Transpiration is a fundamental biophysical process, directly measured in plants by dividing sap flow by total leaf area. Under non-limiting conditions, transpiration and reference evapotranspiration (ETo) are hypothesized to be equal when ETo is normalized by the leaf area index of the reference crop, i.e., LAI = 2.88. Known as the E2.88 model, it has only been tested with ETo derived from Penman-Monteith FAO56. Phenological influences on canopy conductance potentially decouple transpiration from atmospheric evaporative demand and lower the accuracy of E2.88. This study tested the accuracy of 20 E2.88 models in predicting apple (Malus domestica (Suckow) Borkh. var. Granny Smith) and pear (Pyrus communis L. var. Beurre Bosc Pear) transpiration over the 2020-2021 austral growing season. For apple, the Penman-Monteith ASCE-EWRI model had the highest predictive power with 7% error and r2 = 0.89; whereas for pear the Valiantzas (2018, Eq. (7)) showed 2% error and r2 = 0.96 evaluated via linear regression. Generally, models that included a humidity parameter had stronger predictive power than models excluding humidity. Yet, the predictive power of the E2.88 models decreased considering the phenological phases for each crop. For apple, early and late season E2.88 models underestimated transpiration by at least 27%. For pear, late season error increased to 7% as the E2.88 models overestimated transpiration. Canopy conductance and the atmospheric decoupling factor were significantly greater in early and late season for apple and significantly lower in late season for pear. Therefore, phenology decreased the predictive power of the E2.88 model in early and late season by decoupling physiological processes from atmospheric evaporative demand.