Symptoms of plant disease are frequently insufficient for accurate diagnosis of tobacco diseases. Pathogen identification has traditionally involved microscopic examination of affected plant tissue and/or culture techniques to "bait out" the pathogen in the laboratory. Serological assays are now available that provide accurate and robust methods for diagnosing important tobacco diseases, such as tobacco black shank (Phytophthora parasitica var. nicotianae); damping-off, sore shin, and target spot caused by Rhizoctonia solani ; damping-off and root rots caused by Pythium species; and Granville or bacterial wilt (Ralstonia solanacearum). Assays are also available for many tobacco viruses (Tobacco Mosaic Virus, Tomato Spotted Wilt Virus, Impatiens Necrotic Spot Virus, Cucumber Mosaic Virus, Potato Virus Y, etc.). More specific and accurate techniques based upon polymerase chain reaction (PCR) technology are available, but these methods must typically be performed in the laboratory. A number of commercial plant disease diagnostic kits are now available that can be transported to tobacco greenhouses and fields enabling accurate, on-site diagnosis within 15 to 30 minutes. The formats of most currently available serological assays require refrigerated storage, but are very simple to perform, require minimal reagents and equipment, and have shelf-lives of approximately 12 months. The use of on-site serological assays to identify tobacco pathogens has significantly improved the speed and accuracy of tobacco disease diagnosis in Virginia. More accurate identification of tobacco pathogens has improved disease management by focusing use of crop protection agents and disease-resistant tobacco cultivars on where they are truly needed.