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 different 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 action thresholds at 100 and 250 aphids per plant will help build producers' confidence by demonstrating which one provides higher yields/returns. The role of the Ragl aphid resistant soybean in management of soybean aphids in ND will also be determined. Soybean cyst nematode is becoming more common in ND and it is a major pest that negatively impacting soybean yield.
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. 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.

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North Dakota Soybean Council
Management of Soybean Aphids and Interaction with Soybean Cyst Nematode
Executive Summary – June 30, 2017

Investigators:
Dr. Janet J. Knodel, Extension Entomologist, Department of Plant Pathology, NDSU
Dr. Sam Markell, Extension Plant Pathologist, Department of Plant Pathology, NDSU
Cooperators:
Dr. Ted Helms, Soybean Breeder, Department of Plant Sciences, NDSU
Mr. Patrick Beauzay, Research Specialist, Department of Plant Pathology

The overall goal of this work is to provide soybean producers with the integrated pest management (IPM) strategies necessary to successfully manage two devastating pests: soybean aphids and soybean cyst nematode (SCN). By understanding and implementing IPM strategies to manage these pests, soybean yields can be maximized while minimizing environmental impacts due to unnecessary pesticide applications.

The first goal of our research was to compare different pest management strategies, including the use of an insecticide seed treatment, early (R1) foliar insecticide applications and a Rag1 aphid-resistant variety, to a foliar insecticide application made at the economic threshold of an average of 250 aphids per plant. Due to repeated rounds of strong storms with heavy rainfall and high winds, soybean aphid populations throughout the area did not establish and remained very low throughout the 2016 growing season. Because of this, the economic threshold (ET) of 250 aphids per plant was not reached in 2016. However, the following conclusions were determined:
• The use of an insecticide/fungicide combination seed treatment did not demonstrate a significant yield difference compared to the use of a fungicide seed treatment alone.
• Use of a fungicide only seed treatment should be considered in fields with a history of soil-borne fungal pathogens that can be controlled by the active ingredients in the seed treatment.
• The application of a foliar insecticide at R1 did not demonstrate a significant yield difference.
• Weather events can and do provide natural soybean aphid control.
• For best pest management, soybean producers should scout for soybean aphids regularly through the growing season and wait until the ET is reached before making an insecticide application.

The second goal of our research was to examine the interaction of SCN populations in SCN resistant and susceptible varieties to different soybean aphid densities (aphid free, economic threshold, and untreated). Due to the lack of soybean aphids in 2016, we were unable to assess the interaction between soybean aphids and SCN. However, for best pest management of SCN, the use of a SCN resistant variety significantly decreased SCN population growth through the growing season, and resulted in a significant higher yield gain, average of 14 bu per acre, over the SCN susceptible variety.