Natural june thinning of fruitlets and yield characteristics of apple trees growing under coloured anti-hail netting

Abstract

In this study, the spectra of reflectance and transmission of light by different colours of anti-hail netting were studied. At the same time, the impact of different coloured anti-hail nets on chosen parameters of growth, fertility and quality of ‘Braeburn Mariri Red’ apples was defined. For this purpose, anti-hail nets of equal technical characteristics (mesh size and thread thickness) and different colour (red, grey, blue, green and black) were studied. In the red, blue and green nets, spectral distribution of solar radiation differs considerably, while the black and grey nets exhibit a constant pattern of reflectance and transmission across the whole spectral zone of visible light (400-700 nm). Anti-hail netting intensifies the natural June thinning of fruitlets (on average by 12.5%), which can lead to an increased fruit weight and consequently lower fruit flesh firmness. Anti-hail nets (in general) do not affect the vigour or soluble solids content, while grey, blue and black nets slightly postpone fruit ripening (lower starch index). Any differences between coloured nets in the colour intensity of apples are negligible. However, blue, red and green nets apparently induce more rapid colouration. The influence of black netting (the one most frequently used) on fruit yield quality does not differ from that of other coloured nets; in conection to the longest “life span”, this colour of anti-hail net still represents the best choice for growers.