The most likely causes are dry soil conditions, soggy wet soil (poor drainage means roots can't get oxygen), root injury (it would take major physical injury perhaps due to a root rot), or damage from a weed and feed product used in the area of the plant. There is no cure for weed killer damage except time and proper care. The remedy for a soil moisture extreme is obvious. I suggest you contact the Travis County Extension Office (512.854.9600) and see about taking some photo to them or e-mailing some photos for them to help. There is no charge for their services.
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