Managing Citrus Canopy Growth for Higher Productivity: A Review of Plant Growth Regulator (PGR) Applications

Balancing the vegetative and reproductive developmental cycles in a citrus orchard is essential to maintain sustainability. Plant growth regulators (PGRs) offer an effective tool for managing shoot growth rate and fruit production of citrus trees. By moderating shoot elongation and reducing canopy expansion, PGRs help minimise the frequency and intensity of pruning, substantially reducing labour costs and improving orchard management. Evidence from multi-year experiments showed PGR-treated citrus trees can maintain or increase yield efficiency, producing equal or greater fruit/canopy (m3) than untreated controls. Strategic application of PGRs can moderate alternate bearing by promoting more consistent and fruitful shoots, stabilising annual yields. Economic assessments showed significant reductions in labour costs, especially when trees treated with PGRs required less hand pruning. This review synthesises historic and contemporary research and the mechanisms by which PGRs exert their effects in citrus. It identifies knowledge gaps, such as the need for long-term studies, optimal timing for different cultivars, and integrated strategies suited to different environmental conditions. Plant growth regulators could be an effective tool for stable citrus production, offering the potential for more efficient tree canopy management when used responsibly in accordance with regulatory requirements and integrated with other orchard management practices.