Screening of Insecticides and Application Methods for Controlling White Grubs in Next Generation Dryland Rice

Purpose This study aimed to screen effective insecticides, optimal dosages, and application methods for controlling white grubs in next generation dryland rice (NGDR) fields, to evaluate their field efficacy, providing a reference for pest management in production.

Methods Field experiments were conducted in the NGDR planting area of Lancang Lahu Autonomous County, Puer City, Yunnan Province. Various chemical and biological insecticides were applied at two key growth stages (sowing and jointing stages) using methods such as granule broadcasting, seed-dressing, and root irrigation. The control effects against white grubs were evaluated by investigating the damaged plant rate, damage index, and the control efficacy during the rice harvest.

Results White grub damage significantly reduced the effective panicles, grains per panicle, and seed-setting rate of NGDR, leading to yield losses ranging from 31.13% to 60.53%. At the jointing stage, root irrigation with 50% clothianidin (630 g/hm²) and 25% thiamethoxam (3150 g/hm²) showed the best control, with damaged plant rates of 30.86% and 29.89%, and damage index of 15.23 and 12.97, respectively. At the sowing stage, broadcasting 2% lambda-cyhalothrin·clothianidin (75 kg/hm²) and 0.5% clothianidin (60 kg/hm²) achieved the best overall efficacy, with damaged plant rate as low as 4.67% and 2.00%, damage index of 1.17 and 0.83, and control efficacy of 94.89% and 96.35%, respectively. Comparing the two periods, the control efficacy of soil treatment (granule broadcasting) at the sowing stage was significantly superior to that of root irrigation at the jointing stage.

Conclusion Broadcasting neonicotinoid granules such as clothianidin at the sowing stage is the most effective strategy for controlling white grubs in NGDR, as it establishes a protective barrier during the early stages of larval infestation. Root irrigation at the jointing stage can serve as an emergency control measure, with clothianidin or thiamethoxam being recommended. In practice, insecticide rotation is necessary, and attention should be paid to the potential risks of neonicotinoids to non-target organisms like bees and the environment.