The effects of thinning on fruit size on the apple variety gala in Hawkes Bay: A thesis submitted as the requirement for the National Diploma of Horticulture (Fruit) New Zealand

Abstract

Under conditions where a heavy fruit set takes place on apple trees some degree of thinning is normally required to produce fruit of marketable size. Thinning avoids a tendency toward biennial bearing and also helps increase fruit colour and quality ( Batjer, 1965). The amount of thinning normally required varies from one variety to another. Some require little or no thinning at all to produce crops of good size where as other varieties must be heavily thinned to bring fruit up to a size suitable for marketing. Some varieties have an inbuilt ability to self-thin, whereas others require a considerable amount of fruit to be removed to enable the remaining fruit to develop to a desirable size. In the past the practice of thinning by hand was the only method of thinning. In more recent times the use of chemicals (in the blossom-early fruit set period) has gained a great deal of favour. Chemical thinning has the advantage of removing fruit from the tree at a much earlier stage than hand thinning, enabling the remaining fruit a greater period to increase size and also promote flower initiation for the following season. It is a general practice in orchards today to chemically thin the crop early, and then follow up by hand thinning to reduce the crop to the required level at a later stage. In this case chemical thinning reduces the amount of hand thinning required, promotes more regular tearing by removing the bulk of the excess crop prior to flower initiation. Little is known about the effects of different chemicals or the rates required to thin the apple variety 'Gala' in Hawkes Bay. This is also true of the degree of thinning required for this variety either by hand or chemicals or a combination of both to reduce the fruit set to such a level as to produce fruit of a desirable marketable size. It is the purpose of this thesis to determine the degree of thinning required to bring the fruit up to an acceptable size to meet market requirements.