Plant Protection Quarterly Vol.11 Supplement 2 1996 245 International Symposium on Biological Control of Weeds, pp. 495-501. Olivieri, I., Swan, M. and Gouyon, P.H. Ecology of Cirsium vulgare and Silybum marianum (1983). Reproductive system and colo- in relation to biological control nizing strategy of two species of Carduus (Compositae). Oecologia 60, 114-7. E. Bruzzese, Keith Turnbull Research Institute, Co-operative Research Centre Shea, K. (1996). Estimating the impact of for Weed Management Systems, PO Box 48, Frankston, Victoria 3199, Australia. control efforts: models of population dynamics. Plant Protection Quarterly 11, 263-5. Summary The ecology of spear thistle Sheppard A.W. (1996) Weeds in the Spear thistle (Cirsium vulgare) and vari- Spear thistle is an annual or biennial herb, Cardueae: Biological control and pat- egated thistle (Silybum marianum) are depending on its time of germination. Al- terns of herbivory. Proceedings of the two of the most widespread thistles though seed can germinate at any time of International Compositae Conference, which infest pastures in temperate south- the year, there are two main germination Kew, 1994, Volume 2 Biology and Utili- ern Australia. A biological control pro- times in late-summer to autumn and late zation, pp. 291-306. gram targeting these thistles was com- winter to spring (Bruzzese and Heap un- Sheppard, A.W. and Woodburn, T.L. menced in 1985. No specific ecological published). Because of this, infestations (1996). Population regulation in insects studies of these thistles and their preda- can consist of plants of different size and used to control thistles: can we predict tors in the area of origin aimed at the se- ages. Seedlings develop into rosettes, up effectiveness? In ‘Frontiers of Popula- lection of insects for release in Australia, to 60 cm diameter, which generally re- tion Ecology’, eds. R.B. Floyd, A.W. have been carried out. Insects have been quire vernalizing before flowering can oc- Sheppard and P. J. Debarro, p. 227. released in Australia, based on data from cur. Plants resulting from autumn germi- (CSIRO Publications, Melbourne). biocontrol programs against these this- nation become winter annuals and flower Sindel, B.M. (1991). A review of the ecol- tles elsewhere in the world. This paper the following summer (6–9 month life-cy- ogy and control of thistles in Australia. reviews the literature on ecological stud- cle). Plants that germinated in late winter- Weed Research 31, 189-201. ies of these thistles and the effects of their spring act as biennials, growing as rosettes Woodburn, T.L. and Cullen, J.M. (1993). predators. Additional studies from Victo- through summer, autumn and winter and Effectiveness of Rhinocyllus conicus as a ria are summarized. Progress towards the flowering the following summer (12–15 biological control agent for nodding classical biological control of these weeds month life-cycle). A small percentage of thistle, Carduus nutans, in Australia. Pro- in Australia is outlined and conclusions plants which germinate in summer be- ceedings of the 10th Australian and 14th are drawn on the chances of success using come summer annuals, flowering in au- Asian-Pacific Weed Conference, pp. the agents currently available. tumn. Flowers appear in December to 99-103. February and later in higher rainfall areas. Introduction Plants die after flowering and dead plants Spear and variegated thistles (Silybum can remain standing for one or two years. marianum and Cirsium vulgare respec- tively) are two of the most widespread Seed production thistles in temperate eastern Australia Three populations of spear thistle were (Briese 1988, Parsons and Cuthbertson studied at grazed sites in Victoria in 1986– 1992). In an extensive review of the ecol- 87. Seed production per plant (Table 1) at ogy and control of thistles in Australia no the three sites (2668, 4207 and 19 343) was comment was made on the implications of much higher than that recorded in coastal this information for their successful bio- sand dunes in Holland (246–2500 over a logical control (Sindel 1991). Biological five year period on plants undamaged by control programs, commenced in Aus- predation (Klinkhamer and de Jong tralia in 1986, are opportunistic in that they 1993)). It was however comparable to utilize insect species already introduced Australian values reported by Forcella and into other countries. There are consider- Wood (1986). able European ecological data on spear thistle and the effects of general predation Soil seed bank on population dynamics (van Leeuwen Soil seed banks in Victoria (Table 1) show a 1983, de Jong and Klinkhamer 1988a,b, yearly pattern of replenishment after seed Klinkhamer et al. 1988, Klinkhamer and de dispersal, followed by a marked decrease Jong 1993) as well as the insect fauna asso- throughout the following year. The most ciated with spear thistle (Redfern 1968, important decrease, which ranged be- Zwölfer 1965, 1972). Detailed European tween 83 and 99%, was caused by ecological data are lacking for variegated germinations following the autumn rains. thistle, but its insect fauna has been docu- From the results, seed input occurs from mented (Zwölfer 1965, Goeden 1976). This December to March indicating a very long paper compares European and Australian flowering and seed set period for spear information on plant population dynam- thistle. Seed banks were lower during the ics of spear and variegated thistle, outlines second year of monitoring. progress in the biological control of these Victorian results are comparable to two weeds in Australia and elsewhere and those obtained by Roberts and Chancellor discusses this information in relation to (1979) in England who found that more successful biological control. than 90% of all seeds germinated within one year after production. Klinkhamer and de Jong (1993) estimated that less than 246 Plant Protection Quarterly Vol.11 Supplement 2 1996 1% of seed produced is still viable the fol- longevity in the soil but Roberts and replenishment only one to two viable lowing winter and suggested that there is Chancellor (1979) found a few seeds dor- seeds 100 m-2 would remain after five no persistent seed bank. Victorian studies mant after five years. Extrapolations on years. did not include observations on seed our seed bank indicated that without seed Seed, seedling and plant survival to Table 1. Spear thistle seed production, soil seed bank and plant density over flowering time at three sites in Victoria. In Holland, losses in the seed stages were severe (97%), with losses in the seedling Site Lang Lang Derrinallum Wodonga stage accounting for 67% of seedlings Seed production January 1986 (Klinkhamer and de Jong 1993). When Flowering plants m-2 2.8 6.1 2.6 seed production was compared to the seed Heads per plant 53.8 9.3 115.9 banks in Victoria (Table 1), losses between Seeds per head 78.2 286.9 166.9 64 and 95% were found to occur between Seeds per plant 4207 2668 19343 January to March 1986. In the ACT, Seeds m-2 11779 16274 50291 Forcella and Wood (1986) found average Soil seed bank (viable seeds m-2) losses in the seed stage ranged between 85 March 1986 4260 3496 2355 and 90% while losses in the seedling stage May 1986 716 302 37 were extremely high ranging between 99 September 1986 180 175 35 and 99.8%. Losses in the rosette stage were April 1987 647 1389 – 49% in grazed and 51% in ungrazed pas- October 1987 21 748 42 tures. In Victoria the major increase in thistle Plant density (plants m-2) density in 1986 occurred in May at all sites March 1986 2.2 2 4.7 (Table 1). The decrease in thistle density May 1986 33.6 390.5 68 from May to November ranged between August 1986 24.8 27.5 11.2 94 and 99% indicating that survival from November 1986 2 11.2 0.2 seedling to flowering ranged between 1 January 1987 0.5 6.2 0.5 and 6%. Although individual plants were April 1987 12.1 6.7 – not tagged, observations at the three Vic- torian sites indicate that the proportions of Table 2. Insect/mite predators and fungal pathogens of spear and variegated plants is winter annual>biennial>summer thistles in Victoria. annual. Name Plant part Host The natural enemies of spear and Insects and mites variegated thistle in Victoria Hemiptera: Before a biological control program Nysius clevelandensis flowers Silybum marianum against thistles commenced, a survey of Capitophorus elaegni leaves Silybum marianum the natural enemies of thistles was under- Cirsium vulgare taken to establish if specific natural en- Brachycaudus helichrysi leaves Cirsium vulgare emies of thistles were present in Victoria. Myzus persicae leaves Silybum marianum Table 2 lists insects, mites and fungal Coleoptera: pathogens collected and identified on Arsipoda chrysis leaves Cirsium vulgare spear and variegated thistle. Inspections Stegobium paniceum dry seedhead Silybum marianum were carried out during the seedling (au- Lasioderma sp. dry seedhead Silybum marianum tumn), rosette (winter), cabbage (spring) Cortinicara hirtalis dry seedhead Silybum marianum and flowering/seeding (summer) stages Edusella lineata leaves Cirsium vulgare of the thistles’ life-cycle. Of the insect Corticaria japonica dry seedhead Silybum marianum predators collected on spear and vari- Teretrius sp. flowers Cirsium vulgare egated thistle, only the larvae of the moth Desiantha caudata leaves Silybum marianum Tebenna bradleyi was considered damag- Phlyctinus callosus leaves, stems Cirsium vulgare ing. It was found to skeletonize leaves of Melanophthalma sp. leaves Cirsium vulgare spear thistle at all sites during the flower- Sericoderus sp. leaves Cirsium vulgare ing period. Of the fungal pathogens collected, fur- Lepidoptera: ther studies were carried out on the spear Tebenna bradleyi leaves Cirsium vulgare thistle rust Puccinia cnici (Bruzzese et al. Epiphyas postvittana leaves Silybum marianum 1988) and the variegated thistle leaf spot Heliothis punctigera leaves Cirsium vulgare fungus Septoria silybi (Bruzzese and Vanessa kershawi leaves Cirsium vulgare Predebon 1987).