Mid season prediction of fruit size distribution of 'Golden delicious' apples in south Africa

The early prediction of expected fruit size distribution in commercial apple production is considered a useful management tool to assist growers, pack houses and marketers. With a fruit size distribution, the percentage of saleable fruit in the different size groups can be identified relatively early in the season. This information will enable early decisions regarding fruit volumes available for the different markets, as well as the market strategy to be followed by the marketers. Pack house managers can use the information for planning of packing material orders. The fruit size distribution predictions can also assist the producer with thinning decisions late in the season. Diameters of tagged 'Golden Delicious' apples were recorded weekly from 40 days after full bloom during four consecutive seasons to develop a fruit growth curve. Fruit diameters were also recorded on a per tree basis starting mid season (60 - 80 days after full bloom) to determine the fruit size distribution per orchard. The equation developed to predict the weekly growth rate for fruit was used to develop a model for the prediction of the final fruit size distribution at harvest in three 'Golden Delicious' orchards during two consecutive seasons. The predicted and actual size distribution showed similar trends, and differences between orchards as well as seasons could therefore be estimated accurately. Exceptionally high temperatures had a negative effect on the rate of fruit growth and prediction dates had to be adjusted to improve the accuracy of the predictions.