Myrtle rust can travel with nursery plants, and sneaky spores
A recent report of myrtle rust on Bartlett's rātā (Metrosideros bartlettii) plants shipped from a nursery reminds us that, sadly, the disease can travel and potentially be introduced to new places with nursery plants. It is possible that symptoms were not visible at the time the plants were packed. It's the time of year when myrtle rust is rife, especially with all the wet weather some of the country has been having keeping leaf surfaces moist while the temperature is warm, so do keep an eye on any new Myrtaceae foliage - whether the plant has recently arrived at your place, hangs out in a pot on the deck, or is established in the garden. Avoid encouraging new growth by keep the pruning shears in the shed for now.
I have heard from a gardener who was surprised that their pōhutukawa seedlings had myrtle rust, even though they were located in a greenhouse. Unfortunately the spores of the fungal pathogen are highly mobile and can easily sneak around. If you are raising Myrtaceae in a greenhouse, the key thing to remember is to keep the foliage dry - the fungal spores can not infect without water. Therefore, water very carefully and only at the base.
We now also have a record of pōhutukawa fruits being infected on a large mature tree at an Auckland park, adding to evidence that this species is being increasingly impacted by myrtle rust - also being shown by the records posted here. What's the number one thing you can do for our native taonga suffering from a rusty onslaught? Avoid planting exotic Myrtaceae, especially Syzygium species often sold as 'lilly pilly', and Lophomyrtus plants, in your garden. If they are already there - and especially if they are infected - plan to replace them with something not susceptible to myrtle rust.
Comments
Hi
I have a eucalypt and pohutukawa on our verge and seedling pohutukawas pop up all over the place and they have myrtle rust features as does the large pohutakawa and eucalypt. The eucalypt is in a horrible condition and I have complained about it for years. I did email auckland councils biosecurity team about the myrtle rust and have not heard back.
I have a few manuka and kanuka grown from seed that I was going to transplant. I am not sure what is the right thing to do or who to talk to.
Love some advice.
Tim
60 Milton Road, Mount Eden
Hi Tim, myrtle rust presents us many dilemmas and your comment has several of them wrapped up together! I'm not sure what Auckland Council policy on managing street trees with myrtle rust is at the moment, I have passed your note on to them. In terms of the manuka and kanuka, these species, while being susceptible in greenhouse trials in some conditions, are not showing much susceptibility in the field. I would go ahead and plant them. If you do detect myrtle rust on them, please post a report on iNaturalist - scientists and land managers would like to know about it. It may be better to plant them away from inoculum sources (so distant from the pohutukawa and eucalypt) - whilst more studies are needed to confirm the importance of inoculum load on different species, spore load may make a difference here.
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