Bitou bush (Chrysanthemoides monilifera ssp. rotundata) is a sprawling, woody shrub from South Africa. It was deliberately planted in New South Wales from 1946 to 1968 to stabilise mobile sand dunes in sand mining areas.
Unfortunately, bitou bush has proved to be a highly invasive weed, which takes over coastal ecosystems and outcompetes native plants. It is now regarded as the worst weed in the Australian coastal environment, and has recently been listed as one of Australia’s Twenty Weeds of National Significance. It occurs along 660km of the NSW coast, with almost pure stands along 220km. There are concerns that bitou bush will become the dominant species within its current range, and also that it could spread into Victoria and Queensland.
A number of control methods have been used, including hand weeding and the use of herbicides and fire. These techniques have to be repeated over several years in order to be successful in the long term, as bitou bush has a large and persistent seed bank in the soil. In conservation areas these methods are not always appropriate, and having to repeat treatments is time consuming and expensive.
Scientists think that an integrated management approach, including the use of biological control, is the best and most cost effective way to tackle the bitou bush problem. A research program to find suitable biological control agents has been underway since 1987. Several natural enemies of bitou bush have already been released, including the bitou tip moth and the bitou seed fly, and these insects are impacting on seed production and reducing plant vigour. It’s hoped that the release of a new biological control agent, the bitou leaf roller moth, will help to reduce bitou bush to a level where it is no longer a problem, or can be effectively controlled by other techniques.
Bitou leaf roller moth (Tortrix sp.)
The bitou leaf roller moth was identified in South Africa as being the most damaging insect to bitou bush. The larvae feed on the shoot tips, then move to older leaves as they mature. At high densities, they are capable of decimating plants. After extensive testing both in South Africa and Australia, the bitou leaf roller moth has been shown to be host-specific, that is it only survives on bitou bush and its close relative, boneseed, which is found in Victoria, Tasmania and South Australia. Bitou leaf roller moth was first released on boneseed in Victoria in April 2002. The first release in NSW was made at the Broadwater National Park, with others to follow along the NSW coastline.