Measures for the control of Senecio aquaticus in managed grassland

Senecio aquaticus, a plant containing toxic alkaloids, has been increasing in grasslands of Central Europe. This study aimed to identify control measures for established S. aquaticus populations. A multisite field experiment tested six control measures: ploughing followed by re-sowing, harrowing followed by re-sowing, application of a selective herbicide, pulling or digging of individuals, reduction of management intensity to a level of one annual mowing and lastly an untreated control. In the short term, herbicides and mowing once a year reduced the number of individuals of S. aquaticus most efficiently by up to 88%. No clear effects were observed for the remaining measures. Three years following application, herbicides and one annual mowing still performed best, but hardly any significant reduction in S. aquaticus was achieved compared with pre-treatment conditions. Senecio aquaticus formed large seedbanks with more than 1000 germinable seeds m(-2); the seedbank contributed to the failure of control measures, because any elimination of S. aquaticus resulted in germination and replacement by new seedlings. We conclude that owing to its seedbank, the control of established populations of S. aquaticus remains a challenge, requiring control measures over several years. Any measures that hinder the formation of populations of S. aquaticus and its seedbank in agricultural grassland will be the most efficient for its control.