What would make half of an azalea hedge die?
I have a hedge of azaleas all along the front porch. Those on the right of the walkway thrive while those to the left of the walkway have all died. This happened once before. I treated the ground for nematodes, waited and then replanted. They have all died again. Both sides get equal irrigation.
I would first recommend a soil test. Then you can determine what the soil needs or may need to be corrected.
Your local county extension office can help you with a soil test.
Have you used any chemicals on the walkway or porch area?
I have listed a link to help you find an extension office near you.