Sensitive reaction of ragwort (Senecio jacobaea) to cutting dates

Ragwort (Senecio jacobaea L.) is poisonous for livestock and should therefore be controlled on agricultural grasslands. In this study, we tested the influence of different cutting dates on S. jacobaea to find a sensitive growth stage of S. jacobaea, at which regrowth and seed production would be most severely reduced. On 20 experimental plots, 14 seedlings per plot of S. jacobaea were planted in October 2003 onto agricultural grassland. In 2005, when S. jacobaea plants reached the generative stage, plots were cut on three different dates: start of anthesis of S. jacobaea (27.06.05), end of anthesis (13.07.05), and start of seed production (18.07.05). Compared to the control, cutting at the start or the end of anthesis reduced the number of S. jacobaea flower heads by 87 % in the re-established individuals. Further, when cut at the start of anthesis, 30 % of individuals remained as rosettes until the end of the year and ceased producing shoots and flowers. Though impaired by mowing, S. jacobaea was able to re-establish and to form new flowers up to the end of August. Dependent on the cutting date, the proportion of dead individuals ranged between 6 and 10 %. We suggest that the shoot and seed production of S. jacobaea is most effectively reduced by two or more cuts per year. First mowing should take place when 50 % of S. jacobaea individuals in a population start their anthesis. The second mowing should take place when half of the re-established individuals start anthesis again.