For the next month, Don -Villock will spend between 12 and 14 hours a day sitting on his combine harvester as he works to bring in the fields of white corn on his 3,000-acre farm near Edwardsport, a town of about 350 people some 100 miles south-west of Indianapolis, the state capital of Indiana.

While his eyes are on the crop, Mr Villock says his mind is down in Mexico, where much of the corn is destined to end up as tortillas. With the US economic downturn beginning to be felt in the global economy, he is worried about the future of North America's agricultural export markets.