 2 5 —	0.6 abc^y 0.0 c 0.8 ab 1.3 a 1.0 ab 1.1 a 0.3 bc	0.5 b 0.5 b 0.8 ab 1.4 a 1.0 ab 1.1 ab 0.4 b	0.6 bcd 0.0 d 0.8 bc 1.8 a 1.3 ab 0.6 bcd 0.1 cd	1.9 b 0.5 c 1.8 b 2.8 ab 3.3 a 2.8 ab 0.1 c	1.1 cd 0.1 e 2.1 b 3.8 a 3.6 a 1.9 bc 0.4 de	1.8 b 0.0 c 1.5 b 3.5 a 3.6 a 2.1 b 0.3 c

^x Treatments were applied initially on 18 April; sequential treatments (2×) were applied 7 May; and multiple TE treatments (5×) were applied 18 April, 7 and 21 May, and 5 and 18 June 2008.

^y Means in a column followed by the same letter are not significantly different based on Fisher’s protected least significant difference (P ≤ 0.05) test.

Table 3 (cont’d). Scalping in a ‘Providence’ creeping bentgrass research putting green in response to ethephon and trinexapac-ethyl (TE), 2008.

Treatment	No. of applica- tions^x	Scalping (0-5: ≥ 2.5 unacceptable)
Treatment	No. of applica- tions^x	11 Jul	18 Jul	25 Jul	1 Aug	8 Aug
Ethephon TE Ethephon + TE Ethephon Ethephon + TE Ethephon + TE Untreated	1 5 1 2 2 5 —	1.4 b^y 0.0 c 1.0 b 3.1 a 3.3 a 1.5 b 0.1 c	0.9 bc 0.0 c 0.5 bc 2.5 a 2.4 a 1.3 b 0.4 c	0.6 b 0.0 b 0.5 b 2.3 a 2.8 a 2.0 a 0.0 b	0.5 b 0.0 b 0.1 b 1.8 a 1.9 a 1.0 ab 0.1 b	0.1 bc 0.0 c 0.1 bc 0.9 a 0.9 a 0.8 ab 0.1 c

^x Treatments were applied initially on 18 April; sequential treatments (2×) were applied 7 May; and multiple TE treatments (5×) were applied 18 April, 7 and 21 May, and 5 and 18 June 2008.

^y Means in a column followed by the same letter are not significantly different based on Fisher’s protected least significant difference (P ≤ 0.05) test.

Turf quality ratings were obtained from 9 May to 8 August 2008 (Table 4; some data not shown). Plots treated twice with ethephon exhibited reduced quality compared to the control as early as 16 May, which continued until data collection ceased 8 August. Plots treated once with ethephon exhibited reduced quality on most dates between 25 May and 11 July, but the quality of plots treated once with ethephon + TE was equivalent to the control on 25 May and 6 June. Turf quality ratings in plots treated with ethephon + TE 5× were higher than those of plots treated twice with ethephon and ethephon + TE on 13 and 27 June and 4 and 11 July. Hence, there was some improvement in turf quality accorded by multiple applications of TE. On most rating dates after 13 June, the quality of plots treated twice with ethephon was reduced significantly and was judged to be poor to marginally acceptable. As was observed in 2007, ethephon elicited a lime-green canopy color, whereas, TE darkened the bentgrass foliage.

Table 4. Turf quality of a ‘Providence’ creeping bentgrass research putting green in response to ethephon and trinexapac-ethyl (TE), 2008.

Treatment^y	No. of applica- tions^x	Quality (0-10; ≥ 7.0 acceptable)
Treatment^y	No. of applica- tions^x	16 May	25 May	6 Jun	13 Jun	20 Jun	27 Jun
Ethephon TE Ethephon + TE Ethephon Ethephon + TE Ethephon + TE Untreated	1 5 1 2 2 5 —	7.5 ab^y 7.9 a 7.6 a 6.9 c 6.5 c 7.0 bc 7.8 a	8.0 cd 9.0 a 8.3 bc 7.5 d 7.6 cd 7.4 d 8.8 ab	7.5 bc 8.0 ab 8.1 a 7.1 c 7.4 c 7.4 c 8.3 a	8.3 b 8.9 a 8.0 b 7.4 c 7.5 c 8.1 b 8.9 a	6.4 b 7.6 a 6.1 b 5.9 bc 5.4 c 5.9 bc 7.6 a	7.0 b 7.9 a 6.6 b 5.5 c 5.6 c 6.6 b 7.8 a

^x Treatments were applied initially on 18 April; sequential treatments (2×) were applied 7 May; and multiple TE treatments (5×) were applied 18 April, 7 and 21 May, and 5 and 18 June 2008.

^y Means in a column followed by the same letter are not significantly different based on Fisher’s protected least significant difference (P ≤ 0.05) test.

Table 4. (cont’d) Turf quality of a ‘Providence’ creeping bentgrass research putting green in response to ethephon and trinexapac-ethyl (TE), 2008.

Treatment^y	No. of applica- tions^x	Quality (0-10; ≥ 7.0 acceptable)
Treatment^y	No. of applica- tions^x	4 Jul	11 Jul	18 Jul	25 Jul	1 Aug	8 Aug
Ethephon TE Ethephon + TE Ethephon Ethephon + TE Ethephon + TE Untreated	1 5 1 2 2 5 —	7.4 ab^y 8.3 a 7.4 ab 6.0 c 5.6 c 7.0 b 7.9 ab	7.3 b 9.1 a 7.5 b 6.1 c 6.1 c 7.4 b 8.7 a	7.9 ab 8.6 a 8.0 ab 6.6 c 6.6 c 7.1 bc 8.3 a	8.4 a 9.0 a 8.3 a 7.0 b 6.8 b 7.0 b 8.8 a	8.1 ab 9.1 a 8.6 a 7.0 bc 6.9 c 7.3 bc 9.1 a	8.8 ab 9.0 a 9.0 a 7.6 bc 7.5 c 7.5 c 8.9 a

^x Treatments were applied initially on 18 April; sequential treatments (2×) were applied 7 May; and multiple TE treatments (5×) were applied 18 April, 7 and 21 May, and 5 and 18 June 2008.

^y Means in a column followed by the same letter are not significantly different based on Fisher’s protected least significant difference (P ≤ 0.05) test.

Summary and Conclusions

Results of this study showed that two applications of ethephon alone or tank-mixed with TE resulted in significant scalping that persisted from 35 (2007) to 56 (2008) days. Scalping first became evident on a consistent basis between 37 (2008) and 38 (2007) days following the second application of ethephon. Close visual examination of plants revealed that ethephon had caused a distortion in normal shoot development as a result of abnormal elongation of the apical meristem of individual axillary buds. That is, normal shoots were replaced with what appeared to be upright stolons with nodes. A similar phenomenon was reported in Kentucky bluegrass following two spring applications of ethephon, but scalping was not detected until autumn (3). Results of the current study corroborate earlier observations that ethephon can elicit scalping in creeping bentgrass (16). Scalping was not promoted by one application of ethephon in 2007, but one ethephon application promoted scalping for a period of 21 days in 2008. Plots treated once with ethephon + TE did not reduce quality in 2007, but did reduce quality for about ten days in June 2008. Quality was reduced to a greater extent and for a longer period in plots treated twice with ethephon in 2008 versus 2007. In 2008, quality ratings from plots treated twice with ethephon + TE were reduced significantly and to unacceptable levels between 20 June and 1 August. Plots treated with ethephon + TE 5× (TE last applied 18 June) exhibited less scalping and improved quality compared to plots treated with ethephon twice on four dates between 13 June and 18 July 2008. Hence, data show that the additional applications of TE partially mitigated scalping induced by ethephon for a period of about 30 days following the last TE application. This supports other studies that have found that tank-mixing TE with ethephon can mitigate some of the objectionable effects of the PGR in creeping bentgrass and bermudagrass (7,12,14). To mitigate injury, data suggest that TE may need to be applied continuously on a two week interval for a period lasting about 90 days following the final application of ethephon. As previously noted, ethephon applied alone elicited a lime-green color in the bentgrass foliage for about two weeks, but chlorosis was not observed.

It was about 38 days following the second application before scalping elicited by ethephon had manifested itself and it appeared at the advent of summer (early June). Hence, scalp injury to greens treated twice with ethephon in spring is probably being attributed to other causes by the time it is observed by superintendents. According to R. Kane, Agronomist Chicago District Golf Association (personal communication), scalping has not been associated with ethephon use on creeping bentgrass greens in northern Illinois. Scalping and "puffy" creeping bentgrass were noted in an ethephon-treated research fairway in Indiana, but not a similar site in Wisconsin (16). Thus, scalping may be inconsistent depending on the site, weather and cultivar(s) grown. It also is important to note that our studies were initiated in April following 100% green-up of the turf. It is possible that the study may have yielded different results if ethephon had been applied earlier in spring when soil temperatures were lower or had the site been subject to PGRs for many years. Furthermore, this study was conducted on a research green where spoon-feeding of N and continued use of PGRs was not sustained throughout the study period, which also may have impacted results. McCullough et al. (13) reported that the application of water soluble N at 8 kg/ha on a weekly basis reduced the chlorosis induced by ethephon. Hence, future research should consider spoon-feeding N as well as higher rates and/or more frequent applications of TE to determine if they would better mitigate the deleterious effects of ethephon use in creeping bentgrass. Early spring applications of ethephon to greens with a history of PGR treatment also should be assessed. Results from the current study indicate that golf course superintendents should use ethephon with caution in creeping bentgrass since it can predispose putting green turf to significant and objectionable levels of injury. Superintendents also should be made aware that scalping induced by ethephon is a delayed response, which appeared many weeks after ethephon applications were initiated.

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