- Harvesting the crop for forage or leaving it for grain is the main crossroad that wheat growers of semi-arid regions confront around heading time. A decision support system that is based on crop bio-physical status around heading is currently used for solving this dilemma. A spectral index that identifies spike emergence (heading) is needed by this decision support system when using remotely sensed data. It was observed that spike emergence coincides with a drop of the crop water content, which is expressed in a spectral response. A ratio- based narrowband index was able to identify whether the samples were before or after heading with 81% accuracy.