Managing Dieback 

Detection, Diagnosis and Mapping

Managing Phytophthora dieback is most successful when you have determined whether the pathogen is present or absent, and if present, identified what parts of the property or bushland are infested. Management procedures can still be implemented if you are unsure if the pathogen is present. However, without knowing the location of the Phytophthora dieback, management will not be as effective, it will be difficult to monitor the success of your work, and you may be taking some precautions that are not necessary.

The presence of Phytophthora dieback in bushland or home gardens is determined by observing deaths in plants that are considered susceptible to the disease. Common garden plants that are susceptible to the disease include roses, azaleas and fruit trees (e.g. avocado's, citrus, apples, macadamia's). Common native plants that are susceptible include Jarrah, banksia, grass-trees, zamia palms, dryandra and hakea species. Arguably the best indicator species for Phytophthora dieback in WA bushland are the Banksia species.

The following features can also be used to indicate the presence of Phytophthora dieback.

• Look for something that could have introduced the disease, for example, a track, road or vehicle activity. Or within your home garden the disease may have been introduced by planting infected nursery stock, use of contaminated ‘green' mulch or in infested soil/gravel.
• Plant deaths are localised within a distinct area of the property, often at a low lying, water accumulating area. Lines, groups or localised areas of plant deaths are more likely to be caused by Phytophthora dieback than odd scattered individual plant deaths in otherwise healthy vegetation.
• Look for an edge effect in bushland. Edge effects are most obvious when there is a clear distinction between healthy and diseased vegetation.
• Look for old deaths and recently killed plants, that is, an 'age range' in the deaths. This is because Phytophthora dieback moves from plant to plant over time, killing each plant as it goes.
• Look for signs of the disease in a range of different susceptible plant species.

You must be careful to discount other factors that could have caused plant deaths, such as fire, insect pests, flood, drought, nutrient deficiencies or toxicities, herbicide damage; and other plant diseases. If non-susceptible trees, for example red gums, tuarts, flooded gums or wandoo are dying then it is NOT likely that the cause of poor plant health is Phytophthora dieback.

Remember that when you have had bushland surveyed for Phytophthora dieback, the result will only be accurate at that point in time. The disease will spread autonomously and new infections can occur. When planning management procedures for controlling Phytophthora dieback it is important to re-survey for disease movement and new disease outbreaks every one to two years.

There are two options for determining whether Phytophthora dieback is present in bushland:

1. Engage a professional consultant; or
2. Do it yourself

Professional consultants

Professional consultants determine the presence of Phytophthora dieback by using indicator (susceptible) plants and by testing soil and plant samples. The consultants would have undertaken accredited training with DEC and have many years of experience in completing Phytophthora dieback surveys. To arrange a site assessment or mapping of an area for Phytophthora dieback contact either GLEVAN Dieback Consultancy Services (08 9582 7772) or Department of Environment & Conservation (08 9474 7046).

For further detail on how DEC interpreters map Phytophthora dieback in bushland please consult: Phytophthora cinnamomi and disease caused by it. Volume 2 - Interpreter's Guidelines for Detection, Diagnosis and Mapping.

The cost of a survey will vary, depending on the size and location of the bushland, and the degree of difficulty experienced in interpreting disease symptoms. Consultant fees usually do not include the cost of processing the soil and plant samples (sample processing usually costs between $70 and $150 a sample). Discuss costs with the consultant prior to the work being undertaken. Community groups can consider applying for funding from various sources to cover the cost of disease surveys. For more information on these potential funding sources contact the Environmental Officer at your local council or the Dieback Working Group.

Do it yourself

You can complete your own disease survey by studying the plants in the bushland or home garden. You will need to have a very good knowledge of plants, various disease symptoms and other causes of plant deaths for the results of your assessment to be accurate and reliable.

The presence of Phytophthora dieback is determined by observing susceptible plants that are killed by P. cinnamomi. These susceptible plants are called "indicator species". Jarrah, banksia, grasstree, zamia palm, dryandra and hakea are common indicator species.

The tables below list some common plant species and genera from the jarrah forest and Swan Coastal Plain that are susceptible to P. cinnamomi, and can be used as Phytophthora dieback indicator species. For a more detailed list of resistant and susceptible plant species please consult the Dieback Working Group website (www.dwg.org.au).

Laboratory Testing

Like the professional consultants, you can also take plant and soil samples and have them tested in a laboratory. Sample results that are positive for P. cinnamomi mean that the pathogen is present at the site. Negative results don't mean that the site is free of the pathogen, as it may simply have been missed when the sample was taken. The chance of a positive sample being recorded can be significantly increased if the sampled plant has a lesion (decaying tissue) present underneath the bark at the base of the main trunk.

You will need to get instructions from the laboratory on how to take a sample, the best time to take the sample and how to store and transport it. Sampling usually involves digging up a dead plant to get to the roots, and this can be quite a physically demanding task if you are sampling a dead Banksia or Grass tree.

Laboratories for Testing Soil and Plants for Phytophthora dieback

• Department of Environment & Conservation, Vegetation Health Service: Phone (08) 9334 0333.
• Center for Phytophthora Science and Management, Murdoch University: Phone (08) 9360 6272.
• Curtin University. Dr Elaine Davison: Phone (08) 9266 3106.
• Agwest Laboratories, Department of Agriculture:
  Phone (08) 9368 3693.