Use of Ethephon and Calcium Acetate to Manipulate the Foliage Retention Rates of Camphor and Golden Shower Trees

We evaluated the effect of water and ethephon (2-chloroethyl phosphonic acid) under different doses (500 mg·L⁻¹, 1000 mg·L⁻¹,2000 mg·L⁻¹, and 3000 mg·L⁻¹), with and without calcium acetate (CA) in two foliar applications on camphor and golden shower saplings. It was aimed for ethephon to replace pruning in reducing transpiration during transplantation. We adopted a completely randomized design as an experimental design. An adequate dose of the ethephon/CA solution must be able to defoliate more than 50% of the foliage and recover to more than 75% of the foliage between 11 May and 19 July. The result showed that defoliation started within one week of the first spray, reached the lowest foliage retention rates (LRRs) in one month, then re-foliated. The LRRs were correlated with the doses of ethephon in the means, but most of the treatments did not show statistical significance due to the large in-group variations among replicates. Adding CA raised the LRRs and alleviated the dieback, especially on camphor trees. Adding CA was necessary for camphor trees to re-foliate. The final foliage retention rate (FRR) was influenced by the ethephon dose, and different tree species showed different restoration abilities. The adequate dose for camphor and golden shower trees to have an LRR < 50% and an FRR > 75% was to spray 1000 mg·L⁻¹ of ethephon first, then spray another 2000 mg·L⁻¹ of ethephon and 8000 mg·L⁻¹ of CA three days later.