U.S. stocks joined a global selloff, sending the Standard & Poor’s 500 Index toward its first monthly drop since January, as Exxon Mobil Corp. to Micron Technology Inc. tumbled amid weaker corporate results.

Exxon and Murphy Oil Corp. dropped amid concern over output, driving energy companies to the biggest decline among 10 industries in the S&P 500. Micron slid 7.6 percent after earnings from Samsung Electronics Co., the world’s biggest smartphone maker, trailed estimates. Whole Foods Group Inc. dropped 3.4 percent after lowering its 2014 revenue forecast. Kraft Foods Group Inc. declined 4.3 percent after reporting quarterly results that missed estimates.

The S&P 500 slid 1.3 percent to 1,944.22 at 11:15 a.m. in New York, dropping below its average price over the past 50 days. The Dow Jones industrial average declined 184.57 points, or 1.1 percent, to 16,695.79. Trading in S&P 500 stocks was 20 percent above the 30-day average at this time of day.

“The Fed is stepping out of the way and the market’s valuation is high enough that people are quick to take profit,” Wayne Wilbanks, who oversees $2.5 billion as chief investment officer at Wilbanks, Smith & Thomas Asset Management LLC in Norfolk, Virginia, said in a phone interview. “You are going to get more days like today, where investors are more trigger happy, quicker to liquidate. Everybody knows a correction is coming and it will come.”

The S&P 500 had climbed 0.5 percent in July through Wednesday, heading for a sixth straight monthly gain, as companies from Facebook Inc. to Chipotle Mexican Grill Inc. reported a surge in profit, while Time Warner Inc. rallied as Rupert Murdoch’s 21st Century Fox Inc. made a takeover offer. The gauge closed little changed Wednesday as weaker earnings and the Federal Reserve’s decision to keep trimming asset purchases offset better-than-forecast economic growth.

“Maybe the market is getting a little bit tired here,” David Chalupnik, the head of equities at Nuveen Asset Management in Minneapolis, said by phone. His firm runs about $120 billion. “It’s more concern around Europe. We’ve had an extremely easy monetary environment for the past six years. When that changes, it’s going to cause a lot of anxiety.”

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