Margaret CoryOrnamental tree diseases in Sydney

The Australian Institute of Horticulture recently organised a seminar on this topic presented by Dr Edward Liew, manager of the Plant Pathology Section in the Sydney Royal Botanic Gardens. This section comprises the plant disease diagnostic unit and plant pathology and mycology research programme. Dr Liew has been involved in plant disease diagnosis and research for the last 20 years. His research focuses on the evolution, genetics and taxonomy of fungal pathogens. Here are some notes I made from the seminar that you might find useful.

The topics covered:

  • – root and stem diseases such as Armillaria, Phytopthora and Cypress Canker
  • – update on Myrtle Rust and Fusarium Wilt in Date Palms

One of the first comments Dr Liew made was that in Europe values go up when there is a garden full of old established trees. In Sydney the opposite occurs. The general feeling is to “cut it down”!

Eucalypt death from fungal Phytophthora cinnamomi in Cremorne, Sydney

Phytopthora cinnamoni

General Information

  • – This is wide spread in Australia
  • – It is a threat to our biodiversity
  • – There are over 2000 host species
  • – It spreads in soil and water and survives for many years
  • – It is not native and was introduced to our shores in the 19th century
  • – Usually found in an area with an annual rainfall above 500mm
  • – Firstly, there is a root infecting pathogen causing root rot with dieback the secondary symptom
  • – It has the ability to rejuvenate itself in two days
  • – The appearance of the affected tree is similar to drought: stunting, wilting, chlorosis, branch death – all the symptoms
  • – It is found in many of our national parks, including the Blue Mountains National Park
  • – The environment contributes to the development of the symptoms

What to do

  • – Change the soil – fertilise
  • – No water stress – too little or too much
  • – We spread the disease – boots, tent pegs, backpacks, bikes

Management

  • – Cannot be eradicated
  • – Practise containment
  • – Quarantine
  • – Treatment – improve the tree health
  • – Dr Liew suggests calling him to discuss these and other considerations

 

Armillaria mushroom fruiting bodies on tree trunk Photo Tomasz Przechlewski

Trunk, Butt and Root Rots – Armillaria, Ganoderma, Phellinus

  • – These are white and brown rots
  • – Armillaria attacks both live and dead wood
  • – Symptoms are decay: roots, collar, trunk (internal)
  • – There may be no external symptoms at first, then defoliation, bark peeling and upside down ‘V’ shape disfiguration on the trunk
  • – Armillaria grows up the trunk and along the roots
  • – Lacy, fernlike mycelium, plus layered mushrooms growing up the trunk to 3m high
  • – Armillaria will affect anything which is woody
  • – Wounding will enable the spread
  • – There is no effective control of these diseases
  • – Early detection and diagnosis is important
  • – Monitoring is also very important, both external and internal (the Domain trees, for example)
  • – Dr Liew does not agree with drilling holes in trees

 

Canker and Lesions

  • – Caused by many different species of ascomycetous fungi
  • – Improving the health of plants enables them to resist disease – prevention
  • – Malformation and irregularities on stem, branch and trunk
  • – Splits, lesions, cankers, girdling of branch, oozing, bleeding
  • – Internal discolouration
  • – Dieback – a secondary symptom
  • – Healthy trees are good at healing themselves
  • – Norfolk Island dieback – lesions or cankers
  • – Cypress dieback affects the foliage
  • – Cypress canker is caused by a pathogen which affects the trunk – wounding causes splits which cause lesions
  • – No effective fungicidal treatment
  • – Removal is the number one management – some canker branches can be cut out – local eradication
  • – Phosacid is effective
  • – Cleanliness of tools is vital; 70° methylated sprit is very effective for cleaning tools

Questions

  • – Is there a list of susceptible species – yes the RGB has a list
  • – Mulch keeps Phytopthora in check
  • – Promotes soil health
  • – Composting should kill pathogens, except if large chunks of plant material – the compost heap must generate oxygen, heat, etc
  • – Trichoderma kills armillaria infected tissue – it is a pathogen but a good one
  • – Phytopthora affects living roots first
  • – Roots when cut are dark brown to honey coloured to pale
  • – Phytopthora affects root tips, plus wounding in larger roots
  • – Supposed resistant plants, i.e. grasses, can harbour diseases
  • – Councils recommend phytopthora management, as do the National Parks
  • – Disinfecting tools and all equipment is the best practice

 

Fusarium Wilt

  • – This is found in Phoenix canariensis, the Canary Island palm
  • – Also found in Washingtonia sp
  • – Caused by Fusarium oxysporum
  • – Banana plantations can be affected
  • – It was seen in Centennial Park in the late ‘80s
  • – It is elsewhere in Sydney and in Melbourne and South Australia
  • – It is fatal in all cases though it may take a long time
  • – Vascular symptom – vascular wilt diseases
  • – It is spreading around Sydney in older suburbs
  • – The whole canopy of the palm dies
  • – Dead and dying lower fronds
  • – Half a frond will die – one side only affected
  • – One half can be healthy and the other dead
  • – There can be more than one disease in dead fronds
  • – Palms are susceptible to too much phosphorus or to boron deficiency
  • – No effective control of Fusarium wilt
  • – Hygiene is very important: the disease is spread by pruning dead fronds and then using the same, unwashed tools to prune healthy fronds
  • – Ibis may spread the disease
  • – Pink rot has been discovered in the Darling Harbour palms and this is spread by the ibis roosting in the palms

 

Myrtle rust on Waterhousia

Myrtle Rust

  • – This is also called Eucalyptus Rust and Guava Rust
  • – In Central and South America is it called Guava Rust
  • – Uredo rangelii
  • – It affects a wide range of Myrtaceae sp
  • – In April 2010 was first detected in New South Wales
  • – It is now in Queensland and Victoria
  • – It is spread by the movement of plant material and soil
  • – Mainly on young shoots
  • – Typical very bright yellow or orange spores on pustules
  • – Causes leaf and shoot distortion
  • – Causes leaf and shoot death
  • – Then the death of the whole plant
  • – Agonis flexuosa puckering, then pustules
  • – It is easily brushed onto clothing and the wind can carry it
  • – There are 144 Myrtaceae genera, 83 of which are in Australia, many with multiple species
  • – What to do in the bushland?
  • – The RBG removed all Myrtus communis, the true myrtle an exotic species, from their gardens
  • – The disease has been declared non-eradicable
  • – Hosts do not have any way of dealing with this disease

 

Disease Management

  • – Select suitable trees
  • – Protect against stress factors
  • – After six months, no mulch or water
  • – Do not use bark mulch
  • – Use green mulch/compost. This is very important
  • – Quarantine
  • – Tool hygiene – do not use bleach but 70° methylated spirit, but be aware that in hot weather the alcohol disappears, so you could be carrying around a bucket of spores if you keep dipping your pruners into the bucket. Use a spray bottle with the disinfectant in it.
  • – Clothing, footwear and gloves can spread the disease
  • – Monitoring
  • – Accurate diagnosis

 

For Further Information

Contact the Royal Botanic Gardens’ laboratory to have diseases diagnosed. Visit their website at: http://www.rbgsyd.nsw.gov.au/plant_info/pests_diseases

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Margaret Cory

About Margaret Cory

A garden designer in Sydney for over 20 years, Margaret designs the gardens, hand draws the plans, procures the plants and supervises the job from start to finish. Margaret has also written articles for garden magazines, including Outdoor Rooms. She is now focusing on water-colouring garden plans, as some clients still want a hand-drawn plan of their garden as a keepsake and this can be greatly enhanced by being water-coloured. She has been commissioned by Readers Digest to design and water colour a plan for a formal herb garden and this is now featured in their book, The Complete Book of Herbs.

4 thoughts on “Ornamental tree diseases in Sydney

  1. Sandi on said:

    Excellent information. Thank you

  2. That’s such valuable information. I must admit that in my head, I tend to lump together all those different fungal diseases as sort of the same thing, when of course they are not at all.

  3. Rochelle on said:

    Do Canary Island Date palms require pruning? I do think that I have 1 out of 5 sick? what happens if the palms are never pruned?

    • Hi Rochelle – palms don’t need pruning except to occasionally remove the old, lower fronds that have died off as new ones grow from the top. Canary Island date palms get to their full width before they start to get taller. It depends on what’s making your Canary Island date palms sick. Fusarium wilt is very common in eastern Sydney. If it is fusarium wilt, you will notice that one side of each frond looks like it’s dying but the other half of the frond still looks green. There is no cure for fusarium wilt.

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