P.H. Jerie, B. van den Ende, I.R. Dann
Vegetative vigour is inversely related to fruitfulness and the management of the balance between the two is one of the major determinants of orchard productivity. Traditional tree spacing allowed this balance to develop easily at the cost of having large trees with cropping delayed by many years. The ability to manage vigour sets the ultimate limit to high density planting. At any given scion/rootstock/ tree spacing combination the aim of vigour control varies with the stage of development of the orchard in that (i) young trees are required to grow rapidly to fill their allotted area, (ii) after full canopy development minimal growth will optimize fruiting and (iii) management of leaf area is needed in mature orchards to achieve crop quality and maintain fruiting wood. This paper looks at the effects of irrigation, root volume, pruning and paclobutrazol in developing management techniques for the control of vigour and fruitfulness on a short term or seasonal basis.

Vigour appears directly related to the available volume of soil suitable for root growth. Irrigation levels that replace less than evapotranspiration lower vigour as a consequence of developing water stress in the tree and by reducing the volume of wetted soil. Under Regulated Deficit Irrigation the trees are water stressed during periods of rapid shoot growth and fully irrigated during rapid fruit growth, usually for 5–8 weeks before harvest. Relating the level of irrigation to seasonal stages of shoot and fruit development results in a high degree of control over vigour while maintaining or increasing yield. Pruning can control tree size, canopy shape and density. However pruning also increases shoot vigour with negative effects on fruitfulness. The growth retardant Paclobutrazol controls vigour and increases fruit size in stone fruit, cherries being particularly sensitive. Activity in apple and pear is less predictable with undesirable side effects on fruit shape. In stone fruit both the degree and duration of growth retardation are dose related. This suggests that while high dosage can virtually eliminate extension growth, precise treatment with small doses eg. by feeding through the drip irrigation system, will result in short term control over vigour that could be used to manipulate canopy development.

Jerie, P.H., van den Ende, B. and Dann, I.R. (1989). MANAGING TREE VIGOUR AND FRUITFULNESS IN DECIDUOUS ORCHARDS. Acta Hortic. 240, 127-134
DOI: 10.17660/ActaHortic.1989.240.21

Acta Horticulturae