Rust caused by the fungus Melampsora is the most serious disease in short rotation coppice (SRC) willow plantations for renewable energy. Willows (Salix) are grown as a major SRC crop  for energy because of their yield potential and coppicing ability. In most willows, rust only infects expanded leaves (left picture). However, in some willows, such as Salix viminalis and S. caprea, rust also attacks stems and young leaves. When severe, rust defoliates susceptible plantings prematurely (right picture) and reduces yields by as much as 40%. Severe rust also predisposes plants to infections by secondary pathogens which may lead to death of the plants.