The stump does NOT have to be ground out, but stumps with bark intact from infested/diseased tree removal may not extend more than 3” above the ground. If the stump is taller than 3”, it must be completely debarked. Shade tree pests can continue to reproduce beneath the bark of a stump, allowing for the infestation/infection of other nearby healthy trees. If the stump is in a high traffic or mowed-and-maintained area, you may want to consider removing it for aesthetic or safety reasons. However, it is not necessary for insect/disease control.