Plant Pathology
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Citrus Pathology


Programme leader: Dr Paul Fourie


Fungicide application technology

In plant disease control, the use of very effective aqueous remedies (i.e. fungicides, biocontrol agents, GRAS chemicals, etc.) sometimes yield disappointing results whereby growers suffer economic losses. In these cases, disease control failure is often attributed to insufficient application of the remedy. In this research programme, various conventional and novel application technologies are evaluated and optimised in citrus orchards and packhouses in order to ensure biologically effective residue loading onto susceptible plant parts, without exceeding allowable maximum residue levels. Concomitant aims involve addressing cost and time efficiency aspects of application methods, whereby production and environmental costs are directly influenced. The methodology employed involves a proprietary deposition assessment protocol using fluorometry, digital photography and image analyses, as well as residue analysis and biological efficacy tests.

Epidemiology of Citrus Black SpotCBS.jpg

Citrus Black Spot (CBS) is a cosmetic disease of citrus fruit. However, its causal organism, Guignardia citricarpa, is regarded as a quarantine organism in certain countries. The South African citrus industry is the second largest exporter of fresh citrus fruit in the world, and therefore CBS is an economically important disease given the market access implications it poses. In this research programme at USPP, the epidemiology of this disease is studied to understand and predict its behaviour under climatically diverse conditions. This will allow improved control programmes, but will also assist in ongoing market access deliberations. Additionally, population genetics of G. citricarpa will be studied on a global scale in order to ascertain the global movement of this organism and the relative importance of sexual and asexual reproduction under diverse climates.

Available Masters projects for 2022:

  1. Whole genome characterization of mefenoxam sensitivity in Phytophthora nicotianae and P. citrophthora from citrus in South Africa.
  2. Evaluation of the Tree Row Volume concept for the management of pests and diseases in citrus.