Panic in the myrtles

It seems highly unlikely that we will see the end of our coastal pohutukawa to myrtle rust

Myrtle rust – words to strike terror to the heart? We are erring more on the side of a watchful eye at this stage. There is no doubt it is a worry but we have yet to see that it will be a catastrophe that will change our landscape forever, as predicted by some.

The catastrophic predictions are not been helped by the media referring to it as “deadly myrtle rust” and from there, hypothesizing that we could see the manuka honey industry under threat, the loss of our defining landscape pohutukawa trees and, horrors, the ubiquitous home fruit tree, our beloved feijoa. The deadly bit has yet to be proven. But the tone is one of unrelenting high drama. Indeed, the old warhorse, New Zealand First leader Winston Peters wants heads to roll. He has called for the resignation of the Minister of Primary Industries for failing to stop the arrival and spread of myrtle rust.

A future without feijoas seems far-fetched 

The hardy Chilean guava, Psidium littorale, is another myrtle 

A single isolated outbreak in Keri Keri (which is heading up to the most northerly part of New Zealand, for overseas readers) could possibly have been contained. As soon as it was found in nurseries and a garden centre in Taranaki, it raised every red flag for the Ministry for Primary Industries (MPI) and indeed for us. That brings the rust to within 5km of our place. I am sure the first thing MPI did was to find out whether there was any link between the Keri Keri and Taranaki outbreaks. Had any plant material been shared or anybody visited? It appears not.

The discovery of rust at another three locations in Taranaki, including private gardens, changes the picture entirely. There is a lot to find out yet, but odds are that it is widespread and established here already so the possibility of eradication has passed.

Myrtus luma, often grown for its attractive bark, is another member of the large myrtacae family

The fact that the locations include four nurseries and a garden centre has given rise to some downright stupid comments that I have read. It is not the nursery industry spreading the disease. The rust affects juvenile plants with fresh foliage and that is what nursery plants are. It is also a great deal easier for a vigilant nurseryperson to spot the tell-tale signs on plants in tidy rows.

There are equally stupid comments about our border control and not just from the aforementioned political opportunist. Myrtle rust is carried by light-as-air fungal spores. As soon as it got to the eastern seaboard of Australia, New Caledonia and Raoul Island, it was only a matter of time before it reached here. It could presumably be transferred on a traveller’s clothes as well as being blown across. It started in Central and South America but it is also in the Caribbean, Florida and Hawaii so it is not some deadly new phenomenon – just new to this country.

It is early days, but we think it is likely that it is something we will have to learn to live with.

The ever-handy Wikipedia tells me there are nearly 6000 different species spread across over 130 different genera in the myrtacae botanical family. It is really unfortunate that it includes our beloved pōhutukawa and rata and the economically important crop of mānuka along with feijoas and guavas. But all is not lost. The rust does not affect all myrtle family members equally. Nobody has had time to research which of our myrtle members could be badly affected.

There are many variables at stake – whether there are different strains of the rust known as Austropuccinia psidii, which of our core plants it will affect badly enough to impact their growth, flowering and seed set, how it will behave in the range of our climatic conditions here and more.

Backhousia citriodora – the fragrant lemon myrtle

What is known from the Australian experience (and they have a seven year jump-start on us with this unwanted organism) is that it does not appear to have a major impact on mature trees. We are not likely to see the wholesale death of established trees before our very eyes. The impact is on young plants (but only of some myrtle species, as already stated, not all of them) so the long term effect may be the failure of plantings in the wild to regenerate.  If this is the case, then there is hope that over time more resistant specimens can be selected for propagation because there will be variation in how individual plants respond, even within the same species.

The Ministry of Primary Industries is posting information almost daily on myrtle rust and the Department of Conservation is also keeping their website current on this issue. If you want to know more, there is information from Australia. I just scanned the NSW biosecurity site which also points out that “myrtle rust spores require darkness, moisture and temperatures of 15–25°C to germinate. The first symptoms become visible within 3−5 days of initial infection. The new pustules can mature to release spores in 10–12 days. Spores can remain viable for up to three months.” I am no scientist but if that applies in NZ, I would have thought that was a fairly short life expectancy for the spore, especially when combined with a relatively high germination temperature. I note that no country has ever managed to eradicate it.

Of course we could have done without myrtle rust in New Zealand. But maybe it is time to take the finger off the panic button and  stop mourning the impending mass death of huge pōhutukawa trees and the end of feijoas in this country. It is way too early to catastrophise and point fingers of blame.

*Having just listened to yet another anxious news story about it all, I wonder whether MPI should take responsibility for the tone. In trying to impress upon us all how important it is to identify possible myrtle rust so they can track its spread, have they fed the paranoia and angst? Maybe their comms people could tone it down a little? 

We think it likely that history will prove that these Waitara riverside pohutukawa are at far greater risk from the chainsaws of the Taranaki Regional Council than myrtle rust (a reference to earlier stories). 



8 thoughts on “Panic in the myrtles

    1. Abbie Jury Post author

      ‘Research’ might be overstating it a bit, Evan. I just had some doubts about the information I was hearing, looked up some info and combined it with what Mark and I have learned over the years about plant diseases, the spread of these, sprays and containment strategies. And it all seemed a bit over the top, really.

  1. Mark Hubbard

    12 sites now.

    Hopefully it won’t be too drastic, although living in manuka/kanuka bush, and loving doing so, it will be interesting to see if the rust is going to affect those. Of course it has to cross Cook Strait first, but I suspect it can swim as well as fly.

    1. Abbie Jury Post author

      Mark, how nice to hear from you! Yes, more found today but not much new information that adds clarity. I am told that teatree in Australia shows little effect so it may be that our native one will escape impact. It will be interesting to see photos and a botanist’s report on the Raoul Island infestation because MPI are saying that is really bad. Yet those will be dominated by mature plants and the Australian reports on mature trees is that they are not suffering long term ill effects. And the Raoul Island pohutukawa are the Kermadec species, as far as I know, which is different to the mainland one.

      1. Mark Hubbard

        Oh, I’m always here, Abbie. I like to keep track of your garden.

        I’ve been busy getting a waist high vegetable garden up and running now we’re living permanently in Sounds. Not link spamming, but I’ve got a new blog (not political at all, just arts and Daisy dog), and there’s a picture of the build on this page:

        The far u-shaped bed is having a waist-high glass house on it. (And no, the sheet iron home-made dirt ramp didn’t work: took four of us eight hours to get the dirt down to beds from road ).

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