ALLELOPATHIC POTENTIAL OF VEGETATIVE AND FLOWERING RAGWORT (SENECIO-JACOBAEA L) PLANTS AGAINST ASSOCIATED PASTURE SPECIES

The allelopathic effects of vegetative and flowering plants of the annual/biennial pasture weed Senecio jacobaea L. (ragwort) against Lolium perenne L. (perennial ryegrass) and four pasture legumes were investigated using a range of bioassays. Bioassays based on shoot and root leachates demonstrated detectable, although usually slight, allelopathic effects, and these did not usually differ between the two developmental stages of S. jacobaea. However, aqueous extract and tissue decomposition bioassays demonstrated stronger allelopathic effects, particularly for flowering plants, and this was in general agreement with toxicity assessments of soil collected from under S. jacobaea plants in the field. According to our study, flowering plants have the potential to weaken pasture through allelopathy, and decomposition of above-ground litter appears as the most likely mechanism facilitating this. The aqueous extract and tissue decomposition bioassays also revealed that L. perenne was less susceptible to S. jacobaea allelopathy than were the legumes, suggesting that encouraging a strong L. perenne component in pastures has potential for reducing the overall inhibitory effects of S. jacobaea on pasture production.