Brussels - The European Commission has opened an in-depth investigation into a proposed 66-billion-dollar takeover of US agrochemical company Monsanto by German pharmaceutical giant Bayer over competition concerns.

The commission said on Tuesday that the merger could reduce competition in several areas because it would create the largest integrated pesticides and seed company in the world.

"Seeds and pesticide products are essential for farmers and ultimately consumers," said Margrethe Vestager, European commissioner for competition.

"We need to ensure effective competition so that farmers can have access to innovative products, better quality and also purchase products at competitive prices."

The commission to decide whether to give the merger green light

Specifically, the commission has concerns that the merger could reduce competition in the production of pesticides, breeding of vegetable seeds, and the development of useful traits such as height, disease tolerance and herbicide tolerance.

The commission has until January 8 next year to decide whether to give the merger the green light.

The merger has been under scrutiny by competition watchdogs around the globe - a request for US approval is currently pending.

The so-called "mega-merger" has not been welcomed by environmentalists and other aid organisations.

Monsanto has been heavily criticized for its genetically altered produce and use of the pesticide glyphosate.