Inadequate soil preparation can worsen drought problems, because the roots cannot move through the soil quickly enough and far enough to absorb the limited amounts of moisture in the soil. The humid Southeast is a haven for these problems. Diseases, especially fungi, love humidity. They attach to leaves, usually in the form of spots, or they attack the roots and cause root rot. Constant watering of leaves encourages leaf spots to develop, while poor water drainage down through the soil exacerbates the root rot diseases.
Insect damage is easier to identify than diseases.
Diligent efforts at scouting eventually will uncover the culprit. However, some insects feed more often at night, including caterpillars and snails. Walking through the garden with a flashlight can pay big dividends. Also, check the undersides of leaves. If you shake the leaves onto a white piece of paper underneath, something will fall off onto the paper.