This research will provide insight into the optimal insecticide management practices for soybean aphid on soybeans grown in ND. It will provide field demonstration plots on the use of insecticidal seed treatments versus foliar-applied insecticides and help producers determine which insecticide strategy is the most efficacious and economical for controlling aphids. This research also will determine how long thiamethoxam seed treatments provide protection against aphid populations, and if a rescue foliar-applied insecticide is necessary later in the season for aphid control. Data on application at the R1 growth stage regardless of aphid densities and on the economic threshold of 250 aphids per plant will help build producers’ confidence by demonstrating which one provides higher yields/returns. The role of the Rag1 aphid resistant soybean in management of soybean aphids in ND will also be determined. Soybean cyst nematode is becoming more common in ND. This research will provide practical information on the interaction between soybean aphids and SCN, increase awareness and help develop viable future recommendations for IPM of these important pests. Being proactive in detecting potential insecticide resistance in populations of soybean aphids in North Dakota is critical for maintaining the effectiveness of insecticides registered for control of soybean aphid. Insecticides are the main strategy of our IPM toolbox that are used for soybean aphid control. An IPM approach will benefit the ND soybean industry by reducing pesticide costs, soybean damage, and risks of soybean pests developing pesticide resistance, thereby increasing productivity and environmental stewardship.

Updated June 30, 2018:
See attached pdf of Technical Report.

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Management of Soybean Aphids and Interaction with Soybean Cyst Nematode

Investigators:
Dr. Janet J. Knodel, Extension Entomologist, North Dakota State University (NDSU)
Dr. Sam Markell, Extension Plant Pathologist, NDSU
Mr. Patrick Beauzay, State IPM Coordinator & Research Specialist, NDSU
Cooperators:
Dr. Ted Helms, Soybean Breeder, NDSU

The overall goal of this research is to provide soybean producers with the viable pest management strategies to control two economic pests: soybean aphids and soybean cyst nematode (SCN).

In our first study, the effectiveness of different pest management strategies for soybean aphid was compared including insecticide seed treatments and foliar-applied insecticides. Two application timings were tested for the foliar-applied insecticides: an early R1 (beginning bloom) and the economic threshold (ET = an average of 250 aphids per plant). Results indicated that soybean producers should scout for soybean aphids regularly during the growing season and wait until the ET is reached before making any insecticide application. In addition, insecticide seed treatments did not provided an increased yield benefit under low or high aphid pressure over the non-insecticide treated seed with a foliar-applied insecticide at the ET.

The second study examined SCN populations in SCN resistant and susceptible varieties and how they are impacted by different soybean aphid densities. The best pest management strategy for SCN was the use of a SCN resistant variety. The SCN resistant variety significantly decreased SCN population growth, and resulted in a significant higher yield gain, average of 24 bushel per acre, over the SCN susceptible variety. Results suggest that keeping soybeans free of soybean aphids can lead to an increase in SCN. Soybean producers should avoid this practice and use the ET for soybean aphid management whether SCN is present or not.

The third study focused on documenting the status of insecticide resistance in populations of soybean aphids in North Dakota. Pyrethroid (an insecticide group) failure for control of soybean aphid was reported in 9 counties in 2017. Aphids collected from these problem fields were used determine if these populations were resistant to pyrethroid insecticides. Laboratory bioassays confirmed that about 70% of the soybean aphid populations tested were resistance to pyrethroid insecticides. Insecticide resistant soybean aphids will complicate insecticide management decisions for producers creating a new challenge for soybean production.