Application of three surfactants for dose- reduced chemical control of Aphis citricola van der Goot (Linnaeus)

Abstract：【Objective】In order to reduce the pesticide use and delay the development of resistance to the chemical pesticides for controlling Aphis citricola von der Goot, three different surfactants were tested.【Methods】Toxicity of four insecticides, acetamiprid, imidacloprid, lambda-cyhalothrin and abamectin, was first surveyed in the field population of Aphis citricola in Yuncheng using leaf dipping method. Abamectin, the most efficient one, was then selected for this study. Then, surface tension and static contact angle were measured. Suspension drop method was used to determine the surface tension after adding 0.5% GY-T1602, 0.1% NF-100 or 0.3% Maidao to solutions of 5% abamectin EC diluted by 5 000, 6 250, 8 333 or 12 500 times. The control group was the solutions without surfactant. The 30s static contact angles of the abamectin solutions on the upper and lower surfaces of apple leaves after adding the surfactants were measured by lying- down drop method. Finally, field experiments were carried out to evaluate the control effect. Five treatments were set up. They were 5% abamectin EC 150 g · hm^-2 without surfactant, 5% abamectin EC 120 g · hm-2 added with one of the three surfactants and water as control. A knaper-type sprayer was used to evenly spray the whole apple tree. The above treatments were arranged in random zones. Each treatment had 4 replicates (plots), each with 3 trees. The insect population basal number was surveyed on April 29, 2018, and the number of insect population was investigated 3, 7 and 14 days after application. Two branches of each tree were marked according to the positionsin each plot, and the number of living aphids in 5 leaves on each branch was recorded. According to the basal population before the application of pesticides and the population after the application of pesticides, the population decline rate and the control effect in each treatment were calculated.【Results】 Among the four insecticides, abamectin had the highest toxicity to Aphis citricola, which was 18.32- 53.66 times that of the other insecticides. Therefore, abamectin was used as the target insecticide for the study. The results showed that all the three surfactants in all concentrations can significantly reduce the surface tension of abamectin emulsion and the contact angles on the upper and the lower surfaces of the apple leaves. Among the surfactants, GY-T1602 and NF-100 had a better effect than Maidao. The decrease range of surface tension was 3.19-12.59 mN·m^{- 1} . The contact angles on the upper and the lower surfaces of the apple leaves were reduced to 7.54°-31.40° and 16.72°- 47.70°, respectively. The field tests showed that adding GY-T1602, NF100 and Maidao to the treatment of 5% abamectin EC 120 g · hm^{- 2} showed an excellent available effect and lasting validity period on Aphis citricola. The control effect of NF100 addition was 84.95% in 3 days，which was significantly higher than that of abamectin at 150 g·hm^-2 alone. There was no significant difference in control effect among treatments with the additions of the other surfactants and without surfactants. The control effect in all surfactant treatments was 80.02%- 97.08% at 7-14 days after treatment, which was not significantly different from that of abamectin at 150 g·hm^-2 . In summary, with the addition of the three surfactants, abamectin dose could be reduced by 20% to obtain a control effect equal or better than that of abamectin at 150 g · hm^-2 【. Conclusion】Addition of 0.5% GY-T1602, 0.1% NF-100 or 0.3% Maidao could significantly increase the wettability of abamectin to apple leaves, and all the three surfactants could reduce the amount of abamectin by 20% with guaranteed control effect. Abamectin is mainly used to control mites, various Lepidoptera pests and aphids. The reduced dosage will certainly delay the development of resistance of the pests and prolong its service life.