Contrasting weed species composition in perennial alfalfas and six annual crops: implications for integrated weed managementHelmut Meiss, Safia Médiène, Rainer Waldhardt, Jacques Caneill and Nicolas Munier-JolainAgron. Sustain. Dev., 30 3 (2010) 657-666DOI: https://doi.org/10.1051/agro/2009043