Finding rust in Brazil is more likely than in the major soybean-producing region of the north central U.S., according to Iowa State University plant pathologists. Long periods of dew and cool temperatures favor rust outbreaks. In the Cerrado regions of Brazil, rainfall averages 24 in. in the three primary months of the growing season compared to 13 in. in Ames, IA.
Brazilian farmers regularly use fungicides to combat foliar diseases before rust was found there, while Corn Belt farmers are not set up to manage foliar diseases.
A major risk element is the uncertainty about how early in the growing season spores may be picked up by the wind and how many spores will be carried to the area.