A big uptick in raw material prices helped two old-economy powerhouses boost their first-quarter earnings outlooks Wednesday.

DuPont ( DD) took up guidance dramatically, citing unexpected strength in its agriculture and nutrition segment and higher volume across its business lines.

And shares of Georgia-Pacific ( GP) were moving higher after the company said it expects first-quarter earnings to come in ahead of analysts' estimates, citing solid results from its building products businesses.

"These are coincident indicator-type companies," said Howard Simons, a trading consultant and contributor to RealMoney.com, a sister site to TheStreet.com. "You can definitely link them to the commodity rally."

Excluding one-time items, chemical company DuPont expects to earn 95 cents a share, up significantly from previous earnings guidance of 65 cents to 75 cents a share and the Thomson First Call analyst consensus of 73 cents a share. The company's stock was rising $1.21, or 2.8%, to $44.90.

Citigroup Smith Barney analyst P.J. Juvekar thinks most of DuPont's upside comes from a strong agricultural cycle; corn, for example, is at an eight-year high. Corn futures were lately up 1.75% at $319.5 a bushel and the price of corn closed at $311.75 a bushel on April 13, which is up from $226 a bushel on Oct. 21.

Juvekar also said DuPont buys large amounts of raw materials, especially paraxylene, a hydrocarbon aromatic compound. But because the company's supply chain is long, he doesn't think the prices will boost the company's bottom line for three to six quarters. (Citigroup does investment banking for DuPont.)

Simons noted that lower natural gas prices in January and February likely helped DuPont's quarter. "They're an economically sensitive company," he said. "If demand for products is strong, you can live through an increase in natural gas prices. That's what they've done here."

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