by Annie Hill for Russell Lights June 2024 edition

Native myrtles include pohutukawa, northern and southern rata, rata vines, ramarama, manuka and kanuka. Introduced myrtles include eucalypts, feijoas, lily pilly/ monkey apples and Australian Leptospermum. It is a South American fungus, spreading globally over the last 40 years.

In May 2017, a Kerikeri plant nursery reported the appearance of myrtle rust. A few days later, about 60 of us responded to Biosecurity NZ’s call to search for myrtle rust around Kerikeri. No other was found at the time. Over the next year, myrtle rust was found in Taranaki, Auckland, Bay of Plenty, Waikato, Tairawhiti, Manawatu and Wellington. At this point, the Government decided that it was not possible to contain myrtle rust, and instead intended to minimise damage from myrtle rust by:

• Continuing research to investigate and test treatments for myrtle rust, boost resistance, and develop techniques for storage of native myrtle germplasm.
• Collecting native myrtle seeds for seed-banking.
• Having targeted surveillance of high-risk sites.

Beyond Myrtle Rust, a research programme coordinated by Landcare Research, was set up. This focused on:

• The dynamics of the myrtle rust pathogen
• Impacts of myrtle rust on New Zealand ecosystems
• New ways to mitigate impacts
• Kaitiakitanga and Maori-led solutions.

Funding for this programme stops at 30 June 2024. The team will run a few seminars from August to December this year, and will search for other funding. 

We have learnt that myrtle rust has the largest fungal genome known so far. It is capable of sexual reproduction in New Zealand, meaning it can more easily adapt to changing conditions. Honeybees harvest myrtle rust spores, which can remain viable on the bees and in the hive for up to nine days. An Auckland study found that bees harvested myrtle rust spores in preference to nearby nectar, and an overseas study found this may be because the bees obtain protein nutrition from the spores.

Some native myrtles are very susceptible to the impacts of myrtle rust, although a heavily-infected pohutukawa can be nearby others that are minimally-infected. Research has been undertaken into the variable response of manuka. Ramarama and rohūtu are currently the most affected.

The threat status of swamp maire is critical. We have several mature trees on the edge of the Pipiroa Wetland. Impacts on swamp maire have not been studied in depth, although heavily infested trees in Auckland have been removed. We don’t want this for our pipiroa or the magnificent pohutukawa along northern coasts. 

The lead Landcare myrtle rust researcher now recommends the removal of lily pilly/monkey apple/ acmena/eugenia hedges, as these can be a significant source of myrtle rust spores. In addition, monkey apple (Syzgium smithii) is highly invasive and can outcompete native trees. It is listed in the National Pest Plant Accord, ie. it is banned from propagation, distribution and sale.

Keep a lookout for myrtle rust on the Russell Peninsula. If you see it, take a photo and record its location. Then either upload your image to iNaturalist (www.inaturalist.org/) or email to Russell Landcare Trust at contact@russelllandcare.org.nz.