Apple valsa canker (Valsa mali) is mainly distributed in China, Japan, South Korea, and North Korea. It occurs in all apple production areas in China, particularly in the northern cold areas. Apple valsa canker mainly damages the cortex of apple branches, causing the cortex to rot. This chapter describes the distribution and hazards associated with apple valsa canker before going on to consider the pathogen that causes the disease, including its biology, epidemiology, infection process, and pathogenesis. The chapter considers both resistance to valsa canker and control strategies.