The Impact of Insecticides on Soybean at Flowering on Beneficial Insects

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It is important not to use insecticides in soybeans before thresholds are reached (including at bloom for corn earworm or stink bug). All effective insecticides for stink bugs will negatively impact natural enemies. We need to scout these pests and treat only when thresholds are reached.

Click on this link to understand why we should not treat corn earworm during bloom and covers the reasons why I encourage growers to use Prevathon/Vantacor and Besiege/Elevest in cotton, but not in soybean. We also have a new insecticide (Denim) that is very effective for earworms and loopers this year in addition to Blackhawk, Intrepid Edge, or Steward.

My research counterpart Anders Huseth recently posted an article on the impact of plant bug and bollworm insecticides on beneficial insects in cotton. We have similar information for soybean from work done in both Virginia and North Carolina. Beneficial insects are important in the system because they act as bio-residual to hold back potential pests that might flare up later in the season. Therefore it is important that we keep them around as much as possible. This article demonstrates the potential danger of throwing an insecticide in the tank before pests reach threshold.

In the Virginia and North Carolina experiment, we tested two “worm specific” insecticides (the equivalent of Prevathon/Vantacor) against a check and a “worm + stink bug” insecticide (the equivalent of Besiege/Elevest) in six fields. The graph below provides an example of the kind of effects we saw.

Because the Besiege/Elevest insecticide had a pyrethroid included with the worm-specific insecticide, we decreased natural enemies far past the time-point of our spray. This reduced our bio-residual and opened us up to other pests similar to results of the trial highlighted in this post. In that trial, wherever we applied a pyrethroid we flared looper populations compared to where we did not.

 A graph showing four different treatments for natural enemies along with the number of Natural enemies per 30 inches over a 21 day period.

Natural enemy numbers were significantly decreased over time where the worm + stink bug insecticide (Besiege/Elevest) was used compared to the worm-specific insecticide.