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EFFECT OF STEEL AS ALTERNATIVE TRELLISING MATERIAL WITH MECHANICAL HARVESTING
Christo J Maré (Iscor Long Steel Products, Marketing, Special Profiles)

Wooden poles are generally used to erect trellis systems for vineyards. The availability of wood is limited, however, and may be exhausted or become very expensive in future (Avenant, 1997). Research on steel as alternative trellis material started in 1993 and is aimed at reducing the cost component for the industry (table, dried and wine grapes).

Various experiments have been conducted, mainly on overhead trellis systems. During the 1998/1999 season trials were conducted on the farm Panorama in Riebeeck West to monitor the influence of steel trellis material on the mechanical harvesters.

The wooden poles (50-75 mm) of five rows were removed and replaced by steel poles (ISCOR 2 kg/m hedge pole). Specifications for the experimental block are as follows:

  • Type of trellis
    		•  3 Strand Perold (Hedge)
  • Spacing between line poles 
    		•  7 m
  • Row length
    		•  273 m
  • Number of poles
    		•  195
  • Pole length
    		•  1.850 m
  • Type of pole (wood)
    		•  50-75 mm
  • Type of pole (steel)
    		•  ISCOR, 2 kg/m Y-hedge pole

    Photo 1: Braud machine during trial. No additional changes were made to accommodate the mechanical harvester.
    Photo 2: Single Iscor 2 kg/m Y-hedge pole with adjustable foliage wire spacer.
    Photo 3: Double Iscor 2 kg/m Y-hedge pole with foliage wire spacer. If vines are planted in sandy soil or exposed to high cross winds, double poles (or wooden poles) may be planted alternately (every 3rd or 4th pole) to ensure lateral stability.
    Photo 4: Remaining bunches on either side of the wooden pole once the harvesting process is finished.
    Photo 5: Minimal (to no) bunches remain on either side of a steel pole once the harvesting process is over. Very few berries fall on the ground.
    Photo 6: Wooden poles are loosened and even broken during the harvesting process. Notice the "cracks" occurring in the soil around the pole. Some poles no longer bind and may be lifted out of the soil.
    Photo 7: Steel poles are minimally loosened during the harvesting process. As a result of the elasticity of the steel poles, the subterranean section of the poles does not move. Consequently no "cracks' occur in the soil around the poles.

    CONCLUSION

    Iscor as well as the producers in question consider the experiment to be very successful since no damage was noticed to either the trellis material (steel poles) or the mechanical harvester. The poles in question were not removed, however, and will be monitored on a continuous basis. Similar trials are planned in the Robertson and Lutzville regions. Dimensions to be monitored during these trials are i.a.:

    • Stability of the system: stability of the respective rows in wind conditions.
    • Corrosion resistance: resistance to corrosion in vineyard conditions above and below the soil
    • User friendly: during erection of the trellis and mechanical harvest.
    • Environment friendly: effect of steel, if any, on the wine (must) quality.

    Acknowledgement: Thanks to Mr Van der Bijl Brink, Panorama, Riebeeck West for making his vineyard and equipment available.

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