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

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46 Threat Abatement Plan - Invasion of native plant communities by Chrysanthemoides monilifera spraying to determine which herbicides were most effective in controlling bitou bush. Following this further trials were undertaken to determine the impact of over-spray on native species and thereby ascertain appropriate application rates. The results showed that spraying in winter reduced the impact on natives while delivering effective control of bitou bush. In addition, the rate of herbicide required to kill bitou bush during winter was very low (using glyphosate). Trials were subsequently undertaken using aerial techniques at four sites along the NSW coast from Jervis Bay to Yamba. The results supported the ground spraying trials, suggesting that effective control of bitou bush could be achieved using aerial spraying in winter, while limiting off-target damage. Recently best practice guidelines were developed for the aerial boom spraying of bitou bush in New South Wales (see Broese van Groenou and Downey 2006). All aerial spraying programs to control bitou bush in New South Wales should follow these guidelines. Aerial application using low rates of glyphosate (0.76 kg active ingredient/ha) is a very effective technique that is used widely for the control of bitou bush. This technique is very cost-effective ($100–205/ha) and allows large areas to be treated rapidly. The NPWS (now the Parks and Wildlife Division of the DEC) recently gained approval from APVMA to aerial spot-spray bitou bush using a helicopter. Average costs are not yet available but should be similar to that of other forms of aerial spraying. The NSW Pesticides Act 1999 encompasses a range of regulations which users must comply with (see Section 2.2.3 and the Act for further information). Herbicides and physical techniques are often combined to give more effective control, e.g. cutting and painting the stumps of mature plants with herbicide, and strategic burning preceding or following the use of herbicides. In heavily infested areas the cost of this combined technique may exceed $15,000/ha (Jack pers. comm.). Many of these combined techniques form the basis for Integrated Weed Management (discussed further below). Biological control involves the use of other live organisms to control weeds (or other pests). A national research program on biological control of bitou bush has been operating since 1986 (see Downey et al. submitted). Host specificity testing in South Africa revealed 19 possible agents for the control of Chrysanthemoides monilifera (bitou bush and boneseed) in Australia (see Adair and Edwards 1996). Over the past 19 years extensive work has been undertaken to assess and release as many agents from this list as possible. The biological control program for bitou bush in New South Wales has all but exhausted this list; resulting in the release of six biological control agents, four of which have established in the wild: the bitou tip moth (Comostolopsis germana Prout), bitou tortoise beetle (Cassida sp.), bitou seed fly (Mesoclanis polana Munro) and bitou leaf roller moth (Tortrix sp.). One of the released agents, the bitou seed fly is now well established along the NSW coastline and populations of the fly have commonly reduced seed production by over 50%. The latest introduction, the bitou leaf roller moth, has been released at 45 sites along the NSW coast, however it has only established at six sites, all of which are on headlands. Research shows that the bitou leaf roller suffers from predation in dune environments (see Downey et al. submitted). Future releases will be targeted to headlands to aid establishment. At high densities, larvae of the moth are capable of decimating plants and it is the most destructive agent found to date. It is too early to draw any conclusions from these releases, but Australian and South African scientists are confident of the bitou leaf roller moth’s potential to have a major impact on bitou bush in Australia. Without further host-specificity testing in South Africa, it is unlikely that any additional agents will be released to control bitou bush in Australia. For boneseed, however, there
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, 47
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