The strategos of Bari, Eugenius, captured the town of Avellino, besieged Capua, and then Benevento.
In 977, after the Pandulf's release, he joined his father in an expedition in defense of Monte Cassino against the predations of Count Bernard of Alife.
However, the Emperor Otto II, who was in the Mezzogiorno at the time, fighting the Saracens, dispossessed Landulf of the duchy of Spoleto and gave it to Thrasimund, duke of Camerino and count of Penne.
Thereafter, Landulf IV was merely prince of Capua, in which capacity he supported the Cluniac reform and founded the church of San Croce at Caiazzo.
He joined his deposed brother Pandulf II in Calabria, where they fought the Saracens with Otto.