Commit to supervisory and leadership training.
Schedule your new supervisor to shadow another supervisor.
Communicate clearly to your field crew who the new supervisor is.
Not all thoroughbred workers want to be a supervisor. In fact, if you have any really hard-working employees who are making good money, without the pressures of being the boss, dont be surprised if these workers are not interested. We need good workers at all levels and besides, hard-working employees are informally leaders among their peers, so dont be too quick to push them to formally lead.
Finally, dont take the selection and more importantly, training, of the next supervisor lightly. No matter whom you choose, they will make mistakes and will have conflicts on the field level with employees, vendors and customers. Your objective should be to educate your leaders to be professional in all situations, not giving way to anger or foolish talk.