A diagnostician from University of Hawaii stumbled upon an unfamiliar rust on a mamaki leaf in August 2013. The culprit was promptly identified as Pucciniastrum boehmeriae. Additional surveys in nurseries and botanical gardens throughout the Hawaiian Islands failed to detect more occurrences of the rust, although it was detected on Akolea plants on Oahu in 2016.
Rather than to view this fungus as an enemy to fear, I prefer to look at things holistically and think that the fungus is simply another symptom that appears as a sign that the plant is unhealthy. And there are most likely deficiencies in the soil. Basically, a healthy plant in healthy soil will be immune not only to this fungus, but also many more pests.
The world outside of Hawaii is still discovering mamaki. I’m sure that, as its popularity grows and mamaki crops increase in importance to Hawaii’s economy, many more studies will be done to help bring the depth of understanding around mamaki on par with crops like macadamia and coffee which have inspired thousands of university studies.