The Eco-economic Threshold Of Cyhalofop-butyl-Resistant Diplachne Fusca In Paddy Field And Herbicide Screening For Controlling

Sprangletop(Diplachhe fusca(L.)Beauv.)is a gramineous annual weed.In recent years,there has been trend of aggravation,and it’s resistance-cyhalofop-butyl was reported.In order to effectively control D.fusca in paddy fields,the influence of D.fusca on rice growth and yield traits and its eco-economic thresholds were measured.The competition ability between D.fusca resistant population and sensitive population was compared.The efficacy of herbicides application alone or mixed on resistant D.fusca were determined with whole-plant bioassays in different period.The interaction of between metamifop and fluroxypyr on resistant sprangletop was evaluated with the Gowing’s method,and the selectivity on rice to control resistant sprangletop was determined.The main results were as follows:1.The results showed that the number of tillers in rice decreased significantly with the increase of D.fusca density,and the longer the time,the greater the impact.The rice spike length,effective spike number,seed rate,1000 grain weight and yield decreased with the increase of D.fusca density.The relationship between sensitive population density and effective spike number was best fitted by exponential function model,and the quadratic curve was best model on resistant population.The quadratic curve model was best described between the two populations and spike length,seed rate,1000 grain weight and yield,respectively.The power function model was the best to describe the loss of rice yield caused by D.fusca,in while y=2.0917x0.6070 for sensitive population and y=2.2387x0.5625 for resistant population.When 10%metamifop emulsifiable concentrate was applied to control sensitive and resistant populations of D.fusca at the same weeding cost in paddy field,the economic infestation levels(EIL)were 2.24%～2.91%and 2.63%～3.42%,respectively.The eco-economic threshold(1.12～1.72 plants/m2)of sensitivity was lower than that(1.33～2.13 plants/m2)of resistant population.2.In the two-way competition test between the resistant population and the sensitive population,when the resistant population(R)was used as the target plant,the competition curve slope of population S to(R)was 0.0136,which was greater than that of population R to(R)(0.0077),it was indicated the D.fusca population S had stronger competitiveness.When sensitive population(S)was used as the target plant,the competition curve slope of population S to(S)was 0.0099,which was higher than that of population R to(S)by 0.0045.Therefore,the competitive ability of population S to(S)was stronger than that of population R to(S).In the two-way competition test between D.fusca and rice,when rice was used as an adjacent plant,the slope of the competition curve of rice to population(R)was 0.0023,and the curve slope of rice to sensitive population was 0.0016.It showed that the competition of rice to D.fusca population(R)was stronger than that of rice to population(S).3.The foliar spray application tests of herbicides on resistant D.fusca were measured at 2-leaf stage and 4-leaf stage.The results showed that the propanil control resistant D.fusca was the best performance.The efficacy reached 100%at 3840 g a.i./hm2 of propanil on resistant D.fusca,followed by florpyrauxifen-benzyl and metamifop.In the herbicide mixture,the resistant population was effectively controlled by propanil +metamifop(2035+72 g a.i./hm2)at 2-leaf stage and 4-leaf stage respectively,followed by metamifop+fluroxypyr(150+45g a.i./hm2),propanil+cyhmlofop-butyl+fluroxypyr(1800+135+30 g a.i./hm2)and propanil+metamifop+fluroxypyr(1438+60+45 g a.i./hm2).The combined effect of metamifop mixed with fluroxypyr on resistant D.fusca was evaluated with Gowing’s method.In 36 mixed dose combinations,the results showed that the values of objective efficacy(E0)minus the theoretical efficacy(E)(E0-E)of four dose combinations were more than 10%,which showed synergistic effect,while the(E0-E)values of the other 32 dose combinations were between-10%and 10%,which was additive.Therefore,the combined effect of metamifop and fluroxypyr against resistant D.fusca was additive.The Selectivity test results show that the plant height and fresh weight of rice applied with metamifop+fluroxypyr had no significant difference compared with the control.The selectivity index between the Wuyunjing 27 and the resistant D.fusca was 4.5.The index between the Nanjing 9108 and the resistant D.fusca was 3.94.The mixture of metamifop and fluroxypyr had good selectivity on rice to D.fusca.