Population dynamics of the annual plant Senecio vulgaris in ruderal and agricultural habitats

The annual plant Senecio vulgaris has migrated from ruderal to agricultural habitats resulting in weed populations. The population dynamics of S. vulg aris and its naturally associated rust fungus Puccinia lagenophorae were in vestigated as a basis for the biological control of S. vulgaris with the ru st. A detailed basic study at a single ruderal site and a parallel investig ation at each five ruderal and five agricultural sites were conducted from April to November 1997. During the whole period of study the spatial distri bution of plants was aggregated and plants showed a relatively large size h ierarchy as indicated by mean values of the Gini coefficient higher than 0. 5. Seedling establishment appeared to be a major factor influencing the dyn amics of S. Vulgaris. The importance of seedling establishment, together wi th the observed short generation time of 5 weeks and the broad range of pla nt sizes at reproduction classifies S. vulgaris as a ruderal strategist. Th e population dynamics of S. vulgaris differed between the ruderal and the a gricultural habitat. Plants of S. vulgaris at the ruderal habitat survived over winter, resulting in greater population sizes (0.1 to 1 of the maximum ) and a majority of plants in flower and seed set (31.9%) in spring. At the agricultural habitat, where only a few S. vulgaris winter due to weed cont rol measures, population sizes in spring were smaller (0 to 0.16 of the max imum) with mainly vegetative plants (66.7%). The limited number of suitable hosts at the agricultural habitat in spring lead to a delay of rust infect ion until August, in contrast to the ruderal habitat where the rust was alr eady present in April. In both habitats mature plant stages were more susce ptible to rust infection than vegetative stages. Manipulating the dynamics of the host over winter may enhance rust epidemics in spring serving as bio logical control of S. vulgaris.