Effect of Synthetic Hydraulic Fluid on Warm-Season Turfgrass

William L. Berndt, Coordinator, Golf Course Operations, Division of Professional and Technical Studies, Edison College, 8099 College Parkway SW, Fort Myers, FL 33919

Corresponding author: William L. Berndt. lberndt@edison.edu

Abstract

Synthetic hydraulic fluid, which was developed for turf equipment in 2005, was compared to traditional hydraulic oils for its potential to cause turf injury. Effects of fluid type, volume, and temperature on area of injury, percent necrosis, and time to healing were investigated at Edison College in 2005-2006 via three experiments on hybrid bermudagrass (Cynodon dactylon L. [Pers.] × C. transvaalensis Burtt-Davey) or seashore paspalum (Paspalum vaginatum O. Swartz). Synthetic fluid applied on container-grown ‘Tifeagle’ at 1.85 ml/cm² caused minimal shoot necrosis that healed within 10 days, while hydraulic oils caused 100% necrosis of shoots. Synthetic fluid applied on putting greens in the field at a volume of 20 ml caused an average of 70 cm² of injury with 17% necrosis after 5 days. Time to healing was 15 to 30 days. In contrast, hydraulic oils caused larger areas of injury with more necrosis and longer healing times. Increasing volume increased injury area for all fluids tested, but temperature had minimal effect. Increasing volume and temperature increased percent necrosis for synthetic fluid but not for hydraulic oils. Compared to hydraulic oils, synthetic fluid consistently caused less injury to warm-season turfgrasses and is a viable replacement for traditional hydraulic oil in turf management equipment.

Introduction

Many types of turf equipment use hydraulics. If conventional hydraulic oil leaks from equipment it can injure turf and begin an environmental pollution event. Hydraulic fluids that are environmentally friendly and less phytotoxic to turfgrass would be desirable.

Vegetable- or seed oil-based hydraulic fluids have been marketed as alternatives to petroleum hydraulic oils (9). Elliott and Prevatte (6) concluded vegetable oil reduces the long-term effects of hydraulic leaks on ‘Tifgreen’ bermudagrass. Gaussoin (7) reported that creeping bentgrass (Agrostis palustris Huds.) recovered better from a hydraulic spill when it was biodegradable plant seed oil compared to petroleum oils. Still, both oils injured turf in these studies. Vegetable oil caused 100% leaf necrosis of bermudagrass within 10 days, and after 14 days damage from plant seed oil rivaled damage from petroleum oil.

Synthetic hydraulic fluid was developed for the turf industry in 2005 (Danny DaCosta, Enbio Industries, personal communication). Plurasafe EnBio TC S has been designed to replace petroleum oil and vegetable oil in high performance hydraulic applications, such as triplex greenmowers (3). This fluid has been advertised as biodegradable with a no-burn effect on turf.

Research on this synthetic fluid was conducted at Edison College in Fort Myers, FL in 2005-2006. The goal of the research was to assess the potential for synthetic fluid to injure warm season turf by comparing it to injury resulting from the application of conventional hydraulic oils composed of vegetable oil or petroleum oil. Effect of fluid type, spill volume, and fluid temperature, on area of turf injury, percent necrosis, and time to healing was investigated via three separate experiments.

Hydraulic Fluids and Putting Greens

The synthetic hydraulic fluid evaluated in this study was Plurasafe EnBio TC S. It is a polyalkylene-glycol (PAG) fluid (3) developed by Enbio Industries, Inc. (Lake Worth, FL) and marketed by BASF Corporation (Florham Park, NJ). The PAGs are one of six major base stock types used in developing synthetic lubricants (4). The structure of a typical PAG is presented (13):

Conventional hydraulic oils evaluated in this research for comparison purposes were biodegradable vegetable oil (GreensCare ISO VG 46 Biodegradable Hydraulic Oil, Terresolve Technologies, Ltd., East Lake, OH) and petroleum oil (Mobil DTE 15 M Hydraulic Oil, Exxon Mobil Corporation, Fairfax, VA). Water was used as a non-phytotoxic control.

Three warm season greens having differing turf types were also used in this research. The greens were located on the Lee County Campus of Edison College in Fort Myers, FL (26.554N, -81.887W). Cultivars were ‘Tifdwarf’ and ‘Tifeagle’ hybrid bermudagrass, and ‘Sea Isle I’ seashore paspalum. All greens were constructed in 2003 without an intermediate (choker) layer, using identical materials, and according to USGA guidelines (15). Greens were maintained at 0.38 cm height-of-cut, and were irrigated and fertilized as needed.

A Greenhouse Study with Container Grown ‘Tifeagle’

This experiment was conducted in 2005 to determine if synthetic hydraulic fluid or hydraulic oils cause injury to container grown ‘Tifeagle’ hybrid bermudagrass. Schedule 40 poly-vinyl chloride (PVC) piping was used to create turf containers that were 15 cm long, with a diameter of 11 cm. One end of each cut section was sealed with plexiglass and adhesive. Three 0.3-cm diameter drainage holes were drilled into each section about 0.5 cm from the sealed end. Drain holes were spaced at equal distances around the container. Each PVC section was then placed sealed side down and clean pea gravel was placed in the bottom of the container at an even 2.5-cm depth. This gravel blanket was then covered by 90:10 greensmix at a depth of 10 cm. Both gravel and greensmix had been materials used to construct the USGA greens described above.

Plugs of ‘Tifeagle’ were collected from an existing green with a standard cup cutter. Plugs were washed with water to remove soil, and extraneous root tissue was removed using shears. This resulted in live turf plugs consisting of verdure and thatch that were approximately 2 to 3 cm thick. Washed plugs of turf were transplanted into the open end of the containers on top of the greensmix so that the surface of the verdure was 0.5 cm below the top rim of the container. Containers with turf were then placed outside on a table in full sun for 10 days to allow for root development. Turf was fertilized at the time of transplanting with N at 24.4 kg/ha from soluble 20-20-20 and was irrigated daily.

After the establishment period, turf in containers was treated with the various hydraulic fluids, including synthetic fluid, vegetable oil, and petroleum oil. Tap water was used as the control. Treatments were applied on 7 June 2005. Fluid treatments consisted of applying 150 ml of each fluid on the surface of the turf which corresponded to an application rate of 1.85 ml/cm². This volume was used to simulate a catastrophic spill of hydraulic oil mimicking real world conditions (Noel Chandler, equipment manager, Royal Poincianna Country Club, personal communication). The containers were then maintained under natural outdoor conditions, and were irrigated daily.

Turf was subjectively evaluated for percent necrosis over 10 days. Necrosis was rated on a 0 to 10 scale, where 10 = 100% necrosis and 0 = no necrosis. Statistical analysis was conducted on the necrosis rating and then converted to percent necrosis for presentation. At 10 days after treatment (DAT), the clipping yield (g/m²) and chlorophyll content of the clippings (mg chlorophyll A and B per gram of clippings) were determined to provide an indication of turf growth. Yield was established by oven-drying tissue at 105°C for 24 h. Chlorophyll was measured by the method of Johnson (8) to provide an indication of turf color.

This experiment was conducted and analyzed as a completely randomized design (12) with four hydraulic fluid treatments replicated three times. Significant differences were determined by analysis of variance, and means were separated using least significant difference (LSD) at the 1% probability level. This study was conducted in June 2005 and repeated in July 2005.

A Field Study on Warm-Season Putting Greens

The objective of this experiment was to determine if synthetic hydraulic fluid or hydraulic oils cause injury to warm season turf growing on putting greens in the field. In this study, each of four hydraulic fluids, as described above, were applied to each of three putting greens having differing turf types. Treatments consisted of synthetic fluid, vegetable oil, and petroleum oil. Water was the control. Treatments were replicated four times on each green, and plot size was 30.5 × 30.5 cm. Turfgrasses used in this study were ‘Tifeagle’ and ‘Tifdwarf’ hybrid bermudagrass, and ‘Sea Isle I’ seashore paspalum, as described above.

Treatment application consisted of applying 20 ml of each fluid using a plastic syringe. Smaller volumes were utilized in this study to help conserve experimental putting green turf and prevent leaching of oil into the environment. Fluids were applied in a single, straight 30-cm line within the interior of each plot from a height of 0.5 cm. The fluid temperature at the time of application was ambient (i.e., 30°C). No washing of the plots occurred and no irrigation was applied within 8 hours of treatment application.

Area of injured turf (cm²) and percent necrosis were measured at 5, 15, and 30 DAT. Injury measurements of length (L) and average width (W) (4 measurements) were made with a ruler. Area of injury (cm²) was calculated as L × W. This method was used because spills made as described resulted in injury shaped as irregular rectangles. For percent necrosis, a rating scheme of 0 to 10 was used where 10 = 100% necrosis and 0 = no necrosis. Statistical analysis was conducted on the necrosis rating and then converted to percent necrosis for presentation.

This study was conducted and analyzed as a randomized complete block design with four replications of each treatment applied to each of three putting greens having differing turf types. Data from each green for each rating date was analyzed independently by conducting an analysis of variance. Treatment differences were determined by analysis of variance, and means were separated using least significant differences (LSD) at the 1% level of probability. This study was conducted during October 2005, and was repeated in October 2006.

Varying Volume and Temperature

This experiment was conducted in 2006 to determine if varying the volume or temperature of various hydraulic fluids caused differences in the area of turf injury and percent necrosis. This experiment was conducted on the ‘Tifdwarf’ green described previously. Plot size was 30.5 × 30.5 cm. Treatments consisted of synthetic fluid, vegetable oil, petroleum oil, and water, heated to either 50°C, 60°C, 70°C, or 80°C, and then applied to the surface of the turf at volumes of 1, 3, or 5 ml. Based on experience with previous studies, spill volumes were reduced again to conserve experimental putting green turf and prevent contamination of the adjacent environment. The range of temperatures used was selected because it encompassed those encountered in turf equipment in operation in the field (Noel Chandler, equipment manager, Royal Poinciana Country Club, personal communication).

Fluids were heated in a Pyrex 250-ml glass beaker using a hot plate and laboratory grade thermometer, and were applied using a digital pipetter from a height of 0.5 cm. Plots were evaluated weekly for 35 days by measuring area of injury (cm²) and rating percent necrosis using a scale of 0 to 10 where 10 = 100% necrosis and 0 = no necrosis. Statistical analysis was conducted on the necrosis rating and then converted back to percent necrosis for presentation.

The modified average radius method (5) was used to determine injury area, as the spill method used produced turf injury observed as irregular circles. Determining average radius (mm) was done by making four diameter measurements (mm) on each injury from the parametric coordinates 0° to 180°, 90° to 270°, 45° to 225°, and 135° to 315°. Radius values were averaged, converted to cm, then injury area was determined using A = πr².

Time to healing from injury was estimated by least squares linear regression. This was done by plotting injury area means for fluid types averaged over volumes and temperatures at 7, 14, 21, 28, and 35 DAT then calculating linear regression using Y = a + b (x). Time to healing was estimated by predicting x at Y = 0. Homogeneity of regression was tested using Student’s t test (12).

This study was conducted and analyzed as a randomized complete block design with three replications. Treatments were arranged as a 4 × 3 × 4 factorial with 4 fluid types (F), 3 spill volumes (V), and 4 fluid temperatures (T). Means were separated using least significant difference (LSD) at the 1% probability level. This study was conducted in March 2006 and repeated in May 2006.

Hydraulic Oil Killed Container Grown ‘Tifeagle’

All hydraulic fluids except water injured container grown ‘Tifeagle’ (Fig. 1). Synthetic fluid injured turf initially and appeared to stunt growth, but shoots remained upright, turgid, and resilient. At 5 DAT the detrimental effect of synthetic fluid began to fade. By 10 DAT the effect of the synthetic fluid was the same as water (Fig. 2). Turf was green and healthy with no visible signs of injury. In contrast, turf treated with vegetable oil or petroleum oil took on a darkened, oil-soaked appearance, followed by matting of turf, and necrosis of shoots. By 10 DAT shoots appeared to be dead.

Fig. 1. The effect of hydraulic fluids on percent necrosis over time. This experiment was conducted on container grown ‘Tifeagle’ hybrid bermudagrass in southwest Florida during June 2005. Necrosis was rated on a 0 to 10 scale, where 10 = 100% necrosis and 0 = no necrosis. Statistical analysis was conducted on the necrosis rating then converted to percent necrosis for presentation. Lsd values for 4, 5, 8, and 10 days after treatment were < 0.1.

Fig. 2. Effect of hydraulic fluids on container grown ‘Tifeagle’ hybrid bermudagrass in southwest Florida in 2005: SYN = synthetic fluid; VEG = vegetable oil; MIN = petroleum oil; and WAT = the water control.

Hydraulic fluids also affected clipping yield and chlorophyll content (Table 1). Where vegetable oil and petroleum oil had been applied, no green clippings could be collected at 10 DAT, and as a result there was no chlorophyll to measure. Where synthetic fluid had been applied, clipping yield was reduced compared to the control, but clippings had more chlorophyll. This implied that, in this study, the turf injury associated with synthetic fluid had a minimal effect on turfgrass growth.

Table 1. Effect of hydraulic fluids on growth and color of container grown ‘Tifeagle’ hybrid bermudagrass in southwest Florida at 10 days after treatment (DAT). Values are treatment means from June 2005. Synthetic refers to synthetic hydraulic fluid. Vegetable and petroleum refer to biodegradeable vegetable oil and conventional mineral oil, respectively.

Fluid type	Clippings (g/m²)	Chlorophyll (mg/g)
Synthetic	114	9.53
Vegetable	0	0.00
Petroleum	0	0.00
Control	157	9.01
LSD _{p = 0.01}	22	0.40

Greens in the Field Recovered Quickly from Synthetic Fluid

All hydraulic fluids except water injured warm season turf growing on putting greens in the field (Fig. 3 and 4). Each turf type responded similarly to the application of synthetic fluid. In 2005, application of 20 ml of synthetic fluid caused an average of 49 cm² injury and 17% necrosis at 5 DAT. By 15 DAT the injury resulting from synthetic fluid had healed. Injury area resulting from application of synthetic fluid in 2006 appeared larger and seemed to heal slower, averaging 90 cm² of injury area at 5 DAT, with 30 to 45 days required for healing.

Fig. 3. The effect of hydraulic fluids on area of turf injury (cm²) over time. This experiment was conducted on putting greens located in southwest Florida during October 2005 and October 2006. Greens were grassed with ‘Tifdwarf’ or ‘Tifeagle’ hybrid bermudagrass, or ‘Sea Isle I’ seashore paspalum. Numbers within the figure indicated least significant differences (LSD) at the 1% level of probability for measurements taken 5, 15, and 30 days after treatment (DAT).

Fig. 4. The effect of hydraulic fluids on percent necrosis over time. This experiment was conducted on putting greens located in southwest Florida during October 2005 and October 2006. Greens were grassed with ‘Tifdwarf’ or ‘Tifeagle’ hybrid bermudagrass, or ‘Sea Isle I’ seashore paspalum. Necrosis was rated on a 0 to 10 scale, where 10 = 100% necrosis and 0 = no necrosis. Statistical analysis was conducted on the necrosis rating then converted to percent necrosis for presentation. Numbers within the figure indicated least significant differences (LSD) at the 1% level of probability for measurements taken 5, 15, and 30 days after treatment (DAT).

Turf types seemed to respond differently to application of hydraulic oils. Petroleum oil spilled on ‘Tifdwarf’ consistently caused the largest observed injury areas, with an average of 265 cm² turf injury with 100% necrosis, considering all rating dates over both years. Injury area means for ‘Tifeagle’ and ‘Sea Isle I’ in response to petroleum oil were 190 cm² and 96 cm², respectively, with necrosis ranging from 80 to 100%. The effect of vegetable oil on injury area paralleled the effect of petroleum oil for each turf type, but the injury areas were smaller. Injury resulting from both vegetable oil and petroleum oil persisted well past the 30-day experimental period during both years.

Increasing Volume Increased the Area of Turf Injury

Varying the volume or temperature of synthetic hydraulic fluid or hydraulic oils caused differences in area of turf injury and percent necrosis. Increasing the application volume from 1 to 3 to 5 ml increased the area of injury for all fluids tested, but the effect was greater for hydraulic oils (Fig. 5).

Fig. 5. The effect of volume and temperature on area of turf injury (cm²) over time. Data points were injury area means occurring 7 days after treatment (DAT) on a ‘Tifdwarf’ hybrid bermudagrass green located in southwest Florida during May, 2006. The least significant difference (LSD) at the 1% level of probability was 4.7 cm².

Increasing volume or temperature of both synthetic fluid and water also resulted in an increase in percent necrosis (Fig. 6). As the temperature of water and synthetic fluid increased so did the effect of volume on percent necrosis (Fig. 7). Increasing the levels of volume or temperature for vegetable and petroleum oil did not affect percent necrosis. Small volumes of hydraulic oils at cool temperatures consistently resulted in the same high degree of necrosis caused by larger volumes at higher temperatures.

Fig. 6. The effect of hydraulic fluid volume and temperature on percent necrosis over time. Data points were percent necrosis means occurring 7 days after treatment (DAT) on a ‘Tifdwarf’ hybrid bermudagrass green located in southwest Florida during May 2006. Necrosis was rated on a 0 to 10 scale, where 10 = 100% necrosis and 0 = no necrosis. Statistical analysis was conducted on the necrosis rating then converted to percent necrosis for presentation. The least significant difference (LSD) at the 1% level of probability was 21%.

Fig. 7. Plot of the interaction between fluid type (F), volume (V), and temperature (T) on percent necrosis over time. This study was conducted on a ‘Tifdwarf’ hybrid bermudagrass green located in southwest Florida during May, 2006. Necrosis was rated on a 0-10 scale, where 10 = 100% necrosis and 0 = no necrosis. Statistical analysis was conducted on the necrosis rating then converted to percent necrosis for presentation. The significant F × V interaction failed to be the same for each experimental temperature at 7 days after treatment (DAT).

Regressions for fluid types averaged over volumes and temperatures were heterogeneous (Fig. 8). Projected time to healing for injury from synthetic fluid was 33 days. Time to healing from water damage was projected to be 32 days. This compared favorably with observed healing times for these treatments. Times and rates projected for vegetable oil and petroleum oil were 50 and 79 days, respectively. This also compared favorably with observed healing.

Fig. 8. Summary of least squares linear regression analysis of injury area means for each hydraulic fluid averaged over volume and temperature versus time. This study was conducted on a ‘Tifdwarf’ hybrid bermudagrass green located in southwest Florida during May, 2006.

The Nature of Hydraulic Oil Injury

Many turf practitioners suggest transfer of heat from oil is responsible for turf injury from hydraulic spills. Hot hydraulic oil can and does injure turf, but oil applied at ambient temperature in these studies caused comparable injury. Heating petroleum oil or vegetable oil from 50°C to 80°C in 10° intervals did not result in a significant increase in area of injury or percent necrosis at any spill volume, but heating water or synthetic fluid did. This result may have been related to differences in specific heat capacities of the fluids, but that was not determined. However, these data clearly demonstrate that traditional hydraulic oils will cause injury to warm-season turfgrasses regardless of the temperature of the oil.

Injury might also be linked to presence of additives used to inhibit corrosion or prevent wear in hydraulic systems (1). Physical contact which smothers gas exchange surfaces may cause injury, too (2,10,11,14). Smothering is the primary way oil affects mangroves (Rhizophora spp.) and Spartina spp., but the effect of toxicity can exacerbate smothering (2,10). Also, certain fractions of oil, especially lighter fractions, can reportedly penetrate plant tissue after contact, disrupting membranes hence ion selectivity (10).

Conclusions

Results of this research suggested that synthetic hydraulic fluid had less potential to cause turf injury than conventional hydraulic oils composed of vegetable oil or petroleum oil. In three separate experiments, the synthetic fluid consistently produced smaller areas of turf injury and/or less necrosis than the hydraulic oils did. Injury resulting from the synthetic fluid also healed faster. Both volume and temperature were established as important factors influencing area of injury, percent necrosis, and ultimately time to healing for synthetic fluid. Synthetic hydraulic fluid may soon replace conventional hydraulic oils in turf management equipment such as triplex mowers or other tools using hydraulics because it’s less injurious to warm-season putting green turf.

Acknowledgments

The author wishes to acknowledge Bob DuFresne, Danny DaCosta of Enbio Industries, and Noel Chandler of Royal Poinciana Golf Club for their assistance with this research. The author also thanks the editors and reviewers for their time and efforts.

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