Colombia will resume using weed killer to destroy illegal coca crops less than a year after suspending its use due to cancer concerns, the government said Monday.

The defense minister, Luis Carlos Villegas, said instead of dumping glyphosate from American-piloted crop dusters, as Colombia did for two decades, the herbicide will now be applied manually by eradication crews on the ground.

“We’ll do it in a way that doesn’t contaminate, which is the same way it’s applied in any normal agricultural project,” Villegas told La FM radio, adding he hoped final approval to initiate the work would be completed this week.

President Juan Manuel Santos last year banned use of glyphosate following a World Health Organisation decision to classify it as a carcinogen. The ban was heralded by leftists and members of the Revolutionary Armed Forces of Colombia who have long compared the program to the United States’ use of Agent Orange in Vietnam.

But conservative critics warned that without glyphosate Colombia would soon be awash in coca.

After six straight years of declining or steady production, the amount of land under coca cultivation in Colombia jumped 39% in 2014 and 42% more last year to 159,000 hectares (392,000 acres), according to the US government.

Villegas did not say why the government was switching gears or under what circumstances the weed killer would be applied. But he said a surge in coca production would have a ripple effect on the entire cocaine supply chain, both in Colombia and abroad.

The International Agency for Research on Cancer, a French-based research arm of WHO, reclassified the herbicide as a carcinogen last year, citing evidence that it produces cancer in lab animals and more limited findings that it causes non-Hodgkin’s lymphoma in humans.

Monsanto and other manufacturers of glyphosate-based products strongly rejected the ruling. They cited a 2012 finding by the US Environmental Protection Agency that the herbicide is safe.

Many drug experts have long questioned the cost and effectiveness of glyphosate as coca growers moved to national parks and other areas that are off-limits to its use. Applying the herbicide manually is also expensive since heavily armed police patrols must escort eradicators in dangerous areas dotted with land mines and dominated by criminal gangs.

A better eradication strategy, the experts insist, is the one already in place and which the government has been promising to scale up. In that approach, work crews pull up coca bushes by the roots, thus ensuring plants can’t grow back as happens after exposure to glyphosate.

The decision on glyphosate use comes before a United Nations conference this week in New York to debate global strategies in the drug war.