The Colombian government on Thursday night said it would halt the toxic fumigation of coca plant fields, defying a U.S.-backed program that has been in place for decades.

In announcing the decision, Colombian health minister Alejandro Gaviria cited concerns that the active ingredient in the herbicide—glyphosate—causes cancer. The World Health Organization reported in March that the weedkiller, widely used in Mosanto’s Roundup products, was “probably carcinogenic to humans.”

Colombian officials have said that a previous Supreme Court ruling in the country called for an end to the aerial spraying program if health concerns over glyphosate were discovered.

Daniel Mejía, the director of the Center for Security and Drug Studies, a research group in Bogotá, told the New York Times on Friday that the spraying operation was “inefficient and counterproductive.”

“I would recommend attacking the links in the chain of drug trafficking, the labs where cocaine is processed, the large shipments of chemicals, which is really where the hard drug trafficking is, where organized crime is,” Mejía told the Times. “It has been shown that attacking the farmers doesn’t work.”

According to Adam Isacson, senior associate for regional security policy at the research group Washington Office for Latin America (WOLA), halting the program was the right move.

“Ending fumigation is the right choice for more than health or ethical reasons. Spraying with glyphosate simply hasn’t worked. For every acre of coca reduced in Colombia, more than 16 have been sprayed,” Isacson wrote in a blog post for WOLA on Wednesday. “The past 20 years have shown that intense glyphosate fumigation can reduce coca-growing in specific areas for limited amounts of time. But populations, lacking other viable economic alternatives, eventually adapt to the spraying, and the crops return.”

Hannah Hetzer at the Drug Policy Alliance details some of the problems with the spraying operations:

Most coca growers are families netting roughly $1,220 per person a year, Isacson writes. Fumigation chemicals in rural areas have “penetrated their residences and left them with nothing to eat. Most of the time, there was no government effort to help those who had been sprayed, not even with basic food security.”

Isacson continues:

The U.S. ambassador in Colombia, Kevin Whitaker, wrote in an op-ed for El Tiempo that the move would not harm diplomatic relations between the two countries.

In an interview ahead of the announcement, Whitaker said, “This is their sovereign decision to make, and we will respect that and we will continue to use the tools that are available to us, as Colombia wishes us to do, to continue to be a partner with them in this fight.”

Still, ending the spraying program will have little effect on the long-term effectiveness of the U.S.-led War on Drugs in Colombia if it is not followed by a concerted effort to reform government services for civilians, Isacson writes.

“If there is no effort to establish and improve the presence of civilian state institutions in Colombia’s national territory, then coca cultivation can be expected to flourish.”