WAINGMAW, Myanmar—The cultivation of opium poppy and production of methamphetamine in these lawless, northern hinterlands have long made Myanmar one of the centers of the world’s drug trade. Now they are posing an early test for Aung San Suu Kyi’s incoming democratic government.

Christian antidrug vigilantes are asking Ms. Suu Kyi’s party, set to take power in a week, to intervene in a clash with villagers who don’t want to see their undulating hillsides of opium poppies destroyed.

Violence between the two groups in recent weeks, ahead of Myanmar’s harvest season, has injured dozens and underscored the difficulty of controlling the rugged borderlands, where rival factions and business interests thrive.

“I thought I was going to die, I was so afraid, I just kept praying to God,” said Mon Aung, a 42-year-old volunteer with the mostly Baptist Pat Jasan group. He was shot on a recent poppy-clearing mission and was recuperating on a shabby hospital bed in Myitkyina, the capital of Kachin state.

“But even if I died, I would have died for my people and my country,” he said.