2017 ASHS Annual Conference

Sweetpotato, Ipomoea batatas (Olivier), is an important staple food crop in Hawaii and critical to food security in these geographically isolated islands. Production of this crop faces a new challenge from the rough sweetpotato weevil (RSW), Blosyrus asellus, (Coleoptera: Curculionidae). This pest was first detected on a commercial sweetpotato farm on the island of O‘ahu in 2008, with subsequent detection on the island of Hawai‘i in 2014. In contrast to other weevil pests of sweetpotato in Hawai‘i whose immature stages (grubs) feed inside the storage roots, the grubs of rough sweetpotato weevils feed on the surfaces, severely damaging their appearance and reducing marketability. We conducted replicated trials over two growing seasons to compare efficacy of four insecticides (Sevin, Belay, BotaniGard, Provado) against a control treatment. During first season (2015), Insecticidal treatments showed statistically significant differences (P<0.05) in percent of all damaged storage roots. Plots treated with Sevin or Belay had significantly lower percent of damaged storage roots compared to the other three treatments when plots were harvested 4.5 months after planting. Overall mean percent of damaged roots varied from 19.9 ± 8.0 % (Belay) to 51.9 ± 8.5 % (Control). During second season, the overall treatment differences were marginal (p=.05); but comparison of means showed that Sevin- and Belay-treated plots had comparable results to that of first season. Percent of damage was significantly higher during second season (P<0.05) probably because of the proximity of the study area to the previous season’s study area. The range of damage was also higher during second season (39.0 ± 12.1 % (Sevin) to 78.1 ± 5.75 % (control)) compared to the first season 10.68 ± 5.3 (Sevin) to 51.94 ± 8.5 (control)). A similar trend was observed when severity of the damage on the storage roots was assessed visually. Plots treated with Belay and Sevin had fewer percent of storage roots with high damage compared to other three treatments. Based on these two field trials conducted on the Hamakua coast of Hawaii Island, both Sevin and Belay appear to be potential candidates for the chemical control of the rough sweetpotato weevil.