More fine tuning
This month I will cover other very important preharvest husbandry practices necessary to optimise fruit quality.
Colour, flavour and texture are the most important consumer requirements. According to market research reports, high fruit colour’s main role is to entice newer consumers to buy the product. Repeat sales are more dependant on the eating experience. This is flavour and texture, with the latter tending to override flavour. Fruit, when it gets to the consumer, must be crunchy and juicy. Any hint of mealyness is a big negative and likely to stop further buying.
Harvesting, at optimum maturity for storage is the key to maintaining crispness and juiciness.
The crop has to be set up so this can be achieved. For most varieties the optimum harvest window is no more than two to three weeks.
Last season experienced shocking weather over harvest due to frequent rain. This interrupted harvest, made meeting optimum harvest maturity difficult and due to the delays fruit was softer and much more prone to injury by bruising and stem punctures. Also, due to the rain, pre-harvest fungicide cover was thin, so there have been issues with post-harvest rots. All of these problems have resulted in expensive repacking offshore. Avoiding these problems is an easy way to improve grower returns, and much more effective than trying to reduce costs by thinning down the spray programme.
PIT AND BLOTCH
Last season incidences of these disorders were above normal, partly due to the warm growing season we experienced. Pit and blotch is always a bigger problem on apples grown in warm climates compared to cooler climates.
Maintaining the correct nutrient balance will help colour development.
As harvest approaches nitrogen levels need to be almost in the deficiency range. Leaves need to be pale, rather than dark green. Relative to fruit, leaf is a relatively poor sink for nitrogen, so once foliar nitrogen levels move past minimum acceptable levels a small increase in leaf nitrogen may indicate a big lift in fruit nitrogen content. It’s the fruit nitrogen level that determines fruit colour development.
There is also some evidence to suggest that high phosphorus levels relative to nitrogen will result in good fruit colour.
Last season, which was a relatively poor one for fruit colour development, I carried out some comparative leaf and soil testing in a block of Scilate on M9 rootstock which was showing large differences in colour across it. These samples were taken at the end of March.
The table below shows leaf analysis levels.
In these soils, phosphorus levels were similar, as were potassium and magnesium.
As with pH, soil calcium levels were very much higher where colour was good.
Where colour was good, soil was also less dense, and CEC significantly higher indicating a more fertile soil with a better root environment.
The evidence points towards the need or higher phosphorus status but how you achieve higher phosphorus levels is rather unclear. Data out of British Columbia reports increased yields in young orchards from applying soluble phosphorus through fertigation over the flowering period. This has also been shown to lift tree phosphorus levels significantly.
A few years ago, fertiliser companies here used to sell mono-ammonium phosphate in liquid form. Used as fertigation this would be ideal for lifting plant phosphorus status.
Good leaf health is important for colour development. Heavily cropped trees are very prone to magnesium deficiency as harvest approaches. The reason for this is that ripening seed has a high magnesium requirement, so to satisfy this, leaf magnesium is mobilised and moves from leaves to seed. When severe, low magnesium can lead to leaf breakdown.
The anthocyanins responsible for fruit colour have a very high photosynthate requirement so to get good fruit colour leaves must be healthy, therefore a good foliar magnesium programme is necessary.
Irrigation management can play a key role in fruit quality.
Fig 1. Last year we saw more pit and blotch than normal including varieties not generally prone to the disorder such as this Scilate.
Fig 2. These Sciros were thinned to singles, then preharvest reflective mulch enabled almost all the crop to be pricked as soon as the fruit reached harvest maturity.