| Diamondback moth(Plutella xylostella)is the most widely distributed migratory pest in the world and the most serious pest in the production of cruciferous crops.Due to the serious overlap of generations of diamondback moth and the non-standard and unscientific use of pesticides,the resistance of diamondback moth increased too fast.Improving the utilization rate of pesticides and reducing the use of pesticides are the main ways to reduce pest resistance,and it is also the hot spot in the field of chemical control.In this paper,the occurrence and spatial distribution of diamondback moth on broccoli were studied by field investigations.The spatial pattern,sampling technology and suitable period of pesticide application for controlling diamondback moth have been clarified.The fourteen kinds of pesticides were selected have been toxicity bioassay to diamondback moth,and five kinds of pesticides were selected which have high toxicity to diamondback moth have been field efficacy trials.At the same time,abamectin was mixed with six different kinds of pesticides were toxicity bioassay,and the combined virulence and optimum ratio were carried out from this control have been field efficacy trials.The three different spray adjuvants and two kinds of pesticides with high virulence to diamondback moth were mixed and had conducted synergistic toxicity bioassay and field efficacy trials,so as to provide a certain theoretical basis for the effective prevention and control of diamondback moth in broccoli and the pesticide reduct and synergistic effect.The major tests in this paper are listed as follows:1.Field distribution pattern and occurrence regularity of diamondback moth in Helan County in autumn.The distribution pattern of diamondback moth in Helan County was as follows:the pupae was mainly distributed uniformly,a small number of fields were aggregated,and the larvae was also aggregated.The most suitable survey method is the single diagonal sampling method.The outbreak period was mainly in the middle of mid-August,the peak of pest population appeared in early September,and began to decline in the middle of September.The population remained at a low level by the broccoli was harvested completely in the end of October.The occurrence of diamondback moth has exceeded the economic threshold in the middle of August in Helan County,which is a critical period for the control of diamondback moth.Therefore,appropriate pesticides should be selected for controlling of diamondback moth.2.Toxicity bioassay and field control effects of fourteen kinds of pesticides to diamondback moth.The toxicity bioassay was determined by impregnation method of fourteen pesticides and five kinds of pesticides have been for field efficacy trail to diamondback moth,which were selected of these pesticides.The results showed that emamectin benzoate 5%EC had the highest toxicity to diamondback moth,and tebufenozide 20%SC had the lowest toxicity.The LC50 were 1.53 mg·L-1 and 1693.72 mg·L-1 at 48 h,respectively.The toxicities of the fourteen pesticides from high to low were:emamectin benzoate>chlorfenapyr>abamectin>cyantraniliprole>Bacillus thuringiensis>tetrachlorantraniliprol>pyridalyl>gamma-cyhalothrin>chlorantraniliprole>tolfenpyrad>indoxacarb>spinetoram>chlorfluazuron>tebufenozide.The five highly toxic pesticides including emamectin benzoate 5%EC,chlorfenapyr 10%SC,cyantraniliprole 10%OD,bacillus thuringiensis 8000 IU/μL EC and pyridalyl 10.5%EC were carried out field efficacy trail.The field efficacy trials results showed that all the five pesticides reached the highest control effect at 3 days after application,pyridalyl 10.5%EC and cyantraniliprole 10%OD had better control effect on diamondback moth in field.3.Toxicity bioassay and field control effects of abamectin mixed with six kinds of pesticides against diamondback moth.Preliminary screening of toxicity bioassay,avermectin and six kinds of pesticides mixed at a ratio of 1:1 after 48 h,only the compound of abamectin with cyantraniliprole and chlorfenapyr showed synergism,and the co-toxicity factors were 22.84 and 24.44,respectively.The optimal ratio screening results showed that the best ratio of abamectin and tarfenil is 9:1 and the abamectin and cyantraniliprole was 1:9,and the co-toxicity coefficient were 489.69 and 451.81,respectively,indicating that the synergism was significant.The results of field control efficacy showed that the two combinations had obvious synergistic effects,and the control efficacy were as high as 93.74%and 89.20%,respectively.The synergistic effect of abamectin and cyantraniliprole was the most significant when the effective component was 1:9,which was the best combination for diamondback moth control in the field,and had high promotion and application value.4.Three kinds of spray adjuvants for pesticide reduction and synergistic effect against diamondback mothIn order to achieve the purpose of reducing pesticide application and increasing efficiency of three spray adjuvants including nano-network structure loss control agent SC108,Jijian and Qiangliyuan combined with cyantraniliprole 10%OD and pyridalyl 10.5%EC against diamondback moth were measured,and field efficacy trail was also carried.The results of toxicity bioassay show that all the three spray adjuvants can have a better synergistic effect on the two kinds of pesticides.The synergistic effect from large to small is Qiangliyuan>nano-network structure loss control agent SC108>Jijian.The field efficacy trail results showed that the three spray adjuvants can reduce the dosage of the pesticides by more than 20%～40%,but the Qiangliyuan has best synergism. |
