Over the past several weeks, we have received several samples in the Plant and Insect Diagnostic Clinic with irregular blotches and necrotic lesions on the pods.
After eliminating all of the known causes, a sample was screened for several common bean viruses*. The sample came back strongly positive for tobacco streak virus (TSV).
This virus was first identified in Iowa and the United States in 1967. The soybean plants with “pods showing necrotic spots” were noticed in late-planted soybeans. From this earlier report, TSV reduced the number of pods per plant and delayed seed maturation. Other symptoms include stunting, bud blight, leaf mosaic (mottling), dwarfed leaves and stem discoloration. This virus is mainly seed transmitted and several thrips species have been reported as TSV vectors.
If you have soybean pods with similar symptoms, you can send them to the ISU Plant and Insect Diagnostic Clinic. Confirmation of TSV costs $50.
*Testing service provided by Agdia, Inc.