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

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48 Threat Abatement Plan - Invasion of native plant communities by Chrysanthemoides monilifera populations and ecological communities occur. The effects of herbicide are not known for many of the priority species (including those in priority ecological communities) and they should therefore be considered potentially at risk until data are available. Low rates of glyphosate used for aerial application (0.76 kg active ingredient/ha) have minimal impact on most native species, with less than 10% exhibiting mortality or severe damage (Toth 2002). No threatened species were examined in Toth’s 2002 study. The study also only looked at impacts on adult plants, not seedlings. Studies that have investigated the effects of glyphosate on seedlings show that seedlings experience greater impacts than adults. For example, Acacia sophorae seedlings were affected by herbicide while the adults were not (Toth et al. 1996), but Pimelea spicata seedlings and adults were both affected by the herbicides at rates used to control bitou bush (Matarczyk 1999; Matarczyk et al. 2002). In the case of P. spicata this knowledge has influenced control programs (Pomery pers. comm.). Studies have recently begun on the impact of metsulfuron methyl, which is also used in aerial spraying (Toth pers. comm.; Appendix 10B). The effects of herbicides on herbs or annuals have not been examined, however several native terrestrial orchids appear to be susceptible to glyphosate (Jones and Weston pers. comm.). Some formulations of glyphosate contain a polyoxethylene amine (POEA) surfactant that is toxic to some frogs (see Bidwell and Gorrie 1995; Mann and Bidwell 1999). Only formulations of glyphosate containing non-POEA surfactants are registered for use in aquatic situations (NRA 1996). Consideration should also be given to using these formulations in any terrestrial situation that is a potential habitat for frogs, particularly those frog species listed under the threatened species legislation (TSC or EPBC Acts), and at sites identified in relevant recovery plans, e.g. for the green and gold bell frog (NPWS 2003b). Any other herbicide, surfactant or adjuvant that may have adverse effects on aquatic organisms should be avoided in any terrestrial situation buffering an aquatic ecosystem. A list of the aquatic organisms most likely to be impacted is presented in Appendix 10A, Table 10.2, and should be considered in all control programs. A recent examination of leaf litter invertebrates showed no significant effect of herbicides on these invertebrates (see Lindsay and French 2004b). When using other control techniques with biological control agents it may be important to leave untreated patches of the target weed to maintain populations of the biocontrol agents. A recent study of weed impacts on threatened species revealed that bush regeneration and incorrect identification of natives as weeds posed a significant threat to native species (Couts- Smith and Downey 2006). If bush regeneration techniques/activities are to be undertaken within the habitat of threatened entities (species, populations or endangered ecological communities) they must follow an interim draft checklist developed by DEC for such instances [the final checklist was not available at the time of writing]. 7.3 Follow-up treatments Lack of appropriate follow-up treatments will result in re-invasion by bitou bush (Stanley et al. 1989; Vranjic 2000). The extent and duration of any follow-up treatment will depend on many factors including: < the original seed bank size < the length of seed dormancy period (>5 years) < the distance to other bitou bush infestations (i.e. re-invasion source)
Threat Abatement Plan - Invasion of native plant communities by Chrysanthemoides monilifera < the control technique(s) employed (e.g. fire can deplete soils seed banks) < the extent and condition of the invaded native plant communities that are present. Follow-up techniques must be employed prior to seed production from any new cohort or regrowth of surviving plants. Seedlings are capable of producing seed within 24 months, with some observations on the north coast of New South Wales suggesting that newly germinated plants can set seed within 12 months (Thomas pers. comm.). The timing of follow-up control treatments must be sufficiently flexible to allow maximum recruitment, as well as prevent seed production. Follow-up controls should also ensure that enough time has elapsed for most bitou bush seedlings to reach a size/age that makes them easy to see amongst the re-sprouting native vegetation. Seedling mortality appears to be high, therefore delaying follow-up control techniques will also be more cost-effective, provided the follow-up treatment occurs prior to first flowering. Follow-up control techniques will vary depending on the level of recruitment observed for bitou bush and the other weed species present. The two most common methods are hand removal or spot-spraying of seedlings. However, biological control agents can be employed to help limit establishment, particularly in the longer term where they can reduce spread and lower plant vigour. 7.4 A staged approach to bitou bush control At many sites the density and area infested by bitou bush is such that it cannot be controlled in a single control event/action. Thus, the control of bitou bush at these sites needs to occur in stages. The first stage is the removal of bitou bush and other weed species from the immediate vicinity of the species, population or ecological community at risk. This will reduce the direct threat in the short term. The second stage is the expansion of stage one to cover a larger area of the bitou bush infestation at the site. In this stage, the removal of bitou bush should be prioritised to areas containing suitable habitat for the priority species, populations and ecological communities to expand into in the future and decrease the threat by providing a bigger buffer zone between bitou bush and the threatened entity. Stage two involves the follow-up control of bitou bush seedlings that germinate within all previously controlled areas (including stage one areas). The third and subsequent stages involve the further expansion of earlier stages with the aim of removing all bitou bush from the site and surrounding areas to prevent re-invasion. This stage also includes the continual follow-up control of bitou bush seedlings in all previously controlled stages/areas of the site (i.e. stages one and two areas). This staged approach can be beneficial for a number of reasons: < control is focused on an area for which there are sufficient resources available. < land managers are forced to think about the follow-up control constraints. < control can be focused initially on areas where priority species, populations or ecological communities occur, or on other priority areas. < a staged approach aids in the protection of threatened ecological communities (e.g. littoral rainforests as discussed below). < a plan can be drawn up to manage large infestations. 49
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