- RB Cronje and IM Ratlapane
- 2021
- Volume: 24
- Pg 24-32
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In the past decade, changes in autumn and winter climates in the subtropical regions of South Africa caused more frequent flushing during the litchi pre-flowering period and rendered the traditional ethephon spot spray application less effective for flush control, particularly when warm temperatures persisted into winter. This necessitated a new approach to chemical flush control with ethephon. Therefore, trials were conducted in two climatic different production areas, namely Nelspruit and Malalane, on ‘Mauritius’ trees between 2014 and 2017. The aim was to determine whether a single full canopy ethephon application, after the last post-harvest flush has hardened (i.e. dormant trees), could inhibit new flush long enough until temperatures become conducive for flower induction. Ethephon was applied as a single full canopy spray after hardening of the last desired post-harvest flush at concentrations of 0, 500, 750 and 1000 ppm at the end of March, mid- and end of April. Because of the warmer climate at the Malalane site, a double application at 1000 ppm followed by a 750 ppm application two weeks later was included at the Malalane trial site to ensure longer shoot inhibition. The control trees were treated with spot sprays as per standard industry practice (1000 ppm whenever young shoots appeared). For this report, results from all four years were combined to present a general trend in treatment performance for different production areas and application times. The results showed that single full canopy ethephon applications to dormant trees were very effective and successfully inhibited leaf flush during autumn and early winter, delayed flower panicle emergence, reduced the percentage leafy flower panicles, promoted carbohydrate accumulation during the dormancy period and thus increased flowering and yield without delaying fruit maturity. The double application provided a longer lasting dormancy in the warmer Malalane area, where induction takes place later than in the cooler Nelspruit area. Spot spraying of young flush was still effective for removing already existing young flush, however, this practice still permitted earlier panicle emergence under less inductive conditions and thus the development of leafy flower panicles. A single full canopy application on first flush appearance gave an added benefit over spot sprays in terms of flush control and delay of flower panicle emergence, but follow-up spot sprays were still necessary. Time of application (and related temperatures) as well as concentration, played an important role in the success of flush inhibition and delay of flower panicle emergence. In this regard, higher concentrations were more beneficial at earlier application times (end March, early April) or when temperatures remained high and a longer dormancy period was required. Likewise, for later application times (end of April or later), temperatures needed to be considered when deciding on the most effective concentration, particularly to avoid flower failure at low temperatures.
Summary:
Study Objective: Trials evaluated full canopy ethephon applications on dormant ‘Mauritius’ litchi trees as an alternative to traditional spot sprays for controlling autumn/winter flush, aiming to inhibit new growth until inductive temperatures (<20°C mean) for better flowering/yield amid changing climates with prolonged warmth.
Experimental Design: Conducted 2014-2017 in contrasting areas—Nelspruit (moderate autumns/cool winters, sandy soil) and Malalane (warm autumns/moderate winters, clay soil)—using randomized blocks (5 reps, 3 trees/plot); ethephon (Ethapon SL, 480 g/L a.i.) applied once-off full canopy at 500/750/1000 ppm (end March, mid/late April) post last post-harvest flush hardening, plus Malalane double (1000+750 ppm, 2 weeks apart); controls: spot sprays (1000 ppm on young flush) or untreated.
Flush Control Results: Full canopy sprays effectively inhibited flush through autumn/early winter, outperforming spot sprays (which required 2-4 repeats, allowed earlier panicle emergence under suboptimal conditions); higher concentrations/doubles extended dormancy longer, especially in warmer Malalane; promoted carbohydrate accumulation, reducing leafy panicles.
Flowering and Yield Impacts: Delayed panicle emergence to better inductive periods, increased panicles/branch (via axillary bud break), improved flowering uniformity/percentage, and boosted yield without delaying maturity or affecting fruit quality (size, TSS, TA); e.g., early applications (end March) with 1000 ppm optimal for high temperatures/long dormancy needs.
Key Factors and Recommendations: Timing/concentration critical—higher doses for early apps/high temps, lower for late/cooler to avoid flower failure; full canopy on first flush + spots added benefits over spots alone; reduces labor/costs vs. repeated spots, adaptable to climate variability.