Officials said the attack on the farmworkers occurred Sunday in a remote area known as Tierra Caliente, which spans from Guerrero state into Michoacan state, the Los Angeles Times reported.
In Chihuahua state, officials said gunmen killed the editor of an online newspaper Sunday in Ojinaga.
Local media reported seven people were killed Monday by armed assailants in Sinaloa state.
The Tierra Caliente area is home to the Knights Templar cartel, which has scared off residents in a string of small towns, creating "ghost pueblos," the Times said.
Guerrero also is challenged by so-called autodefensa groups -- masked and armed men who have shown up in the troubled state and elsewhere, promising to bring vigilante justice in areas they claim aren't adequately protected by the government, the Times said.
In Chihuahua, gunmen killed the editor of an online newspaper Sunday in Ojinaga. Jaime Guadalupe Gonzalez, who ran an online news site, was shot 15 times as he went to his office, local media reported.
"This site has been suspended," Ojinaga Noticias posted Monday afternoon. "Please come back later."
In Sinaloa, four police officers in El Rosario were kidnapped from a guard booth, the Times reported. Their bodies were found along with the bodies of three civilians.