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21 Oct 2024
Post harvest citrus
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Alternative methods for the control of postharvest citrus diseases

The postharvest diseases of citrus fruit cause considerable losses during storage and transportation. These diseases are managed principally by the application of synthetic fungicides. However, the increasing concern for health hazards and environmental pollution due to chemical use has required the development of alternative strategies for the control of postharvest citrus diseases. Management of postharvest diseases using microbial antagonists, natural plant-derived products and Generally Recognized As Safe compounds has been demonstrated to be most suitable to replace the synthetic fungicides, which are either being banned or recommended for limited use.

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21 Oct 2024
Girdling
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Influence of girdling on the seasonal leaf nutrition status and fruit size of Robinson Mandarin

This study was undertaken to investigate the effects of single and double girdling applications on the fruit yield, commercial size, quality, photosystem II (PSII), leaf chlorophyll and leaf nutrition content of 22-year-old Robinson mandarin (Citrus reticulata). Girdling treatments were performed at anthesis (when 60% of the flowers were opened) with approximately 5 mm trunk diameter in 2014. The fruit was harvested in 2014 at the optimum harvest time (in December) for fruit yield, properties and size. Evaluations of leaf mineral content, chlorophyll concentration and fluorescence measurements were performed at monthly intervals.

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21 Oct 2024
Navel Sweet Orange
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Optimal timing of application of 2,4-D on ‘Navel’ sweet orange reduces the size of the navel-end

‘Navel’ sweet orange [Citrus sinensis (Osbeck)] fruit with large, open, or protruding navel-ends are predisposed to splitting and navel-end rot, and provide an entry point that hampers the control of insect pests. A reliable method to reduce the size of navel-ends, without compromising tree health or fruit quality, would provide multiple benefits.The objective of this study, was to determine the optimal timing and concentration of foliar spray treatments with the synthetic auxin, 2,4-dichlorophenoxyacetic acid (2,4-D), to reduce the size of the navel-end on ‘Newhall Navel’ and ‘Washington Navel’ sweet orange fruit. The effects of 2,4-D treatment on fruit yield, tree health, and fruit quality, were also assessed.Treatments were applied to ‘Newhall Navel’ trees at a rate of 25 mg l–1 2,4-D at 2-weekly intervals, starting at full bloom (FB), and continuing until 4 weeks after 100% petal drop (PD). On ‘Washington Navel’ trees, 2,4-D was applied at 15 mg l–1, 25 mg l–1, or 35 mg l–1 at FB, or at 100% PD.

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27 Sep 2024
Australia Mandarin
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Final Report: Monitoring and control techniques for Australian bug

Icerya purchasi Maskell (Hemiptera: Monophlebidae) (Australian bug) is a polyphagous and cosmopolitan pest of plants that includes citrus. Dense populations of Australian bug cause plant stress, leading to defoliation, fruit drop and a decrease in plant vitality. Australian bug excretes honeydew, which supports the growth of sooty mould, disfiguring the plant. Novius cardinalis (Mulsant) and Novius iceryae (Jenson) (Coleoptera: Coccinellidae) (Vedalia beetles) are natural enemies of the Australian bug that are generally successful in controlling their populations. Vedalia beetles are, however, susceptible to a number of insecticides used to control other insect pests in citrus orchards. High incidences of Australian bug were recently recorded in mandarin orchards in some citrus growing regions in South Africa. In order to better understand the causative factors leading to an increase in incidence of Australian bug, populations of Australian bug and Vedalia beetles were monitored on a monthly basis over two years (May 2021 – May 2023) in four mandarin orchards on four different farms in Mpumalanga Province, South Africa.

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25 Aug 2024
Leaf Analysis
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Evaluation of the usefulness of early leaf analysis to improve nutrition management of citrus

The response of Citrus sinensis ‘Midknight’ (Nelspruit, Mpumalanga, South Africa) and Citrus paradisi ‘Orri’ (De Wet, Western Cape, South Africa) to excessive fertilisation (double the normal rate) with nitrogen (N), phosphorus (P), potassium (K) and magnesium (Mg) was investigated. The goal was to determine whether early-season leaf mineral compositions respond to fertilisation rates so that in-season adjustments of the fertilisation programme can be made.

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25 Aug 2024
Orange on soil
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Nutrient management zones for citrus based on variation in soil properties and tree performance

Site-specific soil management can improve profitability and environmental protection of citrus groves having large spatial variation in soil and tree characteristics. The objectives of this study were to identify soil factors causing tree performance decline in a variable citrus grove, and to develop soil-specific management zones based on easily measured soil/tree parameters for variable rate applications of appropriate soil amendments. Selected soil properties at six profile depths (0–1.5 m), water table depth, ground conductivity, leaf chlorophyll index, leaf nutrients and normalized difference vegetation index were compared at 50 control points in a highly variable 45-ha citrus grove.

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25 Aug 2024
Managing Salinity in Citrus
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Salinity resistance of citrus seedlings in relation to hydraulic conductance, plasma membrane ATPase and anatomy of the roots

The evaluation of the response of three rootstocks to conditions of high salinity (NaCl 90 mmollL) and the relationship with different parameters was the objective of this study. The three rootstocks were Cleopatra Mandarin, considered to be tolerant to salinity, Citrange Carrizo and Citrus Macrophylla, considered to be sensitive to salinity. We related the differences in salinity resistance to water and nutrient uptake, ATPase and anatomy of roots. For this, root hydraulic conductivity, ion concentrations in the xylem obtained under transpiration flow, root plasma membrane ATPase activity and anatomy of the root tips were determined in seedlings grown in a controlled environment.

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