PRUNING, FERTILIZATION, CHEMICAL THINNING AND IRRIGATION AFFECT 'GALA' APPLE FRUIT SIZE AND CROP VALUE

A field study was conducted at Geneva New York State, USA over 3 years (2003-2005) using mature ‘Gala’/‘M.9’ trees. We compared the individual and combined effects of various factors known to influence fruit size of apple (pruning, nitrogen fertilization, chemical thinning and trickle irrigation). Of the four management factors considered, pruning had the greatest effect on fruit size while irrigation had no effect in either 2003 or 2004 but a significant effect in 2005. Thinning treatments had an intermediate effect while N-fertilization had almost no effect on fruit size but did increase yield. The most aggressive pruning treatment was stubbing back pruning which reduced yield the most each year and increased fruit size the most. A more moderate treatment was spur pruning (spur extinction) which had less effect on yield and resulted in a moderate increase in fruit size but had the greatest crop value. The least aggressive, limb renewal pruning treatment served as a control (limb removal of 1-2 limbs annually). When fruit size was adjusted for crop load, stubbing back pruning and spur pruning had greater adjusted fruit size than did limb renewal pruning. In most cases chemical thinning increased crop value. Exceptions were where fruit size on control trees was relatively large. Chemical thinning with benzyladenine (BA) combined with Carbaryl resulted in the best fruit size, but often no better crop value than thinning with NAA+Carbaryl. The combined effects of aggressive pruning, BA+Carbaryl thinning, high fertilization and irrigation gave an average fruit size of 190 g. However, crop value in each year was optimized when average fruit size was between 161-169 g (113-100 count size). This was true despite significantly lower fruit price for these sizes than 80 count size. Achieving 80 count fruit requires too large a reduction in yield, which would negate the higher price for the remaining fruits.