Purdue University | Indiana CCA

Proceedings 2008

Indiana Certified Crop Adviser Conference


SBA Node Counting and Economic Thresholds

Since the invasion of soybean aphid into the North Central Region in July 2000, soybean aphid has become a key limiting factor in profitable soybean production. Soybean aphid has the potential to reduce yields by 50% so it is a pest that must be controlled. The question is how many is too many aphids? But given the volatility in soybean prices over the past couple of years, it is often assumed that because soybean prices are high that the Economic Threshold (ET) must be lower. In reality the ET is not lower which is counter intuitive. In the presentation I hope to demonstrate why the ET is not lower. What has happened is that the Economic Injury Level (EIL) is indeed lower, which means you have less time between the ET and the EIL. We will explore why “insurance” treatments can lead to unintended consequences (retreatment) and why a lower ET is not something the economic entomologists in the Midwest support.

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David Ragsdale Professor, Director of Graduate Studies
University of Minnesota

David W. Ragsdale eared a Ph.D. (1980) in Entomology from Louisiana State University, Baton Rouge, LA where he worked on IPM of soybean insects. He joined the Entomology Department at the University of Minnesota in 1981 and is currently a full professor and Director of Graduate Studies in Entomology. His research has focused on vector ecology with an emphasis on aphid-transmitted viruses. With the recent invasion in the northern Great Plains of the soybean aphid, Ragsdale and his students have focused their research on the management of soybean aphid. His lab led the regional research that resulted in the current economic threshold for soybean aphid of 250 aphids per plant. This threshold is widely adopted throughout North America. In addition, he has collaborated broadly with scientist involved in biological control of soybean aphid, regulation of aphid populations by abiotic (weather) and biotic (predators and disease) factors and has helped soybean breeders across the region screen their advanced selections for resistance to soybean aphid.