Sick Dogwoods - Spray?

I live in a suburb of New York City and have two Dogwoods which appear to be sick. They are close to the street and seem to have suffered the effects of winter salt. They are late to bloom in the Spring and the leaves seem withered and weltered. I've been told that they need to be sprayed.
Any insight/information on what type of spray is necessary as well as any other information on care for these two trees would be appreciated.
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