The use of low-altitude infrared remote sensing for estimating stress conditions in tree crops

Stress conditions in various tree crops, subject to disease, were studied using low-altitude aerial colour infrared (CIR) imagery. A remotely piloted aircraft, carrying a colour video camera and a 35-mm reflex camera, flying at altitudes of 50 to 100 metres, was used for aerial photography. The CIR pictures of citrus, avocado and cashew nut orchards were scanned into a desktop computer and manipulated by image processing software using on-screen interpretation to classify crop stress conditions. In a citrus orchard, lemon trees affected by rootrot could be clearly identified and differentiated from their healthy neighbours. The degree of Phytophthora cinnamomi infestation in avocado orchards was similarly assessed as was the effectiveness of chemical treatment of rootrot-infested cashew nut trees. This technology proved to be a relatively inexpensive and effective way of assessing crop stress conditions.