Browsing by Author "Van Wyk, Tertia"

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    The implementation and validation of reduced volume argrochemical applications in the south African citrus industry using novel technology
    (Stellenbosch : Stellenbosch University, 2019-03) Van Wyk, Tertia; Van Niekerk, Jan M.; Fourie, Paul H.; Stellenbosch University. Faculty of AgriSciences. Dept. of Plant Pathology.
    ENGLISH ABSTRACT: The South Africa citrus industry is the third largest exporter in the world and is considered one of the most important horticultural crops due to high economic export value. However, citrus trees are susceptible to a wide range of insect pests and fungal diseases. This places pressure on producers to deliver high quality fruit that adhere to strict export requirements. The largest and most important export market of citrus is the European Union (EU), which have a zero-tolerance approach towards Citrus black spot [Phyllostica citricarpa (van der Aa)] and false coddling moth [Thaumatotibia leucotreta (Meyrick)]. This leads to high spray volume applications that are seen as insufficient and not sustainable. The high input costs relating to water, labour and equipment as well as the environmental impact is a result of these high demands for 100% clean fruit. Furthermore, these high volumes are determined without taking canopy density into account, which contributed to high volumes being lost to run-off. The potential of reduced spray volumes has been investigated, however limited trials have been done on the feasibility, implementation and biological efficacy of these different spray volumes in a seasonal commercial spray program. Therefore, the aim of this study was firstly to evaluate the possible reduction of spray volumes in the South African citrus industry without compromising on the need to get 100% control of important pests and diseases. Secondly, to investigate the use of the novel technology (LiDAR) to characterize citrus tree canopy density. For the first objective spray trials were conducted in the Limpopo, Western and Eastern Cape provinces on commercial citrus producing farms. Reduced volumes (750 to 3000 L/ha) were compared with the farm’s standard spraying volume (4000 to 9000 L/ha) evaluating spray deposition parameters such as deposition quantity (FPC%), uniformity (CV%) and quality (ICD%). Furthermore, the pest and disease efficacy were also evaluated in terms of clean fruit. For the second objective trials were conducted on three commercial farms in the Western Cape to determine the effect of three different pruning categories on FPC%, CV% and ICD% in combination with two different spray application volumes (1500 L/ha as the reduced volume and 3000 L/ha as the standard volume). In an attempt to develop a non-destructive technique to measure canopy density use of LiDAR technology was investigated and compared with manual canopy measurements. From this study it was concluded that higher spray volumes result in better control of pests and diseases due to better deposition uniformity values. Furthermore, the importance of the penetration of spray mixtures into the canopy to achieve adequate control of pests and diseases is also essential. The manual manipulation of canopy density by pruning proved to be beneficial for spray deposition in creating more ‘spray-friendly’ canopies. The potential of LiDAR to be used as a calibration tool, was seen in this study, detecting differences in canopy densities. However, the LiDAR parameters were poorly correlated with manual measurements. It is suggested that the application be simplified in future studies for better correlation.