An early season
The only thing certain about fruit growing is that each year will be different.
My general impression is that at the end of the first week in November the season was running about 10 days ahead of normal with regard to fruit development. Growing degree days (GDDs) base 10°C accumulated from the beginning of September confirm this opinion. When this season is benchmarked against Gisborne, our earliest apple harvest district, our spring temperatures in Hawke’s Bay have been very close to a normal good Gisborne spring. This means that there is a fair chance that Royal Gala, for instance, will be ready for harvest early to mid February rather than mid to late February. Fruit size and length of time from full bloom to harvest is mainly driven by the temperatures experienced over the cell division period, and the crop load. There are strong relationships between the GDDs base 10°C accumulated over the first 50 days and both fruit size potential and harvest time expressed as days after full bloom (DAFB) for apples.
Early fruit thinning is also a critical part in maximising harvestable yield, fruit size, fruit colour development, fruit pressure and fruit dry matter.
With our good spring temperatures this season, conditions have also been ideal for chemical thinners to work. Vegetative growth has also been lush this spring, due to the good growing conditions giving good chemical thinner uptake, and the necessary competition between shoot growth and fruit to give strong natural fruit drop – which has often been enhanced a bit too much by the chemical thinners. Consequently, there are a few thin crops about. If it continues to be a warm season, better make sure robust calcium programmes are applied to varieties that are prone to pit and blotch.
In some varieties, I have seen early natural fruit drop bring fruitset to ones and twos, as well as many cleared sites without the help of any blossom period thinning sprays.
The impact of poor provision for cross-pollination in apples is more marked this season than usual.
The varieties most affected are Braeburn, which this year had a very early short flowering period, and Scired which is 100% self-infertile and in the absence of dormancy breakers to bring its blossom period forward, flowered when most other varieties were finished.
This is a good year to assess whether your orchard has sufficient provision for cross-pollination. In recent years there has been a trend to plant orchards intensively in large single variety blocks. After two or three growing seasons, trees in the row tend to grow into one another. Once this begins to happen bees travel along the rows rather than across rows, so your pollinators need to be in the rows for good fruitset.
A few years ago, before we began to intensify apple orchards and move into large scale production units, it was traditional to plant varieties in four to six row blocks. The main reason for this practice was to take care of the cross-pollination requirement.
Six rows was generally considered about as wide as you could go before running into fruitset problems due to poor crosspollination. In locations with high densities of orchards, it was possible to get satisfactory fruitset in larger plantings of single varieties. This effect was thought to be due mainly to pollen mixing in the hives through some of the hive working other varieties.
In small, isolated orchards, provision for cross-pollination is much more critical, and I think we are reaching this situation
in our main districts now due to the predominance of large single variety plantings.
I am also of the opinion that many diploid apple varieties have some measure of self-fertility if flower is strong, such as the “on” crop, and temperatures over the pollination period are very good.
In the “off” crop year, which for many Braeburn blocks is this season, flower is too weak to become self-pollinated, but will readily set if there is good cross-pollination.
Incidentally, if there is not good provision for cross-pollination, bringing more bees in is not going to help much.
Immediately prior to hand thinning is a good time to assess pollination.This is easily done and the two things to check are:
1 Any fall-off in fruitset density as distance from other
2 Seed numbers in the fruit.
As a general rule the first three or four rows adjacent to other varieties show good fruitset, then as you move further across the block the fruit begins to disappear. Incidentally, the minimum difference you can see by eye is about 20%, so if you are seeing visual differences it is more than that.
With biennial varieties, it is not unusual for the rows adjacent to the next variety, or the pollinator row, to become violently biennial. For this reason, you need to benchmark your fruitset
through the block against the set in rows three or four from the block boundary.
There is also high bee traffic along the ends of the rows, so in the absence of biennial bearing, fruitset on the end of row trees is usually excessive. Your pollination assessments need to be made a few trees into the block. Experience with fruitset levels in isolated orchards indicates that single tree or branch pollinator influence extends about 10 to 15 metres down the row. This means that dedicated pollinator trees need to be 20 to 30 metres apart for apples. Incidentally, I remember seeing a Red Delicious orchard in the Bay of Plenty which had the rootstock growing instead of the scion variety in one corner of the planting. The only trees that cropped in that orchard were the ones around the flowering rootstock. I saw a similar thing once with Braeburn. In this case there was a very large Malus profusion in the grower’s garden. The Braeburn trees cropped heavily and were quite stunted due to crop load for the first 30 odd metres into the block, then normal canopy size and good cropping performance in the 30 to 60 metre distance zone from the M profusion tree, then beyond that excess vigour and no crop. The apple flower has five locules, each with two ovules, giving a fully pollinated potential of 10 seeds per fruit. For fruitset it is not essential for all ovules to be pollinated, but in my opinion you need at least five, preferably uniformly distributed around the locules.With strong flower and good cross-pollination the number of seeds is more likely to be in the 7 to 10 range. You need this number for good fruit shape and to capture the fruit’s full potential size. If your fruit cutting regime is consistently showing less than four or five developing seeds per fruit, this is a sure sign of a pollination problem.
Some varieties, notably Royal Gala types, will abort seeds during the growing season and in some years there will be no viable seeds near harvest. While we do not fully understand this phenomenon, this seed abortion problem is quite different to lack of initial pollination when the seeds do not grow at all.
Other impacts on crop management from The early season
If the favourable growing conditions continue, it is likely that fruit size is going to be larger than has been seen in the last two or three growing seasons.
Where fruit numbers and distribution allow, and you have good outlets for smaller fruit sizes, crop loads in high red
long-stemmed varieties could be increased a little by leaving a few more twos and threes in the bunches.
I suspect, however, that some blocks will not have enough crop to allow this. In these blocks, there will need to be careful crop assessment to determine if it is worth spending money on expensive hand thinning.
In large-fruited, partial red varieties such as the Pacific series, Scilate and Fuji, diligent hand thinning is still necessary. These varieties need to be singled and spaced out irrespective of crop load if you want to achieve a smooth harvest, high packouts, and pick at optimum maturity to give good out-turn in the marketplace.
The early season, lighter crops and larger fruit sizes has the potential to give overmaturity problems if the harvest is not well-managed, and the fruit is not picked on time.These are the conditions that lead to fruit maturity racing away if you are not ready for harvest.
If your harvest labour supply will not arrive in time for an early harvest, consideration needs to be given to delaying maturity strategies for Royal Gala. The industry has established a reputation in the marketplace for a high quality, crisp and juicy Royal Gala which is selling at a premium to competitor fruit. Do not destroy this progress by shipping large volumes of over-mature product this season because the harvest was not organised on time.
Monitor fruit sizing progress
Towards the end of October I was fortunate to attend the Hawke’s Bay Summer Green meeting at which Professor Luca Corelli Grappadelli, a tree fruit specialist from the University of Bologna, spoke on orchard performance.
Professor Corelli’s opinion was that fruit growth and fruit size were the best parameters to measure when assessing tree performance.
“Over-mature fruit which lacks crunch and good flavour does not go down well in the market and if too much overmature fruit gets through, all the good work in establishing our Royal Gala as a premium product will be lost.”
With good data on fruit size and fruit growth rates, it is possible to predict fruit size distribution at harvest, which is a great help when organising packaging and marketing strategies. Another point that he made was that for our climate, based on data from the international apple tree performance study led by Dr Stuart Tustin, we have about 55 days from full bloom to bring apple crop loads down into the optimum crop load for maximum fruit size response from hand thinning. For this season, 55 days from full bloom would be about the beginning of December.
AgFirst’s OrchardNet programme has a fruit sizing tool which can be used to track the progress of your fruit size. Historical data on fruit sizing indicates that Royal Gala fruit sizing between 30 days and 90 days after full bloom (DAFB) falls within the range of 4 to 4.5mm per week. After 90 DAFB there is a steady fall off in fruit sizing, down to about 3mm per week at 112 DAFB, continuing to fall to 2mm per week at about 140 DAFB, with further decline to under 1.5mm per week at around 150 DAFB.
Where trees are under stress through crop load or water stress, the downward trend in fruit sizing from about 90 DAFB, usually early January, will be much steeper.
By about 50 DAFB it is possible to observe fruit differences for similar aged fruit emerging. For instance, at this stage 110 count fruit should have been 32mm and 100 count fruit 35mm in diameter. At 95 DAFB 100 count fruit should be 60mm, and 110 count fruit 57mm in diameter. After about 50 DAFB, the fruit size hierarchy among the fruits on the tree has become established, so it is possible to size thin with confidence to remove lower value small fruit. As fruitlets will grow at around 4mm per week until late December or early January, it is necessary to adjust minimum fruit sizes to thin to twice a week.
If crop loads are excessive and fruit sizing shows signs of stopping around 90 DAFB, fruit growth can be started by a re-thin, removing smaller or damaged fruits to bring the crop down to what the tree can handle. With late thinning, sunburn can be an issue, particularly where it is necessary to break up bunches and expose hitherto shaded fruit to direct sun.
In the case of Royal Gala, particularly the high red strains, application of Retain before any ripening begins can give 10 to 14 days delay in harvest maturity. Over the last couple of seasons Retain has been particularly effective, with harvest delay of 14 or more days quite common.
These seasons were quite cool over the pre-harvest and harvest period for Royal Gala.The incidence of sunburned fruit in Royal Gala crops was relatively low and I think the absence of sunburn contributed to the effectiveness of Retain because sunburn injured fruit triggers the release of endogenous ethylene in the crop, which reduces the effectiveness of Retain. In normal seasons, Retain application in Royal Gala is made about the last week in January. As this season is running early, optimum Retain timing will also be earlier this season, maybe even mid January.
In early varieties checking for maturity movement needs to commence 10 to 14 days earlier than normal.
Incidentally, a large proportion of our Royal Gala are high colour strain on dwarf rootstocks, which can have high starch content. Because starch concentrations are high, maturity can be more advanced than the starch iodine test would indicate. If soluble solids (Brix) readings are starting to lift and there is no indication of the starch iodine patterns moving, the starch pattern will go fast once it begins to move, so you had better be ready to harvest. If it appears that fruit maturity will be ahead of your harvest labour supply, better consider using Retain to hold the fruit back to improve your chances of harvesting it at optimum export maturity.
John Wilton is a deciduous fruit specialist, AgFirst
In recent seasons New Zealand Royal Gala has commanded a premium in the marketplace due to good colour enabling the crop to be harvested at optimum export maturity. All the pointers we have indicate that this will be an early harvest season. Over-mature fruit which lacks crunch and good flavour does not go down well in the market and if too much over-mature fruit gets through, all the good work in establishing our Royal Gala as a premium product will be lost.