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Dep. of Horticulture, Forestry, and Recreation Resources, Kansas State Univ., Manhattan, KS 66506
* Corresponding author (jfry{at}oznet.ksu.edu)
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: PGR, Plant growth regulator • PLS, pure live seed
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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High water costs and increasing restrictions on its use have also encouraged superintendents to look for alternatives to perennial ryegrass for golf course use. Warm-season grasses have lower evapotranspiration rates and better drought resistance characteristics than perennial ryegrass (Huang and Fry, 1999). Zoysiagrass has been shown to have evapotranspiration rates 19% lower than perennial ryegrass under fairway conditions (Fry et al., 1992).
‘Meyer’ has traditionally been the zoysiagrass cultivar of choice, but it requires vegetative establishment by sodding, plugging, strip sodding, or sprigging (Beard, 2002). Solid sodding an entire 18-hole golf course is costly. Plugging and strip sodding into fallow ground can require more than two full growing seasons before complete zoysiagrass coverage results (Carroll et al., 1996; Dernoeden, 1991; Fry and Dernoeden, 1986). Attempts to establish Meyer vegetatively in existing perennial ryegrass fairways can require several years, even if turf is managed to favor zoysiagrass growth.
Research over the past few years has shown that seeded zoysiagrass may be a viable alternative to Meyer. Korean common zoysiagrass has been established from seed and used on golf course fairways (Portz and Patterozzi, 1985). However, one improved cultivar of particular interest is Zenith, which exhibited good quality in the 1996 National Turfgrass Evaluation Program trial and has excellent freezing resistance (Fry, 1999). Seeding a cultivar such as Zenith can also be accomplished at less than one-tenth the cost of sodding, which is attractive to golf course managers that may not have a large budget for capital expenditures.
It would also be advantageous if perennial ryegrass fairways and tees could be converted to zoysiagrass without removing the existing canopy. Sprigging or seeding zoysiagrass onto fallow ground usually requires that the golf course be closed for a significant amount of time and results in lost revenue. Meyer zoysiagrass has been sprigged into existing perennial ryegrass perennial ryegrass fairways, but this process is more expensive than seeding. Identification of one or more techniques for converting perennial ryegrass to seeded zoysiagrass without closing the golf course would be attractive to golf course managers.
Results from researchers that have conducted experiments to evaluate the conversion of one turfgrass species or cultivar to another indicate that it can be arduous. Efforts to convert ‘Penncross’ creeping bentgrass (Agrostis palustris Huds.) putting greens to the cultivar G-2 were futile unless glyphosate was employed (Kendrick and Danneberger, 2002). Establishing Kentucky bluegrass (Poa pratensis L.) seedlings in a mature stand of perennial ryegrass was unsuccessful unless a high seeding rate (196 kg ha–1) was employed in combination with suppressing the perennial ryegrass by scalping the first few weeks after seeding (Kraft et al., 2004).
There is little information regarding factors that may influence the establishment of seeded zoysiagrass in an existing stand of perennial ryegrass. Our objective was to evaluate the influence of perennial ryegrass treatments, including the use of PGRs, scalping, and glyphosate, with and without traffic, for their effects on establishment of seeded Zenith zoysiagrass.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Before seeding, study areas were core-aerified and verticut. Cores were pulled on 10-cm centers and measured 1.2 cm in diam. and 1.3 to 3.8 cm deep. After aerification, a verticutter with blades on a 9.5-cm spacing was used in two directions over each study area to break up cores and create 3-mm-deep slices in the soil surface.
Zenith zoysiagrass was seeded to provide PLS at 42 kg ha–1 (unless otherwise described below). Pure live seed was calculated from label information. Seed was applied using 946 mL shaker jars containing 61 g of a 6-2-0 (N-P-K) activated sewage sludge (Milorganite, Milwaukee, WI) as a seed carrier, which provided N at 12 kg ha–1. After seeding, siduron [N- (2-methylcyclohexyl)-N-phenylurea] was applied at 5.6 kg a.i. ha–1 for preemergence weed control, and a w12-30-7 (N-P-K) fertilizer was mixed with the siduron to deliver N at 18 kg ha–1.
From 1999 to 2002, average high and low weekly air temperatures were recorded between May and October with a weather station situated with 20 m of each of the study areas (Fig. 1).
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Zenith zoysiagrass was seeded on 18 June 1999 into perennial ryegrass subplots that were treated as follows: (i) untreated (control); (ii) glyphosate applied on 8 June 1999 at 3.4 kg a.i. ha–1; (iii) scalping the perennial ryegrass seedbed three times weekly at 0.6 cm (scalping continued until zoysiagrass tillering was observed on 7 Aug. 1999); (iv) the PGR mefluidide [N-[2,4-dimethyl-5-[[(trifluoromethyl) sulfonyl] aminophenyl]acetamide] applied on 15 June 1999 at 0.14 kg a.i. ha–1; (v) the PGR trinexapac-ethyl [4-(cyclopropyl-
-hydroxy-methylene)-3,5-dioxo-cyclohexane-carboxylic acid ethyl ester] applied on 15 June 1999 at 0.42 kg a.i. ha–1; and (vi) trinexapac-ethyl plus scalping (as previously described). Plant growth regulators were applied in 401 L water ha–1 with a CO2 sprayer at 241 kPa of pressure. Irrigation was applied through a hose-end sprinkler two to three times daily for the first 4 wk after seeding in 1999 to provide 2 mm of water in each session. On 18 July, irrigation was applied twice daily to provide 3 mm of water in each session. Beginning on 31 August, irrigation was applied only to prevent zoysiagrass wilt.
Turf was mowed at a 1.4-cm height three times weekly. Scalping treatments were mowed at 0.64 cm three times weekly until zoysiagrass tillering occurred, at which time mowing height was returned to 1.4 cm.
Urea (46-0-0) was applied to Study I to provide N at 49 kg ha–1 on 12 July 1999; 15 June and 20 July 2000; and 3 May and 29 June 2001. A single application of N at 73 kg ha–1 was also made on 9 Aug. 1999.
The following broadleaf herbicides were applied to all treatment plots with a Terra Master 160 boom sprayer (Broyhill Co., Dakota City, NE) at 138 kPa and 561 L water ha–1: 2,4-D (2, 4-dichlorophenoxyacetic acid, 1.1 kg a.i. ha–1) + mecoprop (dimethylamine salt of 2-(2-methyl-4-chlorophenoxy) propionic acid, 0.3 kg a.i. ha–1) + dicamba (3, 6-dichloro-o-anisic acid, 0.1 kg a.i ha–1) on 1 May and 22 Oct. 1999; 13 March and 24 Nov. 2000; 11 May and 3 Nov. 2001; and 30 March and 10 Nov. 2002. For preemergence control of grassy weeds, dithiopyr [3,5-pyridinedicarbothioic acid, 2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluormethyl)-S, S-dimethyl ester] was applied at 0.25 kg a.i. ha–1 on 11 May 2001. Prodiamine [N3, N3–di-n-propyl-2, 4-dinitro-6-(trifluoromethyl)-m-phenylenediamine] was applied at 1 kg a.i. ha–1 on 13 March 2000 and 30 March 2002.
Study II (2000–2002)
Relative to Study I, the traffic and PGR treatments were eliminated and two seedbed stripping treatments were added. Plots measuring 1.22 x 2.13 m were arranged in a randomized complete block design with nine replications. Perennial ryegrass plots subjected to the following sub-plot treatments were seeded with Zenith zoysiagrass on 10 June, 2000 as described in Study I: (i) untreated; (ii) glyphosate applied on 23 May 2000, as in Study I; (iii) three glyphosate-treated seeding strips per plot (each strip measuring 7.62 cm x 2.13 m spaced 33 cm apart); (iv) six glyphosate-treated seeding strips per plot (each strip measuring 7.62 cm x 2.13 m spaced 13 cm apart); and (v) scalping the perennial ryegrass seedbed (as described for Study I).
To initiate the perennial ryegrass strip-seeding treatments, 1.22 x 2.13 m plywood templates, with cut outs to provide the aforementioned strips, were placed over respective plots and treated with glyphosate (as described for Study I). After glyphosate dried, six 0.6-cm-deep grooves were cut in the soil the entire length of each template strip with a three-pronged hand-held garden trowel. Zenith zoysiagrass (as described for Study I) was seeded in each strip at 84 kg ha–1 with 946 mL shaker jars containing a handful of dry sand as a seed carrier. A stainless steel tube (10.2 x.4 cm) was installed through the lid of each jar so the seed could be applied directly into each seeding groove.
After seeding in 2000, irrigation was applied through a hose-end sprinkler four times daily during the first 4 wk to provide 2 mm of water in each session. On 12 July, irrigation was applied twice daily with an automated system to provide 3 mm of water in each session. Beginning on 18 August, irrigation was applied only to prevent zoysiagrass wilt.
Urea (46-0-0) was applied to provide N at 49 kg ha–1 on 15 June and 20 July 2000; 3 May and 29 June 2001; and 4 April and 21 Aug. 2002. The same herbicide treatments described under Study I were used for broadleaf and grassy weed control in Study II with the exception of the prodiamine application on 13 March, 2000.
Data Collection and Analysis
Data were collected on zoysiagrass seedling emergence (Study I only), coverage, and turfgrass quality. On 8 Aug. 1999, percent germination was determined in each seedbed treatment in Study I. The number of seedlings was counted within a 10- x 10-cm template that was randomly tossed three times per plot, and percentage emergence was calculated by dividing this number by the number of PLS that had been applied and multiplying by 100.
Zoysiagrass coverage was measured in September or October of each year in each study using a vertical point quadrant described by Gaussoin and Branham (1989). The vertical point quadrant was constructed of a polyvinylchloride (PVC) frame with an internal monofilament grid spaced on 100-mm centers. The grid was placed over each plot to estimate zoysiagrass coverage. The presence of any part of a zoysiagrass seedling under an intersection was recorded as a hit. To determine percent coverage, the number of hits was divided by the number of intersections on the grid and multiplied by 100.
Turfgrass quality was rated on a 0-to-9 scale, where 0 = dead turf; 5 = acceptable quality for a golf course fairway or tee; and 9 = optimum density, color, and uniformity. A quality rating was assigned to the treated plot as a whole, without regard to the predominant species present. Quality was rated weekly throughout each study, and data are presented as monthly means.
Data from each study were analyzed separately because of different experimental designs and environmental conditions. The analysis of variance procedure in Statistical Analysis Systems (SAS, 2000) was used to test for treatment effects. Means were separated by Tukey's least significant difference test when a significant (P 
0.05) difference occurred.
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RESULTS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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0.05) traffic x treatment interaction was observed for zoysiagrass seedling emergence in 1999. Fewer seedlings were counted where traffic had been imposed, regardless of seedbed treatment (Table 1). More zoysiagrass seedlings were counted where nontrafficked perennial ryegrass had been treated with glyphosate or subjected to post-seeding scalping. Seedling counts indicated that 13% of the PLS applied had produced a seedling in the glyphosate-treated, nontrafficked perennial ryegrass.
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0.05) traffic x seedbed interaction was observed for zoysiagrass coverage, reflecting the same response as described above for germination. Trafficking treatments reduced zoysiagrass coverage in all seedbed treatments in each year when compared with nontrafficked turf (Table 2). Glyphosate-treated perennial ryegrass exhibited higher coverage ratings than all other treatments at the end of each study year. At the end of the first growing season, 75% zoysiagrass coverage was observed in nontrafficked, glyphosate-treated perennial ryegrass, and plots were completely covered by October of the second year.
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Quality
A significant (P 0.05) traffic x seedbed treatment interaction was observed for turfgrass quality. This resulted because the quality of glyphosate-treated, trafficked turf remained low through Years 2 and 3; whereas, in nontrafficked turf, increasing zoysiagrass coverage resulted in higher quality ratings in 2000 and 2001 (Table 3).
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Perennial ryegrass scalped or receiving trinexapac-ethyl + scalping at the time of establishment exhibited acceptable quality beginning in September 1999 and through the remainder of 2000 and 2001 (Table 3). Quality of turf in trinexapac-ethyl and mefluidide-treated perennial ryegrass was generally acceptable throughout the 3-yr period, with the exception of August and September 2000, when summer stresses caused a general decline in quality.
Study II (2000–2002)
Zoysiagrass Coverage
At the end of 2000, 84% zoysiagrass coverage was observed in glyphosate-treated perennial ryegrass (Table 4). Coverage in other treatments ranged from 1 to 9%, but none of the treatments were statistically different from one another.
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By October 2002, zoysiagrass coverage in strip-seeded treatments was >70% (Table 4). Perennial ryegrass scalped at the time of establishment had 40% zoysiagrass coverage, which was significantly more than the untreated perennial ryegrass.
Quality
Through August 2000, ranking of treatments for turf quality was generally untreated control > glyphosate (3 strips) > glyphosate (6 strips) = scalped (Table 5). By September 2000, progressive zoysiagrass establishment resulted in quality of glyphosate-treated perennial ryegrass having higher visual scores than all other treatments. By September, perennial ryegrass quality was significantly reduced by heat and moisture stress since plots were now managed to favor zoysiagrass growth.
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DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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The PGRs evaluated in Study I were ineffective in promoting zoysiagrass conversion because they did not provide a level of perennial ryegrass suppression that would allow zoysiagrass seedlings to emerge and compete with the existing stand. Although PGRs were evaluated only in Study I, our results, and those of other researchers who observed nominal effects of PGRs on turfgrass conversion (Fry and Dernoeden, 1986; Kraft et al., 2004), convinced us that more aggressive perennial ryegrass seedbed treatments were required to successfully establish seeded zoysiagrass. Fry and Dernoeden (1986) reported that Meyer zoysiagrass spread from plugs introduced into a stand of perennial ryegrass maintained at 4.4 cm was not affected by PGRs applied the first year. By the end of the second season in that test, mefluidide had enhanced zoysiagrass coverage by about 9% compared with nontreated turf. The increased zoysiagrass spread the second year was attributed to phytotoxicity that occurred after mefluidide application, as well as turf decline due to summer stresses.
Kraft et al. (2004) found that mefluidide enhanced Kentucky bluegrass establishment by about 13% 6 mo after seeding in September at 196 kg ha–1 into an existing perennial ryegrass canopy. However, at 21 mo after seeding, mefluidide-treated perennial ryegrass exhibited similar Kentucky bluegrass levels as nontreated turf.
Zoysiagrass emergence in glyphosate-treated, nontrafficked perennial ryegrass was superior to that in all other treatments in Study I. However, only 13% of the PLS applied resulted in seedlings. Although glyphosate applications provided complete eradication of existing perennial ryegrass, plant residue in glyphosate-treated plots may have prevented the level of seed-to-soil contact needed for better seedling establishment to occur (Marshall and Naylor, 1984). Perennial ryegrass leaves and roots have also been shown to be allelopathic to germination and growth of zoysiagrass seedlings (Zuk and Fry, 2002). We used seed that was less than 1 yr old, and relied on label information in calculating PLS. Since this experiment, however, we have observed some variability between label-stated germination levels and actual levels measured in a controlled environment. If a lower level of germination than stated on the label occurred in the lot of seed we employed, our seeding rate may have been lower than 42 kg PLS ha–1, and contributed to the relatively low level of zoysiagrass seed emergence observed in glyphosate-treated perennial ryegrass.
The superior zoysiagrass seedling emergence in glyphosate-treated perennial ryegrass also resulted in 75% (Study I) and 84% (Study II) coverage by October of the first year of establishment. Patton et al. (2004) observed nearly complete Zenith zoysiagrass coverage four months after seeding at 49 to 146 kg ha–1 into glyphosate-treated turf compared with 1% coverage in untreated turf. In our test, glyphosate-treated turf had the lowest quality scores throughout the first season of establishment because of loss of the perennial ryegrass sward. Quality reductions such as these may lead golf course managers to close the golf course to play during the establishment period.
Scalping the existing perennial ryegrass stand at 0.6 cm for the first 7 wk after seeding resulted in 15 times more zoysiagrass seedlings than counted in the untreated control in Study I (Table 1). Zoysiagrass coverage in scalped perennial ryegrass by October of the third season of establishment was 75% in Study I and 40% in Study II. Scalping perennial ryegrass resulted in an initial reduction in turf quality of up to 5 points compared with untreated turf in our test, which would affect the golfer's perception of the course and would likely reduce play should the course remain open. Perennial ryegrass fully recovered after scalping treatments ceased. Although the mower may have had deleterious effects on zoysiagrass seedlings because of soil compaction stress, seedlings were not mown during the process because scalping ceased before seedlings reached the 0.6-cm height.
Evaluation of irradiance and soil temperatures under a perennial ryegrass canopy has indicated that scalping perennial ryegrass as performed herein results in approximately 35% shade exposure of zoysiagrass seedlings, and seedlings under an untreated, 1.4-cm-tall canopy are exposed to approximately 75% shade (Zuk et al., 2005). In a parallel experiment, zoysiagrass seedling emergence, and shoot and root growth, declined dramatically between 40 and 85% shade when established on bare soil (Zuk et al., 2005). Soil temperatures were also lower underneath shaded plots in that study, and in conjunction with reduced light levels, greatly reduce zoysiagrass vigor and competitive ability.
Scalping also reduced competitiveness and vigor of the perennial ryegrass. Even seedling perennial ryegrass is quite competitive and slower germinating species are not able to compete well if too much perennial ryegrass is included in a seed mixture (Fry and Huang, 2004). Hence, the likelihood of individual zoysiagrass seedlings surviving and competing after germination in established perennial ryegrass was low. Scalping was also shown to promote conversion of an established perennial ryegrass turf to Kentucky bluegrass in Kansas (Kraft et al., 2004). In that test, scalping a 1.2-cm-tall, mefluidide-treated perennial ryegrass turf at 0.6 cm twice weekly for 4 wk after sowing primed Kentucky bluegrass seed at 2 kg PLS 100 m–2 into the canopy resulted in 15% coverage 6 mo after seeding; only 9% coverage occurred in the untreated control.
This was the first reported field evaluation of a strip-seeding technique for converting perennial ryegrass to seeded zoysiagrass. The technique eliminates perennial ryegrass competition in a localized area and is not so destructive to the turf stand as to prevent golf from continuing. Seeding zoysiagrass into 7.6-cm-wide glyphosate-treated strips, spaced 33 cm apart, resulted in 5% zoysiagrass coverage the first year, 52% coverage by the end of the second year, and 73% coverage by the end of the third year. Even though seeded strips received twice the PLS as that applied to plots in other treatments (84 vs. 42 kg ha–1), total seed savings using strips on a 33-cm spacing amounted to 63% compared with a broadcast application. Zoysiagrass coverage was not significantly greater where the narrower (13 cm) spacing vs. wider (33 cm) spacing was used in this evaluation. We surmise that this was due to variability in the data; faster coverage would usually be expected if more strips were used per unit area.
Reduction in turf quality using the strip seeding technique for the initial and subsequent years was due to nonuniformity resulting from glyphosate-treated strips initially, and then by the zoysiagrass that became established in the strips. The strips were not noticeable in midsummer, but were clearly visible in autumn and early spring when the zoysiagrass was dormant. Nevertheless, quality reductions in plots where rows were placed 33 cm apart had superior quality to scalped perennial ryegrass during the first year. This technique could be implemented while the golf course remained open for play.
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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Received for publication April 30, 2004.
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REFERENCES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
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seed germination in Study I in response to seedbed treatment x traffic interaction imposed on a perennial ryegrass sward at Manhattan, KS, in 1999.