This study was initiated to evaluate how mowing quality of creeping bentgrass is affected by two different mowing setups and by plant growth regulators. Mower A was adjusted with reel-to-bedknife contact, while no reel-to-bedknife contact was afforded to Mower B. Additionally, the mowing quality of turf treated with Embark 2S (Melfluidide), Primo 1EC (Trinexapac-ethyl) and Proxy 2SL (Ethephon) plant growth regulators was assessed. The study was conducted at the Iowa State University Horticulture Research Station using ‘Penncross’ creeping bentgrass established on a 1/3 peat, 1/3 sand and 1/3 Nicollet soil growth medium. A split-plot design with two-stage randomization, replicated three times, was used to carry out the experiment.

Chemical treatments were made at a six-week interval using a CO₂-powered backpack sprayer calibrated to apply 3.0 gallons of liquid/1000 ft². Two applications of the chemical treatments were made — the first on July 14 and once again on August 25. The chemical treatments of Proxy 2SL, Primo 1EC and Embark 2S were applied at rates of 5.0, 0.25 and 0.10 fl oz of product/1000 ft², respectively.

Mowing treatments began July 28 and were performed three times a week (Monday, Wednesday and Friday) through October 6. Both of the Toro Greensmaster 1000 model greens units were maintained at a cutting height of 0.50 inches - common for creeping bentgrass fairways. There was, however, a difference in the reel-to-bedknife adjustment between the two mowers. Mower B was set up initially so that there was no reel-to-bedknife contact and then operated for a period of six hours. This was to mimic a mower that should be back-lapped to perform optimally — a frequent situation on golf courses. The mower was adjusted during the trial so that it would cut cardstock along the entire length of the bedknife without reel-to-bedknife contact. The mower was capable of cutting 20-lb. office paper at various points across the bedknife at the conclusion of the study. Mower A was adjusted as necessary to maintain slight reel-to-bedknife contact over the course of the experiment and was not used prior to the onset of mowing treatments. Mower A was able to cut 20-lb. office paper across the entire length of the bedknife throughout the study.

Turf assessments were made at weekly intervals. Data collected included an overall quality rating and a measurement of the mowing injury. The overall quality rating was a visual, comprehensive measure of the color, density, and uniformity of the turf based on a 9 to 1 scale with 9=Best, 5=Lowest Acceptable and 1=Worst. Mowing injury was a measurement of the leaf shredding and tip browning found on leaf blades randomly selected from each strip-plot treatment. This evaluation was made under a microscope and measured in millimeters.

The overall turfgrass quality attributed to the treatments can be found in Table 1. In general, the Proxy-treated whole-plots resulted in a much denser, uniform grass stand. However, there was a slight, but acceptable, reduction in color. Initially, Embark applications lowered the quality of the turf — turning the whole-plots predominately brown - but four to five weeks after treatment the plots began to regain a healthy green color. The reverse can be said of the plots treated with Primo. In the three to four weeks following each chemical treatment, the Primo whole-plots would appear a brilliant green color- superior to all other treatments - and then fade in the following weeks until their appearance resembled the untreated controls. No noticeable differences in quality occurred between the two mowing adjustments until five weeks after treatments began. Mower B caused a distinct brown discoloration that was easy to discern from the healthy green appearance of the turf mowed with Mower A. In general, the untreated control + Mower A and Primo + Mower A split-plots rated the best in the first four to five weeks after chemical treatment, while the Proxy + Mower A split-plot performed best in the fourth to sixth weeks after chemical application.

The reel-to-bedknife contact mower adjustment resulted in 60% less mowing injury than the no-reel-to-bedknife contact mower adjustment (Table 2). While large differences in mowing injury are apparent between chemical treatments, mowing injury was highly variable making it difficult to make comparisons between treatments. In some weeks, outliers, or extreme values distorted the mean value of mowing injury within each chemical treatment. While no statistical differences can be derived from the data, it is interesting to note that mowing injury was generally less in plant growth regulator treatments when compared to an untreated control (Table 3).

In addition to the turf evaluations listed above, the chlorophyll content of grass samples from each strip-plot was measured. The chlorophyll content was determined by the method developed by Knudson, Tibbitts and Edwards (Knudson et al, 1977). Chlorophyll was extracted from grass tissue with ethanol and then the extract was measured with a spectrophotometer at 665 nanometers and 649 nanometers. Total chlorophyll content was then determined by making appropriate calculations. The grass tissue used to measure the chlorophyll content was collected on September 15 — three weeks after the second chemical application. Statistically significant differences in total chlorophyll content occurred between the chemical whole plot treatments only (Table 4). As discussed earlier, the Primo and untreated control whole plots were rated with the highest turf quality at this time while the Proxy and Embark whole plots were of an inferior quality color wise — this is quite evident from the chlorophyll content data.

No statistically significant differences in total chlorophyll content resulted between mowing treatments (Table 5). Had statistically significant differences occurred, the amount of mowing injury caused by the two mowing treatments could have accounted for them - brown tissue will not yield chlorophyll. Moreover, there were no statistically significant differences between strip-plots. The variability within strip-plots treatments was too large when compared to the variability between the other strip-plot treatments (Table 6).

Of the two mower settings, the reel-to-bedknife contact mower set up consistently resulted in superior mowing quality compared to the no reel-to-bedknife contact mower adjustment. The Primo and untreated control treatments produced the best turf quality for the first four to five weeks after chemical treatment, while the Proxy and Embark treatments rated the best in the fourth to sixth weeks. Mowing injury was generally largest in the Embark and control treatments, although this data was highly variable. Most often, the Proxy treatment resulted in the smallest amount of mowing injury, but once again the mowing injury data was highly variable and very few statistically significant comparisons can be made.

² Reel-to-bedknife contact mower setup.

³ No reel-to-bedknife contact mower setup.

⁴ LSD_0.05 values are significant for differences between both mower and chemical values.

NS - means between treatments are not statistically significant.

² Reel-to-bedknife contact mower setup.

³ No reel-to-bedknife contact mower setup

Table 3. Mowing injury¹ associated with different chemical treatments.

NS - means between treatments are not statistically significant per Fischer’s LSD test.

² Tissue tested was collected 15-Sep, three weeks after the second chemical application

² Tissue tested was collected 15-Sep, three weeks after the second chemical application

³ Reel-to-bedknife contact mower setup.

⁴ No reel-to-bedknife contact mower setup.

NS - means between treatments are not statistically significant per Fischer’s LSD test.

² Tissue tested was collected 15-Sep, three weeks after the second chemical application

³ Reel-to-bedknife contact mower setup.

⁴ No reel-to-bedknife contact mower setup.

NS - means between treatments are not statistically significant per Fischer’s LSD test.