Phytophthora cinnamomi, (AKA cinnamon fungus), is an exotic water mould that has spread across southern Australia and is deadly to a wide range of susceptible plants. Despite it’s common name, it is a soil-borne water mould, not a true fungus.

Many iconic Peninsula species (banksias, tea-tree, grass trees) are highly vulnerable. The mould attacks plant roots, preventing water/nutrient uptake and causes plant dieback.

Key susceptible plant Families

The most vulnerable groups are:

  • Proteaceae
    • Banksia spp. (e.g. Coast Banksia Banksia integrifolia, Heath Banksia B. ericifolia)
  • Myrtaceae
    • Eucalyptus spp. (stringybarks, peppermint gums)
    • Melaleuca, Leptospermum (tea-trees)
  • Ericaceae / Epacridaceae (heaths)
    • e.g. Epacris, Leucopogon
  • Fabaceae (peas)
    • e.g. Pultenaea, Bossiaea, Daviesia
  • Xanthorrhoeaceae
    • Grass-trees (Xanthorrhoea australis) – very visible indicator species
  • Other heathland/shrub species typical of coastal dunes and heathy woodland

How it spreads

1. Movement of soil

  • Mud on boots, bikes, tools
  • Vehicle tyres, machinery, track maintenance
  • Construction / roadworks
    👉 Human activity is a major driver of spread

2. Water movement

  • Surface runoff after rain
  • Drainage lines, downslope movement
  • Wet soils and puddles
    👉 The pathogen thrives and spreads in moist conditions, often travelling downhill

3. Infected plant material

  • Nursery stock
  • Soil or mulch containing spores

4. Natural root-to-root spread

  • Moves locally between neighbouring plants underground

Preventing Spread

Spread is largely preventable through good hygiene practices:

  • Clean boots/tools
  • Stay on tracks
  • Avoid wet/muddy conditions

You may want to consider the below boot wash procedure when moving in between properties.

The disinfectant can be 70% methylated spirits or a 1% solution of
household bleach which is made by diluting 1 part bleach in 4 parts water.

Phytophthora on the Peninsula

Cinamon Fungus was discovered on a property scheduled for revegetation this autumn (2026), and generated an investigation into this widespread mould, ways of countering it, and whether revegetation can/should be done in infected areas.

It is impossible to eradicate the mould with current technology, so the recommended solution is to seal off the area and isolate it.
But this is difficult to impossible to achieve across our diverse peninsula.

Further, a recent analysis along a 70 km transect from Glenburne to Sugarloaf Reservoir found a remarkably high level of infection from a variety of Phytophthora species (Dunstan et al 2016).

Dunstan et al concluded that “Phytophthora species are widespread, abundant and diverse in natural ecosystems”, and that “We have probably been underestimating Phytophthora diversity in Australia”.

Greg Holland has drafted a briefing note from the extensive literature on this topic, available here. Also provided is a table of the vulnerability of common Peninsula plants.

The results are based largely on the Western Australian experience, and Greg has included “?” to indicate either unknown, or a dicey
finding. They are an indicator only and no guarantees are provided.

Although eradication is not possible, there is a chemical (phosphite) that when sprayed or when injected into plants in an infected area has shown improved survivability of seedlings planted in affected areas.

Mornington Peninsula Landcare Network, is planning a trial planting in the known infection area to gather experience. The young plants will be sprayed before planting. The work will be done under strict quarantine conditions, with knowledgeable volunteers, and under expert advice. More info as it proceeds.

Landcare is collaborating with the Shire’s Regenerating Agriculture and Agroecology folk on coordinating a talk by an expert later in the year.