This measure relieved Farnese from his present peril and he resolved to take advantage of the siege of Montobbio to get possession, in advance of the imperial troops, of some feuds of the Fieschi. He seized Calestano, and then sent Gianantonio Torti with a strong force to occupy Valditaro. As the Fieschi had some imperial vassals in these feuds, Farnese informed Gonzaga that he wished to hold them for the interests and rights of the empire. He did not wait for an answer, but hurried his troops into the feuds. His designs upon Valditaro were thwarted by Scipione and Cornelio Fieschi, who threw themselves into it with about one thousand of their vassals and shut the gates in the faces of the Ducal forces. He called Scipione to himself in Piacenza and persuaded him that the forces of his family were too weak to contend with the empire. Scipione consented that the duke should occupy the castle in the interest of his family. He returned to his vassals and persuaded them to enlist in the service of Farnese, who sent his agent, doctor Giovanni Landemaria, to take possession in his name. The acts of the notary Bartolomeo Bosoni clearly prove these facts.
Gonzaga was enraged at this stratagem of Farnese; and in fact the occupation was of short duration. On the death of Farnese, Valditaro was created a principate by the emperor and passed to Agostino Landi whose ancestors had once held it. The inhabitants always retained their love for the Fieschi house, and remembered long the mild government of their old masters. They several times conspired to restore Scipione who was born among them. In 1552, Gonzaga, incensed at these movements, instigated Landi to dismantle the forts and towers lest they should afford a place of refuge for the Fieschi.
More than ten thousand balls had been thrown at Montobbio; but the Fieschi, safe in their defences, laughed at the rage of the assailants and their own fire often seriously damaged the enemy. The people of the surrounding country scarcely concealed their sympathy for the besieged and furnished the castle with meat and provisions of every kind. The commissioners of the Republic complained of this and said that the inhabitants of Bargagli, Stroppa and other villages never brought even an egg to the camp of the Genoese, while they gave liberal supplies to the enemy. Spinola, despairing of success in the siege, united with the commissaries in urging the government to attempt a new negotiation.