Strategy and Rate Affects Success of Perennial Ryegrass Overseeding into Bermudagrass Athletic Fields Located on the North Edge of the Transition Zone

B. F. Bornino, Graduate Assistant Sports Turf Manager, Department of Intercollegiate Athletics, C. A. Bigelow, Associate Professor, Department of Agronomy, and Z. J. Reicher, Professor, Department of Agronomy, Purdue University, West Lafayette, IN 47907-2054

Corresponding author: Z. J. Reicher. zreicher@purdue.edu

Abstract

Bermudagrass (Cynodon dactylon L.) is used on athletic fields farther north than previously and field managers routinely overseed bermudagrass with perennial ryegrass (Lolium perenne L.) (PRG) to improve color and wear tolerance during late fall use. Our objectives were to determine optimum PRG seeding rates and strategies for overseeding bermudagrass athletic fields on the north edge of the transition zone. Our factorial treatment arrangement included five seeding rates (610, 1220, 2440, 3660, and 4880 kg/ha/year pure live seed and three strategies including applying 100% of the seed in one application (100), 70% of total seed in the initial application plus 10% of total seed in each of three successive applications ten days apart (70/10/10/10), or four equal applications of 25% of the total seed applied ten days apart (25/25/25/25). Perennial ryegrass coverage rarely increased at seeding rates higher than 2440 kg/ha/year regardless of location, seeding strategy, or rating date. The seeding strategy of 25/25/25/25 consistently produced the most PRG coverage, nearly 20% greater than that from the 70/10/10/10 and nearly 50% greater than that from the 100 strategy. Therefore, we recommend seeding a total of 2440 kg/ha/year in four equal applications ten days apart to maximize perennial ryegrass overseeding coverage on bermudagrass athletic fields in the northern transition zone.

Introduction

Bermudagrass is widely used in southern and transitional zones of the United States for athletic fields. Popularity of bermudagrass is due to its recuperative potential via aggressive stolons and rhizomes (8) and tolerance to heat, drought, and low (≤ 2.5 cm) mowing (4). With improved cold hardiness in seeded and vegetative cultivars (17), bermudagrass has been pushed to the northern edge of the transition zone. A major drawback of use in more northern latitudes is extended dormancy and straw-brown appearance of bermudagrass that can last from first frost in fall until soil temperatures at 10 cm rise above 10°C (13), usually late May to early June in the transition zone. To overcome this, turf managers routinely overseed bermudagrass athletic fields with the cool-season perennial ryegrass (PRG) in late summer/early fall to achieve year-round color and improved aesthetic quality. Although dormant bermudagrass can withstand considerable traffic, overseeding can improve resiliency and performance under intense use (13,16,18).

Overseeding bermudagrass with PRG also has disadvantages. From an agronomic standpoint, winter overseeding effectually is growing two types of plants with different management requirements in the same location (6). Perennial ryegrass out-competes the dormant bermudagrass for light, nutrients and water throughout the fall, winter and transition period in spring (2). Another potential disadvantage is scheduling overseeding within the optimum planting window will usually interfere with play on the field. Overseeding too early in fall reduces establishment of the overseeded species because of bermudagrass competition with seedlings, whereas overseeding too late hampers establishment because of reduced germination and seedling development in suboptimal temperatures (19).

Recommendations for overseeding rates of PRG are highly variable and range from 340 to 1120 kg/ha/year on golf course fairways (5,6,9,16), from 1000 to 2000 kg/ha/year on golf course greens (7,11,12), and from 300 to 730 kg/ha/year on southern athletic turf (14,18). Furthermore, Minner et al. (15) and Watschke & Schmidt (24) state that sports turf managers tend to seed at excessive rates (up to 4 times the recommended seeding rate) on trafficked areas, which can reduce tolerance to disease (10,20) or wear (3). While several studies have evaluated the effect of seeding rates when planted on a single date, little research has been conducted evaluating the impact of multiple overseeding events into bermudagrass turf. On a cool-season athletic field subject to heavy traffic, Minner et al. (15) reported that a single seeding of PRG on a bare soil resulted in more coverage than did multiple seedings. Conversely, Rossi (21) reported that 98 to 490 kg PRG/ha seeded weekly into a heavily trafficked cool-season athletic field maintained density and limited weed invasion. Our objectives were to determine optimum PRG seeding rates for overseeding bermudagrass athletic fields in the northern transition zone and determine if multiple seeding events improved overall PRG establishment compared to a single seeding event.

Investigating Overseeding Ryegrass into Bermudagrass

Our field study was conducted at two locations at Purdue University in West Lafayette, IN, which is in USDA Hardiness Zone 5a, approximately 350 km north of zone 6a and 6b which could be considered the transition zone between cool- and warm-season turfgrass adaptability (23). The first location was at the W. H. Daniel Turfgrass Research and Diagnostic Center (DANL) on untrafficked ‘Patriot’ bermudagrass (Cynodon dactylon × C. transvaalensis) on native soil [Mahalasville-Treaty silty clay loam (fine-silty, mixed, mesic Typic Argiaquolls)] with soil test values of 203 kg P/ha, 575 kg K/ha, and a pH of 7.4. This stand of bermudagrass was sprigged in June of 2006 and was not overseeded with perennial ryegrass at any time prior to the study. The second location was the south football practice field (SPRAC) where the Purdue University varsity football team practiced four times per week from August to November. This field was originally sodded with ‘Patriot’ bermudagrass in June 2006 and subsequently overseeded with ‘Riviera’ bermudagrass in May 2007 after approximately 70% turf loss from winterkill. This site was overseeded with perennial ryegrass in fall 2007, but was void of overseeded ryegrass at the initiation of our study. The rootzone at this site was a silt-loam modified using a QwikDrain sand-slit bypass system on 51-cm centers and capped with 3 to 5 cm medium-coarse calcareous sand (GreenOne Industries, Sedalia, CO 80135). Soil test levels on this area were 169 kg P/ha, 220 kg K/ha, and a pH of 7.7 in 2007 and 142 kg P/ha, 103 kg K/ha, and a pH of 7.6 in 2008. Experiments were located in areas of moderate traffic on this site, and bermudagrass stands on both sites were fully established and dense prior to overseeding each year. A randomized complete block design with three replications was used at each location and plot size was 1.5 m × 1.5 m. Treatments were a 3 × 5 factorial with three application strategies and five seeding rates. Seeding rates were 610, 1220, 2440, 3660, and 4880 kg/ha/year pure live seed. Application strategies included applying 100% of total seed in one application (100), 70% of total seed in the initial application plus 10% of total in each of three successive applications ten days apart (70/10/10/10), or 25% of the total seed applied in four events applied on ten day intervals (25/25/25/25). Plots were seeded using a PRG blend (49% ‘SR4550,’ 29% ‘Penguin,’ and 19% ‘Hawkeye’) which is regularly used by the Purdue University Athletic Department. Prior to seeding, a flexible steel drag mat commonly used for baseball infields was used to disrupt the bermudagrass canopy and seed was applied to each plot by hand. Initial seeding dates for both locations were 24 August 2007 and 25 August 2008. Plots were topdressed to approximately 3 mm deep after each seeding with locally available medium-coarse calcareous sand (Shelby Materials, Shelbyville, IN) using a 1-m wide drop spreader. Topdressing sand was manually brushed into the turf canopy with a stiff bristled push broom and plots were fertilized with a starter fertilizer (16-28-10) at 49 kg P₂O₅/ha at the initial seeding.

Site maintenance. Both sites were in full-sun and under management typical for football practice fields. Irrigation was used throughout the fall to supplement rainfall and promote PRG germination. Plots were mowed at 2.5 cm with a triplex reel mower three days per week with clippings returned. Two applications of a 25-5-15 fertilizer containing 10% polymer-coated sulfur-coated urea were applied at 49 kg N/ha on 2 September and 7 October in both years of the study. Propamocarb was applied at 41 kg a.i./ha to control Pythium blight (Pythium spp.) on 4 and 17 September 2007 and 2 September 2008. Glyphosate at 1.1 kg ai/ha was used in early March of each year to kill the overseeded ryegrass and facilitate rating winterkill damage to bermudagrass.

Visual measurements and analysis. Percent PRG coverage was visually rated on a 0 to 100 % scale with 0 = no visible PRG and 100 = complete coverage. Plots were rated weekly beginning 31 August 2007 or 1 September 2008 through the end of the football practice season on 12 November 2007 or 2008 and we report percent PRG coverage every two to three weeks during the growing season. For the 17 September rating date, only the 100 strategy at all five seeding rates was analyzed because seed from the other two strategies was not completely applied by this time. Data were were arcsined transformed and analyzed over years within location because error variances were homogenous. Data were analyzed with PROC ANOVA (Version 9.1, SAS Institute Inc., Cary, NC), means were separated with LSD at P ≤ 0.05, and backtransformed means are presented.

Overseeding Effects on an Untrafficked Turf at the Daniel Center

Averaged over years, PRG coverage on 17 September increased with seeding rate and a single application of ≥ 3660 kg/ha/year or higher resulted in ≥ 83% coverage of PRG (Table 1). Overseeding at 2440 kg/ha/year provided 69% PRG coverage by 7 October and 54% coverage on 12 November when averaged over strategies and years, which was equivalent to seeding rates ≥ 3660 kg/ha/year (Table 2). On the 22 October rating date, 4880 kg/ha/year resulted in 65% PRG cover, which was equivalent to 3660 kg/ha/year at 62% coverage and slightly more than 2240 kg/ha/year at 57% coverage (Table 2). Averaged over seeding rate and years, 25/25/25/25 produced the most PRG coverage on all rating dates in October and November while the 100 strategy produced the lowest coverage (Table 2). A year × strategy interaction occurred on the 12 November rating where all strategies produced equivalent coverage in 2007, but 25/25/25/25 produced 69% coverage in 2008, which was 13% more than 70/10/10/10 and 22% more than 100 (Table 3).

Table 1. Perennial ryegrass coverage on 17 September from a single overseeding event at five rates on bermudagrass at W. H. Daniel
Turfgrass Research and Diagnostic Center (DANL) and south varsity
football practice field (SPRAC).

		DANL^w	SPRAC^v
		DANL^w	2007	2008
		Coverage (%)
Seed rate (kg/ha/year)^x	610	26 d^y	30 ab	33 c
	1220	44 c	25 b	43 c
	2440	70 b	43 a	60 b
	3660	83 ab	30 ab	88 a
	4880	88 a	28 ab	92 a
ANOVA	Year (Y)	NS^z	−	−
	Rate (R)	**^z	**	**
	Y × R	NS	−	−

^v SPRAC means are over three replications.

^w DANL means are over two years and three replications per year.

^x A perennial ryegrass blend (49% ‘SR4550,’ 29% ‘Penguin,’ and 19% ‘Hawkeye’) was initially seeded on 24 August 2007 or 25 August 2008.

^y Means are back-transformed and means in the same column followed
by the same letter are not significantly different with LSD P ≤ 0.05.

^z ** = significant at P ≤ 0.01, and NS =non significant.

Table 2. Perennial ryegrass coverage on overseeded bermudagrass as affected by five seeding rates and three application strategies at the W. H. Daniel Turf Research and Diagnostic Center (DANL) and south varsity football practice field (SPRAC).

		DANL			SPRAC
		7 Oct	22 Oct	12 Nov	7 Oct	22 Oct	12 Nov
		% cover
Seed rate (kg/ha/ year)^u	610	44^vw	41 d	29 c	27 c	26 c	31 b
	1220	52 b	51 c	43 b	34 b	38 bc	41 ab
	2440	69 a	57 bc	54 a	44 ab	53 ab	49 a
	3660	74 a	62 ab	61 a	53 a	56 a	51 a
	4880	75 a	66 a	62 a	54 a	59 a	52 a
Strategy^v	100	56 b^y	43 c	43 b	32 b	29 c	29 c
	70/10/10/10	62 b	54 b	50 a	38 b	46 b	47 b
	25/25/25/25	70 a	70 a	57 a	58 a	63 a	59 a
ANOVA^x	Year (Y)	NS^z	**	NS	*	*	NS
	Rate (R )	**	**	**	**	**	**
	Strategy (S)	**	**	**	**	**	*
	R × S	NS	NS	NS	NS	NS	NS
	Y × R	NS	NS	NS	NS	NS	NS
	Y × S	NS	NS	**	NS	**	**
	Y × R × S	NS	NS	NS	NS	NS	NS

^u A perennial ryegrass blend (49% ‘SR4550,’ 29% ‘Penguin,’ and 19% ‘Hawkeye’) was initially seeded on 24 August 2007 or 25 August 2008.

^v Seed rate means are over three strategies, two years and three replications per year.

^w Means are back-transformed and means in the same column followed by the same letter are not significantly different with LSD P ≤ 0.05.

^x Application strategies were: 100% of total seed in one application (100), 70% of total seed in the initial application plus 10% of total in each of three successive applications ten days apart (70/10/10/10), or 25% of the total seed applied in four events applied on ten day intervals (25/25/25/25).

^y Strategy means are over five seeding rates, two years and three replications per year.

^z NS = non significant, * = significant at P ≤ 0.01, ** = significant at P ≤ 0.05.

Table 3. Perennial ryegrass late-season coverage as affected by three application strategies on overseeded bermudagrass at W. H. Daniel Turf Research and Diagnostic Center (DANL) and south football practice field (SPRAC).

Strategy^x	DANL		SPRAC
	12 Nov		22 Oct		12 Nov
	2007	2008	2007	2008	2007	2008
	% cover
100	38 a^yz	47 c	44 c	14 c	37 c	20 c
25/25/25/25	45 a	69 a	62 a	64 a	56 a	62 a
70/10/10/10	44 a	56 b	52 b	40 b	47 b	46 b

^x Application strategies included 100% of total seed in one application (100), 70% of total seed in the initial application plus 10% of total in each of three successive applications ten days apart (70/30/30/30), or 25% of the total seed applied in four events applied on ten day intervals (25/25/25/25). A perennial ryegrass blend (49% ‘SR4550,’ 29% ‘Penguin,’ and 19% ‘Hawkeye’) was initially seeded on 24 or 25 August in 2007 or 2008 at 610, 1220, 2440, 3660, or 4880 kg/ha/year pure live seed (PLS).

^y Means are over five seeding rates, two years and three replications per year.

^z Means are back-transformed and means in the same column followed by the same letter are not significantly different with LSD P ≤ 0.05.

Overseeding Effects on the Trafficked Varsity South Practice Field

In September 2007, there was no increase in PRG coverage with seeding rates higher than 2440 kg/ha/year when applied in a single application (Table 1). This was primarily attributed to seedling loss due to a Pythium blight outbreak in early September 2007 during unseasonable high temperatures and humidity. Even though fungicide applications were made immediately after damage was noticed, significant Pythium damage occurred in seeding rate treatments ≥ 2440 kg/ha/year. This observation is consistent with previous studies where supraoptimal seed rates were used (11,23,24). Preventative control of Pythium is likely less important with the multiple seeding strategies compared to the 100 strategy because ensuing seedings could compensate for turf lost in the initial seeding. Weather was more moderate in 2008 and Pythium blight was minimized with a single fungicide application. Seeding once at ≥ 3660 kg/ha/year produced the most PRG coverage (≥ 88%) on 17 September followed by 2440 kg/ha/year at 60% coverage (Table 1). However, 610 or 1220 kg/ha/year produced only 33% and 43% PRG coverage in 2008, respectively (Table 1).

Overseeding rates of 3660 or 4880 kg/ha/year resulted in PRG coverage equivalent to 2440 kg/ha/year by 7 and 22 October when averaged over strategy and year, but higher than the 610 or 1220 kg/ha/year seeding rates (Table 2). By 12 November, 2440 kg/ha/year or higher resulted in more PRG coverage (49 to 52%) than 610 kg/ha/year (31%) when averaged over strategy and year. Averaged over seeding rate and year at SPRAC, the 25/25/25/25 strategy resulted in the most PRG coverage throughout the experiments, ≥ 11% more than 70/10/10/10 and ≥ 25% more than 100 on all rating dates (Table 3). In 2007, 25/25/25/25 provided 62% PRG coverage by 22 October, followed by 70/10/10/10 at 52%, and 100 at 44% coverage (Table 3). By 12 November 2008, 25/25/25/25 resulted in PRG coverage 16% greater than 70/10/10/10 and over 40% greater than the 100 strategy (Table 3). This contradicts findings of Minner et al. (15) where a single PRG seeding event prior to the playing season increased turf coverage compared to seven successive weekly seedings. They attributed the success of the single seeding to seeding at the optimum timing for Iowa (1 or 3 September) versus seeding up to six weeks later (mid-October) for the multiple seedings. However, our initial seeding date was one week earlier than theirs and our final seeding dates were 23 or 24 September, which would be at the end of an acceptable PRG seeding window in Indiana.

Overseeding rates and strategies in our study resulted in PRG coverage as high as 79% by November, but coverage often was only 50 to 60% in the best performing plots. Though this amount of coverage would be visually acceptable for spectators, it may appear thin to coaches and players on the field. With the current preference for planting the improved dense and winter-hardy bermudagrass cultivars, achieving high PRG overseeding coverage may not be practical. Askew et al. (1) reported that dense bermudagrass cultivars such as Patriot and Riviera are difficult to overseed successfully with only 20 to 40% PRG coverage when seeded once into fairway height turf at 336 and 672 kg/ha/year in their study.

Though winterkill of bermudagrass is a concern as it is used farther north, no winterkill of bermudagrass occurred in either spring of our study and thus it remains to be seen if our seeding rates or strategies affect bermudagrass winter survival. No anecdotal differences in spring green-up were observed, but green-up data were not recorded. Future research should evaluate effect of seeding rate and strategy on spring green-up and winterkill of bermudagrass planted on the northern edge of the transition zone.

Recommendations

Four equal applications of 25% of the total annual seeding rate applied every 10 days resulted in the most PRG coverage throughout this study, followed by 70/10/10/10 and 100, respectively. Little increase in PRG coverage was gained from seeding rates higher than 2440 kg/ha/year. The 610 kg/ha/year seeding rate consistently produced the lowest coverage in this study and would not be recommended, but 1220 kg/ha/year was occasionally in the top statistical grouping for PRG coverage in this study. We recommend seeding a total of 2440 kg/ha/year in four equal applications ten days apart to maximize PRG overseeding coverage on bermudagrass athletic fields in the far northern transition zone.

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