Establishing the High Density Supported Apple Orchard

Part 2: Choosing Trees for Planting

Table of Contents 

1. Nursery Tree Quality & Sources
2. Planting Density
3. Rootstock Options
4. Cultivar Selection
5. Pollination

Nursery Tree Quality and Sources 

One of the biggest mistakes apple growers make when switching to higher density supported systems is not starting with a quality tree from the nursery. Without a proper tree, the advantages of a higher density system are greatly reduced. Trees that cannot establish quickly will greatly increase the carrying costs of a system that is initially very costly. This delay can be enough to destroy the economic advantage of the higher density supported systems and discourage growers who are trying this approach for the first time. It is recommended that trees be ordered at least two years in advance of planting. This way there is a better chance of getting the cultivar/rootstock and quality of tree you want. 

Feathered Tree

This tree is considered to be the ideal nursery tree and will cost more than a conventional one-year whip. Is it worth it to pay the higher price for the ideal tree? The answer is unequivocally "yes", if you combine that expenditure with the quality orchard-management practices needed to get the most from a high-density planting. An ideal tree poorly cared for will not justify its cost. A high quality tree in a properly managed orchard will return its cost many times over.

Definitions

Feathers - a lateral shoot produced in the same year as the leader.

Branch - a lateral shoot that is one or more years younger than the leader.

The quality of the tree used in high density supported systems cannot be over emphasized. The tree has to be specially prepared to produce fruit immediately at a young age. The ideal apple tree for planting should come with a canopy structure already in place including fruit buds (Fig. 1). 

Such a tree should have a dominant central axis, or leader, and should be 1.7 - 2 m (5 - 6 ft.) in height, including roots. It should have 5 to 7 good quality lateral shoots (feathers) of nearly equal diameter. The first lateral should originate at least 60 cm (24 in.) above where the soil surface of the orchard will be after planting. The laterals (feathers) should be well-distributed, both around the leader as well as along the leader, so that they are properly positioned to become permanent scaffold limbs as the tree develops. A good-quality lateral shoot or feather should be 15 - 20 cm in length at the absolute minimum, and preferably longer.

Figure 1 Example of well feathered tree

One Year Whip

The one year whip will not work as effectively as a feathered tree. A 2 year old branched tree is even less acceptable in high density systems. Where "whips" are chosen, the minimum caliper (diameter of tree 2 - 5 cm above bud union) that should be accepted is 5/8 inch. With whips the technique of bagging will help improve their development.  

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 Planting Density

Until more growers master high density supported systems it is suggested that tree densities of 1500 - 1800 trees per hectare (600 - 720 trees per acre) be the preferred introductory system. The in-the-row spacing between trees is suggested to be perhaps 1.5 m (5 ft.) although 1.2 m (4 ft.) or 1.8 m (6 ft.) could be accommodated quite well depending on cultivar, rootstock, soil strength and support system. Between the row spacing may well be dictated by equipment availability, but 3.6 m - 4.3 m (12 - 14 ft.) is suggested.  

Trees Per Acre at Various Spacings

The higher the final height of the tree the greater the space that must be left between rows to maximize light interception. For first time attempts with the Slender Spindle System (to be described later), a spacing of 5 ft. between trees and 12 ft. between rows has worked well in other areas of Canada. For the Vertical Axis System (to be described later) a spacing of 5 ft. x 14 ft. has worked well.

For maximum light interception the distance between rows is considered to be 1.3 - 1.5 times the final height of the tree.

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 Rootstock Options

There may be several rootstock options possible where higher density supported orchards are concerned. Rootstocks for this type of planting must: control tree size, reduce vigour and induce precocity (early fruiting). M.9 is considered to be the preferred rootstock to start with because of its proven adaptability to high density plantings. Other rootstocks such as: Ottawa 3 (O.3), Budagovsky 9 (B.9), Poland 2 (P.2), and MARK may also be adaptable, but experimentation should not be attempted until M.9 is mastered.

Malling 9 (M.9) produces trees 20-35% the size of standard trees, is very precocious and very productive. Because its roots are brittle and break easily, anchorage is poor. Trees on M.9 should not be grown on light textured, sandy soils, without supplemental irrigation. It is tolerant of collar rot and does well on heavier soils where drainage is adequate. However, M.9 is susceptible to fireblight and woolly apple aphid. Many virus free M.9 sub-clones have been developed by heat treatment to ease propagation in the nursery and increase tree vigour in the orchard. Caution should be exercised if this rootstock is planted in the colder growing districts of Ontario, or on sites which frequently lack snow cover.  M.9 is the least tolerant of hot soils during the growing season. More vigorous strains of M.9 include Pajam 2 and RN29.

M.26 may also be modified for a high density supported system with some cultivars particularly spur types. M.26 is strongly influenced by soil conditions. M.26 is not drought-tolerant and will easily "runt-out" on light, sandy soils without supplemental irrigation. It will do well on intermediate or heavier textured soils if drainage is adequate. While moderately resistant to collar rot, M.26 will not perform satisfactorily on poorly-drained sites. M.26 is very susceptible to fire blight and woolly apple aphid.

 Rootstocks for Trial Use

MARK is an open pollinated seedling of M.9 which was introduced by Michigan State University. It is precocious and has a yield efficiency similar to M.9. MARK performs well in heavier, wetter soils and is resistant to collar rot. It is susceptible to fire blight and woolly apple aphids. Heavy cropping in the early years may stunt growth and fruit size later on. Rootstock trials have shown that MARK often develops soil line swellings, and fine roots grow from the swollen area. This swelling may disrupt movement of moisture and nutrients from the roots to the top of the tree. This soil-line swelling does not occur as much in heavier, wetter soils where the climate is cool and moist. The problem is worse in hot, dry, arid growing conditions. MARK must always be supported to reduce this problem.

In the colder growing areas of Ontario, the greater winter hardiness of rootstocks 0ttawa 3, Budagovsky 9 and Polish 2 could help to reduce risk of tree loss in high density plantings. 

V.1 - A hardy and very productive rootstock out of the Vineland, Ontario breeding program. It is fireblight resistant. It's vigour is similar to an M26.

Ottawa 3 (O.3) is a precocious, winter hardy rootstock bred in Ottawa, from a cross of M.9 with the hardy crabapple cultivar "Robin". Ottawa 3 produces a tree between M.9 and M.26 in size. Difficulty in propagation of 0.3 in the stoolbed has hurt its availability and popularity. This rootstock is resistant to collar rot but is susceptible to fireblight and woolly apple aphid. 

B.9 is one of the hardy Budagovsky rootstock series produced at the Michurin College of Horticulture, in Russia. B.9 displays dwarfing similar to M.9, but is more winter hardy. B.9 may be susceptible to fire blight, and woolly apple aphids, but has greater resistance to collar rot than M.9. 

P.2 is a Polish rootstock with similar precocity and yield potential of M.9. Its winter hardiness is comparable to that of 0.3 and B.9. P.2 is resistant to collar rot, but is susceptible to fire blight and woolly apple aphids. It does not produce root suckers, has few burr knots, but does not propagate easily.

G.30 is a fireblight resistant rootstock out of the Cornell University breeding program in N.Y. State. It may be too vigorous for higher density systems. It is also prone to weak graft union with cultivars like 'Gala'.

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Cultivar Selection 

The choice of cultivars for future plantings WILL BE DIFFICULT. The biggest single advantage to high density supported systems is the ability to bring a cultivar into early production. This allows the initial cost of the planting to be recovered earlier and allows growers to take advantage of new cultivars commanding higher prices on the market. To plant a high density supported orchard to a cultivar with poor market potential and returns may defeat the advantages of using intensive production systems.

Of the traditionally grown cultivars in Ontario, the semi-spurs, e.g. Empire and Idared are well suited to higher density systems as are spur types of McIntosh and Delicious. Non-spur types pose more of a concern because of vigour but can be managed. Some of the newer strains of older cultivars like Cortland have a more friendly semi-spur habit and may be better adapted to higher density planting than the original standard strains.

When establishing new plantings of McIntosh and Delicious only the best quality red strains of these cultivars should be used. These two cultivars should be grown in regions where best quality can be achieved. McIntosh should be confined to areas of the province that are capable of producing the well coloured firm fruit that the market demands. 

The new cultivars on the scene such as Honeycrisp, Ambrosia, Braeburn, Elstar, Fuji, Gala, Golden Supreme and Shizuka, hold promise for some growers if they can get into immediate production. Some apple marketers in Ontario have indicated that growers should not get left behind on these new cultivars if our market is to resist imports. However, regardless of cultivar, count size apples are slowly dominating the Ontario market. Growers should respond to this demand by growing the size(s) and quality the market wants. All growers require a cultivar mix that can be harvested sequentially at the proper time. Consult your marketer before planting any cultivar(s).

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Pollination

Cropping, and especially early cropping, is an essential management factor. Every attempt must be made to assure fruit is produced. To allow for effective pollination, a minimum of 1 in 10 trees should be a compatible pollen source. Usually, pollenizer trees are evenly dispersed through the orchard or in solid rows in such a manner that no tree is more than 30 m (100 ft.) from a pollenizer tree.

An effective pollenizing cultivar is one that is a consistent bloomer every year, and has a large amount of viable pollen. It should bloom at the same time as the cultivar to be pollinated. In the case of triploid cultivars (e.g. Crispin, Jonagold) that do not have viable pollen, two pollenizers are required to get acceptable yields of the pollenizers.

The presence of 3 cultivars allows the pollen requirements of all 3 to be met even though one has nothing viable to contribute. Some growers are interested in crabapple pollenizers. Consult factsheet "Crabapple Pollenizers for Apples" - Agdex 211/21, for further details.

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