Basic and applied studies to evaluate management options for the regulation of Tansy Ragwort (Jacobaea vulgaris)

Jacobaea vulgaris GAERTN. or common ragwort is a widespread noxious grassland weed that is native to Eurasia and invasive in many other continents. Since the pyrrolizidine alkaloids of the plant pose a health risk to cattle consuming this plant, its occurrence in high densities is a challenge for farmers all over the world. However, knowledge about reasons of ragworts invasiveness and environmentally sound management options of the plant in its home range is scarce. Therefore, we followed hypotheses-based approaches to explore the allelochemic and autotoxic potential of this plants litter to gain insights on why and how to manage the weed (Chapter 1 and 2) and tested several mechanical treatments to reduce population density and growth of ragwort, while fostering botanic diversity (Chapter 3). Due to the posed research questions, climate chamber studies onto seed germination of several common and rare grassland species in extracts of ragwort litter have been studied (Chapter 1). Besides, common garden experiments of germination of ragwort under its litter and the influence of ragwort-conditioned soil have been put into practice (Chapter 2) as well as a long-term field experiment studying ragwort population density and growth under seven different mechanical and cultural treatments over a course of four years (Chapter 3). The first study (Chapter 1) highlights the autotoxic potential of ragwort in delaying its germination. It also showed that rare species are not disproportionally more sensitive to ragwort allelochemicals than other plants. Finally, it demonstrated that allelopathy of ragwort in its home range does not seem to be a key factor for ragworts invasiveness as osmotic effects were similar to effects of ragwort extract. The second study (Chapter 2) reassures findings of the preceding study, underlining ragworts autotoxicity, but also showing that hampering of germination, facilitates seedling growth later on and is not reducing the weeds population growth. Thus, incorporating ragwort litter as management tool, seems not be effective. A third study (Chapter 3) underlines the importance of seedling recruitment for population growth. Hence, the data suggests cutting the plant during its bloom and to repeat this cut, when it starts to build flowers again within the same season, to effectively prevent seed production is a vital tool for population management. One cut treatments or seed addition treatments were not able to reduce seedling recruitment, population growth or population density.