Progress towards eradication of bitou bush, Chrysanthemoides monilifera subsp. rotundata in Western Australia

Bitou bush (Chrysanthemoides monilifera (L.) Norlindh subsp. rotundata (DC.) T.Norl.) was first detected in Western Australia in 2012 at Kwinana, an industrial area south of Perth. Since 2012 we have undertaken annual surveys of the population, including mature plants, seedlings and the seed bank, as part of assessing the potential for bitou bush to spread or be eradicated. With the collaboration of landholders, plants found each year were eliminated by weeding, herbicide or excavation with earth moving equipment; leading to a marked decline in plant numbers. Very few mature plants are now found on annual surveys and most new discoveries are of plants of up to one year old and seedlings. The seed bank is also declining, but a residue of viable seeds is still present four years after the removal of adult plants. Any new plant discoveries have been within the delimited area of infestation, as defined by the original surveys made in 2012–2013. However the ongoing inaccessibility of some adjoining areas with dense vegetation prevent the achievement of absolute population delimitation. We discuss the plant characteristics that influence the potential for eradication, and the future prospects for management in Western Australia of this weed of national significance.