Quick Dips

Intensive Apple Production

Intensive apple production systems, involving dwarfing rootstocks and the planting of many more trees per hectare, could boost New Zealand apple production significantly, and are the subject of research at Lincoln University.

Each apple tree is a combination of a rootstock and a scion, joined near ground level by either grafting or budding. The scion is wood taken from a healthy tree of a known variety, while the rootstock is selected from a wide range of apple rootstocks which have been bred for characteristics such as tree size, disease resistance, compatibility with scion and fruiting characteristics.

Apples are unique in that there is an extensive range of rootstocks which growers can choose from. The size of an apple tree can be controlled by rootstock selection, and production systems are matched to the size and growing characteristics of the rootstock used. In New Zealand, most growers use the MM106 rootstock which gives a medium-sized tree and is resistant to the woolly apple aphid (Eriosoma lanigerum). Overseas, however, most modern orchards use dwarfing rootstocks, such as M9, in intensive apple production.

The potential yield of an apple tree is related to light interception. It is therefore very important that the orchard canopy intercept as much light as possible. Trees on dwarfing rootstocks planted more intensively can intercept more light per hectare in the early years of the orchard than trees planted further apart, so can generate higher yields in the early years. In addition, apple trees on M9 dwarfing rootstock fruit earlier in their life than trees on more vigorous rootstocks. These two factors mean that orchards on dwarfing rootstock can generate higher yields early.

As orchards mature, there is likely to be little difference in yield between an intensively planted orchard and a conventional orchard as both have a full canopy to intercept the light. However, fruit colour is enhanced by sunlight -- fruit which is shaded by branches and leaves will often be unacceptable for marketing because of poor colour. In a mature orchard, dwarf trees can therefore produce better quality fruit.

Researchers at Lincoln University have been studying intensive apple production on dwarfing rootstock since 1978. One trial has compared the yields of apples on MM106 planted at 635 trees per hectare with apples on M9 rootstock planted at 1,905 trees per hectare. Results over eight years showed that the M9 growing system gave much higher yields per hectare early in the life of the orchard and at full production yields per hectare were still higher. An economic analysis comparing plantings of the two rootstocks concluded that the intensive system on M9 rootstock was, in economic terms, a viable alternative to the conventional semi-intensive system using MM106.

There are advantages and disadvantages to growing apples intensively on dwarfing rootstock in New Zealand. Higher early yields mean faster returns to repay investment costs, and new varieties can come on stream more quickly. Smaller trees lead to faster pruning, thinning and harvesting, and lower levels of chemicals are required for pest and disease control. Disadvantages include greater establishment costs, and therefore higher risk, and the lack of woolly aphid resistance in the most commonly used dwarfing rootstock, M9. Another important disadvantage to local growers is their lack of experience with growing dwarf apple and lack of information specific to New Zealand.

As more and more New Zealand growers choose to use intensive apple systems, researchers are endeavouring to address the industry information needs. In 1991, Lincoln University began a study to improve the decision support for growers of intensive apples. Yield, fruit quality and tree growth was measured for intensive Braeburn on M9 trees at two different spacings. A computer model was then developed to predict the economic outcomes of different spacing decision scenarios. The model used the results from the trial as well as data from other sources to develop relationships between decisions and economic outcomes.

It is likely that the New Zealand apple industry will follow overseas development and move towards more intensively planted apple orchards in the future. New Zealand has one of the best climates and some of the best soils in the world for apple growing. However, our physical conditions are quite different from other apple growing regions and therefore we must develop our own systems for efficient apple production.

Mandy Cahn, Department of Farm and Horticultural Management, Lincoln University