Colombia is overhauling its anti-drug strategy, aiming to boost voluntary coca eradication to replace U.S.-backed aerial spraying of the crop.

President Juan Manuel Santos unveiled the strategy Tuesday. He said growers who abandon coca will get assistance to support alternative crops. Forced manual eradication will be used as a last resort.

Santos said in May that he was ending aerial spraying, a fixture of the drug war for two decades. The announcement came shortly after a research arm of the World Health Organization reclassified the herbicide used as a probable carcinogen.

The coca plant produces the base ingredient of cocaine. The U.S. government says the amount of land under coca cultivation in Colombia rose 39 percent in 2014 to 112,000 hectares (about 276,000 acres).