Does the Temperature of Hydraulic Oil Influence Injury Area Dynamics on a Bermudagrass Green?.

Hydraulic oil (HO) injures turf, especially on putting greens.  One belief that is widely held is that HO must be at machine operating temperature to injure turf.  The objective of this research was to examine the influence of temperature and HO type on injury area, using digital image analysis and non-linear regression modeling.  The effect petroleum HO (PHO) and vegetable HO (VHO) had on injury area (IA), when applied at 35°C or 80°C, was studied during a 7 d period in 2014 at North Fort Myers, FL on a hybrid bermudagrass (Cynodon dactylon [L.] Pers. var. dactylon x Cynodon transvaalensis Burt-Davy) putting green.  Analysis of variance indicated temperature of HO did not influence IA (p = 0.439), but type of HO did (p < 0.0001).  Oil type and temperature did not interact (p = 0.232).  Curve fitting supported these results.  When a rectangular 3-parameter hyberbolic curve was fitted to IA data with time, an extra sum of squares F-test indicated the curve for VHO at 80°C did not differ from the curve at 35°C (p = 0.9923).  The same was true for PHO (p = 0.3031).  When data points for VHO and PHO were combined over temperatures, differences between regression curves were highly significant (p < 0.0001).  Rearranging the regression equations indicated maximum IA expansion (ME) for VHO was 25.5 cm², occurring 4.3 DAT, while ME for PHO was 40.4 cm² occurring at 5.1 DAT.  These results dispel the myth that HO must be hot to injure turf.  Fitting nonlinear regression models to IA data with time provided more quantitative information than analysis of variance alone, and revealed turfgrass injury behavior previously unknown.