Effects of Selected Low-Risk Insecticides and Rainfall Rate on Bemisia tabaci Population and Pepper Yellow Leaf Curl Indonesia Virus Incidence on Chili

Pepper Yellow Leaf Curl Indonesia Virus (PepYLCIV) is a damaging chili disease in Indonesia. Chili growers depend on synthetic insecticides to control the disease by suppressing its vector population, Bemisia tabaci Genn. This study assessed the efficacy of several low-risk insecticides in suppressing the B. tabaci population and PepYLCIV incidence during the dry and rainy seasons. Treatments consisted of different insecticide active ingredients, namely: Abamectin, azadirachtin, imidacloprid, deltamethrin, and spinosad. Each chemical was applied with three application frequencies: Once weekly, twice weekly, and unsprayed control. Each insecticide was applied through foliar spray at the rate recommended by the respective manufacturer. The treatments were arranged in a split-plot design, application frequency, and active ingredient served as the main plots and sub-plots, respectively. Each treatment combination had four replications of a plot each. Data were analyzed using ANOVA and Duncan’s multiple range test (p = 0.5). In the rainy season, the vector population decreased as the season progressed with increasing rainfall. However, the PepYLCIV incidence continuously increased throughout the season. This seemed to be due to the initial disease infection taking place when the rainfall rate was low and the B. tabaci population was high early in the season. In contrast, during the dry season, the vector population and PepYLCIV incidence went up as the season progressed due to the decrease in the rainfall rate. All insecticides tested were effective in controlling the disease and its vector. One and two weekly applications provided the same efficacy of the pest control, thus, the current local farmers' practice of 2-3 applications per week is unnecessary.