Evaluation of Benzyladenine as a Chemical Thinner on ‘McIntosh’ Apples

Abstract

Abstract Five chemical thinning trials, conducted over 4 years, indicated that BA is an effective thinner for ‘McIntosh’ apples (Malus domestica Borkh.). Although it can thin at concentrations as low as 25 mg·liter−1, in most years a higher concentration was required to thin adequately. It appeared that 14 to 18 days after full bloom, when fruit size was about 10 mm, may be the period when maximum thinning was achieved. Greater thinning occurred when BA and carbaryl were combined than when they were used individually. BA increased fruit weight, flesh firmness, and soluble solids content at harvest relative to no thinning. The storage life of fruit treated with BA was less than that of fruit from nonthinned trees, but this effect may have been an indirect response related to the larger fruit size rather than a direct response to the chemical. BA caused thinning and induced lateral branching simultaneously on young ‘Macspur McIntosh’ trees. Therefore, crop load on trees just coming into production may be significantly reduced when BA is used to induce lateral branching. Chemical names used: N-(phenylmethyl)-IH-purine-6-amine [benzyladenine (BA)], 1-napthaleneacetic acid [NAA], 1-naphthalenyl methylcarbamate [carbaryl].