Orchard Man­age­ment

Even though the har­vest pe­riod is the busiest time of the year, there are a num­ber of crit­i­cal jobs that need to be done now to set the trees up for next sea­son.

The Orchardist - - Contents - By John Wilton

Crit­i­cal post har­vest crop hus­bandry

Rel­a­tive to a few years ago, we have lifted orchard yield and pack­out per­for­mance al­most be­yond what we thought could be achieved sev­eral decades ago. The trees are now work­ing re­ally hard as we push yield and qual­ity to­wards the up­per limit so any im­ped­i­ment to root health or nutri­tion read­ily shows up.

In the last decade from 2007 to 2016, av­er­age gross pro­duc­tion per hectare has gone from 50.4 tonnes to 59.6 tonnes, an in­crease of 18%. There are now many blocks across a num­ber of va­ri­eties close to or ex­ceed­ing 100 tonnes per hectare so we are start­ing to put real pres­sure on the tree’s abil­ity to sup­port the crop. To sus­tain and fur­ther im­prove orchard per­for­mance, all lim­it­ing fac­tors need to be iden­ti­fied and rec­ti­fied as far as pos­si­ble.

CHECK DRAINAGE

A healthy root sys­tem is es­sen­tial for top tree per­for­mance and I am sure many of the tree nu­tri­ent de­fi­cien­cies and fruit­set prob­lems we are see­ing are due to a poor root en­vi­ron­ment. Healthy roots need ac­cess to ad­e­quate soil mois­ture as well as good aer­a­tion to keep them alive and healthy.

The best way of achiev­ing these two op­pos­ing ob­jec­tives is to make sure that the trees de­velop of deep root sys­tem with a lot of soil vol­ume to ex­plore. This means hav­ing good drainage. In the ideal world, win­ter wa­ter ta­bles need to be at least 60 to 70cm be­low the sur­face, prefer­ably over a me­tre. Most or­chards are on soils that have al­ready been drained. The ques­tions we need to ask then are:

(a) Are the drains deep enough as suf­fi­ciently close to pro­vide

ef­fec­tive drainage for a per­ma­nent tree crop?

(b) Do they still work?

Over time drains de­te­ri­o­rate. Plug­ging with shel­ter­belt roots is a com­mon cause of blocked drains. Most of the shel­ter­belt species we use have roots which are at­tracted to drains, par­tic­u­larly Ca­sua­r­ina, pines, wil­lows and poplars. Where drain gra­di­ents vary, silt­ing up can be a prob­lem. Ac­ci­dents to drains also hap­pen, for in­stance, it is not un­known for posts to be driven through drains block­ing them.

Im­me­di­ately post har­vest is a good time to check the con­di­tion of the drains, carry out main­te­nance on them and put in ad­di­tional drains where re­quired.

NU­TRI­ENTS

The post har­vest root flush pe­riod is an ideal time to ad­dress nu­tri­ent prob­lems. We are see­ing in­creas­ing lev­els of ni­tro­gen de­fi­ciency emerg­ing in high per­form­ing blocks. This is not sur­pris­ing be­cause in or­der to ob­tain ex­cel­lent fruit colour it is nec­es­sary to run tis­sue ni­tro­gen lev­els down into the de­fi­ciency range as har­vest ap­proaches.

Around har­vest, leaf ni­tro­gen lev­els should be in the range of 1.8 to 2.2%, the leaves a pale green rather than deep emer­ald green and fruit background colour also a pale green to le­mon colour, with bril­liant red over colour. These low ni­tro­gen lev­els, nec­es­sary for good fruit colour, are in­ad­e­quate to en­sure good fruit­set next sea­son and drive suf­fi­cient spring growth flush to sup­port next year’s crop. Gen­er­ally speak­ing, the ni­tro­gen re­quire­ment for fruit­set and spring growth flush comes from stored ni­tro­gen re­serves in the tree, not from spring fer­tiliser ap­pli­ca­tion. Trees short on ni­tro­gen tend to give bril­liant au­tumn leaf colour and ear­lier leaf drop than those with ad­e­quate or sur­plus ni­tro­gen lev­els. Mag­ne­sium is the other es­sen­tial nu­tri­ent that ap­pears to be linked to poor root health. Mag­ne­sium de­fi­ciency symp­toms are also very com­mon on trees that are over cropped. Ripen­ing seeds have high mag­ne­sium re­quire­ment so trees with ex­ces­sive crop have prob­lems with mag­ne­sium. Ex­ces­sive crop­ping also ad­versely af­fects the au­tumn root growth flush due to the crop soak­ing up most of the avail­able pho­to­syn­thate sup­ply and leav­ing lit­tle sur­plus avail­able to drive root growth. Young, ac­tively grow­ing roots are nec­es­sary for good nu­tri­ent up­take from the soil as many cations, par­tic­u­larly cal­cium, are only taken up through ac­tively grow­ing root tips.

Many of our orchard soils need reg­u­lar ap­pli­ca­tion of mag­ne­sium fer­tiliser some­time over the au­tumn and early win­ter pe­riod to main­tain a sat­is­fac­tory mag­ne­sium sup­ply. Es­tab­lished fruit trees usu­ally have my­c­or­rhizal re­la­tion­ships so are very good at sourc­ing soil phos­pho­rus there­fore, trees are rel­a­tively un­re­spon­sive to fer­tiliser phos­pho­rus ex­cept when newly planted.

Potas­sium is a ma­jor nu­tri­ent with high de­mand for fruit siz­ing and colour devel­op­ment. This de­mand comes on once the crop begins to size in De­cem­ber. Leaf anal­y­sis gives a very ac­cu­rate in­di­ca­tion of the tree’s potas­sium sta­tus. Potas­sium lev­els will also move in­versely pro­por­tional to crop load. The heav­ier the crop, the lower leaf potas­sium lev­els will be.

Many New Zealand soils have huge re­serves of potas­sium so fer­tiliser re­quire­ment de­pends on soil type rather than crop­ping level. Be­cause of the ad­verse ef­fect potas­sium has on cal­cium and also mag­ne­sium up­take, it is im­por­tant not to over fer­tilise with potas­sium.

As crop in­creases, nu­tri­ent de­mand lifts in pro­por­tion to yield but tree’s abil­ity to source it may de­cline.

*Adapted from data pub­lished in “Fruit min­eral re­moval rates from New Zealand ap­ple (Malus do­mes­tica) or­chards in the Nelson Re­gion” NZ Jour­nal of Crop and Hor­ti­cul­tural Science, Vol 34 pp 27-32, JW Palmer, G Dry­den.

TRACE ELE­MENTS

Most trace ele­ments are rel­a­tively im­mo­bile in the leaf and there is lit­tle move­ment of them back into the tree as leaf fall ap­proaches. Boron is the ex­cep­tion. Boron is very mo­bile and read­ily trans­ported back into the tree so post har­vest is a very safe time to ap­ply fo­liar baron sprays.

The other trace ele­ments are best left to spring/early sum­mer or in the case of zinc, per­haps a fully dormant spray of zinc sul­phate.

TREL­LIS MAIN­TE­NANCE

In­creas­ing crop loads are putting tree sup­port struc­tures un­der se­vere pres­sure so re­pairs and main­te­nance of sup­port struc­tures should take high priority once the crop is har­vested. Ev­ery year we see trel­lis fail­ure and this year had trel­lis fail­ures too, largely due to the very strong winds we ex­pe­ri­enced dur­ing Jan­uary. We were very for­tu­nate the Fe­bru­ary and early March rains fell un­der rel­a­tively calm con­di­tions, other­wise there could have been a lot more rows down.

Trel­lis fail­ure is not only con­fined to New Zealand or­chards. A re­cent Good Fruit Grower re­ports they have done some sur­vey work on trel­lis fail­ure to iden­tify the fac­tors in­volved in trel­lis fail­ures. They have iden­ti­fied two types of trel­lis fail­ure:

1 Soil fail­ure in which the struc­ture holds to­gether but the soil is too weak to hold the posts up. I have not seen much of this prob­lem here, apart from end strainer posts lift­ing out of the ground. We also see some lean­ing posts which is an in­di­ca­tion of soil fail­ure.

2 Ma­te­rial fail­ure in which the struc­ture it­self fails. This

is where most of our trel­lis prob­lems come from.

For weak soils, eg sands, they rec­om­mend around 30% of the trel­lis height above ground be driven into the ground. In the case of stronger soils only about 20% of the trel­lis height be driven into the soil.

There are nu­mer­ous ex­am­ples of ma­te­rial fail­ure. The most com­mon one is posts snap­ping off. Bro­ken wired and sta­ples pulling out also con­trib­ute to fail­ure. For us plant­ing trees off line is of­ten the be­gin­ning of trel­lis fail­ure be­cause of the ex­tra crop weight the struc­ture has to sup­port. Most of our sup­port post fail­ure has oc­curred where quar­ter round posts have been used. The knot area is their weak point and this is where they break. Some­times quar­ter and half round posts may split lon­gi­tu­di­nally. Full round posts are much stronger and less likely to break un­der load. Post di­am­e­ter de­ter­mines strength, eg a 125mm di­am­e­ter round post is 50% stronger than one only 100mm di­am­e­ter.

Spac­ing be­tween posts is also im­por­tant. Stud­ies in Washington into trel­lis fail­ure has found that 60% of fail­ures

had post spac­ing greater than 12m. In weak soils, post­ing wider than 6m apart markedly in­creased fail­ure risk.

There are lots of trel­lised in­ten­sive or­chards out there where the trees have de­vel­oped an omi­nous lean in­di­cat­ing that trel­lis fail­ure maybe im­mi­nent. Al­low­ing tree height to ex­tend too far be­yond the height of the trel­lis puts huge stress on the struc­ture and with the weight of the crop we are set­ting in the up­per tree, it does not take much wind with rain to bring the whole row crash­ing down. You only have two op­tions in this sit­u­a­tion, ei­ther bring tree height down to the level that the trel­lis can sup­port or beef up the trel­lis struc­ture to en­able it to sup­port the ad­di­tional trees top weight.

Where posts are too short and too far apart, driv­ing longer in­ter­me­di­ate posts be­tween ex­ist­ing posts is a good start­ing point. Ex­tend­ing trel­lis height to sup­port a greater pro­por­tion of the un­sup­ported tree above trel­lis height can be con­sid­ered pro­vided the ex­ist­ing posts are well enough an­chored to take ad­di­tional load­ing.

Over­seas in windy cli­mates or where tall sup­port trel­lis is re­quired with­out the ex­pense of go­ing to ex­tra long driven posts, it is com­mon prac­tise to brace posts across the block with a ca­ble run­ning along the top of the trel­lis posts, se­cured to a dead­man ei­ther side of the block. Per­haps this is a tech­nique we should in­ves­ti­gate for high value orchard plant­ings in dan­ger of row col­lapse.

Fix up loose or bro­ken wires and make sure wires are se­curely at­tached to trees and sup­port posts.

PRUN­ING

Im­me­di­ately post har­vest is the best time to prune sum­mer­fruit be­cause dis­ease risk, par­tic­u­larly sil­ver leaf, is low­est at this time of the sea­son. Where ap­ple trees have ex­cess vigour or shad­ing branches, prun­ing those out now will help de­vig­o­rate the tree be­cause this will re­duce the amount of pho­to­syn­thate be­ing translo­cated back into the tree to sup­port fu­ture root and shoot growth. Tak­ing out shad­ing branches now will also im­prove bud strength on

the re­main­ing fruit­ing sites.

Where trees have be­come too high and are putting trel­lis struc­ture at risk, they can be topped im­me­di­ately af­ter har­vest. This will im­prove light pen­e­tra­tion into the lower canopy and im­prove bud strength there. Top­ping trees at this time of the sea­son may re­duce the growth re­sponse com­pared to dormant top­ping. How­ever, it will not be as ef­fec­tive for re­duc­ing the vigour re­sponse as top­ping trees in late spring im­me­di­ately af­ter fruit­set when the

crop load is there to take the vigour out of the tree.

As we have had a cou­ple of pro­longed wet pe­ri­ods this

au­tumn, there will now be high risk canker in­fec­tion so good fungi­ci­dal wound pro­tec­tants need to be ap­plied to prun­ing cuts. Ob­vi­ous canker in­fec­tion needs to be pruned out be­fore any gen­eral prun­ing com­mences.

POST HAR­VEST FUNGICIDES

As leaf fall ap­proaches, good fungi­cide cover is nec­es­sary to min­imise canker in­fec­tion. This is an in­sid­i­ous dis­ease which can be very ex­pen­sive to con­trol if it gets away. It can be kept at bay with ef­fec­tive post har­vest fungi­cide pro­gramme.

Har­vest­ing in pe­ri­ods of wet weather can lead to sig­nif­i­cant fruit­ing spur canker in­fec­tion so there are ben­e­fits in ap­ply­ing an ef­fec­tive pro­tec­tant fungi­cide im­me­di­ately af­ter har­vest.

From left: Fig 1. These trees died when the drainage sys­tem be­came over­loaded and wa­ter backed up into the root zone. Fig 2. Low spring ni­tro­gen lev­els of­ten lead to poor fruit­set.

From top: Fig 3. Struc­ture fail­ure is an ex­pen­sive prob­lem. This row fell over be­cause its quar­ter round in­ter­val sup­port posts snapped at the knot. Fig 4. This is the same block as in Fig 3 two years later. The sup­port struc­ture has been strength­ened by driv­ing full round posts be­tween ev­ery sec­ond ex­ist­ing quar­ter round post and tree height was dropped to within about 30 to 50cm of post height when the tops be­gan to break out in mid grow­ing sea­son. Note the orig­i­nal post in the fore­ground and new round post about 3 trees down the row from it.

From left: Fig 5. The trees in the fore­ground are weaker grow­ing so do not need ex­tra up­per tree sup­port. The tall ones fur­ther down the row are too high for the struc­ture and have had to be propped up to pre­vent them bring­ing the row over. Fig 6. These Cripps Pink trees are too tall for the struc­ture. For­tu­nately, this va­ri­ety has strong wood so holds it­self up bet­ter than may other va­ri­eties. Even so, a higher trel­lis is re­quired or the trees should be topped to stiffen their lead­ers so they can con­tinue to hold them­selves up.

Fig 7. This young Jazz™ plant­ing in France shows the trel­lis post se­cured to a con­crete pad, then held in position with a ca­ble run­ning across the top of the posts.

Fig 8. This trel­lis sup­ports both trees and hail net. Ev­ery sec­ond post is cross tied by a ca­ble.

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