White, 22, has led Victoria and Australia Under-19s during his short career and was handed the role ahead of Matthew Wood, the opening batsman. White told the club's website: "I am very honoured to be asked to take on this job with Somerset. Obviously I'm sorry for Ian, who is a great guy, and I hope he gets himself fixed and back out on the park."
Blackwell picked up his injury during the Championship match against Leicestershire and needs surgery. He had only just returned to action after a back problem limited his early season action. The time frame for Blackwell's injury means he'll miss out on the Natwest Series against Sri Lanka and probably also the Pakistan series towards the end of the summer.
With Ashley Giles still some way off making a return to international cricket, Blackwell was beginning to cement a spot as England's leading one-day slow bowler with his nagging left-arm spin.
England Domestic Season
County Championship Division Two