Study On The Biology, Ecology And Chemical Control Of American Sloughgrass (Beckmannia Syzigachne (Steud.) Fernald)

This study focused on the biology, ecology and integrated management of American sloughgrass (Beckmannia syzigachne (Steud.) Fernald), a malignant weed in wheat fields rotated with rice in the Yangtze Delta Region. Results obtained are listed as following:Fruiting traits of B. syzigachne were investigated in wheat fields rotated with rice. Its average plant height was 67.5cm, ear length was 18.0cm, productive tillering nodes were 1.65, grain number per ear was 529, and 1000-grain weight was 0.87g. The mature seeds could keep alive in summer best in soil under nature circumstance and submersed environment. Moreover, treatments with chemicals such as 4000μg/mL GA3 and 1% KNO3, could also break seed dormancy. The influence of environmental factors on seed germination and seedling emergence of B. syzigachne were studied in laboratory and greenhouse conditions. The optimum temperature for seed germination was 10℃and light was not necessary. Seed germination was sensitive to osmotic potential and completely inhibited at osmotic potential of -0.6 Mpa. But it was quite tolerant to salinity, germination occurred even at 160 mmol·L^-1 NaCl (36.3%). More than 80% of seeds germinated at pH values ranged from 4 to 10. Seedling emergence was highest when seeds were placed on the soil surface (90.7%) but declined with burial depth. Few seedlings (2.5%) emerged when seeds were planted at a depth of 5 cm. Information gained in this study will lead to a better understanding of the requirement for American sloughgrass germination and emergence.Ecology exploration of B. syzigachne showed that a main emergence fastigium was observed in winter with majority seedlings and a subsidiary emergence in spring. The competitive ability of B. syzigachne in winter wheat has been investigated in Jurong, China. Data showed that zooming period of plant height and fresh weight of B. syzigachne occurred at 18 WAP (weeks after planting), which was later than wheat by three weeks, and suggestd that chemical control and fertilization should be performed within 18 WAP. Moreover, the number of productive ear, grain number per ear and yield of wheat were declined significantly with increasing density of B. syzigachne but not for 1000-grain weight. The eco-economic thresholds of B. syzigachne control in wheat also have been determined. In the Delta Region of Yangtze River, B. syzigachne could be controlled by spraying 50% isoproturon WP, 15% clodinafop-propargyl WP and manual removing when the weed densities in fields reached to 0.53, 1.11 and 4.9 individuals/m², respectively.The susceptibility of B. syzigachne to 9 herbicides belonging to different classes was determined by pot-spraying method. Based on the ED50, the susceptibility of B. syzigachne to 9 herbicides was in the following order: clodinafop-propargyl> fenoxaprop-P-ethyl> sethoxydim> nicosulfuron> acetochlor> haloxyfop-R-methyl> butachlor> isoproturon > flucarbazone-sodium. According to the principles of expanding kill-weeding table, reducing the costs and increasing the effects, the isoble method was used to filter the proportions of some herbicides as follows: acetochlor to bensulfuron-methyl was 16 to 1, butachlor to bensulfuron-methyl was 19 to 1, isoproturon to flruoxypyr was 7 to 1, clodinafop-propargyl to flruoxypyr was 1 to 3. Four groups of the mixtures were applied in the field, except for the mixture of 60% clodinafop-propargyl·flruoxypyr, other groups got the effects over 85% against the whole weeds and safe for the wheat.