Weeds – the real alien invaders
Box 1 | Cash for weeds
Although the majority of weeds in Australia started as garden plants, a number of important species were introduced for commercial or agricultural purposes. Radiata pine, a commercial timber species, is a weed in parts of Australia where plantations exist. It is a fast-growing, water-hungry species that depletes the soil of nutrients and excludes natives from their natural habitat. It spreads easily because of its winged seeds and because some native cockatoos feed on its cones, carrying them into bushland.
The European olive is another commercial species that has become a weed. Olives are an environmental weed and a health concern in southern and south-eastern Australia. They invade open forests and woodlands, crowding-out native species, and their extremely allergenic pollen triggers hay fever and asthma in those susceptible.
Introduced in 1800, olives have until recently been a marginally profitable crop in Australia due to high picking costs and low domestic demand. Many unprofitable groves were abandoned and these unmanaged groves are responsible for the olive spreading and naturalising in Australia.
For potential weed species currently under commercial cultivation, proper management with a view to weed containment is necessary to reduce the risk of escape into the environment. This includes monitoring nearby bush and road sides for seedlings, and managing birds and other wildlife that might spread seeds.
Selectively bred cultivars of crop plants with reduced fertility and superior fruit are also under development. These new varieties may eventually play an important role in reducing escapes of commercial weeds into the environment.
Boxes
Box 2. How to be a good weed
Box 3. Prickly pear – a biocontrol success story
Related sites
Weeds (Victorian Department of sustainability and Environment, Australia)
Weed risk minimisation: European olive in Tasmania (Weeds Cooperative Research Centre, Australia)
Page updated August 2006.