Cripps Pink fruit that meet marketing specifications for colour can be sold under the trademark name Pink Lady™ but they must have a minimum 40% blush (bright pink) surface coverage.
Achieving sufficient blush for Cripps Pink to meet these Pink Lady marketing specifications can be difficult because synthesis of red anthocyanin pigments in the skin is reduced by shading and high temperature.
To improve colour, there has sometimes been a tendency to delay harvest but this means picking can take place when fruit are over-mature.
Shafiq et al. (2011) showed that delaying harvest of Cripps Pink for up to six weeks after commercial harvest maturity did promote blush development through accumulation of anthocyanins in the skin but this was at the expense of fruit firmness and titratable acidity—both of which were reduced.
Also, later pick, over-mature fruit tend to lose quality faster in storage and can present maturity related physiological disorders like internal browning.
Light and temperature affect blush
Recently, a considerable amount of new information has been gathered on how the environment around fruit affects production of anthocyanin in the skin.
Light and to a lesser extent temperature are the main environmental elements that determine blush development.
Like most red apple varieties, blush on Cripps Pink fruit is promoted by good light exposure, low night temperatures and avoidance of extreme daytime heat during the final weeks of fruit development leading to harvest.
Countering rising global temperatures
With rises in global temperature expected to continue, growers need practical approaches to mitigate negative temperature impacts and maintain or increase current levels of blush.
Over-tree sprinkler cooling can directly counteract high temperatures and has been shown to benefit blush development under some circumstances.
Use of colour enhancing chemical growth regulators is another option. However, tailoring orchard practices to increase fruit exposure to light is an easy and manageable way to overcome the red pigment losses that might be caused by elevated temperatures.
Integrated approach needed for greatest colour development
Various orchard management systems have been shown to increase red blush of red apple varieties by increasing fruit exposure to light.
However, some routine on-farm practices may also have negative influences on blush development, while being essential for orchard productivity in other respects.
Growers need to prioritise and balance potentially counter-productive activities.
In order to produce fruit that meets market demands, an integrated approach to colour development using several approaches may be required.
Good canopy management
Good canopy management is probably the most important factor in improving colour.
Correct style and level of pruning is needed to open up the canopy to allow sufficient light penetration for fruit colouration.
Enough wood needs to be removed to achieve high light levels without reducing yield excessively and without exposing fruit to direct sunlight during summer that may cause sunburn.
Apples require a minimum of 50% full sunlight on fruits and leaves in order to achieve adequate red colour with superior colouring occurring at levels around 70% full sun (Gurnsey & Lawes 2014).
Summer and winter pruning
Good canopy management can sometimes be achieved through winter pruning alone, although summer pruning may be required with some growing systems and high vigour trees.
Branch structure
For Cripps Pink trees, branch structure needs to be simple in middle and upper parts without significant sub-branches and arranged to allow light to pass between branches into the lower fruiting arms (Wilton & Hornblow 2003).
Water shoots
During late spring to early summer, water shoot growth should be pruned or plucked out to promote good light penetration into the fruit bearing zones.
This should be done before temperatures reach the level at which sunburn could occur because fruit that have been previously shaded can be more vulnerable to burning.
Leaf plucking/pruning
Later in the season (20 days prior to harvest), excessively shaded Cripps Pink fruit need to be exposed to light by leaf plucking or pruning back any shading laterals to 2 or 3 leaves (Wilton & Hornblow 2003).
Crop load
(continues next month)
See this article in Tree Fruit June 2015
