The leaves (its a spruce) are turning brown, drying out and falling off. The area where I did not spray is healthy. I continue to water it but am wondering if it will re-generate or if there is something else I should be doing?
Not all species are compatible with all sprays. I am not sure about this species, especially since you have not specified what you have sprayed with.
I suspect that the damaged area will not recover, but there is no point in pruning it right now. I may be wrong, or the dead area may offer some design possibilities.