Sequential Application of Various Insecticides for the Management of Cotton Bollworm (Hubner) Helicoverpa armigera (Lepidoptera: Noctuidae) in Cotton Production
Background: Cotton bollworm (Hubner) (Helicoverpa armigera) (Lepidoptera: Noctuidae) is a major constraint to cotton production and productivity in Ethiopia.
Objective: To determine the best spray sequence of various insecticides as a strategy of resistance management of the pest.
Materials and Methods: Field experiments were conducted during the 2017 and 2018 main cropping season at Werer Agricultural Research Center. Eight different insecticides (chlorantraniliprole, deltamethrin, chlorfenapyr, lufenuron+profenofos, chlorpyriphos, lambda-cyhalothrin, profenofos, and alphacypermethrin) belonging to five major insecticide classes were systematically arranged in six treatments and three spraying sequences along with a control treatment. The experiment was laid out as a Randomized Complete Block Design and replicated four times per treatment. Data were collected on bollworm population, damaged squares, flowers, and bolls at pre and post insecticide application, boll number per plant, and seed cotton yield. Using the modified Abbott’s formula, the percent efficacy was computed.
Results: Significant differences (P<0.05) were observed among the treatments for post spray larvae count, damaged squares, and boll counts in the 2017 and 2018 cropping seasons. Sequential and rotational application of a cocktail of the insecticides, namely, chlorantraniliprole, chlorfenapyr, profenofos, and chlorfenapyr, chlorantraniliprole, lufenuron+profenofos resulted in the best control with 81.8% and 76.4% of H. armigera larvae controlling efficacy. The lowest average cotton boll number (9.69/plant) and cotton yields (2.24 ton/ha) were obtained from the unsprayed treatment.
Conclusion: Applying the insecticides in sequence increased seed cotton yield by 36.2% and 33.9% compared to the yields obtained from the unsprayed plots. The results imply that rotational use of insecticides with different modes of action is the best strategy to control the pest.