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Myrtle rust, August 2017

Peter Berg, New Zealand Tree Grower, August 2017.

Myrtle rust was first identified in New Zealand on 3 May this year in a Kerikeri plant nursery. The rust is a fungus Puccinia psidii, native to tropical South America but now widely spread. As its common name implies it is a pest on many species of the Myrtaceae or myrtle plant family.

Airborne urediniospores released by the fungus permit rapid, long-distance spread and once established in Australia − first identified there in about 2010 − it was expected that its arrival in New Zealand was simply a matter of time. In the early 1970s poplar rust arrived in very much the same way after a period of prolonged westerly weather, being located over a period of only a few days at several locations along the west coast of the North Island.

Myrtaceae species in New Zealand include native species such as manuka and kanuka, pohutukawa, rata and ramarama. Exotic species of significance here are the eucalypts, feijoa and a range of other ornamentals.

Probably blown to New Zealand

After being first identified at Kerikeri other identification has been made in rapid succession in Taranaki, King Country and Te Puke in the Bay of Plenty. Not surprisingly the greatest incidence is in the west-facing Taranaki region. Investigation has not found obvious links between several of the introductions and this lends weight to the possibility that most and possibly all are the result of a wind-borne infection.

The plant species that myrtle rust has been detected on include Lophomyrtus, Metrosideros, Syzygium, Leptospermum and Eucalyptus, but mainly the first two. Myrtle rust has not been confirmed on feijoa. Symptoms to look out for on infected plants are −

  • Bright yellow powdery eruptions appearing on the underside of the leaf in a young infection
  • Bright yellow powdery eruptions on both sides of the leaf in a mature infection
  • Brown or grey rust pustules − older spores − on older lesions.

In addition, some leaves may become buckled or twisted and die off. It is interesting that mostly younger plants are being infected. In Australia, eucalypts are affected mostly at the juvenile stage and with modest malformation resulting. However, in Brazil, larger plants and some clonal material is now being damaged.

MPI ask that if you have seen the symptoms of myrtle rust, do not touch it −

  • Call the MPI Exotic Pest and Disease Hotline immediately on 0800 80 99 66
  • If you have a camera, take clear photographs, including the whole plant, the whole affected leaf and a close-up of the spores and affected area of the plant
  • Do not touch it or try to collect samples as this may increase the spread of the disease.

Incident control is based in Wellington. MPI is acting as the lead agency for the response with support from other central and local government agencies, industry and tangata whenua. Local coordination is based at the DOC Bay of Islands office in Kerikeri.

In New Plymouth, local coordination has been set up at the Taranaki Emergency Management Centre. Generally, destruction and removal of infected plants and their neighbours has been undertaken and surrounding the plants heavily treated with a fungicide and all areas closed off and monitored for further outbreaks.

When this article was written in late June, the most recent identification at Te Puke was the first for a couple of weeks and while in the areas so this is unlikely to mean that the outbreak has been contained. It does indicate that with with good practice the consequences of this new pest may be able to be lessened.


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