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Soybean aphids are a major economic insect pest of soybeans in North Dakota. The main goal of this research was to develop the best pest management (BPM) practices for insecticide resistant soybean aphids. Soybean aphids that are resistant to pyrethroids (bifenthrin and lambda-cyhalothrin) were detected in eastern North Dakota in 2017. Laboratory bioassays confirmed that about 70% of the soybean aphid populations tested were resistance to pyrethroid insecticides in 2017. In 2018, soybean aphid populations were extremely low throughout the state. So, soybean aphids were only found at only one field site near Emerado for conducting the bioassays. These soybean aphids were highly susceptible to both pyrethroid insecticides as all aphids were dead at the 4-hour mortality assessment. In contrast, soybean aphid populations tested from Emerado in 2017 were found to be resistant to bifenthrin only. This suggests that pyrethroid resistant soybean aphids are mobile and may have migrated from other resistant areas in 2017. Since populations of pyrethroid resistant soybean aphids can vary by year and location, screening more populations of soybean aphids in North Dakota is key to determine their presence or absence, and their resistance status. These findings are essential for soybean growers, so they can wisely decide on which BPM practices to use for soybean aphid control. Insecticide resistant soybean aphids will continue to complicate insecticide management for growers and continued research is critical. Extension education was delivered to >1,500 soybean growers in 2018. A grower evaluation survey showed that 91% of growers who attended plan to use IPM strategies for managing soybean aphids. Growers that used IPM strategies to manage pyrethroid resistant soybean aphids saved an estimated annual cost of $12 million and reduced insecticide input by about 700,000 pounds.
Our last objective was to evaluate the feasibility of using drones to scout for soybean aphids. Drone scouting could improve field scouting efficiency and aid in detecting economic populations of soybean aphids quicker. Unfortunately, the drone with the autonomous probe needed for this objective was not available from the company due to some unexpected problems.