Shoots may die back for any number of reasons including water-logging at roots, frost damage, disease problems or general lack of plant nutrients such as potash or phosphates.
Wilting at tip of shoot gradually moves down the stem.
Treatment and control
General tips: Cut back stem below the dead area, but just above a bud. Feed plant in summer with a balanced plant food such as Miracle-Gro Rose & Shrub Plant Food to encourage new strong growth.