A picture might help to see better what is happening and you could also send a branch to your County Extension office to better diagnose the problem.

The plant must be in the ground. Is the area very wet most time? Wet root and over water can promote root rot. I have seen in wet field of camellia plantation in Sichuan, China. They dig trenches at either side for drainage.

Too much sun and poor soil can also cause problem. Even you water the plant but the root gets little water. Prolonged condition would cause the root branches of deterioation and poor plant.

With all the common sense, I think you can fix the problem.