Management of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), in Iowa

Johnson, Kevin
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In North America, the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae) is a pest of soybeans, Glycine max (L.) Merrill. The main goal of this research was to verify the preliminary economic threshold for A. glycines management in Iowa. Secondary goals included; verifying an alternative sampling techniques for estimating A. glycines populations, evaluating the effect of planting date on A. glycines population growth, and investigating the potential of managing both C. trifurcata and A. glycines with a single insecticide program. In 2004-2005, replicated experiments were established at three locations. Results from both years indicate that there is no detectable effect on soybean yield from an insecticide (lambda-cyhalothrin) application made below the current 250 A. glycines per plant economic threshold. Insecticide applications made at 250 A. glycines per plant protected yields when A. glycines populations continued to increase in the control treatment. The insecticide treatment triggered by a binomial sequential sampling (speed scouting) technique resulted in soybean exposure to A. glycines and soybean yield equal to the insecticide treatment applied using an enumerative sampling technique. Insecticide applications triggered by either enumerative sampling or speed scouting resulted in higher yields compared to control treatment when A. glycines populations reached 250 A. glycines per plant. A delay in soybean planting did not result in differences in soybean exposure to A. glycines. However, in both 2004 and 2005 yields in the late planting dates were not protected by insecticide applications. In 2005, foliar insecticides applied based on threshold of 250 A. glycines per plant reduced aphid exposure and protected yield better than preventative insecticide applications (seed treatments). Emphasizing the importance of insecticide timing when managing A. glycines, a foliar formulation of imidacloprid, was applied at threshold of 250 A. glycines per plant reduced A. glycines exposure and had greater yield protection than when imidacloprid was applied as a seed treatment. Experimental evidence from this research supports the current recommendations for soybean aphid management in Iowa (weekly scouting and a foliar insecticide applied when mean populations reach 250 A. glycines per plant on at least 38 plants and are increasing).