Investigation of the main weeds types and varieties in different rotation way in tobacco fields of Guangdong province

The species and amount of weeds in main tobacco fields of 13 towns of Guangdong province were investigated by five-point sampling method,with 45 species to 17 families recorded.There were 13 main species according to the dominance of weeds,including Acalypha australis,Polygonum lapathifolium,Setaria viridis,Monochoriamorsakowii,Ageratum conyzoides,Malachium aquaticum,Echinochloa crusgalli L.Beauv.var.mitis(Pursh) Peterm.,Alternanthera philoxeroides,Erigeron canadensis,Digitaria sanguinalis,Polypogon fugax Nees ex Steud.,Echinochloa crusgalli and Arenaria serpyllifolia.There were diversities among dominant species of the main weeds from place to place in Guangdong tobacco fields.The main species in Nanxiong city were Acalypha australis,Setaria viridis,Echinochloa crusgalli L.Beauv.var.mitis(Pursh) Peterm.,Polygonum lapathifolium and Cyperus rotundus,with Acalypha australis as the most serious species.The main species in Meizhou city were Monochoriamorsakowii,Polygonum lapathifolium,Polygonum hydropiper and Ageratum conyzoides,the amount of Monochoriamorsakowii standing the most huge one.In the tabacoo-dryland rotation field,there were 8 dominant species including Acalypha australis,Polygonum lapathifolium,Setaria viridis,Ageratum conyzoides,Malachium aquaticum,Erigeron canadensis,Alternanthera philoxeroides and Arenaria serpyllifolia;In the tobacco-rice rotation field,there were 9 dominant species including Polygonum lapathifolium,Monochoriamorsakowii,Acalypha australis,Setaria viridis,Echinochloa crusgalli L.Beauv.var.mitis(Pursh) Peterm.,Digitaria sanguinalis,Ageratum conyzoides,Echinochloa crusgalli and Alternanthera sessilis.Acalypha australis,Polygonum lapathifolium,Setaria viridis,Ageratum conyzoides were the common dominant species of weeds which were shared by tabacco-dryland rotation field and tabacco-rice rotation field.