Prediction and control of bitter pit in apples. I. Prediction based on mineral leaf composition, cropping levels and summer temperatures

Abstract

SummaryEarly prediction of the probable incidence of bitter pit is required to enable growers to identify, at harvest time, fruit with a high risk of the disorder so that it may be excluded from long-term storage. Data were collected over four years from 28 orchards to investigate the factors related to its incidence. The mineral composition of leaves sampled in August was unsuitable for forecasting bitter pit, unless the fruit/leaf ratio of the tree and regularity of cropping between trees were also taken into consideration. Bitter pit in stored apples increased with the (K+Mg)/Ca ratio in leaf and fruit, and decreased with a higher fruit/leaf ratio and more regular cropping. Clear differences in the incidence of bitter pit were recorded between years, even where cation ratios and yield levels were comparable. Part of these differences could be attributed to the unfavourable effect of high temperatures in August. However, factor analysis from trials over a 15-year period failed to show any marked association between bitter pit and the weather during August and September.