Neither is E. coli. Although the exact route of transmission has not been identified in the 2006 E. coli outbreak, the FDA's report points to cattle feces from the nearby ranch, feral pigs or river water as possible mechanisms. Cattle are the primary carriers of the virulent strain of E. coli 0157:H7 responsible for the outbreak. And bare earth buffers may actually increase the risk of transmission. University of California researchers tested the capacity of grassland buffers to reduce E. coli in runoff containing cattle feces, and their 2006 report indicated that the grasses were effective in reducing contamination across a range of landscape and rainfall scenarios.

Vegetation planted in waterways and alongside fields not only reduces pathogens like E. coli but also promotes the uptake and degradation of fertilizers and pesticides, explains Jill Wilson, environmental scientist at the Central Coast Regional Water Quality Control Board. "We want to see water quality programs and food safety practices coexist," she says.

Efforts to regulate leafy greens production have been a mixed bag, with varying degrees of scientific and public scrutiny. While the FDA has authority to step in after E. coli outbreaks, it does not routinely inspect produce in the field. In the wake of the 2006 outbreak, the Western Growers Association took the lead in creating the California Leafy Greens Handler Marketing Agreement. With 99 percent of handlers signed on, the advisory board oversaw the development of "good agricultural practices" or metrics, standards for growing and handling produce. California's Department of Food and Agriculture audits growers to ensure they follow those standards.

"The standards don't require that you manage the land any different than you have for generations," says Joe Pezzini, chair of the LGMA advisory board. The latest version, revised after criticism from environmental groups, includes a clause indicating that "fencing, vegetation removal, and destruction of habitat" may harm the environment. In fact, it instructs growers to check government regulations before taking actions that alter habitat.

So why are growers yanking out vegetation and putting up fences? David Runsten, executive director of CAFF, believes that the problem lies not with the metrics sanctioned by the Leafy Greens Marketing Agreement, but with buyers who impose their own arbitrary - and often excessive - standards, so-called "super metrics." "They're competing with each other," he says. " 'If you have a 30-foot buffer, I'll have a 100-foot. If you have them build a 3-foot fence, I'll want a 6-foot fence.' "

For the growers, it means a dizzying array of rules imposed by the handlers who buy their produce. "It's really annoying to have to destroy habitat, I mean, harborage," the anonymous grower says with a wry smile. One auditor wanted him to have a 50-foot buffer of bare earth, not realizing the benefits of hedgerows. And the grower knows he will have to put in fences to keep the buyers happy, despite the prohibitive costs.

"These buyers are so powerful, but nobody talks about the super metrics," says Schmidt. Companies adopting such measures have kept their rulebooks from public scrutiny. Part of the problem is the corporate - and the consumer's - perception of risks. Laura Giudici Mills, director of food and workplace safety for Metz Fresh, points out that it's one thing to deal with contamination from pathogens like E. coli, and another to find foreign material such as seed pods and even frog parts in a package of leafy greens. Fencing may help keep unwanted delicacies out of the salad bowl, but getting rid of beneficial insects and habitat in the name of food safety is a case of throwing out the baby with the bath water.

"The super metrics don't want any animal intrusion," says Pezzini. "We have to get out and educate these buyers that the farm is an integrated system."

Today's small farmer often feels like David vs. Goliath - the interests of industrial agriculture and huge corporations dominate both the marketplace and public policy. The new Farm Bill had provisions for regulating food safety through industry-based measures, but these were cut out in the legislation passed by Congress in May.

Kira Pascoe, CAFF's family farm food safety coordinator, pointed out that most of the attention gets focused on crops in the field even though processing seems to be to blame for the recent disease outbreaks - particularly packaged convenience foods such as ready-to-eat spinach. Processed products were implicated in 98.5 percent of illnesses caused by E. coli in California leafy greens, according to a CAFF analysis of U.S. Department of Agriculture data.

In the 2006 outbreak, processing procedures failed to detect or remove the virulent bacteria contaminating the spinach. A March 2008 congressional report delivered a harsh indictment of the FDA's lack of oversight of processing facilities for packaged fresh spinach. Repeated violations at the company's plant in Yuma, Ariz., received nothing more than FDA calls for "voluntary action" - which were subsequently ignored.

The cumulative impacts of fencing and habitat removal have escaped environmental analysis as well. The California Environmental Quality Act requires public agencies to assess the environmental impact of land use. If the California Department of Food and Agriculture had created the leafy greens standards, says Runsten, such analysis would have been performed. In the wake of the E. coli outbreak, though, the state agency acted quickly, allowing the Western Growers Association to develop metrics. But those industry-defined standards aren't subject to the Environmental Quality Act's requirements - and neither are the super metrics imposed by buyers.

While the big players are setting de facto food safety standards, small growers concerned about habitat destruction want public safeguards. Pezzini hopes the LGMA metrics will become an industry-wide standard. Baumgartner and other farm advocates say there should be a ceiling on all metrics to prevent them from spiraling beyond reason. The science shows that food safety and conservation can go hand-in-hand. Now it's up to consumers and corporate buyers to accept farming in its natural environment, where hedgerows, ponds and wildlife make good neighbors - rather than bare dirt and fences.

"Consumers need to tell their retailers," says Baumgartner, "that they do not want pre-packaged leafy greens to be produced at the expense of wildlife and at the risk to human health."

Li Miao Lovett writes about cultural and environmental issues from the San Francisco Bay Area. Her forthcoming novel, In the Lap of the Gods, portrays the lives of Chinese displaced by the Three Gorges dam.