July 18 (Bloomberg) -- Commodities capped their longest slide since November, dropping as much as 10 percent from a record two weeks ago, on concern that slowing global growth will erode demand for energy, grains and metals.

The Reuters-Jefferies CRB Commodity Index fell 7.4 percent this week, led by crude oil, corn and sugar. The index dropped as much as 1.4 percent today to 426.57, the lowest in six weeks, after reaching a record 473.97 on July 3. The five-day decline was the longest since the week ended Nov. 30.

China's economy in the second quarter expanded at the slowest pace since 2005, a report showed this week. Federal Reserve Chairman Ben S. Bernanke told Congress on July 15 that the U.S. faces ``significant'' risks to growth.

``All of these commodities are starting to show signs that the big bull market is over, and the things that people have really made the most money with in the past seven years will start to substantially drop,'' said Michael Aronstein, president of Marketfield Asset Management in New York.

In June, Aronstein said commodities were near ``some kind of reckoning'' after surging to records this year because of rising demand and limited supplies. This month, oil has dropped 8.2 percent, corn has plunged 17 percent and cocoa is down 12 percent. The CRB index has dropped 7.7 percent in July.

Sixteen of the 19 commodities tracked by the CRB index dropped this week.

``There is a general concern slowing growth is having an impact on commodity prices,'' said Michael McDougall, a senior vice president for Newedge USA LLC in New York.

Corn Plunges

This week, corn tumbled 11 percent, the most in 12 years. Soybeans dropped 9.3 percent, and sugar slumped 11 percent, the most since mid-March.

Traders also sold commodities on speculation investments in equities would garner greater returns, said Adam Klopfenstein, a senior market strategist in Chicago for Lind-Waldock, a division of MF Global Ltd.

``We're seeing rotation into stocks,'' Klopfenstein said. ``We're going through a rebalancing of portfolios.''

The Dow Jones Industrial Average gained 3.6 percent this week, snapping a four-week slide. Gold had the first weekly loss since mid-June.

``You've seen a lot of money come out of gold and commodities in the past few days and go to equities,'' said Matthew Zeman, a metals trader at LaSalle Futures Group Inc. in Chicago.

Commodities finished their best first half in 35 years as the CRB index jumped 29 percent. The rest of the year may not be as rewarding because record prices of oil, gasoline, copper, gold, platinum, corn, soybeans, wheat and rice may damp consumption and spur higher production.

``You get to price levels like we've seen and it really changes people's behavior, and it starts creating demand destruction,'' Aronstein of Marketfield said. ``In two years, all these prices will be substantially lower than they are now.''

To contact the reporter on this story: Millie Munshi in New York at mmunshi@bloomberg.net

Last Updated: July 18, 2008 16:56 EDT