Airborne phytophthora

​​​ Two leaves zoomed in both infected with Phytophthora ramorum causing parts of the leaf to start and die.


Airborne phytophthora

Exotic to Australia

Life form: Oomycete
Origin: Asia
Distribution: North America and Europe
Features: Oomycete causing leaf spots, shoot/branch dieback and stem cankers which often ooze dark red sap and have a fermentation odour, necrosis, plant death
Pathways: Air spores, clothes/shoes, equipment, plant trade, green waste, animals
At risk: Nut industries, plantation forestry, production nurseries, urban trees, native ecosystems


Phytophthora species are oomycete pathogens of a wide range of trees, shrubs and herbaceous plants. Derived from Greek, the word phytophthora means ‘plant destroyer’. Testing on Australian native plants suggests that Eucalyptus, Leptospermum and Melaleuca, among others, may includehighly susceptible hosts.

Sudden oak death caused by Phytophthora ramorum is causing serious and widespread damage in nurseries and natural woodland ecosystems throughout Europe and North America, affecting over a 130 tree and shrub species and killing trees in the millions. Where the disease occurs, some industries have been particularly affected by the pest, including nursery industries.

Phytophthora ramorum, more commonly known as sudden oak death (SOD), causes symptoms on stems, trunks and leaves. It can spread and reproduce rapidly in new environments. Its rapid life-cycle, propensity to reproduce by zoospores and aerial spread (via windblown rain), plus its ability to survive through harsh climatic conditions enhance this species’ invasiveness. It is of particular concern to Australia owing to the susceptibility of eucalypts and other native species.

Other noteworthy examples of airborne phytophthora which produce symptoms on leaves/needles and shoots/trunks include:

  • Phytophthora kernoviae

How to identify Airborne phytophthora

Everyone needs to keep an eye out for phytophthora species.

Phytophthora species are oomycetes (water moulds) which look similar to fungi but their cell walls contain cellulose rather than chitin as is found in cell walls of the true Fungi. They require a moist environment (abundant water in soil or on foliage) to actively grow and reproduce.

Phytophthora ramorum causes two distinct sets of symptoms, depending on the host species. On some hosts, the pathogen causes trunk cankers that usually form on the lower trunk and result in brown or black discoloured outer bark and bleeding sap. These cankers can lead to death of the tree. On other hosts, including many horticultural nursery crops, the pathogen causes a foliar blight and shoot dieback. In shrubs, leaf blight symptoms appear as dark brown spots or blotches usually occurring at the leaf tip. Eventually the leaves completely turn brown to black and then may drop prematurely. Twig blight/dieback results in shoots becoming blackened with or without foliage attached.

Phytophthora kernoviae has similar symptoms to P. ramorum causing dieback and bleeding cankers. Infected shoots and leaves of plants begin to die when the plant becomes infected showing blackening down the mid-vein.

Close up image of plant showing the beginnings of shoot dieback with stems started to brown and blacken towards the tip of the leaf. Two smaller images attached in the photo showing single infected leaves with large sections of the leaf that are dead. 

Airborne phytophthora – a) Shoot dieback of Rhododendron infected with Phytophthora ramorum (image courtesy Everett Hansen, Oregon State University) b) underside & c) top of leaves infected with Phytophthora ramorum (images Bruce Moltzen, Missouri Dept. of Conservation)

Close up image of plant showing the beginnings of shoot dieback with stems started to brown and blacken towards the tip of the leaf. Two smaller images attached in the photo showing single infected leaves with large sections of the leaf that are dead.

Two leaves zoomed in both infected with Phytophthora ramorum causing parts of the leaf to start and die. 

Airborne phytophthora  – Symptoms on Rhododendron leaves caused by Phytophthora ramorum.
SOURCE: Joseph O'Brien ( USDA Forest Service.

The age of the plant, the host species and time of the year can all affect the severity of the symptoms. Wet, cooler periods of the year support the growth of the pathogen.

Phytophthora species are capable of natural spread and through human activities. This pathogen can spread via wind and rain as well as through the movement of infected clothing and shoes, equipment, plants and green compost. Phytophthora ramorum has also been found in waterways.


If you work around imported goods you need to look for symptoms of phytophthora on plant materials.
The pathogen can also spread via human assisted movement of infected clothing and shoes. It is important that people ensure that shoes and clothes are clean and free of soil or plant material when entering Australia.

Growers and home gardeners

Check your production nursery frequently for the presence of new pests and unusual symptoms.
Take action if you see symptoms of phytophthora on shrubs or trees.
If Phytophthora ramorum was to establish in Australia it would have an impact on:

  • amenity trees
  • chestnuts
  • forest species
  • nursery production
  • Australian native plants.

Keep Airborne phytophthora out of Australia

All Australians and international tourists have a role to keep out exotic pests and diseases. Airborne phytophthora are present in a number of countries.

Australia remains free of these exotic pests. We need your help to keep it this way.

Check what you can and cannot bring into Australia, whether you are a:

Stop this plant destroyer

Let’s protect our nursery stock and native species that could be affected by these invasive pathogens.

Import restrictions and biosecurity measures

Some items, by law, are subject to certain import conditions to be allowed into Australia. Please check the Biosecurity Import Condition System (BICON).

Be aware of any phytophthora pathogen biosecurity measures that may be in place for incoming goods and conveyances. Industry advice notices are reviewed regularly and could change.

Secure any suspect specimens

Containment is critical.

It is important to not move samples to reduce the risk of spread. Take a photo, record the location and get it checked by an expert.

Report detections of exotic pests

Any detections of phytophthora pathogen must be reported to the authorities.

Import community

If you receive or work around goods imported from overseas, including mail, you need to be vigilant to phytophthora species and other exotic pests. If you see an unusual pest, secure the goods to limit the movement of the pest and immediately report it to the Department of Agriculture, Water and the Environment’s See.Secure.Report. Hotline 1800 798 636 or by using the online form.

Growers and home gardeners

If you see the symptoms of a phytophthora species or anything unusual, report it to the Exotic Plant Pest Hotline on1800 084 881. This will put you in touch with the department of primary industries or agriculture in your state or territory.

When reporting your concern, you will be given advice on handling the specimen and what to do next until an officer can investigate.

Additional information

Last reviewed: 4 February 2020
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