Help! My Hibiscus mutabilis 'Rubrus' seems to be dying stem by stem. Whole stems wilt, turn yellow, and wilt and die. I applied insecticide after a heavy watering, but still I am losing this long term garden resident, and don't know what may be wrong. Could it be borers? If a wilt disease, would it collapse shoot by shoot? Sorry I can't post a photo of this large, prized plant. I will probably take cuttings from still healthy shoots in case the plant dies.

I can usually find a way to get a reportedly sterile hibiscus to set seed, but not the above described 'Rubrus'. This plant seems more sterile than other "sterile" hibiscuses.