Understanding Peppermint Dieback through Sampling at Lake Clifton

Peppermint trees and Tuarts at some properties in some areas of Lake Clifton have been showing severe signs of dieback, including crown decline and tree death. A sampling program has helped identify the culprits responsible.

Through funding from PHCC’s Lake Clifton Stewardship Program, the Murdoch Centre for Phytophthora Science and Management (CPSM) undertook sampling from peppermint trees at Lake Clifton properties to identify and isolate fungi species potentially responsible for tree death and decline. The aim of the sampling was to identify the species involved with these symptoms to help guide what, if any, management action can be undertaken to prevent further spread and increase the health of the tree species.

Interestingly, no Phytophthora, the fungal disease typically responsible for dieback, was found in laboratory analysis of trunk and branch samples. Instead a total of 5 different fungus species were identified. Little is known about these fungi species, including whether they are native or introduced.

• Neofusicoccum austral: a widespread and opportunistic pathogenic fungus of natural woody vegetation in the south-west of Western Australia.
• Cytospora eucalypticola: a weakly pathogenic fungus frequently associated with twig and stem cackers of Eucalyptus species.
• Umbelopsis isabelline: an oil producing fungus that is globally widespread and impacts trees already under environmental stress.
• Phanerochaeta sp.: white rot fungi that can cause dieback on woody trees and shrubs.
• Alternaria infectoria: a weakly pathogenic fungus that causes leaf spots and branch lesions.

Typically these fungi become problems only when the host plants are already under environmental stress, which can include drought, heat stress, increased salinity, chemical use and exposure. Given this, it is difficult to develop clear management responses to both treat and prevent further spread/decline, however, some site works may assist in increasing the resilience of trees and prevent further outbreaks of dieback diseases. This includes the following activities:

• Ensuring that potting mix and other soils being added to your property is certified dieback-free
• Employing dieback hygiene practices to protect uninfected areas
• Chemical treatment of affected trees using fungicides,
• Pruning infected trees during dry weather and always prune at least 30 cm below any sign of the fungus, and not leaving the pruned branches with disease on site,
• Consider re-establishing understory vegetation in association with Peppermint and Tuart trees,
• If applicable, reduce herbicide and fertiliser usage,
• Consider revegetation with Tuart and Agonis, along with a mix of other native species if possible, in areas where there is greater soil moisture and shelter, and
• Monitoring for disease symptom changes.

This project is supported by the PHCC through funding from the City of Mandurah and Shire of Waroona.