Most seedborne pathogens can cause substantial reductions in yield or quality in the subsequent crop. However, some diseases such as late blight, ring rot and leafroll have the potential to spread quickly through the crop and are therefore considered to be particularly important. Since late blight was present in some seed production areas during 1994, there is a significant danger that some seed tuber lots sold for planting during 1995 will have tuber blight. The purpose of this bulletin is to help seed and commercial growers identify tuber blight, and to minimize the chances that late blight inoculum will be introduced into production fields on seed tubers.