Fruit development and thinning in pipfruit

This season has been characterized by abnormally cold weather during October and November. This will impact on this year's harvest and fruit size.

Cold weather in early October had a huge impact on the flowering period in apples. Taking the Royal Gala variety as an example, some of those treated dormancy breakers flowered before the cold period around the first week of October, whereas those without treatment flowered as late as 20 October. This is going to give a very wide range in early season fruitlet development. For any given calendar date, so when monitoring fruit size development, it will be crucial to express the data in terms of days after full bloom rather than calendar date.

Calendar dates for 50 days and 65 days after full bloom for various flowering dates are shown in the table below.

Full Bloom	50 Days AFB	65 Days AFB
1 October	20 November	5 December
8 October	27 November	12 December
15 October	4 December	19 December
22 October	11 December	26 December

For early flowering Royal Gala in Hawke's Bay, Full bloom 1 October accumulated 182.2 GDD at 50 days AFB and for Full Bloom 8 October 2002, 190.5 GDD were accumulated at 50 days AFB.

Comparable figures for last year were 261.1 and 251.3 GDD respectively. It is estimated that harvest will be delayed compared to last year by about 8 to 10 days for these flowering dates.

The Gisborne area has fared a little better. There, full bloom 1 October 2002 accumulated 204.3 GDD in the first 50 days AFB, and those flowering 8 October have accumulated 223.5 GDD by 50 days AFB. On this data, Gisborne Royal Gala harvest should be around three to five days earlier than Hawke's Bay.

Incidentally, November GDDs in Gisborne for November were substantially ahead of the very cold 2000 November in which only 119.2 GDD were accumulated, compared with 151.3 GDD this year.

In the 2000 spring, trees flowering 1 October accumulated 218.1 GDD at 50 days while those flowering 8 October accumulated 211.4 GDD.

Later flowering apples will fare much better this year, eg, apples flowering 15 October in Gisborne will have accumulated around 250 GDD at 50 days AFB, which is very similar to last year and considerably better than two years ago.

The cool start to the early part of the season will also affect fruit sizing in Royal Gala. Apples flowering in Hawke's Bay during the first week in October may well have their fruit size potential reduced by up to two size counts, whereas those in Gisborne will drop by 1 size count compared to last year.

Later flowering blocks should have similar sizing potential to last year and considerably better prospects than in the cool spring of two years ago.

Hand-Thinning Strategies

Many Royal Gala blocks have responded well to chemical thinners, which means there is no great urgency to get into them yet. Later flowering blocks look as if they will still be shedding fruit as late as the end of the first week in December, so there is no need to start thinning them until the week beginning 9 December.

Short stemmed varieties which tend to set in bunches such as Cox' Orange Pippin, Braeburn and Fuji are already showing signs of bunches closing.

When this happens, hand thinning becomes very difficult. These varieties need to be thinned as soon as possible and certainly ahead of the long stemmed Gala varieties if they have set a bunchy crop.

The early variety Pacific BeautyTM should also be thinned ahead of other varieties. Fortunately, it responds very rapidly to chemical thinning, so its hand thinning can be started early.

Heavier cropping Pacific RoseTM should be thinned early to minimise the adverse effects of heavy crop load on return bloom and foliage condition.

Pacific Queen usually responds well to chemical thinners, does not suffer from biennial bearing, so does not need to have early hand-thinning. With this variety, it is best to wait until after Christmas for hand thinning because by then its russet will begin to show and it can be thinned for cosmetic defects.

With the Gala group, wood quality has a huge effect on fruit sizing potential. There is about a 20 g difference in fruit size between apples grown on spurs and terminal buds compared to lateral bud of one year wood fruit. Strong buds with good bourse shoots will size two or three apples better than even where only one apple is left on lateral bud one year wood or weak older shaded spurs. It is better to clean out these sites with poor fruit sizing potential and compensate for numbers by leaving a few multiples on the better bourse shoot bearing sites.

December 2002