Efficacy of mechanical thinning of apple in Poland

A. Basak, I. Juraś, P. Białkowski, M.M. Blanke, L. Damerow
Trials on mechanical thinning were firstly carried out in Poland starting in 2008 and, thereafter, continued in 2009 and 2010 on 'Gala Must', 'Jonagored' and 'Pinova', apple trees grafted on M.9 rootstocks. Ten different treatments were established on each cultivar: four of them were mechanically thinned setting the Baum device at two tractor speeds (5 or 7.5 km h-1) and two rotors speed (360-380 and 420-460 rpm). All cultivars were thinned mechanically when the flower buds were at the balloon stage and the king flowers mostly opened. In some treatments, mechanical thinning was integrated by chemical thinning with NAA (Pomonit Super 050 SL) at 20 mL 100 L-1 when fruitlets diameter was 10-12 mm or by hand thinning performed after June drop. Trees thinned with NAA or by hand only, were used as additional control. Mechanical thinning reduced fruit set, depending upon apple cultivar and combination of tractor and rotors speed. NAA reduced fruit set more efficiently than mechanical thinning, especially in 'Gala Must' and 'Jonagored'. NAA combined with mechanical thinning strongly reduced fruit set in 'Gala' and 'Jonagored' and increased average fruit weight, skin colour and yield of marketable fruit percent in 'Pinova', and 'Gala Must'. Hand thinning increased the mechanical thinning efficacy in 'Pinova', 'Gala Must' and 'Jonagored', but not as much as NAA application. Hand thinning integration strongly reduced fruit set and increased average fruit weight in all cultivars, especially in 'Gala Must' and 'Pinova', and improved the skin red colour in 'Jonagored'.
Basak, A., Juraś, I., Białkowski, P., Blanke, M.M. and Damerow, L. (2016). Efficacy of mechanical thinning of apple in Poland. Acta Hortic. 1138, 75-82
DOI: 10.17660/ActaHortic.2016.1138.10
hand thinning, Malus domestica Borkh., fruit set, fruit quality, alternate bearing, sustainable horticulture