Cyantraniliprole for the Control of Sweetpotato Weevil, 2017

The objective of the study was to evaluate the efficacy of cyantraniliprole for control of sweetpotato weevils (SW) on tuber in a summer cultivation of sweetpotato, comparing with the conventional insecticide management of the pest with two applications of chlorpyriphos in granular formulation, 2 and 4 mo after the planting. The experiment was carried out in a grower’s farm about 3000 m² in Yaese, about 5 km from the Okinawa Prefectural Agriculture Research Center. On 9 May 2017, fipronil in granular formulation (BASF Japan, Tokyo, Japan) was applied with making ridges at an interval of 80 cm as a conventional preplanting treatment by the farmer. The farm was separated into seven parts after the planting slips of a sweetpotato variety, ‘churakoi-beni’, on this day on each ridge at a 30-cm space. Since the grower did not agree with setting plots without insecticide applications after the planting for control in the same number as the other insecticide treatments, control was assigned to only one part in which three plots were made. In each of the rest six parts, four plots were set and two insecticide treatments were assigned randomly in each part: chlorpyriphos in granular form produced by Nissan Chemical (Tokyo, Japan) or cyantraniliprole of 10.3% by FMC Chemicals (Tokyo, Japan), diluted 4000 times with tap water in volume. Both insecticides were applied two times in this experiment, on 22 Jul and 9 Sep 2017. Thus, two replicates of each insecticide treatment were assigned randomly in each of the six parts. The rest part of the farm was divided into three plots, where no insecticides were treated as control. Each plot covered four ridges, on each of which 26 were planted, and thus, 104 slips were present in each plot. No pesticides other than those examined in this study were applied throughout the cultivation. Three sweetpotato plants were randomly selected in each quadrat on 10 Oct 2017 and dissected to find and count infesting weevils in them. The data obtained after root-square transformation for numeral data and arc-sine for proportional ones were analyzed by ANOVA, followed by Fisher’s protected LSD test at P < 0.05.

Cylas formicarius weevils were collected a lot from sweetpotato plants, especially in no-insecticide treatment. Pupae and adults occurred significantly more in the control than in the two insecticide treatments, whereas no significant differences were detected among the latter (Table 1). Although no significant differences were detected in the total number of weevils per plant among the treatments, both insecticides reduced the occurrence of weevils by half or more.

Almost all tubers were infested in plants of control and three-fourths even in the conventional management by chlorpyriphos (Table 2). Better results were obtained by cyantraniliprole treatment. All measurements other than the weight of damaged tuber were significantly different between control and two chemical treatments, among which no significant differences were obtained in any measurements.

No phytotoxicity on plants was confirmed in any insecticide treatments.

This research was funded by Kyushu Agricultural Research Center.