TY - JOUR AU - Mathanker, Sunil K. AU - Estévez de Jensen, Consuelo AU - Pagán-López, Andrés M. AU - Pérez-Alegría, Luis R. PY - 2019/04/01 Y2 - 2024/03/29 TI - UAV color images for determination of citrus plant parameters JF - The Journal of Agriculture of the University of Puerto Rico JA - JAUPR VL - 103 IS - 2 SE - Articles DO - 10.46429/jaupr.v103i2.18226 UR - https://revistas.upr.edu/index.php/jaupr/article/view/18226 SP - 141-153 AB - <p>Unmanned aerial vehicles (UAVs) or drones are being studied for many&nbsp;agricultural applications. One application is plant phenotyping to reduce the&nbsp;time and effort required in collecting field data. This study aims to explore&nbsp;the use of a UAV, 4K-color camera and a commercial image analysis service&nbsp;to measure citrus plant parameters that are important to a crop scientist&nbsp;or grower with limited technical background and resources. <em>Citrus</em> spp. are&nbsp;important crops in Puerto Rico and the United States. Currently, the citrus&nbsp;industry is struggling to contain the devastating effects of citrus greening&nbsp;or Huanglongbing disease. The disease is associated with a phloem-limited&nbsp;bacteria, <em>Candidatus</em> Liberibacter asiaticus (CLAs), vectored by the Asian&nbsp;citrus psyllid (ACP), <em>Diaphorina citri</em> Kuwayama. The use of insecticides&nbsp;for vector control is the primary strategy used in nurseries and orchards.&nbsp;However, once the citrus plant is infected, there is no effective control&nbsp;available for the disease. In Puerto Rico this disease has reduced <em>Citrus</em>&nbsp;spp. yields by more than 50%; studies are underway to find effective control&nbsp;measures such as supplemental nutrients, vector management practices,&nbsp;planting disease-free vegetative material and protective screen structures.&nbsp;An experiment at the Fortuna Agricultural Experiment Substation, in&nbsp;Juana Díaz, Puerto Rico, was conducted to address the challenges posed&nbsp;by citrus greening. The experiment was established in a four-year-old&nbsp;grove of Tahiti lime (<em>Citrus latifolia</em> Tan.) on Cleopatra mandarin (<em>Citrus&nbsp;reshni</em> hort. ex Tanaka), naturally infected with <em>Candidatus</em> Liberibacter&nbsp;asiaticus. The experiment was arranged in a randomized complete block&nbsp;design with four replicates and three treatments: supplemental nutrients,&nbsp;supplemental nutrients + salicylic acid, and granular fertilization. Tree&nbsp;growth parameters were measured, and laboratory analyses were carried&nbsp;out to determine nutrient levels and disease severity levels from the leaf&nbsp;samples. The color camera, on board the UAV, was employed to acquire&nbsp;images of the experimental plot. Drone Deploy application was used for&nbsp;planning the UAV flights and image analysis. Field-measured plant height&nbsp;and canopy diameter compared well with the parameters determined from&nbsp;the color images. The average errors in measuring canopy diameter (14.5%)&nbsp;and plant height (22.4%) could be considered within an acceptable range,&nbsp;especially for comparing different treatments or crop varieties. However,&nbsp;the average errors in measuring canopy volume (47.5%) were high and can&nbsp;be considered unacceptable. It appears that the assumed conical shape of&nbsp;the trees could be one of the main reasons, besides the algorithms used in&nbsp;calculating plant volume, and built-in inaccuracies of the single frequency&nbsp;GPS (global positioning system) used in estimating altitude. Further studies&nbsp;could help in reducing errors and exploring other applications. The method&nbsp;used can be of importance in evaluating fruit trees.</p> ER -