On April 28, 2011, Victor Burgos went out after lunch to pick the corns of pepper plants growing on his farm in Putumayo, Colombia, when a plane flew overhead and dumped a fine spray of liquid all over his land. Within a year, he lost more than half of his food crops—primarily peppercorn, but also yucca, pineapple, plantain and more. His yearly income dropped nearly 80 percent, while the soil of his 250 acres overlooking dense tropical forests is now irrevocably polluted. His water sources are contaminated too.

The plane, he later found out, was flown by the counternarcotics division of the Colombian National Police, and the spray was an herbicide meant to eradicate illicit crops like the coca plants used to make cocaine and opium poppy; the fumigations were a part of the notorious—and notoriously ineffective—“Plan Colombia.”

Plan Colombia is a joint effort by the Colombian and U.S. governments, initiated in 1999 to end the armed conflict, ongoing since the 1960s, between left-wing guerrilla groups like the Revolutionary Armed Forces of Colombia and governmental forces. The rebels got a lot of their funding from those illegal crops, and the government wanted to cut it off.

But for years, the plan has proved fruitless, according to the Washington Office on Latin America. Though 4.32 million acres have been sprayed since 1994 (when test fumigations began), the program has had very little success in stopping coca production. If anything, it backfired; the coca fields continued to flourish. In 1997, Colombia became the world’s primary cocaine producer and held that title for 16 years. According to the United Nations Office on Drugs and Crime, from 2013 to 2014, the total cocaine production in Colombia rose 52 percent, from 290 to 442 metric tons.

Meanwhile, more and more evidence suggests the herbicide used, glyphosate, is toxic. The U.S. Environmental Protection Agency says long-term exposure can cause respiratory problems, kidney damage and infertility; in March 2015, the World Health Organization’s International Agency for Research on Cancer ( IARC) put out a report suggesting that it causes cancer. Despite the criticism the report garnered from some (including many inside the agrochemical industry) for relying on relatively thin evidence, Colombia’s Narcotics Council agreed to stop the fumigation plan. After nearly 20 years of international and local pressure, Colombia may finally stop spraying carcinogens on its own population in October. Until then, the poison rain continues to fall.