Efficacy of Chlorantraniliprole for Control of Two Sweetpotato Weevil Species, 2019

摘要

The objective of the study was to evaluate the efficacy ofchlorantraniliprole for the control of two serious root pests ofsweetpotato, sweetpotato weevils (SWC), and West Indiansweetpotato weevil (SWE), in an experimental field of the OkinawaPrefectural Agricultural Research Center, located in Itoman on theOkinawa Island, southern Japan, for the summer cultivation of thecrop in 2019. A total of 18 plots were established. Each consistedof six rows of 3.0 m with 0.8 m spacing were made, and threetreatments were randomly assigned to them in six replications.Slips of sweetpotato ‘Tamayutaka’ with strong resistance againstfoot rot disease of sweetpotato (Ichinose, personal observation)were purchased at a commercial market in Ina City, centralJapan, and 10 were planted on each ridge with 0.3 m spacing inindividual plots on 14 Jun. Thus, there were 60 slips in each plot.Chlorantraniliprole of 5.0% (FMC Chemicals, Tokyo, Japan) wascompared for its efficacy on the reduction of infesting weevils androot injuries by the weevil with chlorpyrifos in granular form (NissanChemical, Tokyo, Japan) and an untreated check. Chlorpyrifoswas applied with 2 g on the ground surface around the main stemof every plant as officially registered in Japan. These insecticideswere applied two times during the cultivation, on 24 Aug and 5Oct, equivalent to 250 ml/ha diluted 4,000 times for the former and60 kg/ha for the latter. Roots of four plants randomly selected ineach plot were harvested on 26 Dec, and tubers ≥ 100 g and therest of the root system of each plant were weighted at a precisionto 0.1 g individually. The roots were dissected to collect and countinfesting weevils for each species. Holes made on the root surfacewhen they had emerged were counted, although the speciesthat had made the hole could not be identified. This made the totalnumber of weevils in a given plant larger than the sum of SWCand SWE. The efficacy of insecticide treatments was evaluatedby ANOVA and Tukey’s HSD tests (P = 0.05) on the number ofweevils infesting the root and the proportion of the weight of weevilinjuredroots to that of the entire root system of the plant. In theseanalyses, the weevil numbers, root weight, and injury proportionwere passed through square-root, natural logarithmic, and the rootsquarearcsine transformed, respectively. All means in this reportwere calculated on non-transformed data. Insecticide compounds,formulations, and application rates are provided in Table 1.