Decline of habitat / food trees

For several years now WA peppermint has been showing signs of decline throughout the south-west but in particular in the Busselton area.

The disease processes are not yet fully understood but there seems to be agreement that Phytophthora dieback caused by the pathogen Phytophthora cinnamomi is one of the main issues. This water-borne mould spreads through the soil and can be easily moved to uninfected areas by car tires or boots.
Infected plants are unable to take up water adequately through their root system.
The pathogen Phytophthora multivora has also been isolated from peppermint affected by dieback but its role in the decline seems unclear so far.

Some trees are however dying from the crown down. The canker pathogen Neofusicoccum australe which can cause severe dieback in stressed hosts has commonly been isolated in these instances.  (Dakin et al, 2010)

All stressed hosts are more susceptible to diseases and to insect damage. Thrips damage on peppermint leaves or borer holes in the trunk often appear after the tree has suffered from a pathogen for a while.

Nutrient enrichment (potassium phosphonate injections or nutrient plugs) or systemic insecticide injections have been trialled to improve the health of the trees.

The fungus Puccinia psidii, commonly known as myrtle rust, has the potential to cause significant damage to peppermint trees if it should spread to Western Australia from the eastern states.

www.environment.gov.au/biodiversity/invasive-species/diseases-fungi-and-parasites/myrtle-rust

Diseases have the potential to damage or kill wholes stands of trees; however our pruning practices are able to do the same. (also see: 'Habitat discussion')