Field control efficiency of pelleted radish seeds with insecticides against Myzus persicae and the degradation dynamics

To clarify the control efficiency of thiamethoxam and flonicamid pelleted radish seeds against Myzus persicae and the degradation dynamics of thiamethoxam in the field after seed pelleting, the germination of radish seeds after pelleting treatment with different insecticide-to-seed ratios and their field control efficiency against M. persicae were analyzed. The residues of thiamethoxam in different parts of radish plants and the rhizosphere soil were determined. The results revealed that the germination rates of radish seedlings after pelleting with thiamethoxam and flonicamid at insecticide-to-seed ratios of 1∶100 and 2∶100 under field cultivation conditions ranged from 83.39% to 89.71%, and those under plug transplant conditions ranged from 97.22% to 100%, which were not significantly different from those of the control. After pelleting, the population occurrence of M. persicae were significantly lower than those of the control group, and the effect lasted for more than 30 days. The field control efficiencies of the different pelleting treatments against M. persicae were as follows: thiamethoxam 2∶100 > thiamethoxam 1∶100 > flonicamid 2∶100 > flonicamid 1∶100. The thiamethoxam residue in the soil and different plant parts first increased but then decreased. The maximum concentration in the soil reached 0.016 mg/kg on the 4^th day after seeding, and those in the roots and leaves reached 0.035 mg/kg and 0.079 mg/kg, respectively, on the 7^th day after seeding. The thiamethoxam residues in the different parts were as follows: leaf > root > soil 4 to 10 days after sowing and root > leaf > soil 14 to 28 days after sowing. The degradation half-lives of thiamethoxam in the soil, roots and leaves were 2.60 d, 3.40 d and 1.25 d, respectively. Seed-pelleting with thiamethoxam is safe and feasible for radish production and exerts excellent control over M. persicae. This study provides an effective solution for the prevention and control of the aphids in cruciferous crops at the seedling stage.