Manual weeding of Rumex obtusifolius and its effects on plant species composition in organically managed grassland

Rumex obtusifolius is a troublesome weed especially in organically managed grasslands. Manual weeding is commonly used for R. obtusifolius control, but its effectiveness and effect on plant species composition in upland grassland has never been investigated. Therefore the aim of our study was to reveal the effect of manual weeding by digging out R. obtusifolius taproots to depths of 5 or 15 cm, either once or twice, in: (i) presence of R. obtusifolius plants; (ii) plant species composition. Additional treatments were grazed and unmanaged grassland (both without digging out R. obtusifolius taproot). Digging out taproots twice, to 15 cm, reduced the presence of R. obtusifolius significantly. Grazing without digging out taproots was the treatment that was most favourable for R. obtusifolius plants. Manual weeding had no significant effect on species richness. The empty spaces after plant removal were filled by nutrient-demanding species (Poa pratensis, Poa trivialis, Festuca pratensis and Lolium perenne, Trifolium repens and Taraxacum sp.). On unmanaged grassland the number of R. obtusifolius plants decreased, species richness was reduced, but this allowed the spread of other tall weedy species (Urtica dioica, Galium album and Elytrigia repens). Digging out taproots to a depth of 15 cm, performed twice, can be an effective method for R. obtusifolius control in organically managed grasslands, as this procedure eliminated the majority of R. obtusifolius plants. However, the use of this weeding method over large areas of grassland is limited due to time-consuming and hard physical work.