Determining pest and pesticide interactions as a means to optimize soybean yield

Soybean cyst nematode (SCN), Heterodera glycines Ichinohe, and soybean aphid (SBA), Aphis glycines Matsumura, are significant pests of soybean and can cause substantial yield losses.  Farmers can now use resistant soybean varieties to manage SCN and SBA.  Nematicidal and insecticidal seed treatments can further suppress pest activity.  We studied combinations of resistant soybean varieties for SBA and SCN with different seed treatments.  The field study was conducted at two different locations in Iowa in 2013 and 2014.  Our goal was to determine how these integrated pest management approaches affect soybean yields and pest abundance.  In 2013, we found that resistant soybean varieties suppressed populations of SBA and SCN.  However, the use of a nematicidal and insecticidal seed treatment did not provide additional pest suppression.  Regression analysis showed that higher SCN populations at the time of harvest were strongly correlated to lower soybean yields.  Also, we discovered that the seed treatments did not significantly improve yield compared to untreated seed.  Results from 2014 will also be presented.