Control Threshold on Sweet Potato, Ipomoea batatas L., Damaged by the West Indian Sweet Potato Weevil, Euscepes postfasciatus (FAIRMAIRE) (Coleoptera: Curculionidae)

<Author> Keiji YASUDA
<Year> 1997
<Journal> Jpn. J. Appl. Entomol. Zool.
<Volume> 41
<Issue> 4
<Pages> 201-207
<Notes> Japanese

To obtain the control threshold for the West-Indian Sweet Potato Weevil, the relationship between the occurrence of sweet-potato stems injured by the larvae and the proportion of damaged tubers at harvest was studied in both insecticide-treated and untreated plots. The ratio of damaged tubers at harvest was high in plots where injured stems occurred early and/or the proportion of injured stems was high. The regression equation, Y=20.83+0.95X(r=0.639) expresses the relationship between the proportion of damaged tubers at harvest (Y) and the percentage of injured stems on day 75 day after planting (X). Based on this modified equation, the control threshold level of stems injured during the growing period for a tolerable injury level (13.6% of tubers damaged at harvest) was estimated to be 5%. The insecticide application for this control threshold was as effective as the conventional application; three applications could be reduced to two.