| Huanglongbing(HLB)is a major problem that prevents the sustainable development of citrus industry worldwide.At present,the chemical control of the Asian citrus psyllid(ACP),Diaphorina citri(Kuwayama),is an important measure to control HLB.Foliar-applications exists some problems,including that insecticides are not well-distributed in leaves;it is difficult to control the time and frequency of spray applications.Drip chemigation could apply pesticides to the root zone directly.Pesticides were absorbed by the roots and transported to new leaves and shoots where were inoculation section of ACP.In this paper,17 kinds of systemic insecticides including organophosphates,neonicotinoids,anthranilic diamides,etc)were screened to acquire effective insectides.Besides,this study investigated the efficacy of drip chemigation on ACP.Furthermore,the distribution of effective insecticides in soil and citrus plants was studied.Finally,to evaluate the efficacy of insecticides,sulfoxaflor and clothianidin were applied to field through drip chemigation.1.Effective insecticides for controlling ACP by drip irrigation were selected through excised-leaf assay by orange seedlings.The results showed that organophosphorus and neonicotinoids with higher systemic activity against ACP.The efficacy of dimethoate(DIM)or acephate(ACE)on ACP was more than 90% at 4 days after treatment and sulfoxaflor(SUL),flupyradifurone(FLU),clothianidin(CLO)or thiamethoxam(THI)was about 90% at 7days after treatment.2.To evaluate the efficacy and persistence of DIM,ACE,CLO and THI to ACP,they were studied by pot-efficacy tests with the same dosage.Results showed that DIM and ACE started to have good efficacy at 6 d and 4 d after treatment,respectively.And their persistences were both 12 days.The effective times of CLO and THI were at 8 d and 6 d after treatment,and their persistence were 120 days and 150 days,respectively.These results suggested that DIM and ACE have fast efficacy on ACP,but their persistence were shorter.Conversely,CLO and THI both have a longer persistence on ACP.3.The effective dosages of SUL and FLU were determined with the positive control-THI.The efficacy of SUL(100 mg a.i./tree)on ACP was similar to THI(50 mg a.i./tree).And the mortality of ACP was more than 80% at 7-65 days after drip chemigation with SUL.When the dosage of FLU was 300 mg a.i./tree,the corrected mortality of ACP is greater than 75% at 10-60 days after treatment.Therefore,SUL could be applied at two times and FLU at six times of the recommended rate of THI through drip chemigation.4.The relationships between the concentration of SUL,FLU,CLO and THI in leaves after applying drip irrigation and efficacy were analysised.When the mortality of ACP was greater than 80%,the lowest concentrations of SUL,FLU,CLO and THI in leaves were 36.41(± 2.82),56.28(± 3.67),0.64(± 0.11)and 1.46(± 0.47)mg/kg,respectively.These results showed that the effective concentration on ACP of the four insecticides was FLU >SUL> THI> CLO.5.The distributions of SUL and FLU in citrus trees were investigated in the greenhouse.It was demonstrated the highest concentrations of SUL in upper,middle and lower leaves were 453.03(± 40.75),385.56(± 49.04)and 343.55(± 46.90)mg/kg,respectively.Besides,the concentration of SUL was more than 90 mg/kg at 4-60 days after treatment.In the upper,middle and lower leaves of citrus trees,the contents of FLU were 446.19(± 51.64,434.08(± 60.75)and 408.20(± 37.56)mg/kg,separately.And the content of FLU was not less than 56 mg/kg at 10-90 days after treatment.These results proved that both SUL and FLU had excellent mobility.Furthermore,SUL had the tendency to accumulate in the new leaves and shoots.Therefore,both SUL and FLU could effectively protect citrus shoot from being feeded by ACP.6.The distributions of SUL,FLU and CLO in soil were also tudied.Soil samples which ranged from 0 to 15 cm horizontally and vertically away from the emitter were gathered at 2 h and 45 d after treatment,and then detected and analysed.The results showed that the movement speed of SUL in the vertical direction was quicker than horizontal direction.And the degradation of SUL in soil was fast.In contrast,the migration rate of FLU horizontally was greater than vertically.At 45 days after treatment,FLU was away from the emitter obviously and the migration speed vertically was faster than horizontally.CLO was mainly distributed in the soil ranging from 0-10 cm distancing emitter at 2 h after treatment and the mobility of CLO in soil horizontally and vertically was comparable.At 45 days,it presented semicircular migration in the soil.These results indicated that the distribution of insecticides in soil was influenced by their physical and chemical properties.SUL and FLU could be applied to adult citrus trees in the field owing their higer migration speeds.CLO could be applied to seedlings because of it longer persistence.7.SUL and CLO were applied with drip chemigation in the field to evaluate the efficacy on ACP.The concentration of CLO in upper leaves was ranged from 0.61 mg/kg to 2.04 mg/kg at 1-9 weeks after treatment.And the content of SUL in leaves was greater than 16.40 mg/kg during 10-30 days after treatment.ACP was not detected during the trail.It is proved that drip chemigation could effectively control or prevent the occurrence of ACP.This paper selected out the insecticides suitable for dripping chemigation and studied the relationship between the content of insecticides in leaves and efficacy on ACP.It demonstrated there were significant differences concerning effective concentration on ACP among SUL,FLU,CLO and THI.Besides,the distribution of SUL and FLU in citrus plants was investigated,and it was demonstrated that SUL and FLU were easily transported in plants.Therefore,SUL and FLU could be applied to adult tress to control ACP.The study of distribution of three insecticides in soil indicated that SUL and FLU could move faster and CLO were semicircular distributed.Additionally,this paper studied the efficacy of SUL and CLO in field.It was suggested that it is feasible to control or prevent the occurrence of ACP through drip chemigation.Meanwhile,this paper provides a new solution for the prevention of citrus from ACP. |
