Bushland Weeds Manual - Environmental Weeds Action Network

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42 Chapter 4 Corms, Bulbs and Tubers Targeted application techniques Sometimes the only option for effective control is a non-specific herbicide such as glyphosate. The herbicide needs to be carefully targeted so that only the weed, often growing closely amongst native vegetation, is treated. An example of a successful targeted application technique in practice is the effective control of Watsonia invading native bushland on the Darling Scarp (Day 1993). Using a 500 mL spray bottle with a sponge wired over the nozzle, a 10 % solution of glyphosate is wiped onto individual leaves just before flowering, at corm exhaustion. Community volunteers have controlled large populations of Watsonia and contained the spread of the weed using this method. The effectiveness of this treatment was recorded at three bushland sites across the Swan Coastal Plain from 1999-2001 with some interesting results (case study 4.2). Wiping Watsonia leaves in spring in Shenton <strong>Bushland</strong>. Biological control For the smaller cormous and bulbous species wiping leaves of individual plants is not practical. In Shenton <strong>Bushland</strong> for example there were up to 1700 bulbs of Yellow Soldier in a single 2 m x 2 m plot. With limited resources available wiping individual plants was not an option (case study 4.1). Biological control is presently available for Bridal Creeper. In 1999 CSIRO released a leafhopper that weakens the plant by sucking sap, causing a silver patterning on leaves and reducing seed set. It is a very useful tool for preventing the spread of large infestations that are either inaccessible or beyond the resources of current control programs. A rust fungus has been released and is also available for the control of Bridal Creeper. Infected plants shed leaves early and are severely weakened. The rust is slow to spread through established populations of Bridal Creeper. Recording effectiveness of control methods and regeneration of native plant communities It is important to have in place objective methods for assessing effectiveness of control methods over time so treatments and management strategies can be adjusted accordingly. • Maps of a particular weed species in a patch of bush: These provide good base line information for a control program, and over time, if updated, will provide a record of the effectiveness of that program. • Fixed photo points: Although an interesting record, fixed photo points do not provide quantitative information on the overall success of the program or the degree of follow-up required. They also provide very limited information on the impact of a control program on the native plant community. As long as the limitations are recognised, photo points can be a useful tool for recording change over time. Photos were particularly useful for recording the highly visable changes that occurred following removal of Taro along the Gingin Brook, (case study 4.3), and for recording the change in Watsonia treatment sites, as long as they were accompanied by a detailed species list. They were not so useful for recording change following the removal of smaller cormous weeds such as Harlequin Flower in the diverse plant communities at Brixton Street. For more information Elzinga et al. (2001) provides very detailed information on setting up photo point monitoring and studies where repeat photography has been used to monitor long-term change. Importantly though, distribution maps and photos will not record in any detail changes in weed populations. Recording the density and frequency of particular weeds from year to year is often vital in assessing the effectiveness of a control program. Also, when undertaking any weed management program in bushland, the focus is not simply on eliminating weeds but on protection of intact native plant communities. It is important to have an understanding of what impacts the control work is having and what moves in once the target weed/s have been controlled. In the incredibly diverse flora of south west Western Australia this can be a complex task. At one site on the eastern side of the Swan Coastal Plain there are over 300 native plant species in only 19 hectares and up to 80 in a 10 m x 10 m plot. It is important to know and understand these systems if they are to be managed effectively for nature conservation. Some methods used to collect information on change over time in populations of weeds that die down to underground storage organs and co-occurring native species are described in case studies on Yellow Soldier (case study 4.1), Watsonia (case study 4.2), Taro (case study 4.3) and Harlequin Flower (case study 4.4). Note: With bulbous, cormous and tuberous weeds, until they begin active growth in the growing season following herbicide application, it is often not possible to know how many plants including the storage organ, have been killed. It may be nine months after treatment before you can assess effectiveness of a control program. Key points • South African geophytes are one of the most serious groups of bushland weeds in south west Western Australia. • Once established on disturbed edges they can invade relatively undisturbed bushland, generally via seed or cormels, form dense monocultures and displace native plant communities. • Fire appears to facilitate establishment of seedlings and expansion of populations.
• Fire also offers a valuable window of opportunity for control. • Understanding the life-cycles of these weeds is an integral part of effective chemical and physical control and preventing spread into intact bushland. Dealing with weedy geophytes invading bushland can be a complex task. The information in the following case studies illustrates that with a consistent and carefully targeted effort over time, effective control and containment of populations can be achieved. The case Box 4.4 Timing herbicide treatment Annually renewed corms and bulbs Chapter 4 Corms, Bulbs and Tubers For those species with annually renewed corms and bulbs, the most effective time for herbicide application is when the parent corm or bulb has shrivelled and the new daughter corm/bulb has only partly developed. This usually occurs just before or just at flowering. Apply the herbicide too early and the parent corm/bulb could have enough reserves to survive; too late and the daughter corm/bulb will not be affected. In addition herbicide application at this time prevents the development of bulbils in many species. This is particularly important with Oxalis pes-caprae, O. glabra and O. purpurea where new bulbils are formed on the nodes of underground stems each year (Du Plessis and Duncan 1989, Peirce 1990, 1998). If herbicide application takes place after bulbils have begun to develop they will probably survive and go on to produce new plants the following season. Perennial corms studies cover managing and controlling the spread of the Yellow Soldier, two species of Watsonia, Harlequin Flower and Taro where they are invading wetlands and woodlands around Perth. The final table provides detailed, species-specific information on control techniques where they are known. The information in the table also highlights the many species of weedy geophytes that have similar life-cycles and reproductive biologies. The next chapter looks at a much more diverse group of weeds, the broadleaf herbs that are not geophytes and the sedges and the succulents. Only two species dealt with here arise from perennial corms, Black Flag (Ferraria crispa) and Taro (Colocasia esculenta). Timing for control of Black Flag is quite problematic as the parent corm does not shrivel and die as the new corm develops, so effectively there is no corm exhaustion. In addition there is a series of previous years’ corms below the parent which appear to be joined by a fine thread of living tissue and it is not known if herbicides can be translocated between these corms (Box 4.1) Effective control of Taro was obtained by cutting and painting the bases in early to mid summer with glyphosate and spraying regrowth in late summer with glyphosate and metsulfuron methyl (Case Study 4.3). Some workers have noted that excessive sap movement when cutting bases early in the season prevents cut stumps from taking up herbicide. Perennial bulbs The lowest dry weight of a perennial bulb generally occurs just when all the leaves are up but before flowering (Dafni et al.1981). This is probably the time plants would be most vulnerable to herbicide application. An interesting exception is the Easter Lily (Amaryllis belladonna) which belongs to a group of bulbs that flower as temperatures drop with the first rains – before the leaves come up. Dry weight in the perennial bulbs with this kind of life-cycle is generally lowest as the new leaves emerge, a couple of months after flowering (Dafni et al. 1981) and this is probably the best time to apply herbicide. Perennial tubers developing daughter corm exhausted parent corm remains of previous years’ corms Corm exhaustion in Watsonia meriana – late winter. Herbicide application to Arum Lily is effective throughout its period of active growth (Moore and Hoskins 1997, Brown unpublished data). Early herbicide application prevents the majority of the population flowering and setting seed but misses tubers that begin active growth later in the season. Studies on Bridal Creeper (Asparagus asparagoides) have shown herbicide application to have an impact from flowering through to the green berry stage, although is most effective at flowering (Pritchard 2002). 43
Page 1 and 2: Bushland Weeds A practical guide to
Page 3: Acknowledgments This manual is the
Page 6 and 7: iv Introduction The Banksia, Tuart
Page 8 and 9: 2 Chapter 1 The Project Blue Gum La
Page 10 and 11: 4 Chapter 1 The Project Both Arum L
Page 12 and 13: 6 Chapter 2 Managing Weeds in Bushl
Page 14 and 15: 8 Chapter 2 Managing Weeds in Bushl
Page 16 and 17: 10 Chapter 3 Grass Weeds Many grass
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Page 24 and 25: 18 Chapter 3 Grass Weeds Rhizomatou
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Page 38 and 39: 32 Chapter 4 Corms, Bulbs and Tuber
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92 Chapter 7 Weed Mapping in Remnan
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94 Chapter 8 Herbicide Use in Bushl
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100 Final Note In the end, environm
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102 References 1 Aarssen, L.W., Hal
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104 References 101 Dixon, B. (2002)
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106 References 204 Mann, R. (1998)
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108 307 The Nature Conservancy (200
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