Effect Of Clothianidin Seed Treatment And Granular Application At Bud Stage On Sucking Pest In Cotton Field

Widespread adoption of Bt cotton has successfully controlled cotton bollworm, but piercing-sucking insects, such as cotton aphid, mirid bug and whitefly, have become the major insect pest in Bt cotton field in China. In currently, the main control measures for pest mangement are foliar spraying for smallholder of China. However, foliar spraying has a relatively short effect on pest, and frequent spraying have side effects on natural enemies as well as a high labour cost. Therefore, the new control method for managing pest in cotton field need be reseached. In the study, we evaluated that effect of clothianidin seed treatment and spot application at bud stage on cotton aphid Aphis gossypii(Glover), green plant bug Apolygus lucorum(Meyer-D�r), whitefly Bemisia tabaci(Gennadius) and other suking insects in cotton field. In addition, the dissipation of clothianidin in cotton leaves and soil was determinated. Impact of this control method on natural enemies, plant growth and yield was also assessed. The results were shown as follows:1.Clothianidin seed treatment at the rate of 400 g a.i./100 kg seeds could effectively control A. gossypii at the seedling stage of cotton, and also had some efficiency of A. lucorum. The peak of A. gossypii occurred at 41 days after sowing(on June 7): and the number of A. gossypii in clothianidin seed treatment reached 2400.9 per 100 plants, far lower than that in untreated control, 15617.7 per 100 plants. At the peak, the percentage of curly-leaf was suppressed at 5.5 %, much lower than the economic threshold of A. gossypii.2.Clothinidin spot application at bud stage effectively could control A. lucorum at the bud stage and at the flower and boll stage, and also had some control effect of B. tabaci, Frankliniella intonsa(Yrybom) and leafhopper. The number of A. lucorum in clothianidin spot application at the rate of 0.9, 1.8 and 3.6 kg a.i./ hm2 was significantly lower than that in untreated control beginning at 14 days after application and there were no significant differences in number of A. lucorum among the three rates of clothianidin. The peak of number of A. lucorum occurred at 103 days after sowing(DAS): when the number of A. lucorum in untreated control was 39.1 per 100 plants and by contrast, that in clothianidin spot application treatments were 11.7, 7.5 and 9.2 per 100 plants at the rates, respectively. The leaf injury indexes by A. lucorum in clothianidin spot application treatments were significantly lower than that in untreated control. After application of clothianidin granular, the number of B. tabaci adult and nymph, F. intonsa and leafhopper in clothianidin spot application treatments were lower, but the differences were not always significant. The number of B. tabaci adult at 118 and 125 DAS, B. tabaci nymph beginning at 97 to 125 DAS, F. intonsa at 97 DAS, and leafhopper beginning at 104 to 125 DAS in clothianidin spot application treatments were significantly lower than that in untreated control.3. Clothianidin seed treatment and spot application at bud stage had some side effects on natural enemies in Bt-cotton field. At the seedling stage, the number of ladybeetle, lacewing and hoverfly in clothinidin seed treatment tended to lower than in untreated control, and these differences were significant for ladybeetle adult at 27 and 32 DAS, ladybeetle larvae beginning at 22 to 41 DAS, lacewing at 41 DAS and hoverfly beginning at 27 to 41 DAS. At the bud stage and at the flower and boll stage, the number of ladybeetle adult beginning at 75 to 124 DAS, ladybeetle larvae beginning at 82 to 110 DAS, lacewing at 89, 96, 117 and 124 DAS, hoverfly at 82 and 89 DAS, predatory bug at 89 and 117 DAS and spider at 103 and 124 DAS in clothianidin spot application treatments were significantly lower than that in untreated control.4. The dissipation of clothianidin in soil could be simulated by the first-order reaction kinetics model equation. The equations were as follows: clothianidin seed treatment, C = 1.660e-0.0.0344t; clothianidin granular application at the rate of 0.9 kg a.i./hm2, C = 695.3e-0.0799t; at the rate of 1.8 kg a.i./hm2, C = 682.8e-0.0655t; at the rate of 3.6 kg a.i./hm2, C = 1619e-0.0687 t. At the seedling stage, the dissipation of clothianidin in clothianidin seed treatment was very slow, and the half-life(t1/2) was 20.15 days. After application of clothianidin granular, the dissipation of clothianidin in clothianidin spot application treatments were relatively fast, and t1/2 was 8.67, 10.58 and 10.09 days, respectively. At the last harvest(at 185 DAS): clothianidin was still detected in soil and the concentration of clothianidin at the three rates was 0.005?0.011 and 0.027mg/kg, respectively.5. The dissipation of clothianidin in cotton leaves was fast. The concentration of clothianidin was 0.940 mg/kg at the first sampling(at 16 DAS) and it had reduced to 0.010 mg/kg. After application of clothianidin granular, residues of clothianidin in cotton leaves increased rapidly, and at 21 DAS it reached the highest value, 0.855, 1.073 and 1.555 mg/kg at the rate of 0.9, 1.8 and 3.6 kg/hm2, respectively. Then, the residues reduced rapidly, and it was 0.005, 0.006 and 0.008 mg/kg at 124 DAS(at 63 days after granular application).6. Clothianidin seed treatment and spot application at bud stage could protect cotton plant to grow well and protect cotton from yield loss. The plant height in untreated control was significantly lower than that in clothianidin seed treatment caused by A. gossypii. Until at 82 DAS, the differences were not significant in plant height among these treatments. Cotton yields in the treatments of clothianidin seed treatment and spot application at bud stage were significantly higher than that in untreated control and clothianidin seed treatment used singly. The average number of cotton bolls per plant in clothianidin seed treatment and spot application were significantly higher than that in untreated control, but there were no significant differences in the average boll weight between untreated control and clothianidin seed treatment and spot application.