Large fruit from lightly cropping trees do not generally store well due to mineral imbalance in the fruit and to a low calcium concentration in particular.
Over-cropping trees produce small fruit that lack red colour and have insufficient dry matter for adequate texture, although the fruit is unlikely to develop physiological disorders associated with low calcium.
Judgement of the correct level of cropping to achieve sufficient yield, fruit size and visual quality without unduly compromising storage potential is paramount in achieving profitable production and commercial success.
Adequate thinning will help to ensure that harvest isn’t delayed beyond the optimum period for storage in an attempt to improve size and red colour.
Hand thinning Cox trees to one fruit per cluster at 35-40 days after full bloom has improved the texture and eating quality of CA-stored fruit.
Chemical thinning at the appropriate stage followed by hand thinning as necessary is the best practice to achieve the desired level of crop and help to increase fruit dry matter content. AHDB Project TF 215 reviewed products, technologies and emerging treatments that are being employed in majore apple producing areas.
Thinning sprays may indirectly increase susceptibility of apples to calcium deficiency disorders such as bitter pit and senescent breakdown by increasing fruit size and the leaf to fruit ratio.
The priority should be the achievement of the correct level of crop for profitable production but awareness of the effects of thinning on the mineral status of the fruit is essential for planning storage and marketing.
The lighter the crop the greater the requirement for supplementing calcium nutrition of the fruit by the use of calcium sprays and of pre-harvest mineral analysis to predict storage potential.