Sevin will kill them,but you'll have to re apply often.Ortho makes a systematic insecticide that works well also.
Here's the thing.They still have to feed to injest the pesticide before they die,so you're still going to have some damage.
The Merit you applied will work great for the grubs that are there now as well as the newly hatching grubs.Watch the beetles.They'll feed,breed,and then fly down to the lawn to lay eggs.Even though you've sprayed your own lawn,your neighbors probably haven't,so you'll still get beetles flying over from their lawn to feed on your ornamentals.
IMHO,you need to get ALL of your neigbors spraying their lawns for the grubs or else,all is in vain concerning your ornamental plants.