Myrtle rust spores are microscopic and travel large distances by wind, or via insects, birds, people, or machinery.
The leaves of myrtle plants can become infected when they come in contact with myrtle rust spores. The main way that spores reach a vulnerable plant is through the wind. Insects, birds, people, and machinery can also carry spores. Once the spores reach a susceptible myrtle ‘host’ plant they can germinate on the leaf surface and the fungus will grow inside stealing nutrients and energy from its host.
The likelihood of infection is much higher when there is a combination of factors including new growth, high humidity, water on the plant surface for more than 6 hours and moderate temperatures around 15–25 °C.