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16 Feb 2016
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The Reproductive Phenology of Citrus. I: Introduction to the physiology of citrus flowering

Jakkie (OPJ) Stander
Citrus Research International | Department of Horticultural Science, University of Stellenbosch
E-mail: jakkie@sun.ac.za

Flowers are a critical determinate of eventual yield of perennial fruit trees. Therefore, an understanding of the underlying mechanisms and influencing factors, as well as the general phenology of flower development in citrus, is critically important to the sustainability of successful commercial citrus production.

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15 Feb 2016
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Could Ethylene Metabolism in Lemon Fruit Influence Peteca Incidence?

Paul J.R. Cronjé
Citrus Research International | Department of Horticultural Science, Stellenbosch University
E-mail: paulcronje@sun.ac.za

Peteca of lemon is a postharvest physiological disorder resulting in the collapse of the oil glands. Subsequently, the oil leaks into the adjacent tissue and
causes a darkened depression. The occurrence can be severe, without any specific pre- or postharvest practises to employ to reduce the incidence.

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15 Feb 2016
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Fruit Splitting in Citrus

Paul J. R. Cronje
Citrus Research International | Department of Horticultural Science, Stellenbosch University

Ockert P. J. Stander and Karen I. Theron
Department of Horticultural Science, Stellenbosch University

Various citrus cultivars of ‘Navel’ and ‘Valencia’ orange [Citrus sinensis (L.) Osbeck], as well as mandarin and mandarin hybrids (Citrus reticulata Blanco) are prone to a preharvest physiological rind disorder, known as fruit splitting.

Similar disorders occur as fruit cracking and/or splitting in other commercially important horticultural crops, most notably in apple, apricot, cherry, grape, nectarine, prune, and tomato. Fruit splitting in citrus differs from other crops due to the unique morphology of a citrus fruit, consisting of the pulp and rind, which is made up of the spongy white internal layer, the albedo (mesocarp), and the external layer, the flavedo (exocarp).

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15 Feb 2016
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Postharvest rind breakdown of ‘Nules Clementine’ mandarin is influenced by ethylene application, storage temperature and storage duration

Paul J.R. Cronje and Graham H. Barry
Citrus Research International | Department of Horticultural Science, Stellenbosch University

Marius Huysamer
Department of Horticultural Science, Stellenbosch University

The progressive postharvest disorder of ‘Nules Clementine’ mandarin (Citrus reticulata Blanco), referred to as rind breakdown (RBD), starts to develop during storage, about 3–5 weeks after harvest. Variation within the tree canopy, i.e. inside or outside canopy positions, as well as postharvest handling practices such as ethylene degreening, storage temperature and storage duration, were investigated for their influence on RBD incidence. Two experiments were conducted wherein fruit were subjected, in the first experiment, to ethylene degreening and a delay in commencement of cold storage (2004), and, in the second experiment, fruit were sampled from the inside and outside of the canopy and cold-stored at either −0.5 ◦C or 7.5◦C during 2005 and 2007.

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15 Feb 2016
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Spray application in citrus – Sprayer calibration and checklist

Gideon van Zyl, Paul Fourie, Tian Schutte, Tim Grout (CRI) and Johan van Zyl (Nexusag)
CRI Cutting Edge, Research News from Citrus Research International

Fungicides and pesticides are only as effective as their application. The main objective of spray application is the optimal dose transfer of the well agitated tank mix, which includes one or more active ingredients, from the sprayer to the tree, whilst keeping off-target losses from run-off and drift at a minimum.

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15 Feb 2016
Valencia Leaves
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Assessment of retention and persistence of copper fungicides on orange fruit and leaves using fluorometry and copper residue analyses

Gerhardus C. Schutte and Charl Kotze
Citrus Research International

J. Gideon van Zyl and Paul H. Fourie
Department of Plant Pathology, Stellenbosch University

High volumes of copper hydroxide, cuprous oxide and copper oxychloride were sprayed under natural conditions onto mature orange trees to compare the etention on citrus leaves and fruit over a period of 56 days by means of copper residue analyses and a spray deposition assessment protocol using fluorometry, photomacrography and digital image analyses. Rainfall and increase in fruit size were also recorded to determine if it had an influence on weathering of copper residues.

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15 Feb 2016
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Evaluation of two organosilicone adjuvants at reduced foliar spray volumes in South African citrus orchards of different canopy densities

J. Gideon van Zyl and Paul H. Fourie
Citrus Research International | Department of Plant Pathology, Stellenbosch University

Ewald G. Sieverding
Evonik Industries AG, Goldschmidtstraße, Germany

David J. Viljoen
Evonik Africa (Pty) Ltd, Somerset West

South African citrus fruit producers rely heavily on medium to high volume fungicide spray applications (Grout, 1997, 2003) to protect citrus fruit from challenging diseases such as Citrus black spot (CBS) (Phyllosticta citricarpa (McAlpine) van der Aa (syn. Guignardia citricarpa Kiely)) (Kotze, 1981, 2000; Schutte et al., 1997) and Alternaria brown spot (Alternaria alternata (Fr: Fr) Keissl., tangerine pathotype) (Schutte, 1996).

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15 Feb 2016
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Spray deposition assessment and benchmarks for control of Alternaria brown spot on mandarin leaves with copper oxychloride

J. Gideon van Zyl and Paul H. Fourie
Citrus Research International | Department of Plant Pathology, Stellenbosch University

Gerhardus C. Schutte
Citrus Research International

Inadequate disease control on citrus foliage and fruit is often attributed to insufficient fungicide spray deposition on target surfaces. This study describes a novel spray deposition assessment protocol and determines deposition benchmarks indicative of the biological effectiveness for better interpretation of spray deposition results.
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