Prior to the discovery of the soybean aphid, researchers at the University of Wisconsin-Madison have been researching the cause of several abnormal symptoms of unknown cause common to soybean in Wisconsin. Major symptoms include changes in leaf and pod appearance that frequently are confused with symptoms caused by post-emergence herbicides. Plants with abnormal leaf phenotypes are commonly produce fewer pods, mottled seed, and have stems that remain green while other plants in the field mature normally. Seed from symptomatic plants may have mottled seed coats resulting from hilum pigments “bleeding” into the seed coat. Viruses were regarded as causes of mosaic or mottle leaves and mottled seed. The cause of “green stems” at harvest has remained unresolved.