The Month of Injection Affects Fruit Size, Juice Quality, and Oxytetracycline Residues
Posted August 2025
Researchers: Ute Albrecht
Contact: Ute Albrecht, UF/IFAS SWFREC ualbrecht@ufl.edu
Summary:
Citrus fruit development can be divided into three somewhat overlapping phases or stages: stage I (cell division), from anthesis to the end of physiological fruitlet abscission (June drop), during which cell division predominates and growth is moderate; stage II (cell enlargement), from the end of June drop to shortly before fruit color change, during which cells enlarge rapidly and fruits reach their final size; and stage III (maturation), during which no more growth occurs and fruits begin a non-climacteric ripening process. The month of injection can have a major influence on fruit size, fruit color, and juice quality. Injections during stage I promote cell division, ultimately resulting in larger fruits. The earlier the injection occurs the larger the fruits will be. These larger fruits are likely to need a longer maturation time and, if picked early, will usually be greener and contain fewer soluble solids, i.e., have a lower °Brix. OTC fruit residues will be low as any OTC that has accumulated in the fruitlets will be diluted during cell growth and expansion. In contrast, injections during the cell enlargement stage (stage II) will have a lesser impact on fruit size but will promote soluble solids accumulation, resulting in a higher °Brix. These fruits usually also have a better peel color. The later the injection, the more pronounced this effect will be. However, injections at the end of stage II (e.g., in September) will result in high OTC residues as no more growth occurs, preventing its dilution.
Take Home Message:
- The month of injection determines fruit and juice quality.
- Injections early in the year promote fruit size.
- Injections late in the year promote juice quality but increase OTC residues.
