By Jack Kaskey (Bloomberg)

June 25 -- Monsanto Co., the world's biggest seed producer, dropped the most in eight weeks in U.S. trading after third-quarter profit from corn seed trailed analyst expectations.

Monsanto fell $8.96, or 6.6 percent, to $126.83 at 11:58 a.m. in New York Stock Exchange composite trading. A close at that price would be the biggest decline since April 29. The shares of the St. Louis-based company doubled in the past year through yesterday.

Net income in the three months ended May 31 increased 42 percent to $811 million, or $1.45 a share, on sales of Roundup weed killer and soybean seeds, Monsanto said today in a statement. While earnings topped the $1.35 average estimate of 15 analysts surveyed by Bloomberg, results from corn, Monsanto's most profitable seeds, were worse than analysts from Banc of America Securities and JPMorgan Chase & Co. had projected.

"The gross margin in seeds and traits was down 1 percent, and when a stock is up 100 percent in a year, people are looking for any reason to sell," Michael Pento, who helps manage $1.7 billion, including Monsanto shares, at Delta Global Advisors Inc., said from Holmdel, New Jersey.

Gross profit from corn seeds and related genetic licenses increased 6.6 percent to $565 million in the quarter, Monsanto said in the statement. JPMorgan analyst Jeffrey Zekauskas said in a report he had estimated $746 million.

Sales of corn seeds increased 9.4 percent to $975 million, less than estimated by Banc of America analyst Kevin McCarthy. Full-Year Earnings

Monsanto full-year earnings forecast also may have disappointed some investors, Zekauskas said.

Profit in the year ending Aug. 31 will rise to about $3.40 a share, excluding one-time items, Monsanto said. That's higher than a March forecast of $3.15 to $3.25 a share and trails the $3.41 average estimate of 15 analysts in the Bloomberg survey. Sixteen analysts surveyed by Thomson Financial had estimated $3.39, on average.

"We expect the stock to trade down given the consistent- with-consensus 2008 EPS guidance and weak corn seeds results," Zekauskas said in the report. He rates the shares "hold" and McCarthy rates them "buy."

Net income in the third quarter a year earlier was $570 million, or $1.03 a share.