Pg. 47-57 Effect of autumn water stress in combination with ethephon on flowering and fruiting of ‘Mauritius’ litchi in two different production areas of south Africa

Poor litchi flowering is a worldwide problem, especially in areas where temperatures during the flower induction
period are not low enough. The effect of autumn water stress in combination with ethephon applications to control late autumn flush in order to improve flowering and yield was investigated over a four-year period. The study was carried out on the cultivar ‘Mauritius’ grown in a warm production area near Malalane (with moderate winters), and in a moderate production area near Hazyview (with cold winters). The trees were subjected to four irrigation treatments, which were two stress-induced irrigation treatments and two optimum irrigation treatments without water stress. The water stress treatments were applied during autumn, either between March and April (early stress), or between April and June (late stress). Up to 50% and 70% of the optimum tree water requirement was withheld for the early and late water stress periods, respectively. Ethephon was applied as spot sprays during April whenever young flush appeared to both water stress treatments as well as to one of the optimum irrigation treatments. The second optimum irrigation treatment was not treated with ethephon. At the Malalane trial site, late water stress in combination with ethephon applications successfully controlled vegetative flushing and increased flowering and yield, compared with early water stress and optimum irrigation in combination with ethephon application. Optimum irrigation without ethephon caused the trees to flush in all four trial years, reducing yields significantly. At the Hazyview site, flowering was clearly enhanced by ethephon applications with a small synergistic effect through water stress. Early water stress (March/April) appeared to be more beneficial for increasing flowering in most years, compared with late water stress, provided water stress
was not interrupted by late rains. However, this effect was not carried through to yield due to climatic factors
influencing tree phenology. There was little difference in yield between the treatments over the average of four years. Overall, the late water stress period was more beneficial in the warm production are (late flower induction) and the early water stress period more beneficial for the cooler production area (early flower induction). The use of ethephon with or without water stress remains an indispensable orchard practice for litchi production.