ON BIOLOGY, ECOLOGY AND INTEGRATED MANAGEMENT OF Beckmannia Syzigachne

This paper focus on biology, ecology and integrated management of American Sloughgrass (Beckmannia syzigachne (Steud.) Femald), a new malignant weed developed rapidly in rape and wheat fields following rice recently in the areas of the Changjiang River valley. Results obtained are as follows: The phenological spectrum of B. syzigachne was similar with rape and wheat, although the growth and development were a little later. Mature period of seeds varied among different individuals or different spike positions of the same plant. With 4-5 months long a rest period, mature seeds could keep themselves alive in summer best in soil with sufficient water. This weed could not emerge below 2cm depth in soil. Continues no-tillage would increase the seed number in soil 0-Scm deep, thus would lead to serious infection of this weed. With well-developed ventilating tissue in root, stem and leaf, B. syzigachne could grow well in water logged field. The above epidermal cells arrange in row with a smooth appearance of ave? thus would lower the area to absorb herbicides. Vast majority of B. syzigachne emerged before 9 weeks after crop planting, while fresh weight increased sharply after the middle of March. This weed population had a wider niche breadth, the second widest among 12 major weed populations in weed community, and had bigger niche overlap with Ste//aria a/sine, A/opecurus acquallis, Malachium aquaticum, Foa annua, Polygonum persicaria and Lapsana apogonoides. In rape, wheat or fallow, B. syzigachne was dispersed as negative binomial distribution, because of affections of environment including tillage, crop planting, fertilizer application, weed control, and other natural elements. Beckmannia syzigachne had negative association with Poa annua, Malachium aquaticum and Ste//aria a/sine, and had positive association with Ranunculus sceleratus and Mazus japonicus, etc.. Beckmannia syzigachne had poor adaptability and competition ability in rape or wheat field with no-herbicide application in histoiy, but would become dominant specie in water logged winter fallow, leading to yield loss of rape and wheat after a few years. Due to the growth of B. syzigachne, economic characters of rape such as stem diameter, plant height, branch number and pods per plant had a tendency to decrease, but seeds per pod increased slightly, while 1000-seed weight did not varied. Yield loss of rape was caused by the marked decline of pods per plant. Economic characters of wheat such as plant height, grains per spike, grain-set rate and 1000-grain weight were not affected apparently by weed growth. Yield loss of wheat was caused by the decline of effective spikes. The competition threshold of weed to no only rape but also wheat were 30 to 80 days after crop planting. In greenhouse, herbicides Dowco 453, Quinofop-ethyl, DPX-A788 1, isoproturon, fenoxaprop-p-ethyl, and glyphosate at the general dose could give 100% weed control over B. syzigachne, but in farm some above herbicides could only give lower weed control. Thus imply herbicide efficacy would be affected largely by various elements in environment. R(-)napropamide + DPX-A788 1 in rape field, fenoxaprop-p-ethyl, isoproturon, fenoxaprop-p-ethyl ?chlorsulfuron, isoproturon + chlorsulfuron could provided more than 85% weed control over B. syzigachne and other weeds. The application of natural synergist SD or SDP would provid more control compared with the same dose of the above herbicides.