We need a range of different control options for myrtle rust in New Zealand because the disease affects many plant species, both native and exotic, in many different environments, including natural, urban and commercial.
This research undertook a comprehensive review of literature on the best control options, e.g. cultural, chemical, and biological controls, that have been used to manage myrtle rust and other rust diseases.
Researchers identified some control practices and options that can be implemented immediately for short-term control of myrtle rust in New Zealand.
They also identified further control options that will require more research to determine how specific, effective and feasible they are. Engagement with Māori to incorporate kaupapa and mātauranga to co-develop control solutions is critical. There is no single solution to controlling myrtle rust. Ideally, the most effective way is to use a combination of control methods, known as integrated disease management.
Download: List of overseas researchers
Controlling myrtle rust with fungicides provides a way to prevent infection of valued (native or exotic) trees in the short term, while long-term management strategies are developed.
An extensive review of the treatments used globally to control rust diseases indicated that some fungicides were more effective than others (strobilurins and triazoles).
Researchers trialled products available in New Zealand that contained these types of fungicides, to see if they could be used as preventative treatments against myrtle rust on iconic New Zealand species. The focus of this trial was pōhutukawa.
They determined that combining the fungicide with other substances that maximise spray coverage significantly improved coverage of the fungicide sprays on upper and lower leaf surfaces, particularly Actiwett (an alcohol ethoxylate).
They then tested the preventative effects of three different fungicides (Timorex Gold, Vandia and Radial) in controlled studies.
Of the three fungicides tested for preventative control in these preliminary studies, Radial was the most effective, while the natural product extract or “biological”, Timorex Gold, was not effective.
Download the report: Pilot trials for control of myrtle rust using fungicide
Development of in-depth knowledge on the fungicides likely to control myrtle rust in New Zealand is a high priority since the rust is going to require ongoing management.
This review highlights numerous information gaps and research needs with respect to chemical control of myrtle rust in New Zealand. Researchers say that if addressed, these would improve options for chemical control of the disease. Research needs identified include:
The report notes there is a question around who will pay for the cost involved in spraying native tree species.
Download the report: Chemical control - review of control methods and fungicides