Answer: Small black things could be insects (black bean aphids, flea beetles, etc.) or they could be a sign of disease. Without knowing which, it's difficult to suggest a control measure. I'd first try hosing them off with a strong stream of water. If they return, collect a few in a plastic baggie and take them to your local Master Gardener clinic or a well staffed nursery for identification and control suggestions. Best wishes with your petunias.
Q&A Library Searching Tips