Can Senecio aquaticus be controlled in agricultural grassland?

In recent years, Senecio aquaticus has become increasingly abundant in agricultural grassland of medium-to- high management intensity in Switzerland, Southern Germany and Austria, where its toxicity poses a threat to animal health. This study aimed to identify measures for controlling S. aquaticus. A detailed field experiment was set up at five sites in Switzerland to test the effectiveness of six treatments: ploughing followed by re-sowing with a ley mixture; harrowing followed by re-sowing; application of a selective herbicide; pulling or digging up individual specimens; mowing once a year; and a control in which no measure was applied. In addition, the soil the seed bank of S. aquaticus was recorded prior to the study. In the short-term, herbicide application and mowing once a year were the most effective measures for controlling S. aquaticus, reducing specimens by up to 88 %. No clear effects were observed for the remaining measures. Three years after application, the measures that were most effective in the short-term still performed best, but hardly any significant reduction was achieved compared to pre-treatment conditions. Because S. aquaticus formed large seed banks of over 1000 germinable seeds per m², elimination of individual plants resulted in germination and replacement with new seedlings, thereby contributing to the failure of the treatments. We therefore conclude that controlling established populations of S. aquaticus remains a challenge, requiring the repeated application of measures over several years until the seed bank is depleted. For this reason, the formation of populations with a soil seed bank of S. aquaticus should be prevented by any means.