Don't fertilize. Just cut away the discolored foliage to the ground and pull back the mulch. Never feed a sick plant. Check your mulch source. This looks like some sort of scorch, either from the late frost you mention, from gases being released from the (undercomposted) mulch, or from the chemicals on the lawn. Don't overwater, just keep an eye on the plant and let it recover. It may disappear for this year, but will most likely recover and reappear just fine next year.
