Impact of cutting frequency on the vigour of Rumex obtusifolius

The control of Rumex obtusifolius, even with the use of herbicides, is difficult in permanent grasslands where R. obtusifolius reduces both productivity and nutritive value of herbage. It is important to find alternative approaches to managing R. obtusifolius. Two greenhouse experiments were conducted to compare the impact of different cutting frequencies, which simulated grazing (three cuts), silage making (two cuts) and hay making (one cut) on shoot and root measurements of the vigour of R. obtusifolius. In both experiments the same cutting frequencies were imposed but in Experiment 1 the treatments were imposed for 2 years and in Experiment 2 for 1 year. Compared to the silage-making and hay-making treatments, there was a reduction in the vigour of the aerial parts of R. obtusifolius on the grazing treatment, associated with a reduction in the number of leaves (Experiment 1), in the size of the largest leaf (Experiment 1) and in the herbage mass of dry matter (Experiments 1 and 2). Roots had higher concentrations of total soluble sugar and lower concentrations of starch in the grazing treatment than in the other treatments. These results showed that a reduction in the vigour of R. obtusifolius in permanent grasslands is possible only if the plants are submitted to a high frequency of defoliation under cutting or grazing.