Puccinia helianthi

Puccinia helianthi is a macrocyclic, autoecious rust fungus that causes sunflower rust, also known as common rust or red rust, producing orange-brown and yellow-orange lesions on cultivated and wild sunflower plants. The disease develops readily under modest conditions, needing as little as eight hours of leaf wetness and temperatures between fifteen and twenty five degrees Celsius, making it a recurrent threat in sunflower-growing regions. It is the primary rust disease of sunflower and can substantially reduce both seed quality and yield when conditions favor its spread.