Longevity of Soil Based Seeds of Onopordum Illyricum
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242 Plant Protection Quarterly Vol.11 Supplement 2 1996 goat grazed paddock (Table 1). Within two years of removing goats from part of the Longevity of soil based seeds of Onopordum original experimental plot in 1993 and illyricum where subsequent ineffectual control was exerted on the thistle, soil based seed A B populations increased to 11 million seeds C.J. Allan and P.J. Holst per hectare. (Table 1). A NSW Agriculture, Agricultural Research and Veterinary Centre, Forest Road, Orange, New South Wales 2800, Australia. Seedlings B NSW Agriculture, Agricultural Research Station, Cowra, New South Wales Counts of rosettes at the two leaf stage 2794, Australia. reflected the decline in soil based seed within the goat grazed paddock (Table 2). Summary The number of established thistle plants Seeding was prevented for eight years, in successfully prevented any seed replenish- in May 1996 was 0.05 and 9 plants m-2 in a paddock containing a dense population ing the residual soil based seed popula- goat and sheep grazed paddocks respec- of Onopordum illyricum, initially by tion. The experiment commenced in 1988 tively. grazing with mature bush goats for five and was maintained until 1996. In 1993 the years, then by chemical/mechanical paddock was reduced to 0.5 hectare and Discussion means. The population of residual soil the goats removed. However, prevention Soil based seeds populations of O. illyricum based seeds was monitored annually fol- of seeding was continued by spraying and progressively declined over the duration lowing autumn germination. Initially the chipping the thistle. of the experiment where replenishment of soil based seed population was estimated Soil samples were collected following the soil reserve was prevented by grazing to be 5 million seeds per hectare. After the autumn break in each year; cores to 7 with goats. Little or no control was exerted four years of seeding prevention, the soil cm depth being taken randomly across the in the paddock grazed by sheep and based seed population decreased to 1.6 paddock. The number of cores collected populations of the soil based seed were million seeds per hectare and maintained each year was modified over the duration maintained at a high level producing sig- a steady state at that level. Seedling of the experiment, but ranged from 150 in nificantly higher numbers of seedlings. counts following germination reflect the the 2.8 hectare paddock to 300 in the 0.5 The cessation of seeding in the goat decline in population of soil based seeds. hectare paddock from 1993 onwards. An grazed paddock has produced significant After five years of seeding prevention in adjoining paddock grazed by sheep was visible differences in frequency of O. a 2.8 hectare paddock the area was re- also monitored for soil based seeds of O. illyricum when compared to the adjoining duced to 0.5 hectare. Within two years of illyricum. The seeds, collected by wet sheep paddock. Plants are still present in no seeding control the soil based seed sieving the cores, were cut and their viabil- the goat grazed paddocks, however, at population in the foregone 2.3 hectares ity determined by the presence of an em- levels of 0.05 m-2, the population is more increased to levels commensurate with bryo. Seedling counts were made from manageable and pasture production the population when monitoring began. random 0.25 m2 quadrats across the pad- greater than in the adjoining paddock Plant counts after seven years were 0.05 dock following the autumn break. where pasture had been greatly reduced and 9 plants m-2 in goat and ‘no-control’ due to thistle density (Allan et al. 1993). (sheep grazed) paddocks respectively. Results After reducing the seed population in The initial viable soil based seed the soil for five years, it rose within two Introduction populations in sheep and goat grazed pad- years of ineffective control of seeding to a Longevity of the residual soil-based seed docks were 12 and 5 million seeds per hec- level commensurate with the level at the population is an important determinant in tare respectively. The soil based seed start of monitoring. This has direct impli- devising control or eradication strategies populations of the goat grazed paddock cations for the development of control for weeds. Populations of O. illyricum are quickly declined over the initial four years programs which must annually prevent increasing and traditional attempts at con- to a steady state around 1.6 million seeds seeding. Also, because soil based seeds trol have been thwarted by recurring per hectare. In the adjoining sheep pad- have a strong dormancy characteristic populations after several years of appar- dock, where no control was exerted on the (Young and Evans 1972), a management ent control of seeding. As a component of flowering thistle, seed populations fluctu- strategy would need to be implemented an experiment investigating control of O. ated but were significantly higher than the over a long period to be successful illyricum by grazing with goats (Campbell Table 2. Seedlings per square metre (Campbell et al. 1991). and Holst 1990), residual soil seed following the autumn break in goat populations were monitored. References and sheep grazed paddocks. Allan, C.J., Holst, P.J. and Campbell, M.H. Materials and methods Sheep Goat (1993). Meat Research Corporation Fi- A description of the experiment can be nal Report DAN 057, 69 pp. found in Campbell and Holst (1990). Spe- 1990 7.7 8.0 Campbell, M.H. and Holst, P.J. (1990). Use cifically, mature domesticated feral goats 1991 22.8 1.5 of goats for the control of Illyrian thistle, at 14 per hectare in a 2.8 hectare paddock 1992 20.6 2.5 Onopordum illyricum. Proceedings 9th 1996 77.0 0.5 Australian Weeds Conference, Ad- Table 1. Viable soil based Onopordum illyricum seed (million per hectare) elaide, pp. 493-6. from goat (seeding controlled), ex-goat (seeding controlled for first five years, Campbell, M.H., Nielson, W.J. and Nicol then ineffective) and sheep (seeding not controlled) grazed paddocks. H.I. (1991). Some factors affecting the germination of achenes of Onopordum 1989 1990 1991 1992 1994 1995 1996 illyricum L. Plant Protection Quarterly 10, 70-2. Sheep 12 30 32 17 19 43 23 Young, J.A. and Evans, R.A. (1972). Germi- Goat 5 3.5 4.0 1.6 1.2 1.8 1.6 nation and persistence of achenes of Ex-goat 11.0 19.0 7.0 Scotch thistle. Weed Science 20, 98-101..