Plants introduced to areas outside their home range arrive at their new destinations without natural enemies that would have existed in their native homes. This is one of the reasons why plants can rapidly establish and spread throughout their introduced range. For example, Port Jackson (Acacia saligna) is not considered a weed in its home range in Western Australia, but is an invader plant of the South African coast from the Orange River in the west to Kosi Bay in the east and is also spreading inland. It grows rapidly and produces large quantities of seed, which are dispersed by birds, animals, ants and other human activities.
The city has a long-term management plan in place for controlling Port Jackson. One of the most effective control options is using a natural enemy, a gall rust fungus, Uromycladium tepperianum. A Port Jackson plant infected with this fungus is easily recognizable by the large brown galls on the branches, leaves or flower buds. Heavily infected plants may bear several galls that drain away the plant’s nutrients required for growth. This depletion of nutrients eventually leads to the death of the plant.