Pg. 16-26 Use of rest-breaking agents for the timely stimulation of budbreak to improve flowering and production in litchi

Stimulation of growth by rest-breaking agents in the beginning of winter, when conditions are favorable for flower initiation, can improve flowering and production in litchi. Rest-breaking agents were applied during mid-April (1.5 & 3.0% KNO₃, 0.5% LB urea, 0.05% Ethapon^® and 0.05% Ethapon^® in combination with 3.0% KNO₃), end-April (1.5 and 3.0% KNO₃, 0.5% LB urea, 0.4% Kelpak^® and girdling) and mid-May (3.0% KNO₃) in the Malelane area. Ethapon^® treatments were applied on the mid-April flush. All rest-breaking agents gave a more uniform flushing when compared to the control. Flowering was not significantly affected, but the time of full female bloom was earlier for the Ethapon^® treatments, 0.5% LB urea (mid-April) and 1.5% KNO₃ (end-April). Fruit set was not significantly affected by any of the treatments. The 0.5% LB urea treatment (end-April) gave significantly higher fruit drop while no significant effect was observed on fruit drop for the other treatments. Fruit size was significantly improved by the 0.4% Kelpak^® treatment, probably as a result of the phytohormones in the product. There was no significant improvement in production, although 3.0% KNO₃ (mid-April), girdling (end-April) and 3.0% KNO₃ (mid-May) improved production by 1.0, 0.9 and 1.8 ton/ha respectively. In the Nelspruit area, branch treatments were done with concentration ranges of KNO₃ (1, 2, 3 and 4%) and LB urea (0.25, 0.5 and 0.75%) in order to find optimum concentrations. No significant trends were observed for flowering, fruit retention and fruit size. Three percent KNO₃ applied at the end of April gave a significant improvement in fruit set. Three percent KNO₃ applied mid-April or mid-May (at the time of flower initiation), as well as girdling at the end of April proved, therefore, to be the most promising treatments overall.

Summary:

• The study investigates using rest-breaking agents applied at the beginning of winter to stimulate bud growth, aiming to improve flowering and production in litchi (cultivar HLH Mauritius).
• Treatments were applied in the Malelane and Nelspruit areas during mid-April, end of April, and mid-May, including KNO₃ (1.5%, 3.0%), LB urea (0.5%), Ethapon^®, Kelpak^®, and girdling.
• All rest-breaking agents promoted more uniform bud flushing compared to control.
• Flowering percentage was not significantly affected overall, but some treatments such as Ethapon^®, LB urea (mid-April), and 1.5% KNO₃ (end-April) led to earlier full female bloom.
• Fruit set was generally not significantly influenced by treatments; however, girdling at end-April significantly improved fruit set.
• The 0.5% LB urea treatment at end-April caused significantly higher fruit drop, indicating some negative effects close to flowering time.
• Fruit size improved significantly with the 0.4% Kelpak^® treatment, attributed to auxins and cytokinins in the product promoting cell division and expansion.
• Production increases of 1.0, 0.9, and 1.8 ton/ha were observed with 3.0% KNO₃ (mid-April), girdling (end-April), and 3.0% KNO₃ (mid-May), respectively.
• In the Nelspruit area, no significant effects on flowering or fruit retention were found across KNO₃ and LB urea concentration ranges, but 3% KNO₃ at end-April significantly improved fruit set.
• The study concludes that timely application of KNO₃, girdling, and possibly combinations of these treatments can enhance litchi flowering and production.
• High concentrations of KNO₃ at the end of April may negatively affect flowering and fruit set; proper timing and concentration are critical.
• The use of LB urea, Ethapon^®, and Kelpak^® alone did not consistently improve production.
• The results support the potential of growth regulator and cultural practice combinations to stabilize flowering and production and reduce alternate bearing in litchi.