Abstract: Leaf temperature measurements using handheld infrared thermometers have been used to predict plant water stress by calculating crop water stress index (CWSI). However, for CWSI calculations it is recommended to measure canopy temperature of trees under saturated, stressed and current conditions simultaneously, which is not very practical while using handheld units. An inexpensive, easy to use sensing system was developed to predict plant water status for tree crops by measuring leaf temperature and microclimatic variables in the vicinity of a leaf continuously. The system consists of an infra-red sensor, air temperature and relative humidity sensor, ambient light sensor and wind speed sensor soldered on to a customized printed circuit board (PCB). The system also consists of nylon wire mesh leaf holder to hold leaf steady in front of an infra-red sensor. A solar radiation diffuser dome was used to make sure that light sensor was exposed to same light level as the leaf. This dome diffused direct sunlight flecks and ensured relatively uniform light conditions inside the dome. A wind barrier was installed to suppress effect of wind speed on the transpiration of the leaf; wind speed sensor was installed inside the wind barrier to verify its effectiveness.  This system was connected to a commercially available wirelsess mesh network, eKo pro (Memsic inc., Andover, MA), by installing the system on multiple trees in almond and walnut orchards at Nickel’s Soil Laboratory, Arbuckle, California. Each leaf monitoring system continuously monitored the leaf of a selected tree by logging leaf temperature, air temperature, relative humidity, wind speed and PAR (Photosynthetically Active Radiation) at fifteen minute intervals. Leaf monitor data collected from field experiments were used to develop a daily plant water stress index which was adjusted for light and VPD (vapor pressure deficit) conditions. Data corresponding to first day after irrigation was assigned a stress index value of zero and it was used as reference for rest of the days during that irrigation event. Mid-day stem water potential (MSWP) of trees on which leaf monitoring system was installed was measured using a “pressure chamber” to verify the ability of the continuously leaf monitor to detect plant water stress. The results indicated that stress index values calculated on a daily basis correlated well with measured MSWP and followed similar patterns over the days in both almond and walnut trees. This automated system for calculating daily stress index for any tree has the potential to be used as an irrigation scheduling tool, as it can easily be integrated with a variable rate irrigation system for use as a sensor for feedback control.