The use or abuse of pruning determines the ability of the persimmon tree to produce high quality fruit.

Pruning for structure
Pruning as a training strategy should be limited to developing the tree framework as early as possible after planting. The framework of leaders and subleaders provide structural support for fruiting and replacement shoots (Fig. 1). Avoid the situation where trees are left for a season or more before the training system is imposed on the tree.

One major limitation of pruning at the tree training stage is that vigour tends to be promoted at the expense of early bearing. In training trials at Rukuhia and Manutuke, free-standing trees were slower to come into bearing than those on trellis systems. This was due to an increase in structural pruning required to develop strong free-standing trees.

FIGURE 1: The location of fruiting and replacement wood on a Ruakura 'Y'.

Pruning for fruit
The second stage of pruning is to produce high quality fruit. The quality of a persimmon crop is dependent on conditions occurring over two seasons rather than one. In the first season, flower initiation occurs on current season replacement shoots (during December/January). In the spring of the second season, budbreak occurs and floral laterals are produced from the replacement shoots.

Orchard monitoring studies carried out at Ruakura have identified the characteristics of a typical productive replacement shoot (Table 1).

Table 1
Characteristics of a typical replacement shoot.

No. buds/shoot	7
Total budbreak of buds/shoot	4 (55%)
Budbreak of floral buds/shoot	2 (33%)
No. flowers/flowering lateral	3
No. leaves/replacement shoot	25
(post-budbreak)

Not all replacement shoots produced during the current season will initiate flower buds for the following season's crop (Fig. 2). Shoots which continue to grow during flower bud initiation (Dec-Jan) will not normally initiate flowers. Secondary growth of a replacement shoot limits flower bud initiation, although in some localities secondary growth may initiate flower buds if this growth terminates early.

FIGURE 2: Flower bud initiation.

Defoliation or leaf damage during spring and early summer will reduce or stop flower bud initiation. This situation can arise when late frost, grassgrub, bacterial blast, hail, drought or spray damage reduces leaf photosynthesis on the replacement shoot.

Flower initiation is also limited on shoots which have developed in shaded sections of the canopy. Light exposure is as important in the development of productive replacement shoots as it is in fruit quality. On any training system the grower must aim for a shallow canopy to ensure adequate light exposure of fruit and replacement shoots.

Persimmons have a tip-bearing growth habit which requires careful management. The fruiting zone tends to move away from the leader and subleaders each season if left unchecked (Fig. 3). Ideally the fruiting zone should be located within 0.5m of a leader or subleader. In particular, the maintenance of a narrow fruiting zone on a Ruakura 'Y' is required to avoid wasted canopy space.

FIGURE 3: Tip bearing growth habit of Persimmon.

A renewal pruning system has been developed for the Ruakura 'Y' trellis which can be applied to other training systems. This pruning is based on producing replacement shoots (complete with initiated flower buds) from the leader/sub-leader during a season. Shoots are then cropped the next season. Once a shoot has cropped it is spurred back in the winter to provide a site for the development of new wood.

Summer pruning is used to eliminate vegetative growth which is surplus to reproductive requirements and causing shading problems. This type of growth can also compete with fruit for nutrients and photosynthates.

At any one time the tree should be carrying a balance of both wood initiating flower buds and wood bearing fruit. In a natural situation this type of balance occurs in large mature trees which have been left unpruned. However, time taken to reach this stage would be uneconomic and large tree size would not be suited to intensive culture. Through careful manipulation of the tree by pruning, this balance can be achieved at an early age and can lead to a better control of tree size. This pruning system consists of the following steps:

A. Winter Pruning: June-August (Fig. 4)

• Remove all fruited shoots back to a two-bud spur
• Remove all replacement shoots with secondary growth back to a two-bud spur.
• Retain all well-developed replacement shoots.

FIGURE 4: Renewal Pruning

B. Spring/Winter Pruning: Late October

• The Spring/Winter pruning is a fine-tuning technique which allows the grower to retain highly productive replacement shoots to flower and fruit.
  Poor or non-flowering replacement shoots are spurred (by cutting back to winter wood) to allow new replacement wood to develop during the current season. The main reason for this pruning is that it is difficult to ensure all the replacement shoots retained in the winter will be floral.
• Retain 6-8 floral replacement shoots per metre of leader/subleader. Floral replacement shoots are readily identified by the presence of unopened flower buds on emerging laterals.
• Remove all non-floral replacement shoots back to a two-bud spur.
• Remove all weak floral replacement shoots, surplus to requirements, back to a two-bud spur.

• Remove vigorous laterals which have lost fruit during fruit drop.
• Remove secondary growth.
• Remove water shoots (if a water shoot is required as a future site for replacement shoots, then it can be headed back to four buds).

Crop-load regulation and estimation
For each replacement shoot which is cropped, a grower should aim to harvest an average of two fruit. In our work at Ruakura on crop-loading, we have identified that a minimum of 10-12 leaves/fruit are required to produce quality fruits. In general, fruit should be thinned to one fruit/lateral. A typical replacement shoot produces four laterals at budburst (Table 1). Two of these laterals are floral with three flowers per lateral being produced.

From crop-load studies, it would appear that leaf numbers close to the fruit are more critical to fruit quality than leaf number over the whole tree. After budburst the number of leaves produced from a typical replacement shoot is 25. If laterals are thinned to one flower (or fruit), then a minimum of 12 leaves will be available for each fruit. A vigorous replacement shoot can produce a long apical lateral which can be thinned to carry two fruits that are spaced to avoid proximity marking.

A balance between fruiting shoots and replacement shoots is required during the season to minimise shading effects. When more than eight replacement shoots are allowed to crop per metre of leader/subleader, shading becomes a problem.

Low crop-loads can also cause shading problems due to excessive vigour. In young trees summer pruning allows a canopy to be kept free of vigorous growth. As a tree matures, crop load can be used to control vigour.

A grower can obtain an estimate of the following season's crop from the number of replacement shoots retained during winter. Information would be collected from a sample of trees in an orchard block. The type of training system will influence the length of framework available, per tree for carrying fruit (Fig. 5). Mature centre leader, ebro- and 'Y'-trained trees planted at a spacing of 4m x 4m would, on average, carry 15m, 26m and 42m of leader/subleader per tree respectively.

FIGURE 5: Tree structure for three training systems

The productivity per metre of framework for each system is currently being studied in training trials at Manatuke and Rukuhia. As the season progresses the grower can update the estimate by accounting for fruit drop and expected reject rates.

The key to any persimmon pruning strategy should be one which encourages production of high quality fruit for both the current year and the next.