By Luis Jaime Acosta

BOGOTA, Nov 11 (Reuters) - Colombia is seeking a less toxic herbicide to restart aerial fumigations of coca crops, the director of the national police said, after the Andean country halted spraying with the chemical glyphosate due to health concerns.

The government said in May it would call off aerial spraying of coca plants, which are used to make cocaine, because of World Health Organization warnings that the chemical is carcinogenic.

"We are looking for a different herbicide to glyphosate that will be effective for controlling and neutralizing illicit crops, particularly the coca leaf, so it stops being a risk for people's health and the environment," General Rodolfo Palomino, the head of the national police, told Reuters on Tuesday.

"It's not easy, but it's also not impossible," he said. "The challenge is finding an herbicide that can be dropped from planes without collateral damage."

The police force is experimenting with various chemicals, Palomino added, and hopes to find the right one so it can restart fumigations.

Fumigation had been key to the U.S.-supported anti-drug strategy in Colombia, which produces over 440 tonnes of cocaine annually. Spraying reduced illegal crops by some 70 percent between 2000 and 2013.

The police continue to use glyphosate in manual eradication because it is less risky to human health and the environment than aerial fumigation, Palomino said.

Coca cultivation was up 44 percent in 2014 to 69,000 hectares (170,500 acres) according to the United Nations. The United States predicts the trend will continue this year.

Following the end of a two-decade spraying policy, Colombian authorities have shifted focus in the fight against narcotics production to crop substitution and drug use prevention.

Local communities have expressed concern that exposure to glyphosate has caused illnesses, including cancers and birth defects. Colombia was the only South American country still using the chemical before spraying was halted, authorities have said.

Glyphosate is also a key ingredient in Monsanto Co's Roundup, the world's most widely used herbicide.

Monsanto, which is facing several lawsuits related to the safety of glyphosate, has said repeatedly that regulatory authorities agree the chemical does not cause cancer. (Reporting by Luis Jaime Acosta, writing by Julia Symmes Cobb; editing by Helen Murphy and G Crosse)

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