Integrated Management of Sitona lineatus with Nitrogen Fertilizer, Rhizobium, and Thiamethoxam Insecticide

The pea leaf weevil (Sitona lineatus L.) (Coleoptera: Curculionidae) is a serious pest of field pea (Pisum sativum L.) and faba bean (Vicia faba L.) (Fabales: Fabaceae) in Europe, Asia, Africa, and North America. Foliar feeding by adults and root nodule consumption by larvae reduces seed yield and N contributions to the soil. Foliar insecticides have limited efficacy against pea leaf weevil, prompting this study to investigate an integrated approach. Nitrogen fertilizer, Rhizobium inoculant, and thiamethoxam (systemic insecticide) were assessed alone and in combination for their effects on pea leaf weevil damage to field pea plants and seed yield. Nitrogen fertilizer did not reduce foliar feeding but did reduce root nodules by 35 to 43%. In 2008 only, N fertilizer improved yield by 0.48 t ha−1 relative to nonfertilized plots. Thiamethoxam seed treatment reduced foliar feeding for 40 to 50 d after planting in 2008 and 2009 but had no significant impact on seed yield. Rhizobium inoculation increased yield by 0.74 t ha −1 compared to noninoculated plots in 2008. No effects of N fertilizer, Rhizobium inoculant or thiamethoxam on yield were observed in 2009, probably because root nodule damage was not affected by any treatment. Results of this study suggest that the most efficient method of preventing yield loss due to S. lineatus infestation is to inoculate field peas. Further investigation of thiamethoxam, preferably in large-scale production systems, is required to better understand the efficacy of thiamethoxam against pea leaf weevil.