The European Commission has launched an in-depth probe into Bayer's $66bn (£51bn) takeover of Monsanto, saying the two agro-chemical giants failed to address the watchdog's antitrust concerns.

EU authorities worry that the deal – which would create the world's largest seeds and pesticides company – could reduce competition and result in 'higher prices, lower quality, less choice and less innovation'.

Bayer and Monsanto both submitted plans to address those concerns at the end of July, but the Commission said those commitments were 'insufficient to clearly dismiss its serious doubts as to the transaction's compatibility with the EU Merger Regulation'.

Brussels will now launch an in-depth investigation into whether competitors will find it more difficult to access distributors and farmers once Bayer and Monsanto bundle together their pesticide and seeds businesses.

Authorities said access was particularly worrying given the rise of 'digital agriculture', which sees companies collect information about farms in order to deliver tailored advice or aggregated data to farmers – a business that both Bayer and Monstanto have been exploring.

It comes amid a series of global deals that have effectively shrunk the agribusiness market, including ChemChina's $44bn (£34bn) takeover of Syngenta and the $130bn (£101bn) merger of Dow Chemicals and Du Pont.

The EU's competition commissioner Margrethe Vestager said: 'Seeds and pesticide products are essential for farmers and ultimately consumers.

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

'And at the same time maintain an environment where companies can innovate and invest in improved products.'

It throws a spanner in the works for German pharma giant Bayer, which had been courting the US crops and seeds specialist for months before reaching a deal with Monsanto last September.

Bayer said at the time that sales in the combined agriculture business would be worth as much as 23bn euros (£21bn), based on 2015 figures, adding that its annual research and development budget could total 2.5bn euros (£2.2bn).

The EU Commission said it is now cooperating closely with antitrust watchdogs in other markets where Bayer and Monsanto operate, including the US, Australia, Brazil, Canada and South Africa, to conduct its probe.

A decision is expected after January 8 2018.