CHICAGO, Aug 26 (Reuters) - Asian soybean rust fungus has not beendetected in Iowa soybean fields, despite recent farmer concerns about adisease that turns upper leaves a yellowish-brown or rusty color, an IowaState University professor said."We want to reassure Iowa soybean growers that soybean rust has notbeen found anywhere in the United States this year, and it appears thatthe disease will not arrive at all during the 2004 growing season," GregTylka, Iowa State University professor of plant pathology in a statement,said in a statement late Wednesday.Iowa was the second-largest U.S. soybean producing state last year.Soybean rust, which has cut South American soybean yields, has neverbeen reported in the continental United States, the world's top soybeanproducer. Hawaii was infected in 1994.However, scientists believe the windborne fungus will spread into theUnited States once it moves north of the equator.On Thursday, U.S. Department of Agriculture Secretary Ann Veneman saidshe had no confirmation that the disease had been found in Cali, Colombia,about 5 degrees north of the equator.The USDA estimates an outbreak of Asian soybean rust could cost U.S.farmers between $640 million and $1.3 billion in its first year.Instead of rust, Iowa farmers appear to be seeing Cercospora leaf spotdisease or sunburn, which causes the undersides of leaves to turn a bronzecolor, Tylka said. Yield loss from Cercospora leaf spot is usually slight,he added.Cercospora leaf spot can be seen at the beginning of the pod-fillingstage as a mottled purple to orange discoloration of the uppermost leaves,he noted. While the discoloration is most visible on the undersides ofleaves, it can also be seen on the upper leaf surfaces.When the plant is approaching maturity, the leaves will turn orange orbronze, he said.Severe infection can cause the early death of leaves, while infectionof the seeds can cause a purple discoloration of the seed coat which cancause poor seed vigor and reduced germination if planted the next year,Tylka said."Cercospora leaf spot is fairly common in Iowa during this time of thegrowing season, and turns the upper soybean leaves a yellowish brown colorthat some might describe as 'rusty' looking," Tylka said.