Disease Management


Dr. Jan van Niekerk


Dr. Providence Moyo, Prof. Paul Fourie, Dr. Elma Carstens, Dr. Wilma du Plooy (CRI), Prof. Francois Halleen, Prof. Lizel Mostert, Dr. Cheryl Lennox, Prof. Aletta van der Merwe (SU), Prof. Jacquie van der Waals (UP)


Citrus black spot is problematic in the citrus production regions with summer rainfall. Apart from fruit being down-graded from a blemish viewpoint, the disease is also considered to be of quarantine importance by certain of our existing or new/future export markets. Research and services also focus on other pre-harvest leaf and fruit diseases other than citrus black spot, most specifically on Alternaria brown spot, Botrytis flower blight, Phytophthora root and brown rot and citrus nematode, Tylenchulus semipenetrans. The aspects studied are summarised below:

Market Access

  • Adherence to permitted MRL levels
  • Packaging of local and international research findings to facilitate market access negotiations
  • Circumscription and maintenance of selected production areas as “pest free” or “of low pest prevalence”

Etiology & Diagnosis

  • Develop detection techniques to facilitate rapid detection and diagnosis
  • Characterise variability in pathogen populations present in South Africa
  • Facilitate awareness to ensure early-detection of new invasive pathogens


  • Study epidemiological aspects that would facilitate improvement of management strategies
  • Evaluating and optimising conventional and novel spray application technologies in order to ensure effective residue loading but not exceeding permitted MRLs
  • Studying pathogen population structures on a global scale to determine global movement of pathogens
  • Evaluating new spray programmes and combinations of chemical compounds for disease control but adhering to permitted MRLs and minimising fungicide resistance
  • Validating and improving disease (CBS) prediction models using climatic variables

Disease Management

  • Evaluating and optimising conventional and novel spray application technologies in order to ensure effective residue loading without exceeding permitted MRLs
  • Evaluation of novel and GRAS chemical compounds and biocontrol agents for disease control
  • Structuring of spray programmes to improve control, adhere to MRL and limit fungicide resistance
  • Rootstock resistance against soilborne pests and diseases

Inoculum Management

  • Formulation and evaluation of sanitation strategies that would reduce primary inoculum
  • Implementation and optimisation of pathogen elimination strategies from propagation material


  • Standard operating procedures to maintain phytosecurity of Citrus Improvement Scheme
  • Prevention of phytotoxicity following spray application

Host Resistance

  • Product comparison / evaluation
  • Inoculum Management