disable automatic space advisor in oracle 11G

BEGIN
  DBMS_AUTO_TASK_ADMIN.disable(
    client_name => 'auto space advisor',
    operation   => NULL,
    window_name => NULL);
END;
/

Also, take a look at : select * from DBA_AUTOTASK_CLIENT

See also metalink note : 11g: Scheduler Maintenance Tasks or Autotasks (Doc ID 756734.1)