Pg. 33-40 Optimising the use of ethephon for warm early-season production areas

The climate in the early production areas is characterised by high temperatures during autumn and early winter. Temperatures only start dropping after mid-May. Therefore, flower induction in early production areas, such as Malalane, only takes place from mid-May onwards. These climatic conditions influence tree phenology and necessitate optimisation of certain orchard practices. Due to the high temperatures, trees tend to flush into May, which interferes with flower formation. Flush control is therefore an essential tool for successful litchi production in warm production areas. Currently, ethephon is used as spot spray to control autumn/winter flush. Such applications generally have to be repeated several times due to re-occurring flush and therefore are cost and labour intensive. In order to reduce the number of applications, trials were initiated to determine whether a once-off full-cover ethephon application after the last post-harvest flush has hardened (i.e. dormant trees) could inhibit new leaf flush long enough until temperatures become conducive for flower induction. The trials were conducted in the Malalane area on ‘Mauritius’ trees during the 2014 to 2016 litchi seasons. Ethapon^® (a.i. 48% ethephon) was applied as a single once-off full-cover spray after hardening of the last desired postharvest flush at concentrations of O, 500, 750, 1000 and 1250 ppm at the end of March, mid- and end of April. A double application at 1000 ppm followed by a 750 ppm application two weeks later was included to account for the warmer climate. The control trees were treated with spot sprays as per current industry practice (at 1000 ppm whenever young shoots appeared). Shoot control in the control trees started at the end of March and needed to be repeated two to three times for sufficient flush control. In all years, concentration and timing of full-cover ethephon applications affected growth of leaf flush and time of flower panicle emergence. The higher the concentration applied, the better was flush inhibition during April/May and the later was flower panicle emergence. Climatic conditions during April/May also influenced tree reaction with higher temperatures reducing the dormancy period and vice versa. Temperature, stress conditions and flush maturation time will determine what ethephon concentration is most effective.

Summary:

• The study addresses litchi leaf flush control and flowering in warm early-season production areas like Malalane, where temperatures remain high during autumn and early winter, delaying flower induction until mid-May or later.
• High temperatures in these regions cause continued leaf flush into May, which disrupts flower formation; therefore, effective flush control is critical.
• Water stress is insufficient due to rainfall, so ethephon is used to suppress flush by killing young shoots.
• Current practice uses multiple spot sprays of ethephon as flush recurs; the study tested a single full-cover ethephon spray on dormant trees after the last post-harvest flush at different concentrations (0, 500, 750, 1000, 1250 ppm) and times (end March, mid-April, end April).
• A treatment with two applications (1000 ppm followed by 750 ppm two weeks later) was also tested to address warmer climate demands.
• Control trees received spot sprays with 1000 ppm as needed.
• Results showed:
  • Higher concentrations and later application times better inhibited leaf flush and delayed flower panicle emergence.
  • Flush inhibition was less effective under continuous warm conditions, especially early in the season.
  • Full-cover applications delayed flower emergence and increased flower panicle numbers by killing terminal buds and activating axillary buds.
  • Flowering and yield were improved by sufficient flush control; untreated trees or low ethephon concentrations had poor flowering and yield due to excessive flush.
  • Yield increases were consistent with flowering data; fruit size was unchanged but fruit maturity was advanced by ethephon.
  • Best outcomes were achieved with 750-1000 ppm applications or a double application under very warm conditions.
  • The 1250 ppm concentration provided no additional benefit.
• The study emphasizes that climatic conditions after application strongly influence ethephon’s efficacy; higher concentrations are necessary during warmer autumns.
• Recommendations include applying full-cover ethephon between early April and early May, adjusting concentration and timing based on temperature, to ensure flush suppression and optimal flowering.
• This approach helps preserve starch reserves and sustain yield in warm early production areas facing late flower induction.
• The research was supported by the South African Litchi Growers Association and the Agricultural Research Council.