Humala called the emergency measure after farmers began an indefinite strike Sunday, blocking a major highway that connects the Ucayali department with the rest of the country, El Comercio reported Wednesday.
The strike is a response to the government's policy of forced eradication of coca leaves, the main ingredient in cocaine.
Humala's government temporarily suspended the eradication of coca last month as a drug-control strategy.
The declaration will last 60 days and gives police more power to make arrests and suspends some constitutional rights.
Peru is the largest producer of coca worldwide, officials said.