Author(s): Zemedkun Alemu1* , Ferdu Azerefegne2 and Geremew Terefe3
African bollworm (Helicoverpa armigera) (Lepidoptera: Noctuidae) is a major constraint for cotton production and productivity in Ethiopia. The field experiment was conducted during 2017 and 2018 season at Werer Agricultural Research Center aimed to determine the best chemical alternation sequence for insecticide resistance management strategy. It experiment was laid out in a Randomized Complete Block Design (RCBD) with four replications having seven treatments. The assessed parameters were African bollworm population, damaged squares, flowers and bolls at pre and post insecticide application, boll number per plant and seed cotton yield. In this experiment, three round of spray application was made by using insecticides from different chemical class. Using the modified Abbott’s formula, the percent efficacy was computed. A highly significant difference (P<0.0001) were observed among the treatments for post spray larvae count and damaged squares count in 2017 and 2018 season and non-significance difference among (P<0.05) was observed for pre and post spray flower counts in both season of trial. The insecticide rotation chlorantraniliprole, chlorfenapyr, profenofos, and chlorfenapyr, chlorantraniliprole, lufenuron+profenofos gave better control of H. armigera larva, damaged squares and flowers and significantly high cotton yield and the lowest seed cotton yield was obtained from unsprayed treatment. The repetitive use of conventional synthetic pyrethroid insecticides might have assisted the increase of resistance in H. armigera. The study recommended rotational use of insecticides with different mode of actions. Further studies on monitoring of resistance and evaluation of integrated resistance management methods are recommended.
