The effectiveness of management interventions used to control ragwort species

Ragwort (Senecio jacobaea and S. aquaticus) causes major losses to agricultural revenue and induces livestock morbidity throughout parts of Europe, North America, and Australasia. The introduction of legislation in the U.K. and Australia has meant that landowners can be prosecuted if the plant spreads to adjacent land, which has led to an increase in activities attempting to control these species. Commonly used interventions include natural enemies, herbicide applications, manual and mechanical removal. Through the use of explicit systematic methodology involving comprehensive searches and detailed inclusion criteria, data from primary research are collated for each type of intervention. Meta-analyses show that 2,4-D, Asulam, Clopyralid, and MCPA are effective at reducing ragwort densities. However, when the datasets were analysed for their effectiveness against individual species, 2,4-D and MCPA were only effective against S. jacobaea, while Asulam was only effective against S. aquaticus. Natural enemies Longitarsus jacobaeae and a combination of L. jacobaeae and Tyria jacobaeae appear to have the potential to reduce S. jacobaea densities. Only applying T. jacobaeae does not appear to significantly reduce S. jacobaea densities, but does reduce the number of capitula per plant, seeds per capitula, viability of seeds, and dry weight of the plants. There is insufficient experimental evidence available to assess other interventions such as manual or mechanical removal. Further research into these types of interventions is recommended, as well as more detailed reporting of site characteristics and experimental design to allow full investigation of each intervention to explain possible reasons for variations in their effectiveness.