Myrtle rust

Puccinia psidii

Myrtle rust

Myrtle rust

Legal Status: Notifiable and Unwanted Organism
Status in New Zealand: Not in New Zealand
Organism: Micro-organism

Other common names: eucalyptus rust, guava rust, ohia rust

Photos courtesy of: M. Daughtrey, Cornell University (offsite link to nt.ars-grin.gov); NSW Department of Primary Industries (DTIRIS) and Forest and Kim Starr, Plants of Hawaii.

This fungus is NOT present in New Zealand. If you suspect the presence of myrtle rust on plants in New Zealand, call MPI’s Exotic Pests and Diseases hotline on 0800 80 99 66.
Do not attempt to touch or collect samples as this may increase the spread of this disease.

Guava rust

Description

Myrtle rust (Puccinia psidii) is a serious fungal disease that affects plants in the myrtle family (family Myrtaceae). The myrtle family consists of trees and shrubs originating in both tropical and temperate regions. Well known members of the Myrtle family include eucalypts, guava, bottlebrushes (Callisternon spp.) and New Zealand native species such as pohutukawa, rata and manuka.

Symptoms

Myrtle rust attacks young, soft, actively growing leaves, shoot tips and young stems. Initial symptoms are powdery, bright yellow or orange-yellow pustules on leaves, tips and stems. The developing lesions may cause a deformation of the leaves and shoots, and twig dieback if the infection is severe. Symptoms also sometimes affect inflorescences and fruit. Infection of highly susceptible plants may result in plant death.

Myrtle rust spores can be readily dispersed by wind or on clothing, equipment etc. Both modes of dispersal can transport spores very long distances.

Impact

Myrtle rust has been identified as a threat to New Zealand. The impact of myrtle rust has been particularly severe in Australia where it affects over 200 plant species. New Zealand has a number of species in the myrtle family considered to be at risk if myrtle rust arrives, among them iconic natives such as pohutukawa, rata and manuka, but also feijoa, plantation and amenity eucalypts and numerous ornamental plants.

Guava rust

This fungus has continued to expand the recorded range of susceptible species as it has spread from country to country. It seems likely that myrtle rust will continue to find new susceptible species, or even new susceptible genera, if it reaches New Zealand.

Distribution

This fungus is indigenous to Central and South America and the Caribbean. It also occurs in Florida. Myrtle rust was found in Hawaii in 2005, where it was initially found on ohia (Metrosideros polymorpha) a species closely related to pohutukawa and rata. It was later found on other hosts (all in the Myrtaceae). It reached Australia in 2010, where it was initially detected on a property on the central coast of New South Wales. Since then it has spread across much of New South Wales and Queensland. In 2011 myrtle rust was found in Victoria.

Climate modelling suggests myrtle rust is most likely to establish in low to mid altitude areas of the North Island. Establishment along the northern east coast of the South Island and in the Chatham Islands cannot be ruled out.

Management

New Zealand has strict measures on material that may carry myrtle rust (especially nursery stock and cut flowers and foliage). A pest risk analysis was completed in 2010 and importation requirements for all myrtaceous nursery stock were updated in 2011 to account for the establishment of myrtle rust in Australia. Cut flowers and foliage of the Myrtaceae family from New South Wales, Queensland and Victoria is currently prohibited from importation into New Zealand due to the risk of myrtle rust transmission.

Guava rust

MPI is working to identify approaches to managing this disease. However rust diseases are notoriously difficult to control and so prevention is our priority. If you suspect the presence of myrtle rust on plants in New Zealand, call MPI’s Exotic Pests and Diseases hotline on 0800 80 99 66. Do not attempt to collect samples as this may actually increase the spread of this disease

Resources

Page last updated: 11 March 2014