Ophiognomonia leptostyla

Ophiognomonia leptostyla. This fungus causes yellow, later dark brown spots on the leaves, petioles and walnuts.

recognize blotch and leaf spot walnut tree
Photo: Rasbak – CC BY-SA 3.0

Ophiognomonia leptostyla. Fungus causes yellow, later dark brown spots on leaves, petioles and walnuts. The fungus overwinters in the top buds and on the fallen leaves and husks.

Where to find

  • Walnut Tree


Occurs mostly during cold and wet summers. Clean up fallen leaves and affected husks in autumn.


Prevent disease spread by burning or shredding fallen leaves, affected nuts and branches. Extra fertilization in the fall accelerates the digestion of fallen leaves, which reduces the opportunity for spores to survive the winter.