Overview of Thistle Management in Australia Measures
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Plant Protection Quarterly Vol.11 Supplement 2 1996 285 must be taken into account when consid- ering their response to herbicidal control Overview of thistle management in Australia measures. Biocontrol agents too can be very discriminating, even down to the B.M. Sindel, Department of Agronomy and Soil Science, Co-operative Research level of thistle ecotype. For example, the Centre for Weed Management Systems, University of New England, Armidale, ecology of saffron thistle (Carthamus New South Wales 2351, Australia. lanatus) is quite different to many of the other thistles. Saffron thistle on one hand can be characterized as preferring regu- Summary genetically modify thistles to be spine- larly disturbed areas with coarse dry top- Thistles have a high profile in the weed less? soil, but with good reserves of moisture in flora of Australia and are of particular There are two postcards on my office the deeper subsoil, whereas, most of the concern to graziers in the temperate pin board. Appropriately, the first is from other major thistles reviewed at this work- southern regions where they are often Edinburgh, Scotland, and is of the ‘Scottish shop are typically dominant on soils rich in the dominant weeds of improved pas- thistle’ (Cirsium vulgare). The second post- phosphate and nitrogen, and possibly tures. While thistles have morphological card, this time appropriately from the Uni- regularly cultivated and/or irrigated areas similarities and are closely linked taxo- versity of Oxford, England, says: ‘The (Doing 1972). As a result, saffron thistle is a nomically, they are nevertheless ecologi- more I study the more I know; the more I major weed in both pastures and crops cally diverse, both between species and know the more I forget; the more I forget, whereas many of the other thistles are a within species. Consequently, some man- the less I know; so why study?’ nuisance in pastures alone. So it is worth- agement practices, e.g. biological control, The purpose of this synthesis paper is to while stating again that we are not dealing may need to be aimed at specific ecotypic draw together in broad terms the presen- with a homogenous group of weeds when groups, while other management prac- tations from the Thistle Management we talk about the thistles. Consequently, tices, e.g. pasture competition, may be Workshop and to ask ‘what do we know many control measures will have to be able to be applied more unilaterally. This about thistles’, ‘what don’t we know aimed at individual species, and even paper overviews the presentations made about them’, and ‘what should we try and ecotypes within species. Others, such as at the Thistle Management Workshop find out that will be of practical use in this- pasture competition, may act more unilat- and synthesizes them into three broad tle management’. Do we already know erally. categories—ecology/biology, manage- the key to thistle management (if there is The factors that promote thistle inva- ment tactics, and farmer attitudes and one) or are we still searching? If a key ex- sion (often an increase in soil nutrient sta- constraints on control—and examines ists and we have not yet found it, does it lie tus combined with overgrazing and lack what is currently known about thistles, in obtaining more information, securing of reseeding) are also often responsible for what is not known about them and where more resources, developing new methods changes in the relative abundance of indi- should research be aimed to yield results or in engendering greater commitment vidual thistle species. Such changes, which which will be of most practical use to from those who attempt to control this- are continually occurring in the Australian thistle management in Australia. tles? weed flora (Kloot 1987), further compli- This workshop produced some excellent cate the already complex issue of thistle Introduction presentations of current thinking and re- management. For example, McGufficke There is no other group of plants in Aus- search in regard to thistle management (1996) experienced changes on his prop- tralia, and perhaps in the world, which bet- and if I am to synthesize these papers then erty near Jindabyne, New South Wales, ter epitomizes weeds than the thistles. A by definition I must put them together to from dominance of spear (or black) thistle cursory glance at some local sources of make up a complex whole. And in some (Cirsium vulgare) to saffron thistle and then weed information confirms this idea. The respects, weed management is necessarily Scotch (Onopordum sp.) thistle. Similarly, brochure which describes the Co- becoming more complex as land manag- over the course of 25 years on a property operative Research Centre (CRC) for ers negotiate the trend towards herbicide at Crookwell, New South Wales, an area Weed Management Systems—‘Weaken- resistance, reduced cultivation and an- that was once dominated by native ing Weeds to Strengthen Australia’—has a tagonism to pesticides. Ironically, the com- redgrass (possibly Bothriochloa macra) photograph of Carduus tenuiflorus plexity of the thistle group is one of the changed to subterranean clover, then to (winged slender thistle) on the front. The over-riding themes that has been evident variegated thistle (Silybum marianum) and logo of the Weed Society of New South through the presentations from this work- finally to Onopordum sp. (Carter 1970). Wales, displayed prominently on its news- shop and one which I highlighted in my Although management practices may letter, A Good Weed, is of a thistle. The review of the ecology and control of this- alter the soil and pasture conditions and Australian weed books by Hyde-Wyatt tles in Australia (Sindel 1991). lead to changes in thistle dominance, the and Morris (1980), Wilding et al. (1986), While thistles are often grouped under relative importance of different thistle spe- Auld and Medd (1987), Auld et al. (1987), one broad umbrella (for some very good cies in Australian pastures has not been Parsons and Cuthbertson (1992), and the reasons, not the least of which are their studied. new ‘Crop Weeds of Northern Australia’ morphological and taxonomic similari- by Wilson et al. (1995), all depict thistles of ties), they are nevertheless a group of Significance one type or another on their front covers. plants which are ecologically diverse— There can be little doubt that thistles are a What is it about thistles which gives both between species and within species, major concern for graziers in the temper- them this unique standing? Is it their often as has been highlighted for saffron thistle ate regions of southern Australia. In a re- sharp spines and prickles (for that is what (Peirce 1990). It might be concluded from cent mail survey of grazier attitudes to partly defines a thistle in the family Michael (1996) that part of the reason for weeds on the Northern Tablelands of New Asteraceae), their inherent beauty when this diversity in Australia is also due to the South Wales (Sindel 1996), graziers were in flower, or the combination and tension presence of taxonomic groups which are asked to rank up to five major weeds in between these two features? Someone as yet unidentified, particularly in relation order of importance on their farms. A once said: ‘Give me a thistle without to the Onopordum thistles. score of five was assigned to the top thorns and I will give you a pasture plant’. Peirce (1996) rightly emphasized that ranked weed in each case, a score of four Is technology now at the stage that we can the variability in the behaviour of thistles to the second worst weed and so on down 286 Plant Protection Quarterly Vol.11 Supplement 2 1996 Table 1. The most troublesome weeds among the graziers surveyed from the Ecology/biology Tablelands of northern New South Wales (from Sindel 1996). Baseline data There would be few of the defence force A B Weed Presumed species Number of respondents Score personnel who would not argue that it is Saffron thistle Carthamus lanatus L. 22 90 essential that you first ‘know your enemy’ Blackberry Rubus fruticosus L. s.lat. 12 38 before you make an attack on them. Oth- Nodding thistle Carduus nutans L. ssp. nutans 8 31 erwise, your attack is likely to be ineffec- Bathurst burr Xanthium spinosum L. 7 31 tive and you will not be able to assess what Spear thistle Cirsium vulgare (Savi) Ten. 7 27 damage you have caused once that attack Thistles (generally) 6 20 has been carried out. In this regard, Pettit Scotch thistle Onopordum spp. 4 19 et al. (1996) have appropriately done their Horehound Marrubium vulgare L. 7 18 reconnaissance work on Onopordum and Slender thistles Carduus pycnocephalus L. 5 12 have now laid baseline data against which Carduus tenuiflorus Curtis to assess the effectiveness of biological Variegated thistle Silybum marianum (L.) Gaertner 3 12 control. Rat’s tail fescue Vulpia spp. 3 12 Seed banks in the soil A Number of respondents from the Tablelands who listed a particular species among Sheppard (1996) highlighted the fact that their five worst weeds. nearly all thistle species are relatively B Combined score of weed importance from rankings given by all 29 respondents from short-lived and reproduce entirely by seed the Tablelands. and that this must guide the formulation of control strategies. As a result, the con- to one. Forty six weed species were listed introduction to this country, continues to tinued infestation of pastures and crops by in total by the 29 respondents. Table 1 lists spread (Parsons 1973, Medd and Smith thistles depends largely on the persistence those weeds which had a combined score 1978). of viable seeds on and below the soil sur- of 12 or greater.