Bean pod mosaic virus, soybean mosaic virus, alfalfa mosaic virus, and tobacco streak virus are the viruses most commonly found in the symptomatic plants. To make things more complicated, two or more soybean viruses are often found in the same plant. Multiple infections pose the greatest risk of reduced yield and grain quality.

Each virus is part of a plant-virus-insect complex
Viruses are submicroscopic particles of DNA or RNA that cause disease in plants. They are different from other pathogens in that they can grow and reproduce only inside living cells. They are spread from plant to plant by insects. Each type of virus is part of a unique plant-insect-virus relationship. Recognizing the virus as part of a complex is the key to effective management.

Figure 1. Mosaic pattern in soybean leaves due to infection by the Bean pod mottle virus. Photo credit: Palle Pederson, Iowa State University.

The soybean aphid is able to transmit several soybean viruses in Wisconsin. Click on image to view a larger version.

Insect vectors
Two soybean insect pests, the bean leaf beetle and the soybean aphid, have been increasing in numbers in Wisconsin and throughout the Midwest. In addition to damage caused by direct feeding, both of these pests are capable of transmitting specific soybean viruses from plant to plant. The soybean aphid (Aphis glycines) was identified in late summer of 2000 as a new pest species on soybean in North America. The increasing numbers of bean leaf beetle (Cerotoma trifurcata) is thought to be due to the milder winters in recent years.