I have a row of about eight gardenia plants that are about three years old. They are a lower growing variety but not the true dwarf. Last month they suddenly defoliated and the stems are split as if by cold damage. We have had some cold but these plants have never reacted this way. Usually the leaves are damaged and sometimes drop but I've never seen this symptom in them. I have looked for a gall but don't see one. Other unaffected plants in the area are azaleas, hollies, pittosporum. Thanks for any advice.