Economic Benefits of Additive Insecticide Applications for Root Maggot Control in Replanted Sugarbeet

Abstract

Multiple factors can necessitate replanting of sugarbeet, Beta vulgaris (L.). Later-established plants in replanted fields will typically be smaller and more vulnerable to herbivory by insect pests than those established at earlier, more conventional planting dates. A field study was conducted during 2004, 2007, and 2008 in Pembina County, North Dakota to determine if additive insecticide protection is warranted to manage sugarbeet root maggot (SBRM), Tetanops myopaeformis (Roder), in replanted sugarbeet fields initially protected by conventional at-plant insecticide applications. Replanting with supplemental at-plant applications of terbufos 15G and chlorpyrifos 15G reduced SBRM feeding injury and increased root yields by 8.4 to 11.9 Mg/ha. Replant applications of terbufos 15G, applied to plots initially established with at-plant chlorpyrifos 15G, resulted in 32.2% and 34.8% more root and sucrose yield, respectively, and generated $405 more gross economic return per hectare than the stand-alone at-plant application of chlorpyrifos 15G. Postemergence liquid insecticides provided slightly less consistent control and yield benefits than granular insecticides applied at replanting, although the disparities rarely involved significant differences in gross economic return. The results of this investigation show that additive insecticide applications in replanted sugarbeet provide significant reductions in SBRM feeding injury that translate to major increases in yield and economic return. This study also demonstrates the economic