Effect of permanent shade netting on ‘Nadorcott’ mandarin tree phenology and productivity

Brown, Robert (2018-03)

Thesis (MScAgric)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Permanent shade netting in citrus (Citrus spp.) is implemented to protect high-value fruit and trees from damaging natural elements. However, the use of the technology accompanies inevitable changes in orchard microclimate that impacts on the physiology and phenology of a citrus tree. In this study a 20% white permanent shade netting treatment was evaluated for its effects on citrus tree phenology, its impact on the efficacy of chemical fruit thinning agents, and the long-term profitability of the technology in a young ‘Nadorcott’ mandarin (C. reticulata Blanco) orchard. Shade netting did not enhance the growth of individual vegetative shoots but did increase tree volume over time. In general, flowering was not affected by the shade net treatment, but during the second season, flowering intensity on summer vegetative shoots was higher in the shade net treatment. Fruit set, fruit yield and fruit internal quality were not affected by the shade net treatment, but fruit diameter was increased in the second season. Shade netting did not influence the ability of uniconazole soil-drench treatment to reduce vegetative growth. The shade net treatment did not influence the efficacy of synthetic auxin fruit thinning agents to thin fruit. The synthetic auxin fruit thinning treatments increased the concentration of selected mineral elements in fruit, and treatments resulted in a shift in fruit size distribution, with higher number of large, premium-sized fruit per tree. The effect on fruit size distribution was more pronounced in the shade net treatment. Apart from fruit size, a combination of shade netting and chemical fruit thinning treatments had no effects on other important fruit quality attributes. From the budget model generated in this study, it can be concluded that 20% white permanent shade netting resulted in increased orchard profitability, despite a high establishment cost and increase in production costs. It can therefore be concluded that under typical Mediterranean-type production conditions, 20% white permanent shade netting increased the productivity and profitability of a ‘Nadorcott’ mandarin orchard. The use of the technology can be recommended in areas that experience extensive yield losses due to climatic conditions and possibly also permit citrus production in non-traditional areas.

AFRIKAANSE OPSOMMING: Die implementering van permanente skadunet-strukture om vrugtegewasse teen nadelige natuurlike elemente te beskerm geniet wêreldwyd toenemende aandag. Die tegnologie gaan ongelukkig gepaard met ‘n onafwendbare verandering in boord mikro-klimaat, wat kan lei tot fisiologiese en fenologiese veranderinge in die sitrusboom. Om hierdie rede is die impak van ‘n 20% wit, permanente skadunet op die fenologie en die doeltreffendheid van chemiese vruguitdunning in ‘n model mandaryn kultivar, ‘Nadorcott’ ondersoek, sowel as die winsgewendheid van die tegnologie oor die langtermyn. Die skadunet behandeling het nie vegetatiewe groei van individuele lote bevorder nie, maar wel boomvolume verhoog. Opvolgblom in die lente was oor die algemeen nie beinvloed deur die skadunet behandeling nie, maar in die tweede seisoen het die skadunet blomintensiteit verhoog op lote wat in die voorafgaande somer ontwikkel het. Die finale vruggrootte is verhoog deur die skadunet in die tweede seisoen, maar vrugset, oeslading en interne vrugkwaliteit is nie beinvloed in enige van die seisoene nie. Die effektiwitiet van unikonasool as ‘n grondtoediening om lootgroei te inhibeer is nie geaffekteer deur die skadunet behandeling nie. Die doeltreffendheid van blaarbespuitings van sintetiese ouksiene as chemiese uitdunmiddels is nie geaffekteer deur die skadunet behandeling nie. Daar is ook gevind dat die ouksien behandelings die konsentrasie van sekere minerale nutriente in die behandelde vrugte verhoog het, en gelei het tot meer vrugte in die groter kommersiële vrugklasse. Die skadunet behandeling het hierdie effek van die sintetiese ouksiene op vruggrootte bevorder, en geen effek op die interne vrugkwaliteit gehad nie. Die begrotingsmodel wat saamgestel is het getoon dat ‘n 20% wit, permanente skadunet die vermoë het om die wingewendheid van ‘n mandaryn boord te verhoog, ten spyte van die hoë insetkoste en verhoogde produksiekoste. Deur gebruik te maak van ‘n 20% wit, permanente skadunet kan die produktiwiteit en winsgewendheid van ‘n ‘Nadorcott’ mandaryn boord dus verhoog word in ‘n tipiese Meditereense-tipe klimaat, en kan hierdie praktyk aanbeveel word in areas waar ongure klimaatstoestande tot grootskaalse oesverliese lei.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103904
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