Fastened to a featureless gray cinder-block wall, the small sign offers the only indication of how Case van Steyn's world has changed.
While milking and feeding proceed as they would on any average afternoon on his California dairy farm, the placard makes it sound as if the workers here in this scattered collection of metal sheds and low-slung cattle barns should be wearing moonsuits. "Biosecure Area," it reads, "Visitors by Appointment Only." Mr. van Steyn put it up last week, soon after he eliminated tours and began screening visitors more carefully.
Like most farmers from here to Florida, Mr. van Steyn realizes that agriculture is among America's most attractive and vulnerable targets for terrorism. But since there is no way to adequately patrol the immensity of the American range by foot or car, they're taking their own steps to prevent an attack - from making sure the barn doors are locked every night to taking a closer look at employees. As a result, a new and apparently permanent vigilance about security is taking hold on farms nationwide.
Even a minor biological attack on agriculture could have serious repercussions on exports - and thus the broader national economy. "Clearly [since Sept. 11], there's a hugely increased awareness that this is an issue," says Jerry Jaax, an expert on biological weapons at Kansas State University in Manhattan.
As part of a preemptive approach, some states have put together task forces or special committees to evaluate what can be done to help farmers and ranchers limit terrorists' opportunities. Most states have also made public appeals to farmers to reassess how they protect their land and property.
Ohio, for example, sent a letter to its farmers, asking them to look out for strangers and any missing chemicals that could be used to make bombs. "We're looking at it as if everything has changed down on the farm, and we need to be more security conscious from here on out," says Fred Dailey, director of the state Department of Agriculture. "This won't go away in a month."
What makes agricultural terrorism attractive is its relative ease. Many biological agents that destroy livestock or crops - such as foot-and-mouth disease - are harmless to humans and can therefore be administered safely. In addition, the possibility of being caught is much lower for agricultural terrorism, because farms and ranches are often isolated and open.
At the same time, such strikes - even if they only taint a limited number of animals or plants - could sow worldwide concern about the health of American agriculture. Not only might exports drop, but Americans, too, might lose confidence in the safety of their homegrown agricultural products.
The US system of detection and containment is good, observers say, but time would be of the essence. If an attack were to spread, the costs could become tremendous. In one recent analysis of Indiana agriculture, the money needed to detect, confine, and destroy infected animals ran into the billions if an outbreak merely spilled into a second county.
Biological warfare on crops and animals is not new. Since World War I, when Germany used anthrax to kill Allied horses, the Soviets developed extensive plans to attack American agriculture with biological agents, and Iraq reportedly developed a fungus that would damage rice and wheat.
Targeting America's food supply, however, is not necessarily an effective way to attack humans. While some agents are also dangerous to humans, extensive food-inspection programs would keep the human toll small, many experts say. Given the nature of the attacks so far - fueled by an apparent desire to kill humans - agricultural terrorism may not be a top priority for America's enemies.
But that hasn't eased concern. "Their strategy may be to attack the US in as many different ways as possible," says Mark Wheelis, a microbiologist at the University of California in Davis. "This might be a third- or fourth- or fifth-level priority."
For his part, van Steyn is taking every precaution he can. Not only is he keeping people out, but he's keeping other cows out, as well: He's eliminated bringing in animals from other farms. "I want to quarantine the world from me," says the dark-haired van Steyn, standing in front of a pungent cow paddock. "I know [my cows] are in good shape, so if I can keep whomever it is away from them, I know I'm OK."
Although the suburbs of Sacramento lick the surrounding farmland in tongues of red-tiled roofs, his property still seems as remote as Montana - beset more by flies than freeway traffic. But the skyscrapers of downtown, which can be seen from highway overpasses, are a reminder that people aren't far away.
Van Steyn knows he can't protect his cows 24 hours a day, but he also knows that, if he stays on guard, he's more likely to head off any problems before they happen. Others agree, noting that the current state of high alert - created by the outbreak of foot-and-mouth in Britain last year and intensified after Sept. 11 - will make detection easier.
"I would like to think that a majority of animal owners would be aware to any problem," says H. Leon Thacker a veterinary pathologist at Purdue University in Indiana. "And I would like to think that we would recognize this as something unusual and get on it quickly."