Effect of thinning with metamitron, NAA, BA and naphthenic acids on apple (Malus domestica) trees

Abstract

The successful use of chemical thinners on apples requires programs employing multiple chemistries over the thinning period. A thinning program can be designed using various active ingredients in single or multiple applications. The objective of this work was to compare that standard thinning program (COM-STD), with naphthalene acetamide (NAD), 6-benzyladenine (BA) and naphthyl acetic acid (NAA), to new programs involving Metamitron (ME). Five experiments were conducted over seven seasons, from 2013 to 2019 on Gala and Golden apples. Under the trial conditions, COM-STD (NAD/(BA + NAA)) and ME induced fruit abscission. However, the single applications of ME and COM-STD, made on the same days, showed the same level of thinning efficacy. NAD in petal fall with Tank mix (ME + NAA + BA) application at 11mm increased the thinning efficacy in comparison with applying ME and COM-STD alone. Dose effects were also observed with both ME applied alone and the Tank mix (ME + BA). In general, all combinations involving ME and COM-STD, and especially applying COM-STD after ME, produced greater thinning results than applying either product individually to ‘Gala’ and ‘Golden’ apples. Crop yields fell as the thinning efficacy increased, in all the experiments. There was also a negative quadratic relationship between thinning efficacy and average fruit weight, color and diameter.