The effect of pre-harvest shielding and spraying on yield, scab incidence, phenolic compounds and fruit quality in organic apple production

Summary

Demand of organic apples is increasing but the yield is low due to apple scab disease. The aim of the present study was to investigate the effect of exposing three apple (Malus domestica Borkh.) cultivars ‘Red Elstar’, ‘Rubens’ and ‘Santana’ to different pre-harvest treatments in the orchard during the growing season 2014. Treatments were (i) untreated (control), (ii) sprayed with sulphur and potassium bicarbonate (sprayed), (iii) sprayed with sulphur and potassium bicarbonate and from fruit set supplemented with an extract of Acadian algae (sprayed + Acadian), and (iv) trees covered with a rain shield (shielded). The yield was recorded for every treatment. The incidence and severity of apple scab in the harvested fruits was evaluated. In addition, the content of 7 different phenols in apple peel was determined using HPLC. Further, the quality of apple fruits in relation to physio-chemical parameters was investigated. Results showed that all pre-harvest treatments reduced scab disease where shielding provided the best control: The rain shield reduced scab severity by 85-100 % in the three cultivars compared to the control and meanwhile increased the marketable yield of apple fruits. Control apples contained a significantly higher concentration of total phenols compared to apples receiving a treatment. Pre-treated apples had lower firmness, contained less total soluble solids and acids and had a higher sugar/acid ratio compared to control. It was concluded that shielding of apples showed to be a promising tool to diminish the presence of apple scab, increase yield and positively affect the eating quality at harvest.