Studies On The Influence Of Alopecurus Japonicus And Beckmannia Syzigachne On Winter Wheat And Its Control Techniques

Japanese foxtail（Alopecurus japonicus）and American sloughgrass（Beckmannia syzigachne Steud.）are annual weeds,which have become the dominant weeds in rice-wheat cropping fields in recent years and are difficult to be controlled by using fenoxaprop-p-ethyl.In order to control these species effectively,there were investigated on the loss rate of wheat yield caused by the mixture of A.japonicus and B.syzigachne and their eco-economic threshold,and the competition of A.japonicus with that of B.syzigachne.The combination of tralkoxydim+isoproturon,tralkoxydim+pyroxsulam,isoproturon+pyroxsulam,isoproturon+flucarbazone-sodium and pinoxaden+flucarbazone-sodium was evaluated by the Gowing’s method using whole-plant bioassay for the control of A.japonicus and B.syzigachne;Field weed control trials were conducted on herbicide mix formulations.The main results are as follows:1.The results of the trial showed that spike length,spike number,number of grains per spike,thousand grain weight and yield of wheat decreased with the increasing of mixed weed density.The direct effect of A.japonicus and B.syzigachne on wheat yield is mainly,the direct path coefficient of A.japonicus on wheat yield loss rate was 0.324,and the direct path coefficient of B.syzigachne on wheat yield loss rate was 0.887.The relationship between A.japonicus（density）and wheat yield loss rate is best described by the power function y=2.9570x^0.3731+0.4222;the relationship between B.syzigachne（density）and wheat yield loss rate is best described by the power function y=3.4734x^0.4348+0.6815;when A.japonicus and B.syzigachne are mixed,B.syzigachne is the standard weed,and the relationship between weed density and wheat yield loss rate is best described by the power function y=4.2191x^0.4206-0.3989.When wheat yields ranged from 5250 to 6750 kg/hm²,the effectiveness of control of both weeds reached 90%,and the allowable level of economic hazard was 4.51%～5.80%for the mixture of 50%isoproturon WP and 3%mesosulfuron-methyl OD for control of A.japonicus,B.syzigachne and mixed weed,with the ecological and economic thresholds were2.38～4.97 plants/m²,1.25～2.44 plants/m² and 1.43～2.50 plants/m²,respectively.2.The results of the competition test between A.japonicus and B.syzigachne showed that when the inverse proportional curve was used as the competition model,the slope of the curve was 0.8158 when B.syzigachne as a neighbor plant competed with A.japonicus,while the slope of the curve was 0.4032 when A.japonicus competed with A.japonicus as a neighbor plant,indicating that the competition ability of B.syzigachn was greater than that of A.japonicus;similarly,when B.syzigachn as a neighbor plant competed with B.syzigachn,the slope was 0.4817,while the slope of 0.1467 for A.japonicus as a neighbor plant competing with B.syzigachn species indicates that the competitive ability of B.syzigachn species is greater than that of A.japonicus.3.A whole-plant test was conducted to control the A.japonicus or B.syzigachne by herbicide mixture,and the Gowing’s method was used to evaluate the interaction between herbicide respectively.The results showed that,the effectiveness of tralkoxydim+isoproturon（480+450）g a.i./hm²,tralkoxydim+pyroxsulam（480+13.50）g a.i./hm²,isoproturon+pyroxsulam（450+13.50）g a.i./hm²,isoproturon+flucarbazone-sodium（450+8.10）g a.i./hm²and pinoxaden+flucarbazone-sodium（60+8.10）g a.i./hm² reached 100%for controlling 2-leaf-old A.japonicus.The E₀-E values of the 16 mixed combinations in each of the mixing trials ranged from-10%to 10%,indicating that combination of the two herbicides in the control of the A.japonicus was additive.In test of 2-leaf-old B.syzigachne,the efficacy of tralkoxydim+isoproturon（120+450）g a.i./hm²,tralkoxydim+pyroxsulam（480+13.50）g a.i./hm²,isoproturon+pyroxsulam（450+1.69）g a.i./hm²,isoproturon+flucarbazone-sodium（450+4.05）g a.i./hm²,and pinoxaden+flucarbazone-sodium（60+32.18）g a.i./hm² reached100%.The E₀-E values of the 16 mixed combinations in each of the mixing trials ranged from-10%to 10%,indicating that combination of the two herbicides in the control of the B.syzigachne was additive,too.4.Herbicide mixture in the overwintering period as foliage treatment for control of A.japonicus in field trials showed that isoproturon+pyroxsulam（900+11.25）g a.i./hm² was the most effective,with plant and fresh weight control above 99%at 80d after application.There were above 95%of efficacy by tralkoxydim+pyroxsulam（480+10.125）g a.i./hm² or tralkoxydim+isoproturon（480+1125）g a.i./hm².It was showed that these mixed formulas could be used to control of gramineae weeds,especially A.japonicas in winter wheat field.