Non-linear Regression Modelling of Hydraulic Oil Injury on a Bermudagrass Green

Hydraulic oil (HO) injures putting greens. Fitting a nonlinear regression model to injury area (IA) with time may help assess injury response to treatment. Modeling was used to determine if washing spills of three HOs with water changes injury dynamics. Effects of HO type and washing on rate of change of IA, time to maximum IA expansion (ME), and IA contraction (healing) times were studied in 2014 at North Fort Myers, FL, on a hybrid bermudagrass green [Cynodon dactylon (L.) Pers. var. dactylon ´ C. transvaalensis Burt-Davy ‘TifEagle’ (PP11163)]. Washing changed injury dynamics for synthetic HO (SHO) but had less effect on vegetable HO (VHO) and petroleum HO (PHO). Washing spills of SHO slowed the initial rate of injury expansion from 7.0 to 5.4 sqrt-cm² + 0.1 sqrt-d⁻¹ (p = 0.0969) and increased the rate of injury contraction from −0.36 to −0.83 sqrt-cm² + 0.1 sqrt-d⁻¹ (p < 0.0001). In unwashed SHO plots, IA decreased from a maximum of 21.7 cm² at 4.5 d to 12.6 cm² at 38 d (D IA = −42%). In washed SHO plots, IA decreased from 18.5 cm² at 3.8 d to 2.2 cm² at 38 d (D IA = −88%). Calculated healing time for SHO injury was 224 d (unwashed) vs. 65 d (washed). For VHO and PHO, healing took >400 d washed or not. Curve fitting was a novel approach to assessing HO injury response to treatment and illustrated injury behavior that was previously unknown.