Hard to be certain the cause. Could be FMV. Regardless, I'd recommend some mild fertilizer. Not overly heavy on nitrogen. Maybe 10-10-10 (or any flat ratio fertilizer like that). Good luck with it.
Mike central NY state, zone 5a
p.s. watch to see if there are any particular insects on it too. If so, treat with something mild. Looks more like FMV to me though. Regardless, things that improve overall health tend to reduce the symptoms of FMV.