Turfgrass managers routinely use mowers and other machinery that operate hydraulic implements to maintain turfgrass surfaces and surrounding landscapes. These hydraulic implements rely on highly pressurized fluids to move various components and activate motors on equipment. Not unlike other pieces of equipment, hydraulic implements have the capability to malfunction or break down during operation. When this happens, highly pressurized and hot hydraulic fluid has the potential to leak or spill onto the turfgrass. Most conventional hydraulic fluids are phytotoxic to turfgrass and, if the leak is not detected and turf not immediately remediated, can create extensive turfgrass necrosis (Johns and Beard, 1979).
Conventionally, hydraulic fluids are petroleum-based oils comprised significantly of hydrocarbons. Hydrocarbons are toxic to plants and animal life, and leaks or spills can create long-term environmental hazards (Aislabie et al., 2004; Bai and Li, 2013). In addition, these introduced hydrocarbons are hydrophobic and coat soil particles while also increasing carbon-to-nitrogen ratios in the soil that limit plant nutrient availability (Aislabie et al., 2004; Everett, 1979).
Conventional petroleum-based hydraulic fluids leaks often result in rapid phytotoxic effects on turfgrass. Reports have noted drying and curling of leaves that darken in color immediately after a spill, with leaf chlorosis taking place within 24 h on ‘Tifgreen’ hybrid bermudagrass (Cynodon dactylon × C. transvaalensis) (Elliott and Prevatte, 1995; Johns and Beard, 1979). Complete necrosis to all aboveground plant tissue has been observed within 48 h, and residual effects in the soil are reported to impact turfgrass performance from 4 months to 1 year after the spill (Bai and Li, 2013; Elliott and Prevatte, 1995). In addition, Berndt et al. (2018a) documented significant reductions in visual green color for the first 3 d after a petroleum-based hydraulic fluid spill on a ‘TifEagle’ hybrid bermudagrass putting green using digital image analysis. After 3 d, the turf appeared fully necrotic and there were no further significant reductions in visual green color.
During the early 1990s, vegetable-based oils for hydraulic fluids were developed as an environmentally safe and nontoxic alternative to petroleum-based fluids (Cheng et al., 1991). When tested on turfgrass, both petroleum- and vegetable-based fluids resulted in complete leaf necrosis. However, the rate of necrosis was much slower on turfgrass applied with the vegetable hydraulic fluid, occurring 7 d after application compared with petroleum hydraulic fluid producing full necrosis after 2 d (Elliott and Prevatte, 1995). No differences in percent turf recovery were observed, but chlorosis as a result of petroleum-based fluid remaining in the soil for a longer period was still evident more than 1 year later. Berndt et al. (2018b) provided further confirmation when simulated spills resulted in significantly greater injury area for petroleum-based fluid compared with a vegetable oil-based fluid over a 139-d period. Nonlinear regression modeling and simulation of these data predicted full recovery after 494 and 303 d for petroleum and vegetable oil hydraulic fluids, respectively.
In addition, synthetic hydraulic fluids are often designed to improve lubrication, stability, and optimal performing conditions in comparison with petroleum- and vegetable/seed-based oils and are derived from six major base stock types including polyalkylene glycols and diesters (Beatty and Greaves, 2006; Sumerlin, 2010). Synthetic hydraulic fluids were first developed for the turfgrass industry beginning in 2005 and were marketed as biodegradable and less phytotoxic than petroleum and vegetable oil hydraulic fluids (Berndt, 2007). In a greenhouse experiment on ‘TifEagle’ ultradwarf hybrid bermudagrass, a synthetic polyalkylene hydraulic fluid resulted in 40% necrosis 4 d after treatment (DAT) but recovered completely by 10 DAT, whereas turfgrass treated with vegetable and petroleum hydraulic fluid were completely dead (Berndt, 2007). In field experiments on putting greens of multiple warm-season turfgrass varieties, Berndt (2007) reported that a synthetic hydraulic fluid treatment consistently produced significantly smaller injury area, less necrosis, and quicker recovery than both vegetable and petroleum oil treatments. Furthermore, injured area on a ‘TifEagle’ hybrid bermudagrass putting green decreased by 30.9% from 1 DAT to 38 DAT following a simulated spill of a synthetic hydraulic fluid, whereas petroleum- and vegetable oil-based fluids increased the injury area by 120.3% and 73.9%, respectively (Berndt et al., 2017). Despite these observations, synthetic hydraulic fluids have yet to be tested on cool-season turfgrass putting greens. Considering the less aggressive rhizomatous growth habit of cool-season turfgrasses such as creeping bentgrass (Agrostis stolonifera), the potential for synthetic hydraulic fluid to serve as a viable replacement to conventional petroleum-based hydraulic fluids requires additional evaluation.
In addition, posthydraulic spill remediation practices are important in limiting turfgrass phytotoxicity and necrosis, and accelerating recovery. Powell (1981) evaluated various methods of remediation practices after spills on a ‘Penncross’ creeping bentgrass putting green that included various detergents soaps, activated charcoal, and calcined clay. A diluted detergent applied to the turfgrass immediately after spill, scrubbed in, and rinsed thoroughly was the recommended practice to promote the quickest recovery (Powell, 1981). In a separate study on ‘Tifgreen’ hybrid bermudagrass, a granular detergent drenched to form suds and then rinsed off provided 90% recovery within 4 weeks, whereas activated charcoal and calcined clays achieved 25% and 15% recovery, respectively (Johns and Beard, 1979). However, visual observations have indicated that high concentrations and quantities of detergent soap could cause phytotoxicity to the turf, exacerbating phytotoxicity even further (Berndt, 2018). Berndt et al. (2017) used nonlinear regression modeling of the hydraulic fluid injury area to demonstrate that a water rinse after spill reduced healing time from 224 to 65 d from spill of a synthetic polyalkylene glycol fluid on a ‘TifEagle’ hybrid bermudagrass green. However, the water rinse treatment was not effective for petroleum and vegetable hydraulic fluid spills, with a healing time longer than 400 d regardless of whether rinse treatment was applied. If synthetic hydraulic fluids are to become widely adapted for use in the turfgrass industry, additional evaluation of remediation methods after synthetic hydraulic fluid spills on cool-season turfgrass is needed to develop best management practices to limit turfgrass injury and promote recovery.
Therefore the objectives of this study were 1) to compare the phytotoxic effects of four hydraulic fluids of different types when applied to a creeping bentgrass putting green and 2) to determine the influence of postapplication remediation treatments on reducing injury.
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