Abstract
A leaf-mounted sensor is described which detects condensing water vapour originating from leaf transpiration, taking advantage of a passive temperature gradient across the sunlit leaf and the underneath sensor plate, and simultaneously monitors incident solar radiation. The simple and low-cost device enables the qualitative assessment of plant water status by comparing the diurnal patterns of leaf transpiration and solar irradiance. A close correlation between condensation and irradiance occurs in conditions of unrestricted water supply, whereas a deviation of their course likely indicates a suboptimal plant water status.