Thinning and crop load both critical
Late winter and early spring have been cold. This has held back bud break so once the heat arrives bud break will be rapid and compressed. There is good scientific data to show that pipfruit crops which follow a cold late winter tend to be heavier than usual.
It’s likely the industry will be facing another record crop. This will put harvesting and post-harvest facilities under pressure. It’s therefore very important to grow the best quality fruit we can. This will minimise wastage and make harvest much easier. Getting thinning and crop loading correct is key to achieving these objectives.
Unlike last year when frost wiped out a substantial portion of the European crop giving us a strong market, light crops are invariably followed by larger crops so the market, initially at least, will be well supplied with pipfruit product. Extremely high summer temperatures in the Northern Hemisphere this year may have adversely affected fruit quality and storage life there. The market may be awash with poor quality Northern Hemisphere product, so we will need a crisp, juicy, well flavoured fruit to differentiate our product so that it will command premium prices.
Managing thinning and crop load well, followed by harvesting at optimum maturity is the best way to grow the high quality product needed to achieve this objective.
We have very effective post-bloom chemical thinning tools these days so with diligent use of chemical thinners it should be possible to bring the hand thinning task down to manageable levels, unlike last season when a timid approach to chemical thinning led to some very high hand thinning bills.
MAXIMISE HAND THINNING BENEFITS – START EARLY
Where metamitron products are used response is rapid, usually within 21 days. Once the chemical thinning drop is largely over, hand thinning can commence.
I am of the opinion that to grow high quality fruit of high value varieties, two hand thinning passes are necessary. The first pass needs to be completed before the really hot weather arrives. Get through it before Christmas.
Where you have good numbers of fruiting sites and relatively uniform distribution of fruit over the whole tree, single fruit is the best way to go, particularly for coloured large fruited varieties such as Fuji, Scired, Sciros and Scilate. These varieties should also be at the head of the thinning priority queue.
Smaller-fruited varieties with relatively long stems such as the gala group, Cripps Pink and Scifresh can support twos and in the case of the gala group maybe threes or more in the bunches on favoured sites.
In the ideal world, growing fruit in singles will give the best results in regard to colour and quality, but with these smaller- fruited varieties you need very large fruiting canopies to achieve this and also have enough crop load to control tree vigour.
The hand-thinning size benefit is greatest the earlier it is done, then falls in a straight line down to less than 10 percent at around 130 days after full bloom. Initially crop load does not appear to have a large influence on fruit sizing, however, at about 90 days after full bloom fruit sizing will stall if the crop load is too high. 90 days after full bloom will usually occur in early January. Regular fruit measuring over the mid-December to mid-January period may identify if crop loads are too heavy for the tree. Further thinning at this stage by fruit size will eliminate undersized fruit and once the crop load is brought down the remaining larger fruit will resume normal growth again.
At about this time a 150 count Royal Gala will be around 45mm in diameter.
Normal Royal Gala growth rates around 90 days after full bloom are about 3.5mm a week, having fallen from around 5mm per week at about seven weeks after full bloom. Close to harvest diameter growth rates for Royal Gala drops down to around 2.5mm per week for optimum crop loads.
PLAN YOUR HAND-THINNING STRATEGY WELL
By hand-thinning time the fruit set levels and its distribution should be obvious. Before starting hand thinning do some fruit cluster counting to determine the number of fruiting sites, and fruitlet distribution among them. Where the chemical thinning has been successful, most of the crop should already be down to singles, some doubles and maybe a few larger clusters. Interfruit competition has a huge influence on fruit set behaviour.
We did some whole tree fruit set counts a few years back in Scifresh for one of our chemical thinning trials. There was a two-fold difference in flower clusters per square cm trunk cross sectional area (TCA) among the trees. Final fruit set counts immediately before hand thinning showed fruit number, expressed as fruit per square cm TCA, was similar across all trees. This means that where flower numbers were low, the trees set twice as many fruit per cluster.
Critical steps in developing a hand thinning plan include:
Identify your market requirement in regard to fruit size range.
Prioritise the hand-thinning programme based on fruit set levels, variety behaviour in regard to colour development, fruit size and intended harvest window.
Give high priority to varieties with high returns for large fruit sizes eg. Scilate and Smitten .
“On” crop biennial varieties need to be thinned within four to six weeks of full bloom to improve return bloom.
Bunchy crops of short-stemmed varieties need thinning before the bunchs close.
• Weak growing, over-cropped trees need urgent
Leave varieties with long stems and tendency for heavy late fruit shedding, eg. Royal Gala types, until the shedding is well under way.
Incidentally, large canopy, well settled Royal Gala types with good chemical thinning programmes may not need a lot of hand-thinning attention if the fruit is destined for small fruit Asian markets.
Recognise individual variety requirements. Some varieties such as Sciros are very sensitive to crop load so need to be well thinned to spaced singles. Trying to compensate for light fruit set in these varieties by leaving doubles, or excessive numbers of singles on branches which had good fruit set generally gives fruit quality problems due to poor colour and flavour.
Understand the fruit sizing and quality attributes by variety and block behaviour. Review past crop performance and use this as a guide to thinning and crop load requirements. But remember, doing the same old thing each season usually ends up with the same outcome. Where there is need to lift block, or variety performance, factors limiting performance and fruit quality need to be identified and overcome.
GETTING THE THINNING JOB RIGHT
This is much easier said than done. There are two critical aspects of this task:
Train the thinners properly.
Monitor and supervise the results. Apart from established recognised seasonal employer (RSE) programmes which now have well skilled, experienced workers returning year after year, most of the thinning labour force are inexperienced so need to be well trained and supervised.
Instructions need to be clear and simple. Where fruiting site numbers are adequate on the majority of trees, thinning down to singles will keep the job simple. Do not be tempted to allow doubles, as it’s not long before most of the crop will be in doubles. Keep decision-making among thinners to a minimum. Decision-making takes time and reduces work progress. Try not to complicate the job by getting the thinning team to do too many different tasks.
Where it is necessary to space fruit, leave this for the second pass.
If you are not harvesting thinnings for acid juice, make sure that the thinning team know not to drop thinnings down through the tree.This bruises fruit and fruit injured in this way will be rejected at harvest.
Where vigour is a problem and shoot ripping is necessary, this is best done as a separate job ahead of the thinning team.
Removing excessive annual shoot growth ahead of the thinning team also makes the thinning job easier because the fruit is more visible.
The thinning team need to be able to confidently work from ladders. This takes skill and knowing how to position the ladder in the tree is a key part of attaining good productivity. These days ladders are much smaller and lighter than they used to be. 50 to 60 years ago heavy wooden 12 to 14 rung ladders were common, so it was very necessary then to know how to “walk” the ladder rather than lift it to avoid fatigue problems towards the end of the day. Ladder movement efficiency is greatest if thinners work down between two rows rather than a thinner to each side of the inter row. Working both sides means you can “walk” the ladder from one side to the other, minimising the need to lift the ladder between trees.
Handling ladders on sloping ground can be tricky. Try to avoid positions where the ladder is facing down the slope.
Also, to avoid ladders tipping over, it’s necessary that the centre of gravity of the ladder plus worker on it always falls within the triangle made by the three ladder legs.
MONITORING AND SUPERVISION
This is a key part of hand thinning.
Before the thinners arrive in a block, do some tree fruiting site counts to determine what the thinning strategy will be. Then thin a few trees down to crop load to give a picture for the thinners of what the thinned tree should look like.
Whole trees are difficult and expensive to count, so for monitoring and assessing the quality of the thinning, working on branches or sub-branches and expressing the fruit numbers as fruit per square cm branch cross sectional area (BCA), or in young trees TCA is a very efficient method for measuring and expressing crop load.
TCA is a very useful measurement when trees are young and have not filled their allotted space, but loses its relevance once trees begin to mature. In young trees, 10 to 12 fruit per square cm TCA appears to be the crop load target.
Optimum BCA crop loads for branch units in the region of
2cm in diameter is around four to five fruit per square cm BCA. Crop loads for large fruit, such as Scilate, may need to be a little lower in order to give the fruit enough space to size.
Incidentally, recent data coming out of the FOPS programme is indicating that vertical cordon crop loads should be around double that of the horizontal or pendant branches. It is probable that upper tree leader crop loads from 2cm diameter and higher should be around double the lower tree branch loads when expressed as fruit per square cm TCA, provided upper tree support is robust enough to hold this level of crop.
SETTING CROP LOADS
The sooner you can get crop loads down to optimum levels, the more fruit the tree can support.
Good chemical thinning programmes can achieve this early in the fruitlet development period. The objective of the chemical thinning programme should be able to bring crop loads down to 120 to 130 percent of the desired crop. This is only possible where blocks are very uniform, particularly in regard to vigour. Where tree vigour is variable, high vigour trees shed fruit easily where as low vigour trees will hold their fruit tightly. Always plan on the need for some hand thinning and crop grooming.
Crop load levels have a huge influence on fruit quality. Colour, flavour and fruit size are all crop load dependent. Some studies we have done also indicate that sunburn susceptibility is increased by heavy cropping.
As already discussed, setting up crop load by trunk size in young trees, and branch size in mature trees is an effective method at individual branch level that is easily measured. For mature cropping trees, this method assumes that the tree has the optimum number of branches and sub-branches. If there are more branches than there should be, then setting crop load on a per branch basis will lead to over-cropping. Where there are too few branches, fruit numbers will be on the light side and annual shoot growth liable to be excessive. In this situation the tree needs more fruiting sites, and weaker lower vigour branches which tend to fruit rather than grow.
Annual extension growth in mature canopies exceeding 20 to 30cm per shoot for a dwarf rootstock, or 30 to 40cm for a semi-intensive block on rootstocks such as MM106 or MM116 indicates excessive vigour and the need for more crop load, or failing that, adoption of other vigour control measures.
In established orchards historical yield and out-turn quality is a good guide for setting crop loads and a good starting point for establishing the crop load aim. The other important factors to take into account are market requirements in regard to fruit size, colour and harvest period.Incidentally, in recent years, there has been a shift in optimum size range for some of our varieties, notably the Royal Gala group where premiums paid for large fruit have evaporated due to oversupply in the US market. This may mean you may have to re-think your production policy in regard to fruit size range for some varieties.
It’s also necessary to factor into your crop load calculations the natural fruit drop which occurs between thinning and harvest. Our data indicates that between 15 and 20 percent of fruit numbers on the tree after hand thinning do not get harvested.These either drop or have failed to reach acceptable quality at harvest so remain unpicked.
There is an incredible range of orchard performance in the industry. Our OrchardNet™ database shows the following differences between average performance and upper quartile performance.
Fig 1. A well thinned fourth leaf Lady in Red block at harvest. Note balanced growth, good fruit colour, good vigour control and balanced growth. Crop load is your best vigour control agent.