Effective fertilizer management and accurate nutritional analysis are critical for healthy tree growth and maximum yield. Citrus trees perform best in the optimum range of each nutrient, and a deficiency or excess can result in poor tree growth and yield. Accurate fertilizer management decisions for citrus trees begin with proper leaf sampling. To accurately assess tree nutrition status, the appropriate time and procedure for collecting leaves for nutrient analysis must be followed. Historically, nutrient management for healthy citrus trees involved annual leaf sampling from July to August, with subsequent year fertilization plans based on single nutrient analysis. Currently, nearly all commercial Florida citrus orchards are affected by Huanglongbing (HLB), a systemic bacterial disease that affects all citrus varieties and rootstocks, causing extensive tree health decline. Studies suggest that a good nutrition program can improve the tree health and production of HLB-affected trees. However, the key is to supply the nutrients that are deficient or low. This widespread prevalence of HLB needs new approaches for managing fertilizer programs by regular leaf sampling to identify tree nutrient status and requirements. Thus, this study focuses to improve and revise the leaf nutrient sampling guideline for HLB-affected trees by determining the optimal time for leaf sampling and adjusting fertilization for increased production and tree health. Key objectives include assessing the frequency of leaf sampling required per year to capture the tree's nutritional status effectively and adjust fertilizer accordingly to establish the correlation of leaf nutrient concentration with the yield, fruit drop, and canopy density. For this study, spring and summer emerging flushes were tagged on HLB-affected ‘Hamlin’ and ‘Valencia’ mild and severe sweet orange trees in a central Florida orchard over two years. The leaves from tagged branches were collected every 3 months for leaf nutrient analysis and the results of both spring and summer leaves were used to adjust the fertilization plan accordingly. It was found that the spring emerging flush was optimal in adjusting the fertilizer for the highest yield compared to the summer emerging flush. With the use of precision fertilization, the improvement in tree canopy density and fruit yield was more obvious in mildly HLB-symptomatic trees compared to severely symptomatic trees. Our results demonstrate the growers should be performing nutrient sampling quarterly and use this information to precisely manage fertilization and improve tree productivity.
