Cleavers bigger threat to rape yields than is realised

brassica napus contamination crop yield date de semis economic thresholds encuestas escarda fecha de siembra galium herbicidas herbicide herbicides losses malezas mauvaise herbe metazachlor metazacloro perte plant competition production de semences quinmerac rendement des cultures rendimiento de cultivos seasonal variation seed seed production semence semillas sowing date surveys weed control weeds