Yahoo! News, Agence France Presse, reports that American farmers got a new set of tips from the US Department of Agriculture this harvest season: how to protect themselves from a terrorist attack.

Few were likely to worry much in the quiet rural communities that have so far been untouched by the low cloud of anxiety that has settled over urban areas with the dense populations, which offer anonymity to outsiders and potentially high casualty counts.

"Out here things are still pretty quiet," said cattle rancher Rod Findley as he finished feeding his Hereford heifers in an early morning fog that drifted across the Missouri hillsides. "I would think a terrorist would be a little out of place around here."

But a recent E. coli outbreak that killed one woman and sickened nearly 200 in 26 states showed just how vulnerable the population is to a contaminated food supply.

Mega farms send their products to even bigger processors who sell the food to grocery chains that distribute nationwide. It can take days to identify an outbreak of food-borne illness and weeks to trace its source. In the meantime, panic can ensue as people worry over what they can safely eat.

The E. coli outbreak appears to have been caused by the use of manure as fertilizer. But deliberate attacks could be equally hard to trace and significantly more harmful, warned FBI Deputy Director John Pistole.

"The threat from agroterrorism may not be one you recognize," Pistole told a recent symposium in Kansas City, where about 1,000 farmers, police officers, scientists and economists gathered to discuss better ways to protect agriculture. "But the threat is real," he said. "And the impact could be devastating."

Information about US agriculture was found in terrorist hideouts in Afghanistan, Pistole warned.

"The bottom line is that agriculture, just like buildings, bridges and tunnels, is a critical infrastructure in need of defense," he said.

Food and agriculture produces 140 billion dollars in annual revenue and accounts for 18 percent of US employment, but farm security has traditionally been little more than making sure the gate is latched.

Targeting the food supply could be as simple as driving a truck of sick pigs past several hog farms or poisoning apples at a grocery store, suggested David Kaplan, director of the USDA’s emergency and domestic programs.

The robustness of US agriculture means there is little chance of a disruption of the food supply, said Greg Pompelli, a USDA economist. There are enormous surpluses – about 25 percent of food that is served gets thrown out – and an incredible diversity of crops and growing areas.

"Staple crops – like corn, wheat, soybeans and oats – are grown in more than two-thirds of counties" of the United States, Pompelli said, explaining that this lessens the chance that one region’s economy could be decimated.

"Even some fresh produce – apples, tomatoes and peaches – are spread broadly, with a third of all counties growing these," he said.