Injecting phosphite
- Photo © Parks and Wildlife

Phosphite is a systemic, biodegradable fungicide that protects plants against Phytophthora dieback.

  • It is environmentally safe, inexpensive and has a very low toxicity to animals.
  • Phosphite does NOT eradicate Phytophthora dieback, but can help control the spread and impact of the disease.
  • Depending on how it is applied, phosphite can provide protection for vulnerable plant species against the killer disease for up to five years.

How it works

We don't fully understand how phosphite works, but it appears that the progress of Phytophthora cinnamomi infection is halted when it comes into contact with phosphite in plant tissue.

  • High phosphite concentrations may interfere with Phytophthora's internal phosphorus utilisation cycle essential for its survival.
  • The plant's self-defence mechanism may also be triggered to wall-off and isolate the invaded root cells. Treated in time, plants in poor health have been shown to fully recover and remain healthy for a number of years.
  • Protection from aerially applied phosphite normally lasts for about two years, however, stem injection may provide protection for up to five years.
  • Find out more about how to apply phosphite treatment.
Aerial phosphite spraying- Photo © Parks and Wildlife

History of Use

  • Previously called phosphonate, phosphite has been used to protect avocado, pineapple and cocoa crops against Phytophthora disease since the 1970s.
  • In the late 1980s, research staff at the department's Dwellingup office began to investigate whether the fungicide provided any additional protection to Western Australian native species. These treatments, where phosphite solution was injected into jarrah (Eucalyptus marginata) and several banksia species, showed considerable promise, slowing and stopping the growth of the pathogen within the plants under attack.
  • This early success sparked a research effort over the next decade and included field trials ranging from the northern sandplain near Eneabba to the Fitzgerald River National Park east of Albany.
  • Aerial application of phosphite to native plant communities was tested for the first time in 1993 near Albany and proved a success.
    • Aircraft allow for relatively cheap and rapid treatment of entire plant communities containing rare plant species, suitable for areas where ruggedness of the terrain would make ground application prohibitively expensive.
    • The main focus of spraying has been on protecting critically endangered and endangered plants such as Dryandra montana, Leucopogon gnaphilioides and Andersonia axilliflora in the Stirling Ranges and Lambertia echinata ssp. echinata in ironstone shrubland near Busselton.

The future

Research into phosphite and its application is continuing. Among the areas requiring research is the refinement of application rates, times and frequencies for different vegetation types.

Phosphite cannot eradicate Phytophthora cinnamomi from an area once it has established, but it does provide us with some ability to protect endangered plants that might otherwise become extinct in the wild within a few years.

The major strategy for limiting the environmental damage caused by Phytophthora dieback still remains:

  • quarantine
  • high standards of hygiene
  • prevention of transporting infested soil into uninfected areas.