The photo shows areas of necrotic tissue. There can be a number of causes for this. Winter sun/wind/cold damage is probably the most common. When the leaves roll tightly in response to cold temperatures, the area along the leaf midrib is left exposed and causes areas of leaf tissue to dry out severely and die. Caterpillars can also be a cause as can some fungal infections. All in all, the leaves look quite healthy so physiological winter damage seems the most likely cause.

Thank you very much for your response. We did have a rough winter and these plants are sometimes subjected to high winds. I agree he overall condition appears healthy, but I was concerned that the discoloration might be the beginning of a disease.

I appreciate you providing your opinion. Thanks