Firstfruits

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. However, application of these alternatives by themselves may not always provide a commercially acceptable level of control of postharvest citrus diseases comparable to that obtained with synthetic fungicides. To provide more effective disease control, a multifaceted approach based on the combination of different postharvest treatments has been adopted. Actually, despite the distinctive features of these alternative methods, several reasons hinder the commercial use of such treatments. Consequently, research should emphasize the development of appropriate tools to effectively implement these alternative methods to commercial citrus production. Click here to read the full article. https://lnkd.in/dGq5m6BN

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. Leaf samples were taken in eight periods for analysis of plant nutri-elements. It was determined that double girdling was the best application in terms of fruit yield and percentage of marketable fruit. The treatments did not significantly affect fruit internal quality. Girdling reduced PSII and leaf chlorophyll concentration but did not affect leaf mineral content. However, we observed a tendency toward a decrease in nitrogen levels in the girdled trees. According to the results of the present study, girdling treatments significantly affected fruit yield and size together with several macro-micro plant nutri-elements. Click here to read the full article on our web. https://lnkd.in/dy5DFjQ7

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. Click here to read the full article on our web. https://lnkd.in/djexVt94

Citrus Fruit-Cracking: Causes and Occurrence Citrus fruit creasing or cracking is a complex pre-harvest physiological disorder that causes significant economic losses. Recent studies have indicated that citrus fruit creasing or cracking is caused not only by genetic factors but also by environmental factors. By reviewing the relationship between citrus fruit creasing or cracking and peel mechanical properties, the cellular wall ultrastructure, cellular wall metabolism and modification, this paper summarized the mechanism of citrus creasing or cracking and further explained the effects of genetic factors and environmental factors (light, temperature, humidity, mineral nutrition and plant growth regulators) on citrus fruit creasing or cracking rate. Further studies were proposed to provide a sound theoretical basis on citrus fruit creasing or cracking. Click on the link below for the full article. https://lnkd.in/dbSATef8

ARTICLE ON OUR WEB 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. Chemical application programmes for the selected orchards were obtained and correlated with Australian bug and Vedalia beetle populations. High populations of Australian bug (>60% trees infested) were recorded between May and July 2021. After July 2021, there was a rapid decline in both Australian bug and Vedalia beetle populations. This decline was attributed to the use of chemical insecticides targeting spring pests. Populations of Australian bug returned the following year (2022) but remained low. Vedalia beetles were only recorded on two of the farms in 2022 as compared to all four farms in the first year of the study. In the second part of the study N. iceryae were released into four selected orchards with little to no chemical application histories. Novius iceryae was able to control I. purchasi populations in two of the orchards where there were no chemical interventions. It was evident from the study that insecticidal applications disrupted the biological control of Australian bug in mandarin orchards. Click here to read the full article on our web.

ARTICLE ON OUR WEB 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. A specific focus was the changes in the nutritional status of the trees as expressed by leaf analysis. Except for N, a lack of responsiveness of the trees to excessive rates of mineral nutrition was observed. Consequently, it was concluded that using foliar analysis to make in-season changes to fertilisation rates of orchards that are amply fertilised cannot be justified. Click on the link below to read the full article. https://lnkd.in/dvpe5AFT

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. Regression analysis indicated that 90% of spatial variation in tree growth, assessed by NDVI, was explained by average soil profile properties of organic matter, color, nearinfrared reflectance, soil solution electrical conductivity, ground conductivity and water table depth. Regression results also showed that soil samples at the surface only (0–150 mm) explained 78% of NDVI variability with NIR and DTPA-extractable Fe. Excessive available copper in low soil organic matter areas of the grove apparently induced Fe deficiency, causing chlorotic foliage disorders and stunted tree growth. The semivariograms of selected variables showed a strong spatial dependence with large ranges (varied from 230 m to 255 m). This grove can be divided into different management zones on the basis of easily measured NDVI and/or soil organic matter for variable rate application of dolomite and chelated iron to improve tree performance. Click on the link below to read the full article on our web. https://lnkd.in/dTh-hfYH

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. Click on the link below to read the full article. https://lnkd.in/dm8VH4mD

Tiaan Snyman, our Firstfruits Technical Manager, gave a talk on low-flow drip at the 12th CRI Citrus Research Symposium. Congratulations to Tiaan on completing his MSc Cum Laude! Vir meer inligting: www.1stfruits.co.za #firstfruits #CRICitrusSymposium2024 #CRI #cricitrusresearchsymposium

Etienne Rabe at the 12th CRI Citrus Research Symposium 2024 in the Drakensberg this week. He is sharing HLB lessons he learned in California, because Etienne is our international, technical consultant. For more information about Firstfruits: www.1stfruits.co.za #firstfruits #CRI #CitrusResearchSymposium2024 #citrusconsultancy #1stfruits