Chemical defoliation of apple rootstocks and the influence of rootstocks type on the defoliation of 'Jonathan' scion

Abstract

The following substances were used to defoliate apple rootstock instead of hand defoliation before digging out: KI, CuSO₄ · 5H₂O, Mg(ClO₃)_{2< · H2O, ethephon (Ethrel 68-250 and CKB 1131), preparation N252, and the mixtures: ethephon (Ethrel) with copper sulphate, or with gibberellic acid, morphactin (EMD) with ethephon, and morphactin with ethephon and copper sulphate. Among the inorganic defoliants tested, only Mg(ClO3)2 · H2O gave satisfactory results in defoliating apple rootstocks. When applied at the end of September this chemical did not decrease winter hardiness of the rootstocks. Ethrel and the preparation CKB 1131,caused satisfactory defoliation, but when used in optimal concentrations for defoliation they decreased the winter hardiness of plants. The mixture of ethephon with copper sulphate in which both components were used in low concentrations also appeared highly effective. Ethephon in low concentration mixed with EMD caused only partial defoliation of the rootstocks. Addition of gibberellic acid did not improve the effectiveness of ethephon. Preparation N252 in a concentration of 0.15% effectively defoliated the rootstocks and did not cause a subsequent decrease of frost hardiness in the conditions of this experiment. The response of 'Jonathan' scions to defoliants was modified by the rootstock.}