Thiamethoxam seed treatment for control of rice thrips (Chloethrips oryzae) and its effects on the growth and yield of rice (Oryza sativa)

Rice thrips (Chloethrips oryzae Williams) is one of the key pests of rice (Oryza sativa L.), and is usually controlled by labor-intensive foliar sprays of agrochemicals under field conditions. To reduce labor intensity and increase the utilization of agrochemicals, thiamethoxam seed treatment was studied as a simple and accurate control technology for C. oryzae. Field plot experiments were conducted to investigate the control efficacy of three methods of thiamethoxam seed treatment for C. oryzae, and their effects on growth and yield of rice in 2014-2016. Excellent control of C. oryzae was achieved using thiamethoxam 350 FS (flowable concentrate for seed treatment) seed treatment at a rate of 70 g ai/100 kg of seeds, at 17-28 days after sowing. Better control of leaf-tip rolling was observed when for seed treatment application rice seeds were soaked firstly in water for 8-10 h and then dried at room temperature, then coated with thiamethoxam 350 FS solution, soaked again in water and germinated (method A) or when rice seeds were coated firstly with thiamethoxam 350 FS solution, soaked in water and germinated (method C) than when rice seeds were soaked firstly in water for 8-10 h and then plus thiamethoxam 350 FS solution, then soaked again in water and germinated (method B). Field observations indicated that thiamethoxam seed treatment at this rate had no negative effects on the timing or percentage of seedling emergence, establishment, and key seedling characteristics including plant height, root length, and fresh above-ground and underground weight. However, rice yields of thiamethoxam seed treatment were increased significantly compared to untreated control. These results suggested that treatment of rice seeds by thiamethoxam using the method A or C was more effective against C. oryzae than using the method B for up to 28 days after sowing under field conditions. Use of thiamethoxam seed treatment was not phytotoxic to rice and represents an important alternative for C. oryzae management in the crop.