Evaluating Increase in Pyrethroid Potency Using an Insecticide Synergist for Alfalfa Weevil Control in Oklahoma
ISSN 2158-9429
Volume 18, Issue 2 - December 2025
Editor: Bindu Poudel-Ward
Abstract
Insecticides are an important component of any integrated pest management (IPM) program and, in most cases, provide a last resort for controlling damaging insect pests. The alfalfa weevil (AW) Hypera postica (Gyllenhal), an invasive insect, is an economically damaging pest of alfalfa in North America. Two-thirds of current labeled AW products are pyrethroids, limiting alternative mode of action (MoA) groups available for alfalfa weevil control in forage alfalfa systems. In addition, their extensive use has led to the emergence of varying levels of resistance to pyrethroids throughout alfalfa producing regions. One option is the use of insecticide synergists such as piperonyl butoxide (PBO) to enhance effectiveness of existing products. The objective of this study was to evaluate increase in pyrethroid potency using an insecticide synergist for alfalfa weevil control in Oklahoma. A field trial was conducted in Stillwater, Oklahoma (Payne County). Six chemical insecticides were evaluated in combination, as stand-alone or PBO tank mixes, for efficacy in controlling AW larvae infesting the first crop of a 5-year stand of “DK A44-16 RR” alfalfa. In all but one PBO tank mix, the synergist did not significantly increase mortality compared to stand-alone products. The highest percentage efficacy for PBO tank mixes was 77% and occurred in a non-pyrethrInsecticides are an important component of any integrated pest management (IPM) program and, in most cases, provide a last resort for controlling damaging insect pests. The alfalfa weevil (AW) Hypera postica (Gyllenhal), an invasive insect, is an economically damaging pest of alfalfa in North America. Two-thirds of current labeled AW products are pyrethroids, limiting alternative MoA groups available for alfalfa weevil control in forage alfalfa systems. In addition, their extensive use has led to the emergence of wide-spread resistance to pyrethroids One option is the use of insecticide synergists such as piperonyl butoxide (PBO) to enhance effectiveness of existing products. The objective of this study was to evaluate increase in pyrethroid potency using an insecticide synergist for alfalfa weevil control in Oklahoma. A field trial was conducted in Stillwater, Oklahoma (Payne County). Six chemical insecticides were evaluated as stand-alone or PBO tank mixes, for efficacy in controlling AW larvae infesting the first crop of a 5-year stand of “DK A44-16 RR” alfalfa. In most treatments, PBO did not increase mortality compared to the stand-alone products. The highest percentage efficacy for PBO tank mixes was 77%. Findings indicate that synergists may improve pyrethroid performance and reduce resistance development, though they are not a universal solution. Effectiveness depends on type and level of resistance, insect genetics, local conditions, product availability and cost, and level of management for this IPM tool.oiInsecticides are an important component of any integrated pest management (IPM) program and, in most cases, provide a last resort for controlling damaging insect pests. The alfalfa weevil (AW) Hypera postica (Gyllenhal), an invasive insect, is an economically damaging pest of alfalfa in North America. Two-thirds of current labeled AW products are pyrethroids, limiting alternative MoA groups available for alfalfa weevil control in forage alfalfa systems. In addition, their extensive use has led to the emergence of wide-spread resistance to pyrethroids One option is the use of insecticide synergists such as piperonyl butoxide (PBO) to enhance effectiveness of existing products. The objective of this study was to evaluate increase in pyrethroid potency using an insecticide synergist for alfalfa weevil control in Oklahoma. A field trial was conducted in Stillwater, Oklahoma (Payne County). Six chemical insecticides were evaluated as stand-alone or PBO tank mixes, for efficacy in controlling AW larvae infesting the first crop of a 5-year stand of “DK A44-16 RR” alfalfa. In most treatments, PBO did not increase mortality compared to the stand-alone products. The highest percentage efficacy for PBO tank mixes was 77%. Findings indicate that synergists may improve pyrethroid performance and reduce resistance development, though they are not a universal solution. Effectiveness depends on type and level of resistance, insect genetics, local conditions, product availability and cost, and level of management for this IPM tool.d combination. Results from this study suggest synergists may have some effect on increase in efficacy and slowing development of resistance to pyrethroids, but they are not a cure all or one size fits all. Effectiveness depends on type and level of resistance, insect genetics, local conditions, product availability and cost, and level of management for this IPM tool.
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