May 2022 | Michael A. Fidanza, Ph.D.; Christian M. Baldwin, Ph.D.; Matthew Koch, Ph.D.; S. Lucas Freshour; and Robert Harriman, Ph.D.

Filed to: Kentucky bluegrass, Greens mowing

Figure 1. Overview of the “POGO” turfgrass canopy height measuring tool. Photo by S. Lucas Freshour

The foundation of a successful turfgrass management program is the implementation of three agronomic cultural practices: nutrition, water and mowing. While each cultural practice is vital to optimize turfgrass health, mowing is perhaps the most impactful and most labor-intensive. In a recent golf course management survey, labor was identified as one of the golf industry’s biggest challenges, with 74% of respondents indicating equipment operators were the most difficult labor to retain (4). Despite the need to identify grasses that require less mowing that can help ease labor requirements, limited research exists on documenting the genetic diversity of turfgrass cultivar mowing requirements.

Specific to Kentucky bluegrass (Poa pratensis L.), cultivars are generally categorized within large groups or types as medium, low growth (BVMG) or low and compact growth (Compact America/Midnight) (1). Although current Kentucky bluegrass cultivars are categorized in existing groups based on growth habit, new genetically modified Kentucky bluegrass cultivars with a dwarf growth habit have been developed and branded under the name Scotts ProVista (PV). Specifically, the transformation in PV is described as an overexpression of the gibberellin (GA) 2-oxidase that reduces functional GA levels in the plant resulting in a dwarf phenotype (3). However, the extent to which this overexpression translates to a reduction in mowing in the field is unknown.

Given the new innovation in turfgrass genetics (3), labor challenges in the golf course industry, and the lack of relevant information on an important aspect of turfgrass management (mowing requirements), the primary objective of this research was to quantify the required number of mowing events of PV and various turfgrass species all maintained at a height of 3.0 inches (7.6 centimeters).

Table 1. Mowing requirements and frequency of required mowing (days) of Pro Vista Kentucky bluegrass cultivars, conventional Kentucky bluegrass cultivars and blends, conventional fescue cultivars and blends, and species mixtures at Penn State University (Reading, Pa.) in 2018 and 2019.

a. A mowing event was considered a requirement if a plot exceeded the one-third mowing rule. For example, each plot was mowed to 3 inches; therefore, if a plot height reached or exceeded 4.5 inches, this triggered a mowing event.

b. Mowing events were quantified from May 7 to Nov. 14, 2018, and May 6 to Nov. 8, 2019.

c. Days between required mows is based on the one-third mowing rule calculated as total number of days/total yearly mowing requirement. *Cultivars selected using the multiple comparison with the best (MCB) procedure, with p=0.95 that the “best” cultivar has been selected.

KBG1: Kentucky bluegrass blend — 14.6% Right, 14.6% Abbey, 12.2% Jump Start, 7.3% Juliet

KBG2: Kentucky bluegrass blend — 43.8% Ridgeline, 29.3% Blue, 12.2% Jump Start, 7.3% Juliet

PV1-PV4: four individual ProVista Kentucky bluegrass cultivars

SS1: sun and shade mixture — 10.2%, Secretariat II GLSR perennial ryegrass, 9.7% Wendy Jean creeping red fescue 9.7% Premium perennial ryegrass, 9.7% Fenway creeping red fescue, 4.8% Gaelic Kentucky bluegrass, 2.2% Fielder Kentucky bluegrass, 2.2% Jumpstart Kentucky bluegrass

SS2: sun and shade mixture — 39.2% Pennington ATF1254 tall fescue, 19.5% Greystone tall fescue, 19.5% Pennington ATF1258 tall fescue, 7.3% Pennington ASC295 red fescue, 7.3% Survivor chewings fescue, 5.6% Action Kentucky bluegrass

TF1: tall fescue blend — 17.1% Endeavor, 17.1% Gazelle II, 9.7% Faith, 9.7% Dynamic II

TF2: tall fescue blend — 34.4% Pennington ATF1376, 24.4% Greystone, 19.7% Pennington ATF1254, 19.7% Pennington ATF1258

Research was conducted at the Center for Agricultural Sciences and a Sustainable Environment (Pennsylvania State University, Berks Campus) located in Reading, Pa. A total of 20 cultivars, blends and mixtures of Kentucky bluegrass, tall fescue, chewings fescue (Festuca rubra L. ssp. commutata), strong creeping red fescue (Festuca rubra L. ssp. rubra) and perennial ryegrass (Lolium perenne L.) were seeded on Aug. 22, 2016. Of the 20 treatments, there were eight Kentucky bluegrass cultivars (Abbey, Endurance, Julia, Juliet, Kenblue, Midnight, Noble and Prosperity), four PV Kentucky bluegrass cultivars, three Kentucky bluegrass blends, two sun and shade mixtures, two tall fescue blends and one tall fescue cultivar (Bonsai) (Table 1). During the two-year study period (2018 and 2019), nitrogen was applied as a granular fertilizer four times per year with an analysis of 32% nitrogen, 0% phosphorous, 4% potassium for a total of 3.2 pounds nitrogen per 1,000 square feet (156.2 kilograms per hectare) per year. Prior to implementing mowing frequency treatments, mowing heights were maintained at 3 inches once per week using a rotary mower (Toro Company, Bloomington, Minn.).Irrigation was applied as needed in equal amounts over all plots to prevent wilt stress. Preemergence and post-emergence herbicides were applied as needed to maintain plot integrity to ensure plots were weed-free to maximize accuracy when measuring turfgrass height. No fungicides or insecticides were applied throughout the trial.

Mowing height was determined using a POGO turfgrass canopy height measuring tool (Hoffman Manufacturing, Corvallis, Ore.) (7). Briefly, the retractable metal rod was randomly placed within the plot, avoiding any mounds or depressions, assuring that the rod was as close to the soil surface as possible. The metal tube was then lowered until the plexiglass disc came into contact with three blades of grass. Turf height was then determined by documenting the position of the washer within the column in relation to the millimeter scale on the adjacent ruler affixed to the outside of the tube

A mowing event was considered required if a plot exceeded the one-third mowing rule. For example, each plot was mowed to 3 inches prior to measuring initial heights; therefore, if a plot height was ≥4.5 inches, this triggered a mowing event. Each plot was measured using the POGO every Monday, Wednesday and Friday from May 7 to Nov. 14, 2018, and May 6 to Nov. 8, 2019. Days between required mows for each season in 2018 and 2019 was calculated by dividing the total number of days in each season by the total number of mowing events in each season.

Visual turfgrass quality (TQ) was rated in the spring, summer and fall in 2018 and 2019 and then averaged seasonally. Visual TQ was based on turfgrass color, density, texture and uniformity with a rating scale from 1 to 9, where 1=brown, poor turf, 6=minimal acceptable quality and 9=ideal green, healthy turf (6). To capture spring green-up, photos were taken in April 2018 and 2019 with a light box and photos digitally analyzed with SigmaScan Pro (Systat Software Inc., San Jose, Calif.) using methods described by Richardson et al. (10).

Figure 2. Genetic height differences at the Pennsylvania State University (Berks Campus) research plots between PV1 (top) and conventional Kentucky bluegrass. Photo by Mike Fidanza

Figure 3. ProVista lawn freshly mowed using a mulching mower. Note the lack of clippings on the lawn surface and good turfgrass quality following mowing, despite not being mowed for the six prior weeks. Photo by Christian Baldwin

The objective of this research was to quantify the number of required mowing events over two growing seasons based on the one-third rule (Table 1). Four cultivars in the top statistical group over the two-year research period were four PV cultivars averaging ≤21 mowing events, while the other turfgrasses averaged ≥41 mowing events. Regarding days between mows, all PV cultivars required an average of  ≥20 days, while all other turfgrasses required an average of ≤10 days. All other turfgrasses were statistically similar regarding mowing events and days between required mows across all seasons. Mowing data in the field confirms the GA 2-oxidase overexpression reported by Harriman et al. (3) and resulted in PV cultivars requiring half as much mowing and double the number of days between mows compared to the Kentucky bluegrass blends, tall fescue blends or mixtures containing predominantly perennial ryegrass or the two previously mentioned species in this study.

For spring TQ, few differences were noted, as only Abbey, Julia and Juliet were not in the top statistical group (Table 2). In the summer, cultivars in the top statistical group were Bonsai, My Holiday Lawn, Midnight, Prosperity, PV1, PV2 and PV3. In the autumn, cultivars in the top statistical group were Midnight, Prosperity, PV1 and PV2. Few differences were noted for spring green-up. Of the 20 turfgrasses, six were not in the top statistical group. Only PV1 had the greatest number of statistically highest rankings (4 out of 4) when considering TQ and spring green-up (Table 2). This cultivar also consistently required fewer mowing events throughout the duration of the trial (Table 1). Previous research is aligned with these findings, where reducing clipping yield removal leads to improved TQ (8). Similarly, plant growth regulators have long been noted to reduce mowing frequency yet increase TQ following routine applications (2, 5).

Table 2. Seasonal visual turfgrass quality (2018 and 2019) and digital image analysis of spring green-up (percent green cover) of ProVista Kentucky bluegrass cultivars, conventional Kentucky bluegrass cultivars and blends, conventional tall fescue cultivars and blends, and species mixtures at Penn State University (Reading, Pa.) in 2018 and 2019.

a. Visual turfgrass quality rated on a scale of 1 to 9, where 1=brown, dead turfgrass, 6=minimally acceptable turfgrass and 9=ideal, green healthy turfgrass.

b. Rating dates in 2018, spring: April 15, May 30, June 20; summer: July 25, Aug. 17; autumn: Sept. 26, Oct. 25, Nov. 14. Rating dates in 2019, spring: April 15, May 19, June 17; summer: July 17, Aug. 21; autumn: Sept. 27, Oct. 30, Nov. 29.

c. Top statistical group based on Trenholm et al. 1999 analysis method. The highest number of times in the top statistical group is 4.

*Cultivars selected using the multiple comparison with the best (MCB) procedure, with p=0.95 that the “best” cultivar has been selected.

The PV technology described by Harriman et al. (3) represents new turfgrass genetics with the novel trait of reduced mowing. This research quantified the impact of the overexpression of the GA 2-oxidase gene in the field. Under the conditions of this research, PV required half as many required mowing events and double the number of days between mows compared to the other cultivars, blends and mixtures over a two-year period. The impact of reduced mowing has many benefits, which include increased TQ; reduced mower emission, noise and use; as well as flexibility in labor allocation for golf course superintendents since mowing frequency can be extended. Future research should evaluate mowing requirements in other environments to determine if there are any differences due to climate and/or soil types. Other areas of research to pursue given the dwarf growth habit of PV would be to quantify the shade tolerance (9) and nitrogen-use requirements of these Kentucky bluegrass cultivars in comparison to other Kentucky bluegrass cultivars and fine fescues, the former of which are known to have excellent shade tolerance and low nitrogen requirements.

Scotts MiracleGro provided funding to Penn State Berks Campus to support Dr. Mike Fidanza's teaching and research program.

M.A. Fidanza, Ph.D., is a professor of Plant and Soil Sciences at Penn State University Berks Campus; C.M. Baldwin, Ph.D., is a senior scientist, M. Koch, Ph.D, is a product development lead, S. Lucas Freshour, M.S., is a scientist, and R. Harriman, Ph.D., is a vice president, biotechnology and live goods, all at the Scotts MiracleGro Company, Marysville, Ohio.

Filed to: Kentucky bluegrass, Greens mowing

Copyright 2022, all rights reserved. 1421 Research Park Drive, Lawrence, KS 66049

Copyright 2022, all rights reserved. 1421 Research Park Drive, Lawrence, KS 66049