Potatoes are confronted with a wide range of pathogens wherever they are grown. The infection of the crop and spread of the disease is influenced to a large degree by the climatic conditions, individual weather episodes, and the susceptibility of the cultivar being grown. Black dot gets its name from the black, dotlike structures called stroma that form on the stems of dying plants. The disease survives as stroma and can become severe when potatoes are grown continuously. The common scab organism is a filamentous bacteria and a low-grade saprophyte that survives on plant material in the soil and may infect a fairly broad host range. Early blight is a fungal disease found in all potato growing regions and is most severe in areas of high humidity and frequent rainfall. The disease, late blight, caused by Phytophthora infestans, is the most famous and widely spread of the potato diseases.