The fungus that hinders plant growth and drastically cuts crop production first appeared in Brazil in 2001 caused the loss of 4.5 million tonnes of soybeans in the 2003-04 (October-September) season.
However the detection comes at a time when most US soybeans have been harvested, and the US department of agriculture said the impact of the fungus should be minimal this year.
Nevertheless soybean prices rose about 3 per cent yesterday on the Chicago Board of Trade, largely due to news of the disease.
Prices for the crop, increasingly used as a health food ingredient, reached 15 year highs in recent months on the back of a drawdown in global stocks last year.
Relief is expected this year but rising productions costs and freight rates will continue to affect the price of imported crop inputs.
The US department of agriculture said it was sending a team of scientists and regulators to Louisiana to help identify the fungus and conduct surveillance around the detection site to determine the extent of the disease spread.