Exporting Weeds: Since European settlement Australia has become home to many noxious and obnoxious plants. These plants, free from the natural controls that were exerted in their homelands, have taken over large areas of the continent forcing out native flora and fauna. Two examples are: Blackberries (Rubus spp.) and Bitou Bush (Chrysanthemoides monilifera). The former came from Europe whilst the latter is a native of South Africa.
Australia has not just been the recipient of unwanted plants. There has been an environmental two-way traffic. A number of our native plants have become noxious and obnoxious weeds overseas. One of the most environmentally damaging is one of our favourites, Hakea sericea. This species is a tall prickly shrub with white or pink flowers and woody fruits. Small native birds nest in the protective foliage.
Seeds were taken to South Africa in 1830. Hakea sericea was used as a hedge, sand binder and as a source of firewood. Without natural controls the species soon became invasive. In some parts of South Africa it was considered a problem as early as 1863. Since then this Hakea has covered almost 4,800 square kilometres or 14% of the area of mountain Fynbos. What is Fynbos you may ask?  We asked the same question and searched the Internet for an answer. Fynbos is a South African vegetation community similar to Australia’s dry sclerophyll and heath communities. Proteas, Ericas and a host of other plants endemic to South Africa are all found in the Fynbos. The Hakea invasion has put many Fynbos species at risk of extinction.
Three Australian insects have been introduced to control the spread of Hakea sericea. A seed eating weevil, a leaf-eating weevil and a seed moth have been enlisted in the war against Hakea sericea. There has also been some success with a fungus that kills adult plants and seedlings.
It is a sobering thought that 20% of South Africa’s declared noxious weeds are natives of Australia and Australian Casuarinas and Melaleucas have become a problem in the Florida Everglades.