The implementation and validation of reduced volume argrochemical applications in the south African citrus industry using novel technology

Van Wyk, Tertia (2019-03)

Thesis (MScAgric)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse sitrusbedryf is die derde grootste uitvoerder ter wêreld en word beskou as ‘n belangrike gewas as gevolg van sitrus se hoë ekonomiese uitvoerwaarde. Sitrusbome is egter vatbaar vir 'n wye verskeidenheid van insekplae en swamsiektes. Dit plaas druk op produsente om vrugte van hoë gehalte te lewer wat aan streng uitvoervereistes voldoen. Die grootste en belangrikste uitvoermark van sitrus is die Europese Unie (EU), wat 'n zero toleransie benadering tot Sitrus Swart Vlek (Phyllostica citricarpa (van der Aa)) en vals kodlingmot [Thaumatotibia leucotreta (Meyrick)] het. Dit lei tot hoë chemiese spuitvolumes wat as onvoldoende en nie volhoubaar beskou word. Die hoë insetkoste met betrekking tot water, arbeid en toerusting, sowel as die omgewingsimpak, is die gevolg van die vereiste om 100% siekte- en plaagvrye vrugte te produseer. Verder word hierdie hoë volumes bepaal sonder om die boomdigtheid in ag te neem, wat daartoe bydra dat hoë volumes as afloop verlore gaan. Die potensiaal van verminderde spuitvolumes is al voorheen ondersoek, maar beperkte proewe is gedoen oor die haalbaarheid, implementering en biologiese effektiwiteit van hierdie verskillende spuitvolumes in 'n seisoenale kommersiële spuitprogram. Die doel van hierdie studie was dus om eerstens die moontlike vermindering van spuitvolumes in die Suid-Afrikaanse sitrusbedryf te evalueer om steeds 100% beheer oor belangrike plae en siektes te kry. Tweedens, om die gebruik van die nuwe tegnologie (LiDAR) te ondersoek om sitrusboomdigtheid te karakteriseer. Vir die eerste doelwit is spuitproewe in die Limpopo-, Wes- en Oos-Kaap provinsies op kommersiële sitrusplase uitgevoer. Verlaagde volumes (750 tot 3000 L/ha) is in vergelyking met die plaas se standaard spuitvolume (4000 tot 9000 L/ha) geëvalueer. Spuitafdeposisieparameters soos deposisie kwantiteit (FPC%), uniformiteit (CV%) en kwaliteit (ICD%) is ondersoek. Die plaag- en siekteeffektiwiteit is ook geëvalueer in terme van die persentasie skoon vrugte. Vir die tweede doelwit is drie proewe op kommersiële plase in die Wes-Kaap uitgevoer om die effek van drie verskillende snoei kategorieë op FPC%, CV% en ICD% in kombinasie met twee verskillende toedieningsvolumes (1500 L/ha as die verminderde volume) en 3000 L/ha as die standaard volume) te bepaal. In 'n poging om 'n nie-destruktiewe tegniek te ontwikkel om die boomdigtheid te meet, is die gebruik van LiDAR-tegnologie ondersoek en vergelyk met fisiese metingsmetodes. Uit hierdie studie is bevind dat hoër spuitvolumes beter beheer van plae en siektes tot gevolg het, as gevolg van beter deposisie unifomiteitswaardes. Verder is die belangrikheid van die penetrasie van spuitmengsels in die boom uitgelig om voldoende beheer oor plae en siektes te verkry. Die fisiese manipulasie van die boomdigtheid deur snoei het bewys dat dit voordelig is vir spuitdeposisie deur die skep van meer 'spuitvriendelike' bome. Die potensiaal van LiDAR om as 'n kalibreringsinstrument gebruik te word, is in hierdie studie beklemtoon, waarby verskille in boomdigtheid waargeneem is. Die LiDAR parameters was egter swak gekorreleer met fisiese metings. Daar word voorgestel dat in toekomstige studies ‘n eenvoudiger benadering gevolg word vir beter korrelasie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105707
This item appears in the following collections: