The use of hail and shade nets in the deciduous fruit industry.
Hail and shade nets have been used in agriculture for some time, however nets have recently been a hot topic. The use of nets is becoming more lucrative everyday with increased pressure for more and better quality fruit and increased risk for damage to crops being the two biggest drivers. The independent horticultural study group, The Fieldsman’s, met on Friday 28 March 2014 to discuss the practical and physiological implications of using shade nets on deciduous fruit. Danie Kritzinger and Mico Stander attended the event on behalf of Agrimotion and would like to share their experience.
The proceedings started in Grabouw with lectures from:
Dr Wiehann Steyn, HORTGRO Science – The physiological effects of shade nets on deciduous fruit production.
Willie Kotze, HORTGRO Science – Results from net trials at three sites.
and Daan Brink, Two-A-Day – The practical factors of farming under nets.
Thorough research on the use of shade nets specifically in the apple industry is rare. The application under South African conditions is also limited given that most of the research has been done in countries like Australia and Europe. HORTGRO Science shared some results from their net trials in the South African industry.
According to Dr Steyn’s literature review, farmers can expect variation regarding the following factors when farming under shade nets:
A 12-20% decrease in the visible light spectrum and a 20-28% decrease in ultra violet light spectrum when using a 20% shade net. The variation observed in the light that reaches the tree is due to the different types of net used i.e. white, blue, yellow, grey, “pearl”, red etc.
A decrease of 1-3oC in air temperature, a 3oC decrease in leaf temperature, a 6oC decrease in fruit temperature and a 0.5-1oC decrease in soil temperature. The variation in results is due to difference in aspect, region and type of net used.
Wind speed can be reduced by up to 50%. The effect varies according to the percentage of net cover. For example the netted Orchard of the Future trial at Oak Valley Estate has been covered along all the side which, amongst other uses, reduces wind damage. The main reason for the side cover is however for pest and disease management.
Bud Break and Fruit set:
Fruit set and return bloom can be lower under nets and production can alternate from year to year. Effects on fruit quality may also vary although the general trend is that red apples have weaker colour development and green apples present with better colour development. Sunburn is greatly reduced but not completely absent as sunburn is still observed in very warm seasons. The reduction in sunburn on fruit is accepted as the biggest advantage to using shade nets.
The TSS is lower due to less light reaching the tree. There is a natural fruit thinning effect under the nets due to the lower light levels and thus increased competition.
There is no statistical proof but trends in Grabouw suggest that vigorous orchards set less fruit when placed under net and that weaker growing orchards set better under net and thus production increases in the latter case.
Growth is more vigorous as the number and length of shoots increases.
Water use is less due to the reduced water vapour deficit between the soil, plant and atmosphere. Drip irrigation can possibly be more practical under nets and should thus be considered. Reduced water use is however not the case for all crop types as commented by one of the Fieldsman’s members.
The conversion of dry mass to fruit mass will be determined by the rootstock and the selection thereof is thus crucial. There is a lot of excitement around the use of dwarfing rootstocks under net, especially the dwarfing M9 and GENEVA 222, which under some may not be vigorous enough. A formal trial to investigate the behaviour of different rootstocks under shade net is currently being considered.
Pest and Disease control:
Improved spray efficiency will lead to, amongst others, better control of Fusi. Control of woolly aphid and weevil under nets has however been difficult up to date. Moth and fly behaviour under net is difficult to predict and should thus be monitored.
Willie Kotze made the following conclusions from his research results:
- Cultivar choice greatly affects whether a positive or negative response is observed in fruit quality. Results show that there is less sunburn and less class 3 fruit, however apples that depend on light for colour development may show a decline in quality.
- Rootstock selection is critical in order to control vigour, especially given the increased vigour under net.
- The aspect and soil potential will impact the success of the project and should be investigated and considered throughout the project.
- Management practices which may need to be implemented are:
o Pruning: (To maintain adequate light penetration for bud development)
o Thinning (Fruit abscise more readily under nets) and
o Spraying (Use of products such as Regalis to control growth).
Daan Brink shared some of his practical experience:
- Every effort should be made to secure the anchors when erecting the structure. These anchors determine the integrity of the entire structure.
- The rope and wirework becomes more simplified as the technology improves.
- The structural poles should be planted in a diamond pattern with a pole every 12 to 16m in the row. This will ensure that there is a wire running across every 6 to 8m to support the net.
- The purpose of the net will determine the material to be used: Hail nets require a stronger material and the structure should allow for the nets to open as to allow hail (or snow) to fall through. A less durable net would be sufficient as a shade net.
- A 0.5 to 1m space should be left vacant above the tree tops to allow for adequate bee activity. A 4.5m high structure would thus be sufficient.
We are very grateful that the speakers and consultants involved are willing to share their results with the industry. Hopefully there will be some more results to share at the HORTGRO Symposium in June 2014. In case there are any topics you wish to see at the Symposium please send your suggestions to us and we will direct them to the organizers.
Agrimotion will also stay up to date with these developments so that our clients can keep getting advice that is scientific, independent and precise.
In conclusion; the typical recommendation under nets: Granny Smith on a dwarfing rootstock, under a white net, with double the normal number of beehives.