Efficacy of Chlorantraniliprole for Control of Two Sweetpotato Weevil Species, 2019
Arthropod Management Tests
Section Editor: John Palumbo Potato (sweet) | Ipomoea batatas Sweetpotato weevils (SWC) | Cylas formicarius F. West Indian sweetpotato weevil (SWE) | Euscepes postfasciatus (Fairmaire) The objective of the study was to evaluate the efficacy of chlorantraniliprole for the control of two serious root pests of sweetpotato, sweetpotato weevils (SWC), and West Indian sweetpotato weevil (SWE), in an experimental field of the Okinawa Prefectural Agricultural Research Center, located in Itoman on the
... inawa Island, southern Japan, for the summer cultivation of the crop in 2019. A total of 18 plots were established. Each consisted of six rows of 3.0 m with 0.8 m spacing were made, and three treatments were randomly assigned to them in six replications. Slips of sweetpotato 'Tamayutaka' with strong resistance against foot rot disease of sweetpotato (Ichinose, personal observation) were purchased at a commercial market in Ina City, central Japan, and 10 were planted on each ridge with 0.3 m spacing in individual plots on 14 Jun. Thus, there were 60 slips in each plot. Chlorantraniliprole of 5.0% (FMC Chemicals, Tokyo, Japan) was compared for its efficacy on the reduction of infesting weevils and root injuries by the weevil with chlorpyrifos in granular form (Nissan Chemical, Tokyo, Japan) and an untreated check. Chlorpyrifos was applied with 2 g on the ground surface around the main stem of every plant as officially registered in Japan. These insecticides were applied two times during the cultivation, on 24 Aug and 5 Oct, equivalent to 250 ml/ha diluted 4,000 times for the former and 60 kg/ha for the latter. Roots of four plants randomly selected in each plot were harvested on 26 Dec, and tubers ≥ 100 g and the rest of the root system of each plant were weighted at a precision to 0.1 g individually. The roots were dissected to collect and count infesting weevils for each species. Holes made on the root surface when they had emerged were counted, although the species that had made the hole could not be identified. This made the total number of weevils in a given plant larger than the sum of SWC and SWE. The efficacy of insecticide treatments was evaluated by ANOVA and Tukey's HSD tests (P = 0.05) on the number of weevils infesting the root and the proportion of the weight of weevilinjured roots to that of the entire root system of the plant. In these analyses, the weevil numbers, root weight, and injury proportion were passed through square-root, natural logarithmic, and the rootsquare arcsine transformed, respectively. All means in this report were calculated on non-transformed data. Insecticide compounds, formulations, and application rates are provided in Table 1 . Fewer SWE were detected than SWC in all treatments. The occurrences of SWE were higher in the untreated check, but the difference from the insecticide treatments was not significant. However, both SWC and the sum of both weevils were significantly higher in the former than in the latter, and no significant differences were detected between the two insecticide treatments. Root yield was significantly less in the chlorantraniliprole treatment. Mean root injury in the untreated check was 49.5, 25.5, and 68.