This type of problem is easy to fix either by preparing a better seed bed or by planting specialty beans in a field with a low infestation. Conventional tillage also can reduce seedling disease problems if no-till fields are involved. Seed treatment can be another effective fix. Some seedborne diseases cause discoloration in harvested seeds, which may affect seed quality of specialty beans. One type of discoloration is purple seed stain caused by Cercospora kikuchii .
Infected seeds have seed coats with purple blotches.
The stage of this disease in the summer is called Cercospora leaf spot, a fungal disease that has recently increased in importance. The fungus survives in infected seeds or soybean debris and during the growing season infects soybean seeds at pod set. To avoid purple seed stain, one should not save seeds from infected soybean plants because this disease is seedborne. If the seed coat has a purple discoloration, it is an indication of infection. Planting infected seeds may cause emergence problems and result in further buildup of the disease on new crops.