Section 1. Optimising the pre-harvest management of orchards to maximise the storage and eating quality of fruits
Orchard management practice should always be geared towards maximum yields of class 1 fruit. The influences of such practices on storage quality need to be considered in order that appropriate marketing strategies can be put into place.
Where such practices adversely affect storage or eating quality, remedial measures need to be taken where these are available. The influence of pre-harvest factors on storage quality operate primarily through effects on yield, fruit size and vegetative growth.
Cropping level, fruit size and thinning
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.
Vigorous growth competes with the developing fruit for available nutrients and water and can often exacerbate problems due to 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 (see Part 1 of the Guide) at the appropriate stage followed by hand thinning as necessary is the best practice to achieve the desired level of crop.
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 (see Section 3).
The lighter the crop the greater the requirement for supplementing calcium nutrition of the fruit by the use of calcium sprays (see Section 2), post-harvest calcium treatments (see Section 7) and of pre-harvest mineral analysis to predict storage potential (see Section 3).
Avoid hard pruning in the winter and use an appropriate chemical growth regulator as a means of controlling shoot growth in the spring and summer months.
Late summer pruning reduces susceptibility of stored fruit to bitter pit and other calcium deficiency disorders and improves red colour and the efficacy of calcium spraying in the orchard. However, this form of pruning should be limited to the vigorous upright one-year-old shoots and not done too early as re-growth may occur.
Effects of the growth regulator ‘Cultar’ (paclobutrazol) on the storage quality of Bramley apples have generally been positive but is known to induce diffuse browning disorder in Cox apples on some farms, particularly when used in conjunction with triazole fungicides such as myclobutanil or penconazole (see Section 13). Prohexadione (‘Regalis’) may be the preferred growth regulator for use in Cox orchards.
Growth regulators applied to improve skin finish (‘Regulex’) do not appear to cause adverse effects on storage quality.
·Currently no growth regulators are available in the UK for use in the orchard to specifically improve storage quality of apples. ‘ReTainR‘ is a product approved #.and used in some parts of the world that contains an ethylene inhibitor (aminoethoxyvinylglycine or AVG).
‘ReTainR‘ is applied as an orchard spray to retard fruit maturity, extend the picking period for storage and delay the rate of ripening and senescence of fruit in store. Unfortunately plans to register this product for use in the UK have been abandoned by the manufacturers despite results on Cox, Gala and Bramley being particularly encouraging.
Herbicide-based soil management may reduce phosphorus uptake into leaves and fruits and increase susceptibility of fruit to low temperature breakdown during storage. Apply phosphorus sprays (see Section 2) in Cox and Bramley orchards where phosphorus levels in the fruit are consistently low.
Ensure sufficient weed-free areas in Bramley orchards to reduce the competitive effects of grass on nitrogen uptake. Intense competition will reduce yield and fruit size and will promote red colour and reduce the intensity of greenness in the background colour.
Reductions in fruit phosphorus and calcium due to increased area of bare soil and nitrogen application should be countered by the use of orchard sprays containing phosphorus and calcium respectively.
Safeguard storage potential by routine application of calcium sprays and correct harvest date. Fruit on lightly cropping trees tend to be ready to harvest earlier than those carrying heavier crops. However, fruit from lightly cropping trees are likely to contain more starch and this can give a confusing picture of maturity based on the starch-iodine test. Results obtained with the starch-iodine test on young trees need to be interpreted carefully (see Section 4).