Pg. 6-15 A management program to improve yield and fruit size of litchi, cv. HLH Mauritius – Final report

In 2005 an orchard management program, consisting of irrigation, soil and foliar applications of fertilizers and plant growth regulators, as well as horticultural techniques like pruning and girdling to promote sustainable litchi production, was started. Five management programs were developed and compared with one another according to their effects on yield and fruit size.

In the four years of data collection since 2005 similar results were achieved regarding tree phenology, yield and fruit size. The plant growth regulator Maxim^® applied at the 3 g fruitlet stage and girdling at the 2 g fruitlet stage consistently increased fruit size. It was found that optimal fertilization and irrigation as well as the use of Ethapon^® are the main contributors to consistent and good cropping. Foliar application of fertilizer could not increase yields above these general management practises. Results for the four seasons are discussed and a summary as well as conclusions are given.

Summary:

• The study started in 2005 to develop and compare five orchard management programs aimed at improving yield and fruit size in litchi cv. HLH Mauritius over four years.
• The management programs involved irrigation, soil and foliar fertilization, plant growth regulators (PGRs), and horticultural practices like pruning and girdling.
• Key treatments included applications of Maxim® (an auxin-like PGR) at the 3 g fruitlet stage and girdling at the 2 g fruitlet stage to improve fruit size.
• Optimal fertilization, irrigation, and use of Ethapon^® (a growth inhibitor) were found to be the main contributors to good and consistent cropping, with foliar fertilization alone not increasing yield beyond these basics.
• Treatment 1, focusing on improving fruit set through micronutrients, cytokinins, KNO₃, and Ethapon^®, increased yield and fruit size compared to control but not significantly.
• Treatments 2, 3, and 4 specifically targeted fruit size, with girdling (Treatment 4) consistently increasing fruit size and producing the highest percentage of extra-large fruit.
• Treatment 5 combined multiple applications aimed at increasing both fruit set and size but did not consistently outperform the standard Treatment 1 in yield.
• Irrigation management was crucial, with scheduling guided by the “Litchi Production Planner” software and supported by soil moisture probes to avoid stress, especially during flowering and fruit set.
• Phenological monitoring showed that flowering and fruit set were sensitive to temperature fluctuations, with low temperatures promoting better fruit set in some seasons.
• The study highlighted the importance of controlling late autumn flush with Ethapon^® and water stress induction to ensure flower bud dormancy and successful flower induction.
• The economic analysis found that Treatment 1 and Treatment 4 (which included girdling) were most profitable due to low input costs and good impact on yield and fruit size, whereas costly treatments with Maxim® had higher input costs and variable economic returns.
• Recommendations emphasized optimizing basic orchard practices first: irrigation, fertilization (based on leaf and soil analysis), pruning for light management, and managing late autumn flush, followed by targeted foliar sprays and girdling to improve fruit size and set.
• Further research was suggested on flower induction biology under South African conditions and fine-tuning irrigation to avoid heat or drought stress during critical growth stages.