Going by the suitably alarming tag of "agroterrorism", attacks on the US's ability to produce - and, importantly, export - food could bring the country to its knees, the experts say. Arguably more worrying is that inflicting such a blow would require neither specialist knowledge nor the hard-to-come-by materials so often needed for other acts of terror.

The Kansas meeting was organised by the FBI, which would be responsible for investigating if terrorists launched an attack on the US domestic food supply. If the list of presentations given at the meeting is anything to go by, the range of potential targets is vast. Food could be tampered with, cattle infected with any number of exotic and highly contagious diseases. Obscure pests and viruses could cut swathes through fields of crops. In a country where agriculture props up 18% of domestic employment and accounts for 13% of the GDP, the damage that could be inflicted is nothing short of immense.

Even a minor attack could cause widespread disruption. The vulnerability of the world's food chain was amply demonstrated by the recent health scares over the imported food dyes Sudan 1 and Para Red.

While the Kansas meeting was the first time the FBI has convened an international meeting on agroterrorism, the concept is decades old. During both world wars, several countries, including Britain and the US, developed means of crippling a country's ability to feed itself, among them anthrax and wheat rust, and recruited devastating crop pests into their armoury.

More recently, attacks have focused on food at the consumer end of the long and vulnerable chain that brings food from the field to the table. In the 1980s, the cult of Bhagwan Shree Rajneesh sprayed salmonella on salad bars in Oregon, an act that poisoned around 750 people. In 1989, Heinz introduced tamper-proof jars after blackmailers began interfering with its products.

For the FBI, the main concern is an attack at the heart of the country's food supply - its cattle and cash crops. Estimates suggest that if terrorists managed to infect US cattle with foot and mouth disease, it could make a $30bn dent in the US economy and require the slaughter of tens of millions of livestock. Britain's own miserable experience with foot and mouth disease in 2001 has served as an example to other countries of how a chance infection can cause rampant destruction. So useful is the story of the outbreak that Ann Waters, head of contingency planning at the Department for Environment, Food and Rural Affairs (Defra), was brought to the Kansas meeting to give details of the painful affair.

Although Britain's foot and mouth outbreak had a huge effect on raising awareness of the weaknesses of the food-supply chain and the strategies that work best to contain diseases, the potential for terrorists to spread animal diseases is still high.

"One of the problems is that many of these diseases occur in other parts of the world, so you wouldn't need an enormous amount of specialist knowledge to get hold of infectious material and introduce it to a country. Put it in a market where you've got vast numbers of animals mixing, and bingo, you've got a disaster on your hands," says David Paton at the Institute of Animal Health.

Of course, there is potential to cause major disruption without even possessing the raw disease-causing microbes. A bluff that a disease had been introduced to a country could just as easily trigger widespread alarm and put exports at risk.

Since 2001, Britain has tightened its border controls in an attempt to reduce the risk of another foot and mouth outbreak, but such measures are still aimed at the accidental introduction of the disease. Faced with terrorists intent on bringing infectious material into the country, such measures will never be foolproof. "It only has to be a tiny amount you bring in. How you would police and prevent somebody bringing that in among the multitudes that come and go with all their luggage is almost impossible," adds Paton.

For Britain, an agroterrorist attack could be damaging, but experts believe the US is far more vulnerable. "The industry here is so huge, it's highly vulnerable," says James Roth, professor of veterinary medicine at Iowa State University, who spoke at the Kansas meeting on hazards to livestock. "If their goal was to bring down the US economy, this would be one of the easiest ways to do it," he adds.

The US Department of Homeland Security has started to stockpile vaccines in anticipation of an agro-terrorist strike, but stockpiles take time to build up and vaccines are often effective only several days after being given, meaning that a disease can still spread quickly in the first week after being introduced.

George Teagarden, livestock commissioner for Kansas, who was also at the meeting, says that foot and mouth is the one disease the state's animal health experts most fear. The state is highly dependent on agriculture, slaughtering some 7m head of cattle a year and transporting around 50,000. The movement of the cattle to markets, where they are free to mingle with others from inside as well as beyond state boundaries, means that a pocket of infection could rapidly spread across and out of the state.

In York, scientists at Defra's Central Science Laboratory hold a list of some 250 viruses, bacteria, fungi and pests, all of which have been prioritised according to the amount of damage they could cause if introduced to Britain, whether they would persist here and what, if anything, could be done about them. By and large, the contingency plans - which would be thrown into action regardless of whether an outbreak was an act of terrorism or not - amount to stockpiling vaccines for animals and insecticides and fungicides for crops.

Among the more worrying diseases that might be released in a terrorist attack are so called zoonotic diseases, those that do more than shut down the countryside and cripple the agricultural community. Avian flu, which is already rife in south-east Asia, or rabies, could heighten the terror element of an attack by infecting humans. "That would immediately have very severe knock-on effects," says Paton. Understandably, he is reluctant to discuss the diseases that occupy the top rungs of the risk list.

According to scientists at the Central Science Laboratory, the risk of an agroterrorist attack on Britain's crops is believed to be minor, simply because even if it were successful, it is unlikely to be very dramatic. Colorado beetles, for example, could cause devastation in some parts of the world, but would struggle to survive in parts of Britain. "We get about 200 coming in a year on imported parsley, but we deal with those already," says Ian Barker, a scientist at the lab.

Ironically, Britain's intensive farming could also make it more resilient to an agroterror attack. Unlike the US, Britain's crops are commonly farmed with insecticides and fungicides, so a maliciously introduced disease might be quickly wiped out anyway. "We'd be very annoyed and very unhappy, but we'd cope with it. Even in your wildest dreams, it would probably only mean a few extra sprays on their crops," says Dr Barker.