Pg. 23-32 Optimising the use of ethephon for cooler mid-season production areas

In mid-season production areas such as Nelspruit and Hazyview, flower induction in ‘Mauritius’ litchi takes place between mid-April and mid-May. Although water stress is a good way to suppress leaf flush before and during flower induction, late autumn rains often make it impossible to apply water stress properly. Therefore, the only way to control autumn/winter flush for mid-season areas is the application of ethephon to burn off the unwanted flush. Currently, ethephon is used as spot spray to control autumn/winter flush, but such applications generally have to be repeated several times due to re-occurring flush. 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. T he trials were conducted in the Nelspruit area on ‘Mauritius’ trees during the 2014 to 2016 litchi seasons. Ethapon® (a.i. 48% ethephon) was applied as a once-off full-cover spray after hardening of the last desired post-harvest flush at concentrations of 0, 500, 750, 1000 and 1250 ppm at the end of March, mid- and end of April. The control trees were treated with spot sprays as per current industry practice (at 1000 ppm whenever young shoots appeared). Shoot control on the control trees started at the end of March and needed to be repeated two to three times for sufficient flush control. In all three 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. Drought conditions prolonged the dormancy period, even in the untreated trees. Temperature, stress conditions and flush maturation time will determine what ethephon concentration is most effective.