Canna rust is a fungal disease of canna caused by Puccinia thaliae. Symptoms include yellow to tan spots on the plant's leaves and stems. Yellow spore-producing structures called pustules are produced on the lower (abaxial) leaf surface, and these are the signs of the disease. Spots on the upper leaf-surface coalesce and turn to brown-to-black as the disease progresses. The infected leaves eventually become dry and prematurely fall.