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

Threat Abatement Plan - Invasion of native plant communities by Chrysanthemoides monilifera
7 Control of bitou bush and boneseed
7.1 Control techniques
A range of techniques is available for the control of bitou bush and boneseed and often a
combination of methods is used: aerial and ground application of herbicides; biological control;
physical removal; slashing; and burning. In addition, revegetation can be used to suppress
recruitment of seedlings once the initial control has occurred. These techniques have changed
little over the past decade (see earlier review by Stanley et al. 1989). In part this is because sitespecific
conditions dictate which methods can be used (Stanley et al. 1989; Adair and Ainsworth
2000; Vranjic 2000: further discussion presented below). The introduction of new biological
control agents is the main exception. Best practice guidelines recommend an integrated approach
to control spanning several years, with the final combination of control treatments being sitespecific
(see Adair and Ainsworth 2000; Vranjic 2000).
Physical techniques include the use of machinery, hand removal (e.g. the removal of individual
plants by hand) and fire. These techniques are typically employed in densely infested areas
containing few native species. Any potential disturbance to aboriginal sites as a result of these
techniques needs to be addressed in site-specific plans (see below and Appendix 9). Machinery is
used to slash or knock down dense infestations, often as an initial operation to allow other
techniques to be used. It is impractical for use over large areas. As many plants re-sprout after
such treatments, follow-up control is nearly always required. The cost of using machinery varies
depending on access, topography, vegetation and the equipment being used. Average costs are
$900–1,200/ha. Hand removal is used to remove small to medium sized plants, particularly in
lightly infested areas or for isolated plants. Hand removal can be very effective following
previous control programs. The cost of hand removal varies depending on access, topography,
vegetation, and the infestation level. Average costs exceed $600/ha. This method is best suited to
volunteers and the costs can be reduced substantially if volunteers are used. Fire can kill mature
plants and reduce the seed bank through heat/smoke stimulated germination. The effects will
depend on the intensity and duration of the fire (see Downey 1999). The need to consider impacts
to non-target species, protection of life and property and the need to obtain a permit add
considerably to the time and cost involved in using this technique. In addition, follow-up control
is essential because of increased seedling recruitment. Fire may also cause additional problems
such as erosion, habitat loss for fauna and the provision of a suitable environment for other weed
species to establish.
The use of herbicides is the most effective method of controlling bitou bush. Glyphosate is the
most commonly used herbicide, although when impacts on grasses need to be avoided
metsulfuron methyl is preferred. Glyphosate and metsulfuron methyl are typically applied in
winter when bitou bush is flowering and the growth or activity of native plants is reduced.
Herbicide application during winter reduces off-target effects in most native plant communities
(see aerial spraying section below for more detailed information). Herbicides can be applied as a
foliar spray or by painting the herbicide onto cut stumps. Average costs are $300-500/ha for spotspraying
using a vehicle mounted spray-rig, and $800+/ha for painting cut stumps, depending on
site conditions (as documented above for hand removal).
The NSW aerial spraying program for bitou bush was developed following trials undertaken by
NSW Agriculture (now DPI) in the late 1980s and early 1990s. Initial trials focused on ground
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