Or­chard Man­age­ment

Thin­ning and crop load both crit­i­cal

The Orchardist - - Contents - By John Wil­ton

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.


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.


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.


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.


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.


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.

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