With 3000 trees per hectare or more of patented cultivars growing on multi-wired trellises, such systems must generate a significant return on investment that begins early in the life of the orchard and that is sustained for at least 15 years.
With some high-value cultivars fetching very high returns per carton in the market, any fruit that is damaged and unmarketable represents significant losses to the grower.
In contrast to the larger trees of older systems, these high-density systems have narrow canopies where fruit are more directly exposed to adverse weather and high sunlight conditions, which can result in losses from hail damage, sun damage and sunburn.
Netting research in Italy
In Italy for example, high-density commercial orchards are using overhead netting for both protection from hail and to reduce sunburn.
The commercially available nets that are being evaluated by Italian researchers include the industry standard traditional black netting but also coloured nets including pearl, yellow, red, and blue.
The coloured nets transmit more sunlight (less shading) than the black nets and provide other benefits such as more uniform skin colour and improved size.
By filtering the sunlight, these coloured nets can alter, not just the quantity of light used in photosynthesis, but also the quality of light used for other physiological processes.
This light filtering can alter the orchard microclimate and reduce tree heat stress.
Hail netting is widely used in the major tree fruit production areas of Italy and South Africa.
Alternatives needed
Sunburn is a very significant cause of fruit damage.
One widely used technique to reduce sunburn is the combined use of overhead sprinklers or misting (for evaporative cooling to reduce fruit skin temperature).
Washington State University Tree Fruit Research and Extension Centre, plan to conduct several long-term commercial trials in Washington under the high sunlight conditions in central Washington, especially for high-value apple cultivars that are sunburn sensitive.
continued next month
For more information, see Tree Fruit May 2014
