Myrtle rust in Whanganui here to stay: Public asked to report finds and manage disease themselves

Ministry for Primary Industries staff removed two bushes infected with myrtle rust from a central Whanganui garden on May 17. Photo / Stuart Munro

People finding the killer fungus disease myrtle rust are asked to keep reporting it - and those with affected plants in their gardens will have to manage it themselves.

The disease was confirmed in New Zealand in May last year. It was probably blown across the Tasman Sea from the east coast of Australia, where it is well established.

The South American disease can kill plants in the myrtle family, including bottlebrush and native pōhutukawa, rātā and ramarama.

In the Ministry for Primary Industries' (MPI) latest report, there are now 731 infected properties in New Zealand. They are across the North Island, and the top of the south.

There are at least two infected properties in Whanganui and others in Waverley, Raetihi and near Lake Taupo.

More than 5000 infected plants have been formally destroyed so far, including the first found in Whanganui last month. Future finds here are unlikely to be destroyed because there will be other local sources of infection.

People finding infected plants are asked not to touch them but to contact MPI by ringing 0800 80 99 66. They will receive advice on how to deal with the plants - most likely by sending them to landfill.

At the moment, the advice is not to try spraying infected plants with fungicide. People with the most susceptible plants - the native ramarama - may want to remove them in case they get the disease and spread it.

The New Zealand regions most affected by myrtle rust are Taranaki (276 properties), Bay of Plenty (152) and Auckland (107). The plants most affected are ramarama (631), pōhutukawa and rātā (398) and monkey apple (157).

Fears the disease will affect plants grown for commercial use have come to nothing so far. Only five feijoa plants have been infected. It seems they are not very susceptible and also at low risk of spreading the disease.

Only three mānuka plants have been infected. In Australia, plants in that tea tree family have been relatively unscathed. Only one New Zealand eucalyptus (gum) tree has been affected.

Myrtle rust likes humidity and high temperatures. Gardeners can keep it at bay by keeping their plants healthy, pruning in dry weather, cleaning tools between plants and watering soil rather than leaves.

Bees carry the tiny fungal spores from plant to plant. It was feared spores stored in hives would remain viable, and hive movements could spread the disease, but this doesn't appear to be happening.

Gardeners may want to keep planting vulnerable species as eventually some may be resistant.

The Government is putting $4.5 million into myrtle rust research, and into saving seed in case the disease wipes out whole species.