Brazil soybean and corn farmers may face a repeat of a 2005 drought that damaged 13 percent of the grain and oilseed crop, a government weather forecaster said.

Since October, the South has received below-average rain because of the La Nina weather pattern, raising concern crops being planted now will be damaged before next year's harvest, said Expedito Rebello, head of research at the government's Meteorology Institute, known as Inmet. The southern states of Parana, Santa Catarina and Rio Grande do Sul account for 41 percent of Brazil's corn output and 37 percent of its soybeans.

In 2005, total grain and oilseed production fell to 113.5 million metric tons, compared with an initial forecast of as much as 130.9 million tons, amid the worst drought in 40 years, according to Agriculture Ministry data. Similar damage may occur this year should dryness continue, according to Rebello.

"We've seen days with too much rain followed by long periods of drought, which isn't good for soybeans and corn," Rebello said in a telephone interview from Brasilia. "If dryness continues in December, we may see the 2005 phenomenon get repeated."

Corn can't tolerate more than 15 days without rain. Soybeans can take about 30 days of dry weather, with possible losses, he said. A better forecast on how the dry spell will affect the harvest will be available by Dec. 15, he said.

David Fuller's view We have seen sharp pullbacks recently for corn, soybeans and wheat but give turbulent weather patterns, reduced stockpiles and the underlying bases evident on the charts above, I do not think that the rallies are over.