The hollow statue, which juts out of a mountainside in Benguet province, lost its eyes, nose and forehead in the blast, as well as a large chunk of its right cheek.
The identity of the perpetrators remains unclear. Suspects include left-wing activists, members of a local tribe - or possibly looters hunting for one of Marcos' legendary treasure troves.
The bust was built in the early 1980s when Mr Marcos was still in power, but fell into disrepair after he was overthrown in a popular revolt in 1986.
He died in exile three years later.
'Sad' Imelda
The bust had been the cause of controversy ever since its inception - in part because its construction led to the displacement of members of the Ibalois tribal group.
After Marcos fled the Philippines, Ibalois tribesmen slaughtered a water buffalo and bathed the statue with its blood to "exorcise" his spirit.
The former president's widow Imelda Marcos said in a statement she was "very sad" to hear of the destruction.
The Marcos family remains under investigation in connection with human rights abuses carried out under their rule, and the government alleges that they robbed the nation's economy of up to $10bn.
Imelda Marcos is to be tried next month on charges of hoarding millions of dollars, illegally acquired, in overseas banks.
Rumours circulate in the Philippines that the Marcos family also stashed treasure in various locations around the country, possibly explaining why looters might have wanted to examine the inside of the bust.
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