Diagnosing the signs of pests and diseases

February 29, 2008

Pests and diseases are now widely recognised by the South African forestry industry as being threats of increasing magnitude.

Chrysoporthe canker Wood staining Insect damage
Chrysoporthe canker leads to wilting and death in infected trees. A clear example of wood staining. Evidence of insect damage.


In this regard, recognition, accurate diagnosis and knowledge of the biology of the causal agents are among the best weapons that we have to combat the problems. Thus, the Tree Protection Co-operative Programme (TPCP) and the Centre of Excellence in Tree Health Biotechnology (CTHB), based at the Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria (www.fabinet.up.ac.za) offers a diagnostic service to members of the research programmes. Here, assistance is offered in identifying pests or pathogens and advice is provided on their management and long-term strategies to reduce their negative impact. In order for the clinic to effectively diagnose a particular problem the samples provided need to be submitted appropriately. Guidelines for submitting samples were presented at the recent South African Forestry Institute (SAIF) Pest Awareness Symposium and the group was asked to share the details which are as follows:

Selecting samples for diagnosis

  • Symptoms of diseases and pest infestation include wilting, dying branches, gum/resin exudation, wood staining, stem cankers, leaf spots and foliage discolouration. Other signs can include fungal fruiting bodies and insect egg capsules.
  • Wilting and foliage discolouration can be caused by either a root problem, wilt pathogens or disease of the stem or branches.To determine which, it is important to examine the entire tree, including roots, main stem and branches. Look for gum/resin oozing from any part of the tree, cracks and sunken areas as well as discoloured areas. If these symptoms cannot be found above ground, it will be necessary to expose and examine the roots of the tree for any discolouration or death.
  • To identify the affected part of the tree, look for the margin where the green tissue ends and the dying or dead tissue starts, known as the lesion margin. The diseased part is often visible to the trained eye as a slightly sunken area, or by scraping off the bark surface. Diseased areas will be discoloured, while healthy areas will be green/white in colour.
  • A good sample will include both healthy and diseased tissue with a clear lesion margin.

Submitting samples

  • It is very important to contact the clinic before a sample is sent. This is so that the responsible/appropriate people are aware of the sample submission and can provide advice on what to send and how to send it.
  • Courier the samples via same day or overnight delivery. To minimise damage to the samples during shipping, place them in a sturdy container or box.
  • Keep the samples from drying out by wrapping them in moist (not wet) paper such as newspaper and placing it in a plastic bag (paper bags and envelopes disintegrate when wet).
  • Refrigerate the samples if it cannot be sent immediately. Samples should not be kept for longer than one week, after which fresh samples will have to be collected.
  • Mark the sample clearly.
  • Include a letter with the following information:
  • Contact details: address; telephone, mobile and fax numbers; e-mail address
    • Species or clone affected
    • Area, Plantation and Compartment number where samples were collected
    • Date planted
    • Description of symptoms
    • Percentage infection or mortality
    • The GPS coordinates of your sample
  • Samples can include diseased roots, stems, foliage, soil, or growth medium, but it is important that they:
  • Are representative of primary symptoms
  • Are from at least three trees
  • Do not send insect pests! Contact Brett Hurley (brett.hurley@fabi.up.ac.za) or Bernard Slippers at the FABI (Tel: 012 420 3938) and they can assist you from there.
  • Water samples require a certain level of expertise and are done on site with prior arrangement.
  • It is important to send the sample or notify us as soon as the first symptoms are noticed.

Prior communication is essential. Some diseases have similar symptoms and it is only possible to tell them apart through isolation and identification using microscopy/molecular techniques. Thus, communication between members and the diagnostic clinic is essential as without prior discussion the wrong samples can be sent and the problem misdiagnosed.

Responsible diagnosis is important for the following reasons:

  • It impacts the accuracy of the disease database.
  • Misleading information about tree health in South Africa can have an impact on risk assessment and decision-making.
  • New and potentially devastating pathogens or pests can be overlooked.
  • Suitable control recommendations can be misdirected.

Fighting pests and diseases starts with awareness. Continual monitoring is essential as new incursions or adaptations of pathogens already present an impact on quarantine regulations and trade. Knowing what is where is essential to ensure appropriate and timely control measures.

(Photos courtesy of FABI)

Published in January/February 2008

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