Could invasive weed Syzygium smithii be about to join NZ's myrtle rust host list?

A recent find of myrtle rust on the invasive weed Syzygium smithii and reported on iNaturalist highlights that we may still see the disease on 'new' hosts, even five years after the fungal spores that cause it blew upon our fair shores. Curiously, even though Syzygium species are typically highly susceptible, this host is not on the MPI list of species known to be infected in New Zealand. It has been reported as a host on iNaturalist before, but MPI has not confirmed the host species. This needs to happen before the host list can be updated. It is not easy to identify the different Syzygium species present in NZ. For more information about them and how to tell them apart, see here. Syzygium smithii is listed on the National Pest Plant Accord meaning it is banned from distribution, propagation, and sale but it can still be found in gardens following historical plantings. MPI is following up on this recent report so we may soon see the plant added to the list of NZ hosts.

Over time, we can expect myrtle rust to further establish in New Zealand. This will see the 'spore load' (amount of spores in the air) continue to increase. This may mean new hosts become infected, and/or known hosts suffer from more severe infections. Strains not known to be present in New Zealand may also arrive, threatening hosts not susceptible to the current strain. If you think you have a record of infection on a new host in NZ, please let MPI know. If you are interested in whether the species may have been recorded as susceptible in other parts of the world, a global host list is available here (scroll down to find the list.) The new record of the disease on Syzygium smithii shows iNaturalist continues to be a valuable source of information about the spread of myrtle rust in New Zealand, so do continue to upload sightings.

Posted on August 23, 2022 12:33 AM by reneejohansen