Twelfth Australian Weeds Conference

CONTROL OF SERRATED TUSSOCK – PROBLEMS IN DEVELOPING IWM SYSTEMS David Michalk1, David Kemp2, Malcolm Campbell1 and David McLaren3 CRC for Weed Management Systems 1NSW Agriculture Orange Agricultural Institute, Forest Road, Orange, NSW 2800 2University of Sydney, Leeds Parade, Orange, NSW, 2800 3Keith Turnbull Research Institute, PO Box 48, Frankston, VIC, 3199

Abstract Serrated tussock ( trichotoma) is producers, especially in non-arable land where one of the worst weeds confronting livestock produc- Frenock® could be aerially applied without damaging ers in the higher rainfall perennial pasture zone of trees. southern Australia where it currently infests more than The loss of Frenock® has had a twofold effect. First, it one million hectares. Frenock® (fluproponate) provided has focused attention on finding alternative herbicide an effective means of killing serrated tussock until its tactics to at least limit the spread of serrated tussock. recent withdrawal from sale. This has created an op- Second, it has refocused our attention on the develop- portunity and challenge to develop integrated weed ment of IWM practices that combine both control (e.g. management (IWM) practices using both control meth- herbicide, fire, biological control agents) and manage- ods (e.g. herbicide, fire) and management (e.g. strate- ment (e.g. strategic grazing, pasture over-sowing, fer- gic grazing, pasture over-sowing, fertiliser). The CRC tiliser) strategies. Initially, the CRC for Weed Man- for Weed Management Systems is committed to initi- agement Systems had only a limited R&D program for ate new research and value-add to existing programs serrated tussock because Frenock® was providing ef- to improve our understanding of the ecology of grassy fective control. However, the changing circumstances woodlands to facilitate the development of low-cost with Frenock® provide an opportunity and challenge IWM systems especially for non-arable landscapes. for the CRC to assist with the development of IWM This paper aims to identify the gaps in our knowledge systems for serrated tussock control. about the ecology and management of serrated tussock and outlines the strategies being implemented by the Inadequate knowledge of the biology and ecology of Weeds CRC to generate the information needed to de- serrated tussock (particularly in non-arable areas) to- velop effective IWM systems for serrated tussock con- gether with economic constraints of livestock enter- trol. prises that preclude the use of current control prac- tices, has limited the development of IWM systems. In INTRODUCTION much of the area infested with serrated tussock it is Serrated tussock ( (Nees.) Arech.) either no longer economic to sow a replacement pas- is one of the worst weeds confronting livestock pro- ture or the potential carrying capacity of the land is ducers in the perennial pasture zone of southern Aus- below the economic breakeven point for control prac- tralia. It is a declared noxious weed in New South tices at current wool prices (Jones and Vere 1998). Wales, Victoria and South Australia where it currently Low-cost tactics that damage existing , reduce infests more than 1 million hectares of pastoral land seed-set, limit recruitment of new tussock plants, and with the potential to invade another 32 million hec- enhance both the productivity and competitiveness of tares (McLaren et al. 1998). Control costs and losses desirable companion perennial grasses need to be de- in livestock production from serrated tussock infesta- veloped for effective control of serrated tussock. tions are significant, currently exceeding $5 million The aim of this paper is to identify the gaps in our per year in Victoria and $40 million in New South knowledge about the ecology and management of ser- Wales (Jones and Vere 1998). rated tussock and to briefly outline the strategies be- Over the past 20 years, Frenock® (fluproponate) has ing developed by the Weeds CRC in conjunction with proved to be the most effective and economical method co-operating agencies to address these problems. to selectively remove serrated tussock from both sown and native pastures (Campbell 1997). However, the recent withdrawal of Frenock® from sales has signifi- cantly limited the control options available to

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BIOLOGY AND ECOLOGY tussock control in Victoria and NSW that the CRC is supporting honours students and a doctoral program As with other weeds where herbicides have dominated to further investigate ecotypic variation in serrated as the main control method over a protracted period, tussock and its implications for control practices. This there is a dearth of information available on the biol- also includes biological control agents, as preliminary ogy and ecology of serrated tussock. Yet it is this in- work by Hussaini et al. (1999) suggests that genetic formation that underpins the development of effective variability also determines the susceptibility of serrated IWM systems. Some of the more important ecological tussock to various pathogens. topics where information is still required include: Some general information is available on potential • Definition of ecotypic variation within serrated densities and seed production (Campbell 1998, Gar- tussock in NSW and Victoria. dener and Sindel 1998), but a better understanding of • Investigation of the surface soil conditions that the dynamics of serrated tussock populations is needed serrated tussock seed needs for germination to identify the most vulnerable stages in the weed’s (e.g. mulch or bare ground). life-cycle. Since the success of serrated tussock is at- tributable to its potentially large, long-lived seedbank, • Definition of the impact of fertiliser on the research into the fecundity and seed bank dynamics of competition between serrated tussock and de- serrated tussock is an obvious starting point for the sirable pasture species. development of successful IWM strategies (Gardener • Investigation of the population dynamics of and Sindel 1998). The main objective of a CRC-funded serrated tussock and the effect of control tac- PhD program is to provide this basic information on tics on plant demography and soil seed re- plant demography for both serrated tussock and desir- serves. able native companion grasses when subjected to a range of control tactics (including fire) so that appro- • Investigation of the relative response of ser- priate low-cost IWM strategies can be devised for non- rated tussock and other companion species to arable pastoral land, especially in NSW. The observa- fire. tion that some native grasses (e.g. macra, There is a need to define the possible impact of ecotopic Themeda triandra) resist serrated tussock invasion variability on the development of serrated tussock con- when maintained in a productive state is seen as a key trol practices. Some data suggest that the difference in element for the control of serrated tussock in non- susceptibility to glyphosate of serrated tussock arable by manipulating the system to favour populations in NSW and Victoria may be due to the desirable component. ecotypic variation. For example, preliminary informa- HERBICIDE DEVELOPMENTS tion indicates that low glyphosate rates (<3 kg a.i. ha- 1) controls serrated tussock in Victoria, particularly The loss of Frenock® has created the need to develop when applied to tussock regrowth after a strategic burn alternative herbicide tactics, and most of the current (Miller 1998), whereas up to 11 kg a.i. ha-1 of research is focused on the use of glyphosate. Since glyphosate was needed to kill tussock in NSW glyphosate is a non-selective herbicide, the damage to (Campbell et al. 1999). non-target and desirable plant species can be consid- erable. While this damage may have a positive effect The consequence of ecotypic variation is that in creating a suitable seedbed for establishing phalaris delineation of the boundary between possible or cocksfoot on fertile or arable land thereby prevent- glyphosate susceptible and resistant populations may ing re-infestation by serrated tussock, it has a negative be required so that appropriate regional herbicide effect on native by reducing biodiversity recommendations can be developed. Morphological and production of the native perennial grass compo- differences that distinguish serrated tussock from the nent. Herbicide research now needs to focus on ways two populations will make this delineation possible. to minimise these negative impacts through: A further challenge related to ecotypic variation is that as serrated tussock areas in Victoria are amenable to • better definition of the formulations, applica- control with glyphosate in the short-term, they could tion rates, additives and application methods be re-invaded by NSW ecotype, particularly along the for glyphosate; and boundary of the two types. This potentially poses such • identification of new herbicides that pose less major problems for recommendations for serrated environmental risks than glyphosate.

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In 1998, trials were established in NSW and Victoria crown rot, and “smut” spores replacing seeds could by CRC partners to clarify and further investigate the potentially kill serrated tussock plants and reduce seed- effectiveness of glyphosate on serrated tussock as there set (Hussaini et al. 1998). If the specificity and viru- are many variations in formulations, adjuvants and rec- lence of these fungi can be proven, this discovery could ommended rates that needed to be evaluated for effi- reduce significantly the time, expense and risk associ- cacy. Preliminary results suggest that glyphosate can ated with importing exotic pathogens. be effective at any time of the year provided the tus- However, since there is no overlap in these potential socks are actively growing, but that effective applica- agents with those found in South America, there is also tion rate will depend on location (Campbell et al. ample justification to continue the search for other 1999). Correct application rate is critical as over-use specific pathogens in the rich and incompletely known of glyphosate could easily produce unstable pastures mycoflora of the Argentine grasslands where Nassella dominated by annual weeds. Due to the non-selectiv- grasses are endemic. The Weeds CRC has assisted in ity of glyphosate, there is also a need to test new her- funding a comprehensive project to survey the range bicides as they become available to selectively control of pathogens found on N. trichotoma and to evaluate serrated tussock, especially for aerial application where potential biological control agents in Argentina. The glyphosate is unsuitable. anticipated end-point of this work is one or two patho- BIOLOGICAL CONTROL AGENTS gens with epidemiology and impact on population dy- namics defined for field populations in areas eco- Early assessments of the potential for biological con- climatically most similar to infested areas in Australia. trol suggested that fungal pathogens control serrated Additional work will investigate the ecology of ser- tussock populations in South American grasslands. rated tussock in its native range to complement simi- Efforts to identify and develop biological agents for lar work in Australia. serrated tussock control in Australia were initially sti- fled by the contention that serrated tussock was “too INTEGRATED WEED MANAGEMENT closely related to native spp.”. However, recent IWM practices for serrated tussock need to be devel- revisions of the stipoid taxa suggest that pathogens from oped in a landscape context. Earlier work done by Nassella may be more specific than previously thought Campbell (1974) developed an IWM system for fer- thereby posing no threat to Australia’s native grasses tile land that included herbicide use, over-sown pas- (Briese and Evans 1998). This, coupled with the iden- ture seed, fertiliser application and rest from grazing tification of suitable fungal pathogens in more recent for the first three spring-summer periods after sowing surveys (Briese and Evans 1998, Hussaini et al. 1998) to smother serrated tussock seedlings. However, this has provided greater optimism in finding a suitable package was less effective on poorer non-arable land biological control agent for serrated tussock. where sown perennial grasses were not vigorous The Weeds CRC has been instrumental in facilitating enough to prevent the rapid re-invasion of serrated the continued search for serrated tussock control agents tussock seedlings (Campbell 1974). It is now clear that both in Australia and overseas through: effective long-term control in non-arable areas will depend ultimately on implementing management prac- tices that strengthen and maintain native grasses in a • the investigation of the specificity and viru- competitive state rather than focus exclusive on eradi- lence of endemic fungi previously found on cation of serrated tussock. serrated tussock in Victoria (Hussaini et al. 1998); and, The Weeds CRC is taking up the challenge to facili- tate the development of IWM systems for serrated tus- • the identification of pathogens in Argentina sock, especially in non-arable landscapes, by support- with demonstrated potential for biological con- ing projects that fill the substantial gaps in our knowl- trol of serrated tussock and Chilean needle edge of the biology and ecology of native grassy wood- grass. lands and their response to management. For some land Hussaini et al. (1998) identified fungi resident on ser- classes this may require a change in land use ranging rated tussock in Victoria that had not previously been from complete retirement from agriculture to recorded in Australia. The combination of Zinzipegasa conservation use (e.g. nature reserves, windbreaks, argentinensis (Spegazzini) Nag Raj attacking the flow- and corridors for wildlife movement) that may attract ering culms and inflorescences, Fusarium sp. causing future revenue from carbon credits after being

22 Twelfth Australian Weeds Conference re-afforested with appropriate trees and shrubs. In in- Hopefully, the recent classification of serrated tussock vestigating the role of re-afforestation in serrated tus- as a “Weed of National Significance” by the Federal sock control, Campbell and Nicol (1996) concluded government may provide funding for the implementa- that Pinus radiata and native eucalypts warrant fur- tion of the above serrated tussock control program. ther research for use in non-arable situations. When From a producer’s viewpoint IWM will need to be applied to selected parts of a property, such alternative shown to be profitable, relatively simple, biologically land uses may help to achieve sustainability and bio- feasible and environmentally safe before they will adopt diversity goals on a landscape scale. such programs. For parts of the landscape where livestock enterprises REFERENCES are considered to be viable, more appropriate grazing Briese, D.T. and Evans, H.C. (1998) Biological control practices can be strategically implemented once they of serrated tussock (Nassella trichotoma): Is are developed for our native grasses. For example, there it worth pursuing? Plant Protection Quarterly 13, is no technical reason why strategic rests which have 94-7. proved to be an important tool to manipulate pasture composition in other pasture types cannot be used to Campbell, M.H. (1974). Efficiency of aerial techniques manage plant community dynamics to disadvantage for long-term control of serrated tussock (Nassella serrated tussock and strengthen desirable perennial trichotoma). Australian Journal of Experimental grasses. Identification and assessment of the value of Agriculture and Animal Husbandry 14, 405-11. strategic rest periods in conjunction with other tactics such as herbicide application, fertiliser inputs and fire Campbell, M.H. (1997). Pasture weeds. In “Pasture are central to programs being implemented by Weeds Production and Management”, eds. J.V. Lovett and CRC partners in central NSW and Victoria. J. M. Scott, pp. 254-68. Inkata Press, Melbourne. In addition to developing IWM systems for specific Campbell, M.H. (1998). Biological and ecological im- situations, research is also needed to define important pacts of serrated tussock (Nassella trichotoma interactions between different control options. For (Nees.) Arech) on pastures in Australia. Plant Pro- example, Hussaini et al. (1998) infer that the activity tection Quarterly 13, 80-5. of Z. argentinensis, a fungus that attacks the flowering Campbell, M.H. and Nicol, H.I. (1996). Establishing culms and inflorescences of serrated tussock, was only trees on non-arable land to control weeds. Pro- found in areas that had not been sprayed with herbi- ceedings 11th Australian Weeds Conference, pp. cides for some time (Hussaini et al. 1998). Due to the 493-6. effectiveness of Frenock® the positive and negative impacts of such interactions on the overall efficacy of Campbell, M.H., Miller, L.G. and Michalk, D.L. (1999) IWM systems have not been fully explored for ser- Alternatives to flupropanate for the control of ser- rated tussock. rated tussock (Nassella trichotoma (Nees) Hack.). Proceedings 12th Australian Weeds Conference, CONCLUSIONS Hobart, Tas (in press). The answers to these and many more questions are Gardener, M.R. and B.M. Sindel. (1998). The biology perquisites for developing a low-cost IWM system for of Nassella and Achnatherum species naturalized serrated tussock. Emphasis should be given to systems in Australia and the implications for management for use in non-arable, marginal grazing lands where on conservation lands. Plant Protection Quarterly site potential and finances precludes the successful 13, 76-9. introduction of existing IWM packages. These mar- ginal lands account for the largest proportion of the Hussaini, I.P., A.C. Lawrie and D.A. McLaren (1998) present tussock infestation (308,000 ha in NSW alone) Fungi in Victoria with biological control potential and cannot be ignored any longer. The Weeds CRC is for Nassella trichotoma (serrated tussock). Plant committed to initiate new research and value add to Protection Quarterly 13, 99-101. existing programs to improve our understanding of the Hussaini, I.P., A.C. Lawrie and D.A. McLaren (1999). ecology of grassy woodlands to facilitate the Pathogens on and variation in Nasella trichotoma development of low-cost IWM systems for non-arable (: ) in Australia. Proceedings 10th landscapes. International Symposium on Biological Control of Weeds, Bozeman, Montana (in press).

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Jones, R. and D.T. Vere. (1998). The economics of ser- American stipoid grasses (Poaceae: ) in rated tussock control in New South Wales. Plant Australia. Plant Protection Quarterly 13, 62-70. Protection Quarterly 13, 70-6. Miller, Lisa. (1998). Management of serrated tussock McLaren, D.A., Stajsic, V. and Gardener, M.R. (1998). in farming areas. Plant Protection Quarterly 13, The distribution and impact of South/North 91-3.

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