MAZAMARI, Peru (AP) — About four times a day, a single-engine plane drops onto a dirt airstrip in the world's No. 1 coca-growing valley. The planes deliver cash and pick up cocaine. Then they fly back to Bolivia.

Police say roughly half of Peru's cocaine has departed this way since the Andean nation became the world's top producer in 2012.

Drug corruption is rife in Peru. But an Associated Press investigation found the narco-flight plague to be a failing of Peru's military because it controls the remote Apurimac, Ene and Mantaro river valley where the planes land.

A new law gives Peru's air force the go-ahead to begin shooting down drug planes. But its fate is in doubt as the government scrapped plans to buy the state-of-the-art radars needed for the job.