The Salzburg Festival opened Thursday for the first time in more than three decades without conductor Herbert von Karajan, who died earlier this month. President Kurt Waldheim opened the five-week festival with a tribute to Karajan, the former Berlin Philharmonic maestro, who died July 16 at age 81. “The man Herbert von Karajan is missing, but his musical work will survive,” Waldheim said. A black flag flew in mourning for Karajan, a native of Salzburg who had conducted at the festival since 1948. Sir Georg Solti then conducted Verdi’s opera “Un Ballo in Maschera,” with Placido Domingo in the starring role.