Monsanto Co., the world's biggest seed maker, said Wednesday its fiscal third quarter net income dropped 45 percent on declining herbicide sales.

Monsanto said cheaper, generic versions of its Roundup herbicide continued to eat into its results.

As Roundup sales have flagged, Monsanto has accelerated its longterm strategy to shift its business from chemcials and herbicides to genetically altered seeds. But the the declines in Roundup has been surprisingly steep, the company has said, as generic competition from China has expanded.

The St. Louis company said its net income dropped to $384 million, or 70 cents a share in the quarter ended May 31, down from $694 million, or $1.25 a share, a year ago.

Analysts had been looking for a profit of 79 cents per share, according to a survey by Thomson Reuters.

Revenue fell to $2.96 billion from $3.16 billion a year ago. Analysts expected revenue of $3.17 billion.

Sales in Monsanto's agricultural productivity unit, which includes Roundup, fell 34 percent to $600 million in the quarter. Seeds and genomic sales, by contrast, rose 5 percent to $2.36 from the same period last year.

Corn seed sales remained flat at $1 billion dollars, while soybean sales rose 2 percent to $549 million.

Monsanto shares slipped 51 cents to $46.83 in premarket trading.