Effects of droplet density,spraying volume and spraying equipment on efficacy of abamectin microemulsion against Panonychus ulmi in apple tree

Abstract: 【Objective】Unsuitable spraying equipment and spraying volumes seriously limit efficient useof pesticides in apple and other fruit crops. In order to get a high control effect,farmers spray too muchpesticides to control pests. These poor measures may cause negative effects,such as pesticide dissipa-tion,lasting pollution and residue in fruit,etc. To solve these problems,the effects of droplets density,spraying volume and spraying equipment on the control efficiency of abamectin microemulsion against Panonychus ulmi were studied so as to obtain technical parameters for minimizing pesticide spraying in or-chards.【Methods】A high-voltage static sprayer(3WBJ-16DZ),a plunger pump sprayer(LX-52) and amist sprayer(SSA-E500) were used to spray droplets of 3% abamectin microemulsion indoor and in appleorchard. UV VIS spectrophotometer(UV2800) was used to measure residues of abamectin on leaves andground. Three droplet densities were sprayed by a high-voltage static sprayer,including a low density(coverage rate of pesticide was 30%-35%),a middle density(coverage rate 45%-55%) and a high densi-ty(coverage rate 65%-75%). These droplet densities were sprayed in apple orchard to measure their con-trol efficacy against Panonychus ulmi. Abamectin residues were measured by a UV VIS spectrophotome-ter. According to control efficacy,abamectin residues and appropriate droplet density were obtained. Thecontrol effects of 3% abamectin microemulsion were studied by three spray volume sincluding 1.5 L pertree,2.0 L per tree,2.5 L per tree,with three concentrations,3 000 fold dilution,4 500 fold dilutionand 6 000 fold dilution. The control effects of plunger pump sprayer and mist sprayer against Panonychus ulmi were studied in a Red Fuji apple orchard with about 22-year-old trees. The doses for plunger pumpsprayer were 5 L per tree,4 L per tree and 3 L per tree,with a working pressure of 2.0 MPa and a bore di-ameter of 1.0 mm. The doses for mist sprayer were 3 L per tree and 2 L per tree,with a working pressureof 1.5 MPa and a bore diameter of 1.5 mm. 85 mg·L^-1 dye temptation red 85 was added into abamectin so-lution to measure residue of abamectin on leaves and ground. Based on effects of abamectin microemul-sion against Panonychus ulmi,this study proposed appropriate droplet density,spraying volume and ef-fective spraying equipment.【Results】Droplet density and dilution folds of 3% abamectin microemulsionhad significant effects in controlling Panonychus ulmi. Spraying abamectin microemulsion(3%) diluted by3 000 folds with high density could effectively control Panonychus ulmi,with a control efficiency higherthan 92% at 3 and 7 d. Lower droplet densities and higher dilution folds had poor control against Panonychus ulmi. Mist sprayer enabled even spray of abamectin on leaves in different positions of apple trees andhad less drip into ground. The efficiency of the spray at 3 000 fold dilution of 3% abamectin microemul-sion with a volume of 2-3 L per tree was above 95%. The plunger pump sprayer generated uneven spraywith higher loss and lower coverage,especially in the underside of the leaves at lower spray volumes. Asa result,the treatment had poor control effects against Panonychus ulmi. Using plunger pump sprayer,the control efficacy of spraying at 3 000 fold dilution and 5 L per tree was higher than 95.0%. With thespray volume of 4 L per tree at 3 000 fold dilution,the control efficiency was above 92.0%,and with 3 Lper tree,it was lower than 90%. Droplets test cards was used to test spraying effect. The result showedthat abamectin particles were less deposited on the underside of leaves no matter what type of sprayer wasused. Yet,there was enough abamectin deposition when mist sprayer was used. If plunger pump sprayerwas used with high density and high spray volumes of 4-5 L per tree,abamectin deposit in the undersideleaves was too high to be measured with droplets test card,and its deposition reached 0.333-0.517 μg·cm-2,which was 1.5 to 2.5 times that of the high density treatments. If sprayed at 3 L per tree with middle drop-let density,abamectin distribution was enough in the underside of most leaves,but its deposit was 0.147μg·cm-2in the inner leaves,which did not meet the control need. All results showed that control effectand spray effect of the mist sprayer was better than those of the plunger pump sprayer. Mist sprayer gener-ated smaller droplets and a larger coverage,which enabled a better abamectin deposition on leaves. Themist sprayer had a better control effect against Panonychus ulmi than the plunger pump sprayer. The con-trol effect of spraying with the plunger pump sprayer at volumes of 4 and 5 L per tree had no significantdifference,but was significantly better than that of 3 L per tree at 3 d after treatment. The effect of spray-ing with the mist sprayer at 3 L per tree was similar to that spraying with the plunger pump sprayer at 5 Lper tree. The control effect of mist sprayer at 2 L per tree was significantly higher than that of plungerpump sprayer at 3-4 L per tree. The plunger pump sprayer at 3-5 L per tree had higher losses of pesticidethan the mist sprayer at 2-3 L per. The plunger pump generated a loss of 1.98 times that of the mist spray-er at 3 L per tree.【Conclusion】Farmers generally use plunger pump sprayer,“a washing type”to controlpests. This study showed that the plunger pump sprayer could not produce an even distribution of abamec-tin between the upperside and underside of leaves when applied at low doses. Only higher dosage applica-tion enabled sufficient chemical deposit in different parts of trees to effectively control Panonychus ulmi.Droplet density can be directly determined using test card. In orchards,conventional spray equipmentsneed large volumes to obtain a better control effect. By these too much pesticide liquid was deposited ontest paper card to observe its droplets. This study set different densities of droplets treatments with newequipments and measured chemical deposition and their control effects. By this study,we got appropriatedroplets density and deposition to control Panonychus ulmi effectively,providing effective pesticide appli-cation methods in orchards. Farmers are suggested to select mist sprayer and low dosage in orchards.