The Effect of Chemical Defoliation on the Development of Apple Spurs

Abstract

An analysis was made of bud development on apple spurs sprayed with copper sulphate in late spring. The treatments caused the spur buds to break into a second flush of growth and eventually to form a new resting bud. The failure of these later buds to become fruit buds was correlated with the time in the season when they began to form, and was determined by the number of leaves and bud scales preceding the buds. The number of leaves in the second flush was related to the extent to which shoot tips and spurs were killed by the sprays; the number of leaves in the first flush and the number of bud-scales between these flushes of growth was also altered by the chemical. The factors affecting the number of nodes in each of these zones of growth are discussed, and it is suggested the sprays reduced the level of endogenous auxins in the leaves and endogenous gibberellins in the shoot tips. Differences associated with the vigour of the trees and with seasonal factors were also observed. The difficulties in estimating these factors limit the commercial value of this technique.