Phytocoenological features and control strategies of weeds.
A survey of 810 sites in the N. of Heilongjian Province, China, revealed 132 species of weeds belonging to 96 genera. The 6 most common weed communities were dominated by Echinochloa crus-galli, Setaria viridis, Avena fatua, Chenopodium album + Amarathus retroflexus + Polygonum bungeanum, Galiopsis bifida and Polygonum [Fallopia] convolvulus. All except the S. viridis community (which was often located in millet, maize and sunflowers) were found in soyabeans and wheat. Most of the weeds were annuals with a 100-140 d growing period beginning in late Apr. and a therophyte lifeform (principally tussocks of grass or erect broadleaved plants). A weed control strategy was advocated that involved the careful selection of crop seeds, improved crop management (e.g by dense sowing and pre-em. herbicide applications) and the appropriate rotation of crops and herbicides.