Zebra Net, Titanium Net, Transparent Net and New Hail Net: New Names, New Structures, Stronger Fibres for Better Durability and Longer Lifespan? : Refined Structure, Composition, Mesh Size and Large Portion of Crystalline Translucent Fibres Improve Light Transmission of the New Hail Nets | Zebra Net, Titanium Net, Transparent Net and New Hail Net: New Names, New Structures, Stronger Fibres for Better Durability and Longer Lifespan? : Refined Structure, Composition, Mesh Size and Large Portion of Crystalline Translucent Fibres Improve Light Transmission of the New Hail Nets

Four new types of hail net were examined as part of an MSc thesis. Hail nets in Germany consist of two interwoven longitudinal fibres (parallel to the tree row) and a single transversal fibre (perpendicular to the tree row); fibres were HD-PE monofilaments. Composition, fine structure, mesh size, fibre strength and light transmission of the zebra net, titanium net, transparent net and MaBo’s new grey net were studied. The fine structure was assessed in the lab by stereoscan light microscopy, while light (PAR, 400–700 nm and UV, 285–315 nm) transmission was measured 0.5 m underneath the hail net in the field near Bonn (50°N) at noon on a sunny and on an overcast day in July. 1. The ‘titanium hail net’ (Helios Co.) comprised of two longitudinal translucent fibers anda single white transversal, UV-stabilized fibre with titanium of about 0.31 mm diameter, and a medium mesh size of 2.8 mm × 8.0–8.4 mm. Light transmission, assessed in the orchard,ranged from 78 % (cloudy) – 82 % (sunny) for UV-B to about 86 % for PAR compared to the geometric light transmission, calculated according to Blanke (2007) as 90 % PAR. 2. The ‘zebra hail net’ (Fruit Security Co./MaBo (Marktgemeinschaft Bodenseeobst eG)) consists of longer (95 cm) patches of white and shorter (30 cm) ones ofabout 0.32 mm transversal black fibers (8 %) weaved toone of the largest mesh sizes of 2.9–3.0 mm × 8.7–8.8 mm. The black transversal, and black longitudinal fibres to reinforce the edges, provide sufficient strength to attach the clamps.The zebra net transmitted 84 % (cloudy) – 86 % (sunny) (UVB) and 87–90 % (PAR), which compared favourably with its theoretical geometric light transmission of 90–95 % PAR. 3. Thenew grey hail net (Fruit Security, MaBo)with one of the largest mesh sizes of 2.9 mm × 8.7–9.0 mm consisted of two interwoven, translucent and a single soot-impregnated transverse black fibre. The latter increases tearing strength, resulting in 2/3 translucent and 1/3 black fibres.The grey hail net transmitted 80 % (cloudy) – 83 % (sunny) UVB and 84–85 % of PAR relative to the calculated transmission value of 90.5 % (PAR). 4. The ‘transparent hail net’ (Brändlin Co.) comprisedtranslucent fibers of about 0.33 mm diameter and small mesh size of 3.0 mm × 7.0 mm with black longitudinal fibres to reinforce the edges. Light transmission of the transparent net, assessed in the orchard,ranged from 77 % (sunny) – 80 % (cloudy) for UV-B to about 88 % for PAR compared with the calculated geometric light transmission of 92–95 % PAR. 5. Overall, the four new hail nets provide a good compromise between high light transmission, good strength and long durability and offer a promising alternative to the present either black (78–82 %) or translucent (88–92 % light transmission) hail nets.The UV transmission of the four hail nets was 2–12 % lower than for PAR. 6. Thecalculated geometric light transmission values proved an elegant way when light transmission cannot be measured, e.g. in an office or during manufacture. 7. The light measurements showed that theoriginally+ 4 % additional light transmission in the calculation for every translucent fibre in a hail netcan be reduced to+ 2.5 %, if the two translucent fibres are interwoven e.g. as longitudinal fibres.