Thinning golden delicious apples using ethephon sprays

In southern Tasmania ethephon sprays were applied at two stages of bloom and after bloom at concentrations from 350 to 1 400 ppm. At both the balloon blossom stage and 42 days after full bloom (AFB) 350 ppm ethephon caused satisfactory thinning of fruit by decreasing fruit set and increasing the number of fruits 70 mm or more in diameter. Higher concentrations of ethephon at these stages overthinned. At full bloom concentrations below 1 050 ppm ethephon did not remove significant numbers of fruit but both 1 050 and 1 400 ppm spray concentrations satisfactorily thinned the fruit. The spray of 1 400 ppm ethephon 42 days AFB significantly restricted fruit growth. Shoot length was reduced by all ethephon treatments and return bloom in the following spring was heavy in all thinned treatments. A mathematical model describing numbers of fruit set was developed and used to demonstrate a three-dimensional response surface to ethephon thinning sprays.