Bayer has asked the European Union to approve its $US66 billion ($85 billion) combination with Monsanto, the last of a trio of mega-deals reshaping the global agrochemicals industry.

The German chemical giant's filing kickstarts an initial review with an August 7 deadline. Bayer said it's still seeking to close the deal "before the end of 2017," a sign the company is hoping to sidestep a lengthy second phase probe that could add a further four months to the process.

The Brussels-based commission extracted extensive concessions before clearing Dow Chemical $US77 billion merger with DuPont and China National Chemical's $US43 billion takeover of Swiss pesticide maker Syngenta.

The deals have drawn intense scrutiny, with regulators saying they want to ensure fewer suppliers of crop-protection products and other critical inputs for farmers won't lead to higher prices that could push up the cost of food for consumers. The EU also looked at how merging Dow and DuPont might harm research efforts.

Monsanto chief executive Hugh Grant said earlier this week he still expects the deal to win competition approval in Europe, China, India and the US by the end of 2017. BASF SE and Syngenta are among companies that have submitted preliminary bids for assets Bayer plans to sell in order to get regulatory approval for its takeover, according to people familiar with the matter.

Bayer has already filed for approval in the US and the Justice Department could require additional asset sales to resolve competition concerns.

Agricultural businesses have been dogged by falling crop prices globally. Bayer has said it expects a slight recovery in the seed and crop protection market this year, though it expects the industry to remain volatile. Falling crop prices and a quest for greater efficiency triggered a cascade of deals in the industry.