NSW Bitou Bush Threat Abatement Plan - Department of ...

Threat Abatement Plan - Invasion of native plant communities by Chrysanthemoides monilifera
are several potential agents, three of which are currently being tested/examined (see Downey et al.
submitted).
Biological control programs are a long-term option for control, the time frame of which can be
influenced by the longevity of the target species. For example, the actions of a seed fly which
parasitises the seeds of a long-lived plant (e.g. 25 years) will not alter the longevity of an
individual plant, but rather will reduce the seed bank, leading to a reduction in recruitment and
plant density over subsequent generations.
Integrated weed management (IWM) strategies and best practice management guidelines (see
Adair and Ainsworth 2000; Vranjic 2000) outline holistic approaches using a combination of
control techniques (Sindel 2000). This is because the use of a single technique is rarely successful
in the long term (Groves 1989; Holtkamp et al. 1999) and may lead to negative outcomes (e.g.
herbicide resistant biotypes). In essence, an holistic approach aims to remove existing plants,
deplete the soil seed bank, reduce re-invasion (either by the same or other weed species), and
rehabilitate and re-vegetate the site with desirable indigenous species (i.e. locally occurring
natives). In addition, IWM establishes a framework to manage sites following the initial control
event. The nature of bitou bush invasions means that an IWM strategy for this weed needs to be
long-term if it is to reduce the initial infestation as well as deplete the soil seed bank. Lack of
appropriate follow-up controls or commitment to follow-up controls will quickly result in reinfestation
by bitou bush (Vranjic 2000).
7.2 Issues associated with bitou bush and boneseed control
Often there is more than one weed species present at a site and in many cases, the control of one
species may provide an opportunity for another to proliferate. Where there is more than one weed
species present, bush regeneration techniques should be adopted (see Buchanan 1989). The ideal
strategy is to replace bitou bush with native species in such a way that the process of natural
regeneration and succession is sustainable and bitou bush is not simply replaced by other weeds or
re-invades itself. Some of the species that flourish after bitou bush control are even more difficult
to control, e.g. glory lily (Gloriosa superba), ground asparagus (Asparagus aethiopicus), mirror
bush (Coprosma repens) and ehrharta (Ehrharta villosa), or at least as difficult to control, e.g.
lantana (Lantana camara). The cost of multiple weed control varies depending on the weed
species present, the density and age of the infestation/plants, and the control methods used.
Average costs are $600–20,000/ha.
Concerns over the use of herbicides have been raised with respect to their potential impacts on
non-target species. Best practice guidelines for aerial boom spraying have been developed to help
limit some of these concerns (see Broese van Groenou and Downey 2006). Even so, recent studies
and reviews have revealed that some native plant and animal species are susceptible to herbicide
application as used to control bitou bush (e.g. Pimelea spicata). Species that are susceptible to or
potentially susceptible to herbicides are presented in Appendices 10A and 10B as well as in the
best practice aerial spraying guidelines. These species, along with any others identified in the
future should be considered when undertaking herbicide control of bitou bush or boneseed. The
lists in Appendix 10B contain information on the susceptibility of 280 species to Round-up ® 360
and 85 species for metsulfuron methyl. However, different formulations of glyphosate or the
use of surfactants or other additives could alter the response of the species on these lists. In
addition, herbicides should be used with extreme caution in areas where priority plant species,
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