By Ben St. Clair and Amrith Ramkumar 

U.S. stocks tumbled Wednesday in a broad selloff led by the energy and materials sectors, as the Dow Jones Industrial Average and S&P 500 posted their fifth decline in the past six sessions.

After mostly rising to start the month on the back of strong corporate-earnings reports, U.S. stocks have been pressured in recent sessions as investors worry that Turkey's economic crisis could spread to other emerging markets.

Some investors expect steady U.S. earnings and economic growth to continue supporting major indexes, but analysts say the market is starting to pay more attention to the challenges gripping other countries.

"The level of growth was so far above a sustainable trend that the only logical thing to assume was that it was going to moderate a bit," said Jonathan Golub, chief U.S. equity strategist at Credit Suisse.

The S&P 500 slumped 21.59 points, or 0.8%, to 2818.37, while the Dow industrials declined 137.51 points, or 0.5%, to 25162.41. The S&P 500 is up less than 0.1% during August, while the blue chips -- which are more sensitive to trade tensions -- are down 1%. The technology-heavy Nasdaq Composite fell 96.78 points, or 1.2%, to 7774.12 Wednesday and is up 1.3% month to date.

Commodities, including oil and metals prices, also dropped sharply Wednesday, putting pressure on energy and materials companies in the S&P 500. Those sectors fell 3.5% and 1.6%, respectively.

Only the utilities, telecom, real-estate and consumer-staples sectors rose in the S&P 500. All four groups are considered safety plays because of their hefty dividend yields.

"The story for this week is clearly centered on Turkey, tariffs, the dollar and weakness in the equity market," said Kevin Giddis, head of fixed income capital markets at Raymond James, in a note.

Investors were also weighing economic data showing Americans boosted their spending in July, a robust start for consumer spending in the third quarter amid a strong labor market and consumer confidence.

Among individual stocks, Macy's dropped $6.67, or 16%, to $35.15 after the department-store operator reported a slight drop in sales in the latest quarter as it tried to strengthen its bricks-and-mortar business with store remodels and off-price locations. The shares dragged down a number of other retail stocks, including Kohl's and Gap.

Earnings reports from other retailers, including Walmart, J.C. Penney and Nordstrom, are on deck for Thursday.

Corona brewer Constellation Brands slumped 13.54, or 6.1%, to 208.27 after saying it is investing $4 billion into Canadian marijuana grower Canopy Growth, a big wager on the potential for cannabis-infused drinks and other products.

Chipotle Mexican Grill rose 32.57, or 6.6%, to 525.89 after Morgan Stanley analysts upgraded the burrito chain's shares to "overweight," saying the company has a clear path to recovery thanks to new management and "low-hanging" opportunities to drive sales.

Write to Amrith Ramkumar at amrith.ramkumar@wsj.com

(END) Dow Jones Newswires

August 15, 2018 19:31 ET (23:31 GMT)