Efficacy of transplant insecticides against black cutworm Agrotis ipsilon (Lepidoptera: Noctuidae) in tobacco

The black cutworm, Agrotis ipsilon (Lepidoptera: Noctuidae), is a critical soil pest of tobacco (Nicotiana tabacum) in the early season. Although numerous studies have shown that chemical insecticides through soil-surface or foliar application provide adequate management of black cutworms, relatively little is known about the efficacy of transplant applications. Here, we evaluated the efficacy of insecticide transplant treatment against black cutworm in tobacco in pots and in the field. We also investigated the impact of chlorantraniliprole on tobacco, including dynamic residue concentrations in tobacco and variation in agronomic traits of treated seedlings. Bioassays showed that LC50 of chlorantraniliprole was 0.28 mg AI/L against black cutworm. In a potted plant experiment, chlorantraniliprole treatment at 15, 30, and 75 g AI/ha reduced the number of damaged tobacco seedlings and increased the mortality of black cutworm within 30 d. When tobacco seedlings were treated with chlorantraniliprole 24 h before transplanting in the field, the control efficacy of chlorantraniliprole treatment at 75 g AI/ha was 45.5%–59.6% at 20 d after treatment. The concentration of chlorantraniliprole in tobacco seedlings treated with 15 g AI/ha was found to degrade to 0.033 mg/kg after 28 d (t1/2 = 2.54 d), which affected the height of seedlings but not the number of leaves after 28 d. Chlorantraniliprole treatment of seedlings during transplanting is a practical and effective strategy to manage black cutworm in tobacco.