By Meryam Manzoor, Jamie D. Burrow, Taylor Livingston and Tripti Vashisth
Effective nutrient management and accurate nutritional analysis are critical for tree growth and maximum yield. Historically, nutrient management for healthy citrus trees involved annual leaf sampling from July to August, with subsequent fertilization plans based on a single nutrient analysis.
Almost all commercial citrus groves in Florida are affected by huanglongbing (HLB). HLB-affected trees have small, weak root systems that need a constant supply of nutrients to meet their nutritional needs. Studies suggest that small, frequent doses of fertilizer improve the tree health and production of HLB-affected trees. The widespread prevalence of HLB needs new approaches for managing fertilizer programs by regular leaf sampling to identify tree nutrient status and requirements.
University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers conducted a field study on sweet oranges to improve and revise the leaf nutrient sampling guidelines for HLB-affected trees. The goal was to determine the optimal sample collection method and assess the frequency of leaf sampling required per year to capture the tree’s nutritional status effectively and adjust fertilizer accordingly.
For this study, emerging spring and summer flushes were tagged on HLB-affected (mild and severe) Hamlin and Valencia trees in a Central Florida grove over two years. The leaves were collected four times per year for nutrient analysis. Results of both spring and summer leaf analysis were used to develop the fertilization plan.
Two years of evaluation indicate that fertilization based on leaf nutrient analysis resulted in improved tree health with increased canopy growth and less decline in both varieties. Spring leaf nutrient levels correlated to canopy density. Yield illustrated that nitrogen and iron support tree canopy health in the spring. These nutrients promote healthy leaves and vegetative growth.
Later in the year, potassium and boron became more crucial as the focus shifts toward fruit development and quality. This shows at least two leaf samples (June and September) are needed to improve the canopy and fruit growth of HLB-affected trees. Interestingly, a random leaf sample is comparable to spring flush in the June and September period.
Meryam Manzoor is a visiting scholar, Jamie D. Burrow is an Extension program manager, Taylor Livingston is a biological scientist, and Tripti Vashisth is associate center director and associate professor — all at the UF/IFAS Citrus Research and Education Center in Lake Alfred.
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