Study On The Technologies On Increasing Efficiency And Decreasing Dosage Of Herbicides For Controlling Alopecurus Aequalis In Wheat Fields

In the wheat fields of the middle and lower reaches of the Yangtze River,various weeds occur and cause severe damage to crop production,in which the dominant grass weed species are Alopecurus japonicus,Beckmannia syzigachne,Alopecurus aequalis,and broadleaf weeds are Stellaria media,Galium aparine,Capsella bursa-pastoris,Vicia gigantea and Malachium aquaticum.At present,the main measure to control field weeds is chemical control,e.g.using herbicides.As the continuous mono-use herbicides with the same mode of actions,resistance of weeds to herbicides evolved,and consequently,increased dosage of herbicides were used by farmers to obtain desired control efficiency on weeds,which bring a series of problems on environment and herbicide residue.It is urgent that technologies that could reduce the dosage of herbicides and increase their efficiency on weeds need to be developed.In the present work,a representative grass weeds in wheat fields,A.aequalis,was taken as the study object to screen herbicides with high bioactivities by whole plant bioassay against annual grass weeds in wheat fields,as well as some broadleaf weeds.Furtherly,screened herbicides were mixed and the combined actions were evaluated by different methods based on the perpose to obtain synergetic formulae.And the herbicidal spectrum of these formulae against common weeds in wheat fields was explored,as well as their safety to wheat.Then some formulae with good performance in lab were bring into field trials for further evaluation.Combinations of herbicide-adjuvant that could increase the toxicity of herbicides were screened,and their mechanism was explored.Finally,the application technology for some screened herbicide mixture formulae were studied,in which the factors that might influence the performance of herbicide(environmental temperature and the organic contents in soil)were included.Detailed results are as follows:By the whole plant bioassay,the sensitivity of A.aequalis to common herbicides in wheat fields was determined.The results showed that folia-applied herbicides such as isoproturon,chlortoluron,mesosulfuron-methyl,pyroxsulam,pinoxaden,and soil-applied herbicides such as flufenacet,isoproturon,chlortoluron could effectively inhibit the fresh weight of A.aequalis in green house.Moreover,carfentrazone-ethyl,fluroxypyr and halauxifen-methyl could effectively inhibit the fresh weight of certain broadleaf weeds in wheat fields,which suggsested that the possibility to mix them with the above herbicides against grass weeds to expand the herbicidal spectrum of mixture formulae.The combined effect of the above herbicides was evaluated by different methods.The results showed that the optimum ratio for flufenacet:isoproturon,flufenacet:chlortoluron,mesosulfuron-methyl:isoproturon,pyroxsulam:pinoxaden and pyroxsulam:isoproturon were 1:10,1:75,1:75,1:5 and 1:36,respectively,based on the the equivalent line method.And by the colby method,the optimum ratios for pyroxsulam:pinoxaden:isoproturon and mesosulfuron-methyl:pinoxaden:chlortoluron were 1:5:100 and 1:5:150,respectively.By the gowing method,the optimum ratio of mesosulfuron-methyl:halauxifen-methyl,me so sulfuron-methyl:fluroxypyr,mesosulfuron-methyl:carfentrazone-ethyl,pyroxsulam:fluroxypyr and halauxifen-methyl:pinoxaden were 1:2～6,1:7.5～15,1:1～6,1:15～30 and 1:2～4,respectively.In the evaluation of safety to wheat,all the evaluated herbicide mixture formulae exhibited to be safe to wheat.In addition,the mixture formulae of flufenacet·isoproturon,mesosulfuronmethyl · halauxifen-methyl,pyroxsulam·pinoxaden·isoproturon and mesosulfuronmethyl · pinoxadenvchlortoluron all exhibited a fairly good growth inhibition on Alopecurus japonicus,Beckmannia syzigachne,Alopecurus aequalis,Stellaria media,Capsella bursa-pastor is.To verify the field efficiency and the possible recommending dose for these screened herbicide mixture formulae,field trials were performed in 2019.The results showed that good field controlling efficiency against annual weeds could be obtained for flufenacet · isoproturon(1:8),meso sulfuron-methyl·halauxifen-methyl(1:2),and pyroxsulam·pinoxaden·isoproturon(1:5:100)at the dose range of 750-900,12-15 and 600-800 g a.i./ha,respectively.The synergism to weeds and safety to wheat of the combination of herbicides(50%isoproturon WP,7.5%pyroxsulam WDG and 30g/L meso sulfuron-methyl OD)and adjuvants were evaluated by whole plant bioassay The results showed that all the four adjuvants could increase the inhibition of these three herbicides on A.aequalis.Among them,the 0.15%herbicide-specific synergist used in combination with the three herbicides has the greatest synergistic effect,while the auxiliary agent 0.4%Maisi has the second synergistic effect on the three herbicides.Furtherly,the synergism mechanism of Maisi on mesosulfuron-methyl and herbicide-specific synergist on isoproturon were explored.It was found that by adding adjuvants,the surface tension,the surface contact angle and the dry duration were significantly decreased.The influences of environmental temperature and organic content in soil on the herbicidal activities of selected herbicdes were analyzed by whole plant bioassay.The result show that the activities of flufenacet-isoproturon,pinoxaden-pyroxsulam and pinoxaden-halauxifen-methyl were increased with the increasing of environmental temperature at the range from 10℃ to 20℃.For the organic content in soil,at the range from 0.8%to 4%,which were a normal range of soil organic contents in the middle and lower reachers of Yangtze River,the activity of flufenacet-isoproturon on A.aequalis had no obvious change.It can be speculated that the organic content in soil would not affect the activity of flufenacet-isoproturon on A.aequalis,which also inferred the possibility of this screened formula to be applied in a wide range of wheat cultivating area.