Shade netting reduces sunburn damage and soil moisture depletion in ‘Granny Smith’ apples

Abstract

The benefits associated with the use of protective netting for apple orchards have been assessed in several growing regions, but no studies exist for Washington State, USA. This region experiences semi-arid conditions characterized by long days, high light intensity and high temperatures which increases the risk of plant stress and fruit sunburn damage. The aim of this study was to assess the effect of anti-hail nets on orchard microclimate, soil moisture and fruit sunburn. Seven-year-old ‘Granny Smith’/‘M9-T337’ apple trees were covered in 2014 with 20% white shade net sheltering a rectangular area. Uncovered trees served as control. Shade net reduced the maximum daily photosynthetically active radiation (PAR) by 32%, with a maximum PAR value on a sunny day of 1649 and 1222 μmol m-2 s-1 in the control and netted areas, respectively. Canopy air temperature was slightly lower during the day and higher at night under the net compared to the control. Shade nets reduced soil moisture depletion at 0-30 cm depth, resulting 20% higher than the control. No significant differences were observed deeper in the soil profile. Netting significantly decreased fruit sunburn, with 92% of harvested fruit having no sunburn damage compared to control in which 51% had no sunburn damage in 2014. Although preliminary, these results show that shade netting has the potential to reduce sunburn damage in ‘Granny Simith’ apples and water requirements in semi-arid environments and might represent an important tool for increasing yields of high quality fruit.