Jacobaea aquatica (Asteraceae) growing in wet grasslands with low management intensity is regarded as a noxious weed with pyrrolizidine alkaloids (PAs), which cause health problems to livestock. The influence of different management practices on the production of PAs and on the proportion of J. aquatica in the fodder was studied. Five cutting regimes were applied during 4 years on permanent plots in lower Austria. The toxicity of the fodder was assessed by recording dry weight and alkaloid content of J. aquatica and total aboveground biomass. Different cutting regimes had significant effects on the PA content of J. aquatica and on its proportion in the fodder. The content of J. aquatica was lowest in fodder of June and October cuts and highest in second cuts in July and August. Total alkaloid contents exceeding 100 mg/kg were found in fodder harvested in July and August. After cutting, the toxic plants regenerated quickly and produced new flowering stalks within 4-5 weeks. Six macrocylic PAs were evaluated, with Z-erucifoline as the most abundant compound. The alkaloid levels were highest in plants cut during summer when flowering plants were present. Consequently, this fodder should not be fed to livestock over a long period of time.
Keywords: Jacobaea aquatica; Senecio aquaticus; erucifoline; management; marsh ragwort; pyrrolizidine alkaloids; senecionine; toxicity of forage; weed control.