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. T herefore, 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.