By Tripti Vashisth, Johann Hiller and Taylor Livingston
Poor fruit quality has long been a significant hurdle for sweet orange growers in the HLB era. With high fruit drop rates and challenges in harvest management, many growers find themselves picking fruit earlier than ideal, resulting in subpar Brix levels. To effectively improve the Brix of the fruit, it is essential to understand the key factors affecting Brix in HLB-infected trees.
MORE LEAVES MEANS BETTER BRIX
In February 2025, the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) conducted a comprehensive survey of four mature Valencia groves. Fruit was collected from branches with both high and low leaf numbers, along with their adjacent leaves. Each fruit was individually analyzed for quality. A thorough leaf-nutrient analysis was performed on the fruiting-branch leaves.
Findings across all sites confirmed that the number of leaves on the fruiting branch is a strong predictor of juice quality. A greater number of leaves consistently leads to higher Brix levels.
NUTRIENT FINDINGS
A significant positive correlation was discovered between calcium and Brix. Higher calcium content in fruiting leaves was associated with increased Brix levels. This trend extended to potassium and magnesium as well. Conversely, manganese and zinc content were found to be lower in leaves adjacent to fruit with high Brix.
Artificial intelligence modeling indicated that leaf boron levels are the most critical predictor of Brix, followed by zinc and calcium. It’s vital to understand that while a strong predictor does not imply a linear relationship, maintaining these nutrients within an optimal range is essential, as any deviation from deficient or excess levels can adversely impact Brix.
STUDY TIMING
It’s important to note that leaf-nutrient data were collected from fruiting branches in February and March. In contrast, traditional leaf-nutrient analysis is typically conducted on non-fruiting leaves in July and August.
Therefore, this data should not be compared to the usual leaf-nutrient analysis that growers do. Fruiting and non-fruiting branches have different nutritional profiles, which change over the years.
GROWER POINTERS
What does this mean for growers heading into fall?
1. Promote high leaf density.
2. Optimize nutrient management.
3. Utilize leaf-nutrient testing.
4. Avoid fertilizing past mid-October, as nutrient absorption will significantly decline.
While these findings are still preliminary and require further evaluation on a larger dataset, maintaining a robust canopy through fall and winter is critical for achieving better juice Brix levels.
Tripti Vashisth is associate center director and associate professor, Johann Hiller is a research scholar, and Taylor Livingston is a biological scientist, all at the UF/IFAS Citrus Research and Education Center in Lake Alfred.