| The root application of neonicotinoid insecticides has been gradually popularized due to their excellent absorption and conductivity.Root application technology can avoid potential threats to pollinators.However,some studies have shown that the rapid uptake and translocation process of pesticides after root application leads to the time when the pesticides arrive at the target site is not consistent with the occurrence period of pests,which leads to the waste of pesticides.The sustained-release pesticide could prolong the duration and improve the utilization rate and safety of pesticides by using pesticides as core materials and the natural or synthetic materials as shell materials,which could release the pesticides slowly under the appropriate conditions.This study represented by new neonicotinoid insecticide-clothianidin(CLO),using of sodium alginate as the skeleton and natural materials of tannic acid(TA)and Fe(Ⅲ)coordination reaction formed the coated shell(TA/Fe(Ⅲ))prepared sustained-release granules.And its physical and chemical properties were characterized;pot experiment was used to verify the control efficacy of sustained-release granules on aphids of broad bean;then the effects of formulations and coating materials on uptake and translocation behaviors of clothianidin in cucumber plants and the effects of coating materials on oxidative stress and growth of cucumber plants were investigated.The main findings are as follows:1.The sodium alginate as the skeleton and the coordination reaction of metal ions and tannic acid as the coated shell(TA/Fe(Ⅲ))was used to successfully prepare clothianidin sustained-release granule.The particle size of large granules(FR granules)was approximately1.2 mm;and the particle size of small granules(SR granules)was approximately 500 μm.The FR granules were completely released within 6 h;SR granules were sustained release of approximately 24 h.In addition,the coated shell TA/Fe(Ⅲ)in nutrition solution can be hydrolyzed to TA and Fe(Ⅲ).2.The control efficacy of sustained-release granules was verified by using broad bean aphids as the test object.Within 1-7 d of application,foliar spray of 10% clothianidin suspension concentrate treatment had better control efficacy on broad bean aphids than other treatments.After 14 d of application,the root application technology showed advantages.After3 d of application of FR granules,its control efficacy was significantly higher than that of 0.5%clothianidin granules with the same active ingredient(10 mg/plant).After 14 d of application,the control efficacy of FR and SR granules were 98.0% and 99.0%,respectively,at a dose of10 mg/plant of active ingredient,which was significantly higher than that of 0.5% clothianidin granules(92.1%).After 21 d of application,the control efficacy of SR granules(96.9% and100.0%)under the two application doses was significantly higher than that of FR granules and0.5% clothianidin granules(70.9%-94.8%).Therefore,the FR granules have a certain fastacting property;while the SR granules prolong the duration of pesticide.3.The uptake,translocation and accumulation behaviors of the coated clothianidin in cucumber plants were studied.Within 21 d of application,the treatment of sustained-release granules reduced the initial exposure concentration of pesticide;after 21 d of application,the treatment of sustained-release granules was beneficial to prolong the duration of clothianidin.In addition,the residues of clothianidin in flowers(0.020 mg/kg and 0.010 mg/kg,respectively)and fruits(0.002 mg/kg and 0.008 mg/kg,respectively)treated with SR and FR granules were lower than 10% clothianidin SC treatment(0.350 mg/kg and 0.011 mg/kg).Root concentration factor(RCF)and bioconcentration factor(BCF)are two indicators that indicate the absorption capacity of roots for clothianidin and the ability of plants to accumulate clothianidin.Compared with 10% clothianidin SC treatment,the mean root concentration factor(RCF)and bioconcentration factor(BCF)of SR granules treatment increased by 27% and 38%,respectively.The mean RCF value of FR granules treatment is equivalent to that of 10%clothianidin SC treatment,while the BCF value is increased by 30% compared with the control pesticide.Therefore,the treatment of sustained-release granules could significantly increase the absorption capacity of roots and the enrichment capacity of plants to clothianidin.4.The effects of the hydrolysate-tannic acid(TA)of coating material on the uptake and translocation behaviors of clothianidin in cucumber plants was investigated.It was found that the addition of exogenous TA can promote the roots to absorption of clothianidin and significantly increase its bioaccumulation amount in cucumber plants.When the concentration of exogenous TA was 1 mg/L and 10 mg/L,the average bioaccumulation amount of clothianidin in roots and leaves increased by 144%,171% and 59%,55%,respectively,compared with clothianidin treatment alone.The addition of 1 mg/L and 10 mg/L of TA significantly improved the root absorption and bioaccumulation of clothianidin by cucumber plants.When the concentration of exogenous TA was 1 mg/L and 10 mg/L,the average RCF and BCF values increased by 43%,108% and 189%,133%,respectively,compared with the treatment without TA.5.The effects of coating material hydrolysate-tannic acid(TA)on the oxidative stress and plant growth of cucumber under root application of clothianidin was investigated.In the hydroponic system,the application of clothianidin alone will cause certain oxidative stress on cucumber plants and affect plant growth.However,low concentrations(1 mg/L and 10 mg/L)of exogenous TA can reduce reactive oxygen generation,relieve lipid peroxidation,improve free radical scavenging ability,enhance antioxidant enzyme activity,and increase chlorophyll content and root vitality,and then increase plant biomass.In summary,the new sustained-release granules prepared in this study show certain advantages and application potential in terms of prolonging the duration of clothianidin,enhancing the uptake and accumulation of clothianidin in plants and the ability of plants to resist oxidative stress. |
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