The hills surrounding Sinaí, a village in southwest Colombia, are blanketed in a green patchwork, ranging from the bright chartreuse of coca-plant seedlings to a darker clover color that indicates the leaves are ripe for picking and processing into cocaine.

It is areas like this that have helped to boost Colombia's estimated cocaine output 37 percent since 2015 to an all-time high of 710 tons in 2016, according to the U.S. government. Some 188,000 hectares of land are now planted with coca, up from a low of 78,000 in 2012.

One reason for the rise seems counterintuitive: the signing last November of a peace deal between the government and the FARC rebel group. It was supposed to reduce coca cultivation; the FARC had extorted a tax on coca crops and trafficked cocaine, and under the peace deal it is to support the government's eradication efforts.

But the deal's terms were years in the crafting, and many of its provisions were clear well in advance — including that there would be payments for coca farmers who shifted to different crops. The government created a perverse incentive to plant more.

And as the peace talks progressed, the government scaled back aerial crop spraying — according to its critics, in order to placate the FARC. In 2015 it suspended spraying entirely, citing a study by the World Health Organization concluding that glyphosate, the herbicide dumped out of planes, was "probably carcinogenic."

Instead, Colombia's government is putting its faith in crop substitution. It is aiming at a cut of 50,000 hectares in the area under coca cultivation this year in 40 municipalities.

If a community signs up, each family will receive subsidies and assistance of about $7,800 in the first year that they eradicate their coca, and will be helped to acquire title to the land and to find other means of support. In areas where no deal is struck, the army may come in to root up plants by hand.

Since the end of January, more than 58,000 families representing 49,000 hectares of coca have signed up. But suspicion born of long disappointment is holding others back.

In Argelia, the municipality to which Sinaí belongs, no one has agreed to take part. Marcela Montoya, of Ascamta, a peasant organization in Argelia, says that although the region's coca growers are in principle willing to switch crops, they doubt the government's promises. They should reduce their coca production only gradually, she said, and wait and see whether the government comes through.

Generations of Colombian coca farmers have subscribed to alternative-development programs intended to support the transition from coca, only for funding to dry up.

In 2015, unarmed farmers in Argelia clashed with soldiers and government eradicators, burning the bus they were riding in. One farmer was shot dead and five others, as well as two soldiers, were injured. The government's intention is that the FARC's cooperation will help to lessen such resistance.

As the guerrillas relinquish territory and make the transition to civilian life, it hopes that they will encourage farmers to make the switch away from coca. The FARC has shown a "clear and definite" commitment to convincing peasants to give up coca, said Eduardo Díaz, the government's director for crop substitution. Mauricio Jaramillo, a FARC commander in Guaviare Province, said the guerrillas will have more influence than the government, because in many parts of the country coca growers have relatives who are members.

But the FARC was never the only armed participants in the drug trade. As the group withdraws, other criminal groups are moving in, including the National Liberation Army, a smaller guerrilla outfit. Argelia's coca farmers have a new slogan: "resistance" — to both the eradication pacts and the new armed groups trying to muscle in.

Some U.S. officials said they think that stopping aerial crop-spraying was a mistake. Barry McCaffrey, a retired general who oversaw Plan Colombia, the United States' 15-year-long anti-drugs effort in the country, under President Bill Clinton, told El Tiempo, a daily, that "the minute they decided to stop aerial fumigation they lost control over the problem." But the Americans are not publicly advocating a return to spraying.

Colombia currently seems determined to attack the problem on the ground, farm by farm. It needs quick successes to build trust among coca growers and calm U.S. fears. In the longer term, though, so long as the world retains its taste for cocaine, farmers and gangsters will find a way to satisfy this demand. Those who spray are no match for those who pay.