Or­chard Man­age­ment

Tack­ling the mixed ma­tu­rity prob­lem

The Orchardist - - >>contents - By John Wil­ton

New Zealand ap­ple pro­duc­tion is fo­cused at the pre­mium mar­ket and needs to be there to sus­tain the vi­a­bil­ity of our in­dus­try in our high-cost econ­omy.

This means that we need to de­liver the con­sumer crisp, juicy, flavour­ful fruit ca­pa­ble of gen­er­at­ing re­peat sales from loyal cus­tomers pre­pared to pay the pre­mium our fruit needs to cover costs.

Judg­ing by the com­ments com­ing back from the mar­ket re­gard­ing the con­sis­tency of our prod­uct, we are in dan­ger of los­ing the pre­mium po­si­tion if we are not care­ful. Mixed ma­tu­rity lead­ing to poor out-turn of some fruit af­ter long term stor­age ap­pears to be part of the prob­lem.

I also sus­pect that sun-tint­ing and mild sun­burn may be is­sues. With good fruit colour, mild sun­burn symp­toms tend to be masked out by high skin colour. So there’s a ten­dency for har­vest of this fruit to be de­layed un­til the sun tint­ing is no longer ob­vi­ous. By this stage, the fruit is likely to be over-ma­ture and not at all suit­able for medium or long term stor­age.

Post-har­vest scan­ning tech­nol­ogy for in­ter­nal de­fects is ad­vanc­ing rapidly so it is prob­a­bly only a mat­ter of time be­fore prob­lem fruit can be seg­re­gated from the line and kept out of fruit des­tined for pre­mium mar­kets. When this hap­pens we might see vis­ually good fruit headed straight for the re­ject bin.

Pack­house op­er­a­tors may need ex­pe­ri­ence in psy­chol­ogy when this hap­pens to be able to ex­plain to irate sup­pli­ers why their pack­outs are so low.

To main­tain pack­outs and avoid this prob­lem, mixed ma­tu­rity and sun­burn dis­or­ders will need to be man­aged in the or­chard be­fore and dur­ing har­vest.


Warm re­gions with daily tem­per­a­tures ex­ceed­ing 28 to 30°C may have a sun­burn risk to ex­posed fruit. As fruit size in­creases, sun­burn risk rises. At about 45mm fruit di­am­e­ter, fruit be­comes vul­ner­a­ble to in­jury. The level of sun­burn in­jury is de­ter­mined by fruit sur­face tem­per­a­tures (FST). Mild

sun­burn in­jury, re­ferred to as sun-tint­ing or skin brown­ing, usu­ally oc­curs when FST is in the range of 45 to 49°C, with more se­vere necro­sis in­jury oc­cur­ring at FST above this level. FST on calm, sunny days is usu­ally in the range of 14 to 17°C above am­bi­ent air tem­per­a­tures. A slight breeze will re­duce FST by about 3°C. This prob­a­bly ex­plains why there is more sun­burn in­jury in the lower tree fruit than the more ex­posed up­per tree fruit.

In ad­di­tion to th­ese two lev­els of sun­burn in­jury there is a third form which can oc­cur at lower tem­per­a­tures. This sun­burn symp­tom ini­tially shows up as a white patch on the fruit and is known as photo ox­ida­tive bleach­ing. It oc­curs when there is a sud­den change in light ex­po­sure. This is the typ­i­cal sun­burn you see from late thin­ning, se­lec­tive pick­ing, ex­ces­sive sum­mer prun­ing or branch move­ment as crop weight comes on to branches. Stud­ies into sun­burn in­ci­dence shows that it’s the midafter­noon sun that causes most in­jury. This is the hottest and dri­est part of the day so fruit ex­posed to sun at that time gets the harsh­est sun and is also likely to be un­der mois­ture stress as well, so tran­spi­ra­tional cool­ing is min­i­mal.

As al­ready men­tioned, mild sun­burn brown­ing will of­ten mask out as fruit colour in­ten­si­fies to­wards har­vest. While such fruit may now ap­pear un­af­fected, its in­ter­nal qual­ity has been changed and the fruit is less suited to long term stor­age. The main in­ter­nal changes in­clude more starch degra­da­tion, prob­a­bly be­cause the fruit is more ma­ture by the time there is enough colour to dis­guise the sun­burn, in­creased flesh firm­ness and dry mat­ter, higher su­gar lev­els but lower fruit acid­ity and lower flesh mois­ture con­tent. Af­fected fruit there­fore, has poorer flavour and drier fruit tex­ture.


Sun­burn is made worse by;

• Over crop­ping. This leads to higher fruit to leaf ra­tios and lower lev­els of an­nual ex­ten­sion growth nec­es­sary to give ad­e­quate leaf cover pro­tec­tion for the fruit.

• Wa­ter stress. This has a ma­jor in­flu­ence on sun­burn in­ci­dence, par­tic­u­larly for va­ri­eties ripen­ing in the first half of the har­vest sea­son when tem­per­a­tures are high. Wa­ter stress as har­vest ap­proaches can eas­ily drop pack­outs by 20 per­cent due to sun tint­ing in­jury.

• Nu­tri­ent de­fi­ciency. Any­thing which re­duces leaf qual­ity may in­crease sun­burn in­jury. The lit­er­a­ture re­ports ni­tro­gen de­fi­ciency to in­crease sun­burn and here mag­ne­sium de­fi­ciency is cer­tainly a fac­tor.

• Spray and spray in­jury. Leaf in­jury from cal­cium chlo­ride or sul­phur sprays dur­ing pe­ri­ods of high tem­per­a­ture.

• Fruit size. Larger fruit have lower sur­face area to vol­ume so will de­velop higher flesh tem­per­a­tures than smaller fruit.

• Late thin­ning and se­lec­tive pick­ing of bunchy crops.


Thin the crop early and well. Spaced sin­gles will min­imise sun­burn in­jury dur­ing later crop groom­ing and har­vest. Try to avoid wa­ter stress dur­ing the heat of the sum­mer. There is good ev­i­dence to show that mulching will con­serve soil mois­ture, lower root tem­per­a­tures and re­duce mois­ture stress in the tree. Mulching re­duces sun­burn in­jury and with

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