Seedling emergence and longevity of Senecio madagascariensis Poir. (fireweed) in coastal south-eastern Australia
B.M. SindelA and P.W. MichaelB, School of Crop Sciences, University of Sydney, New South Wales 2006, Australia.
A Department of Agronomy and Soil Science, University of New England, Armidale, New South Wales, 2351, Australia.
B 5 George Street, Epping, New South Wales, 2121, Australia.
Monitoring of the population dynamics of Senecio madagascariensis Poir. (fireweed), an introduced African weed of pastures in south-eastern Australia, showed that population size varied greatly between sites and between years; peaks were reached in autumn and spring, coinciding with flushes of germination. Small numbers of seedlings emerged throughout most of the year. Survival curves typically showed rapid mortality following germination and again nearing senescence in late spring and summer. Mean life expectancy was 1.5 months at a site where the pasture was grazed and relatively vigorous, compared with 3.7 months at two less-productive, ungrazed sites.
The biennial behaviour of plants depended more on site characteristics, e.g. soil condition, than climatic factors. Complementary data on the demise of S. madagascariensis were obtained from a high density population (>5000 plants m-2) which was stimulated by cultivation. Fertilizing of pastures in autumn increased the rate of seedling emergence, growth and development, while slashing once during early vegetative growth reduced S. madagascariensis survival by up to 38.2%. Fast growing plants flowered within six weeks of emergence. Vigorous pasture growth reduced emergence of S. madagascariensis despite favourable climatic conditions for germination. Early autumn cohorts and large over-summering plants would appear to have the greatest potential to increase the soil seed population.
Plant Protection Quarterly (1996) 11 (1) 14-19.