For many years the New Zealand apple industry has relied upon production from the intermediate vigour rootstocks MM.106 and M.793 with trees planted at 5-x 3 m (666 trees/ha). These orchards have produced some of the highest recorded yields in the world. Although the planting density has not changed greatly in New Zealand over the last thirty years, there has been considerable improvement in yield and fruit quality with the change from multi-leader trees to slender pyramid training. At the same time the New Zealand industry has been one of the world leaders in the rapid introduction of new cultivars.

New Zealand's production, however, is dominated by the export market and therefore very sensitive to the increase in the world apple supply generally and specifically to alternative suppliers of cultivars such as Royal Gala, Braeburn and Fuji. In the light of the long distance to the consumer markets for New Zealand's products, economic viability can only be maintained by continuing to hold a position in the market for premium rather than commodity produce.

This will be achieved by
1) the rapid introduction of new cultivars with a market premium,
2) further improvements to fruit quality and
3) reductions in the costs of production.

In other parts of the world, particularly Europe and more recently N. America, growers have moved into intensive planting systems on dwarfing stocks in response to similar economic pressures. Intensive systems with smaller trees have been adopted to take advantage of high prices for new cultivars, to improve fruit quality, to reduce production costs and to improve spraying efficiency. All these advantages arise from the smaller tree with its ease of picking, pruning, spraying, thinning and the good exposure of the fruit to light to enhance fruit quality.

The New Zealand industry has been slow to adopt intensive plantings on dwarfing rootstocks. There are a number of reasons for this reluctance - high total yields are achieved by the current systems, trees on dwarfing rootstocks are not available in sufficient quantity, tree quality on these stocks is often disappointing, there are genuine concerns over woolly apple aphid and sunburn, and there has, until recently, been a general lack of experience with intensive systems in this environment.

Tree densities as high as 20,000 trees/ha have been tried in Europe but the low cost per kilo for the fruit and the relatively high cost per tree here in New Zealand would make such high densities economic disasters for the grower. It is likely for the New Zealand situation that profitable intensive systems would be single row plantings at tree densities of 1200 - 2200 trees/ha on dwarfing rootstocks such as M.26, Mark or M.9.

One of the major drawbacks of intensive systems is their higher establishment costs compared to traditional systems, although this is counterbalanced by the improved precocity, fruit quality and the reduced production costs. Obviously with the high investment costs of high tree densities, precocity is of paramount importance, not only to produce cash flow as quickly as possible but also to reduce the vegetative vigour of the trees. Precocity is strongly influenced by the choice of the rootstock, M.9 being a particularly precocious rootstock, but also by the number of feathers on the tree at planting.

The feathers, or silleptic shoots, are formed while the tree is in the nursery row and are characterised by relatively flat branch angles. A well-feathered tree therefore has the basal tier of branches already present. This not only provides the site for the spur flowers in year two but as the branch angles are flat, the feathers need little tying down in the first year in the orchard. Well-feathered trees on M.9 rootstock have given yield increases of two to three fold in years two and three compared to unfeathered trees. An ideal well-feathered tree would have 7-8 feathers at a height of 70-100 cm above the ground.

Although all single row intensive systems, other than V trellises, are trained to a conical tree form to enhance light penetration, there are two main schools of thought on management of the central leader. The Dutch slender spindle was designed to be picked, pruned and thinned from the ground. In order to restrict tree height, the centre leader was replaced annually with a weaker lower shoot so that the leader itself had a somewhat twisted form to reduce the vertical extension of the tree. This is in marked contrast to the French vertical axe where the leader was allowed to grow unhindered and cropping was relied on to ultimately reduce it's vertical extension. Consequently the slender spindle is typically 2-2.2 m tall and the vertical axe 3-4 m tall.

In terms of yield and fruit quality, the most extensive records we have are from experiments in Nelson with Royal Gala on M.9 grown as slender spindles at a range of spacings on research orchard plots and on grower sites. Mean yield per tree from these trials has varied from 3 to 11 kg in year two, illustrating the good precocity of M.9. Storage work confirmed that fruit from such young trees was of exportable quality. (The impression that fruit from young trees does not store well was probably derived from work on lightly cropping young trees on more vigorous rootstocks where fruit size if often excessively large). Yields per tree have shown a rapid increase with age and have given a plateau yield at year five. On good sites this was an average yield of 75 tonnes/ha with trees at 2000 trees/ha.

Royal Gala does not normally suffer serious problems of russet or sunburn and therefore is perhaps an "easy" cultivar to try on M.9. In our other trials we have seen serious downgrading of Fuji due to russet, particularly in the Nelson Region. Some of the problems of russet in Nelson in the early years were probably aggravated by overspraying, emphasising the importance of matching spray application to tree row volume. In drier regions such as Marlborough, we have not seen such serious problems of russet on M.9. Sunburn levels on Fuji and Braeburn on M.9 reached 12% and 9% in Nelson in the bad sunburn year of 1997/98.

This is somewhat higher than growers experienced on larger trees, although this was counterbalanced by good colour and high soluble solids. Even on traditional systems of production, sunburn losses may increase as growers seek to open up trees to enhance light penetration to improve fruit colour. Although the spectre of woolly apple aphid remains, we have not seen to date any serious problem on trees on susceptible rootstocks.

Intensive systems do offer the grower new production possibilities, particularly as we look forward to a rapid switch on of new cultivars and responding to both the current and future requirements of the international pipfruit market for enhanced fruit quality.