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Reflective materials under hailnet improve orchard light utilisation, fruit quality and particularly fruit colouration

Meinhold, Tobias, Damerow, Lutz, Blanke, Michael
Scientia horticulturae 2011 v.127 no.3 pp. 447-451
adverse effects, aluminum, apples, autumn, climate change, color, energy use and consumption, fruit quality, fruits, grasses, greenhouses, hail, labor, light intensity, mechanization, orchards, paper, photoperiod, plastics, prices, ripening, screening, sugars, taste, Europe
The increase in hailstorms, possibly due to climate change, has led to installation of hailnets in fruit orchards worldwide. This is associated with poorer fruit quality, particularly fruit colouration, which is determined by the light conditions viz diminishing light intensities and shorter day length in the autumn. To overcome these adverse effects of hailnets, five materials were examined as possible ground covers as to their light reflection and the subsequent effect on fruit quality including fruit colouration, using a 9-year-old apple orchard cv. ‘Gala Mondial’ on M9 under black hailnet near Bonn. The ground covers included the woven white plastic Extendayᴿ/Daybright™, the kaolin-coated, bio-degradable paper UniSet O™ and the aluminium-coated plastic Mylar™ and Svensson ILS Alu™; the latter is a white plastic interwoven with aluminium strips used as energy saving screen in greenhouses. The ground covers were spread in the alleyways 4–5 weeks before anticipated harvest; adjacent uncovered grass strips under the hailnet served as control. Light reflection, measured perpendicular at 1m height in the alleyways at the time of fruit colouration, was 79–80% by Extendayᴿ/Daybright™, 75% by UniSet O™, 68% by Mylar™ and 58% by Svensson Alu ILS™. Apple fruit with any of the reflective ground covers ripened 2–3 days earlier without affecting internal fruit quality and sugar as indicative of taste. The reflective ground covers under black hailnet improved the proportion of well-coloured class I fruit relative to the control (uncovered grass) by an averaged 9%. Economic analysis showed that Extendayᴿ, with an expected lifetime of ten years (based on 4–6 weeks spread time per year) under hail nets in North-Western Europe, scored best based on 45tha⁻¹ yield in cv. ‘Gala Mondial’ and 0.40€kg⁻¹ farm-gate price, resulting in 200€ha⁻¹ net return. Manual labour for spreading and retrieving the ground covers had the major share of the overall gross cost and offers scope for improvement by mechanisation.