Pg. 18-19 The effect of water stress in autumn and winter on flower induction in litchi and the role that Ethepon can play: A preliminary report

Various studies in literature indicate that flower induction in litchi is solely triggered by temperature differences. However, reducing soil moisture by withholding water in autumn and early winter to levels below the water requirements of the trees can assist them to enter a rest period, especially in warm areas where high soil moisture would cause trees to flush continuously and in doing so prevent good flower formation. But a prolonged withholding of water could also lead to unnecessary stress to the trees. Furthermore, the use of Ethepon^®, an ethylene releasing compound, to burn-off unwanted flush in autumn has more and more become an important management tool for good flowering.

How do all these management practices fit together, what role does the timing of withholding water play and is withholding water in autumn still necessary if Ethapon^® can control autumn flushing efficiently on its own?

In 2009 a new trial was started in an attempt to give answers to these questions. Trial details and first observations are presented.

Summary:

• Flower induction in litchi is primarily triggered by temperature differences, but soil moisture reduction in autumn and early winter can help trees enter a rest period, especially in warm areas where high soil moisture causes continuous flushing and poor flower formation.
• Prolonged withholding of water may cause unnecessary stress to the trees.
• Ethepon^®, an ethylene-releasing compound, is increasingly used to burn off unwanted vegetative flush in autumn, improving flowering.
• The study investigates how water stress management and Ethepon use interact, questioning the necessity of water withholding if Ethepon controls flushing effectively.
• Trials were conducted in two South African commercial orchards (Malelane and Hazyview) with differing soil types (clay and sandy) and irrigation systems.
• Treatment effects were monitored through phenology, starch sampling, stem water potential, chlorophyll content, and soil moisture.
• Preliminary data shows that chlorophyll content in green leaves is much higher than in stressed leaves, indicating water withholding combined with high solar radiation can cause photo inhibition and reduce photosynthetic rates, especially in sandy soils.
• Soil moisture probe data confirmed irrigation scheduling impacted soil moisture, but unusually high rainfall during the trial period prevented drying soil to desired stress levels.
• Yield and fruit size data will be evaluated after the 2009/10 harvest to assess treatment impact.
• The research explores optimizing water stress and the role of Ethepon in managing vegetative growth for better flower induction and production.