FRESNO, Calif. – Farmers in "America's Salad Bowl" are turning into hunters – stalking wild pigs, rabbits and deer – to keep E. coli and other harmful bacteria out of their fields.

It's part of an intense effort to prevent another disaster like the 2006 spinach contamination that killed three people, sickened 200 and cost the industry $80 million in lost sales.

The exact source of the contamination was never discovered, but scientists suspect that cattle, feral pigs or other wildlife may have spread the E. coli by defecating near crops.

The pressure to safeguard crops comes from the companies that buy fresh greens.

In response, some farmers are taking gun-safety classes to learn how to shoot animals that could carry the bacteria. Others are uprooting native trees and plants and erecting fences to make their land inhospitable to wildlife.

Spinach grower Bob Martin has even poisoned ponds with copper sulfate to kill frogs that might get caught in harvesting machinery or carry salmonella on their webbed feet.

But some officials have questioned whether such drastic measures are necessary.

"We're trying to talk now with the companies, buyers, retailers, wholesalers to bring things back into balance," said Scott Horsfall, executive director of the Leafy Greens Handlers Marketing Board, which oversees new farming standards drawn up after the 2006 E. coli contamination. "There's a real pressure out there on growers that goes beyond what the science justifies."

In the Salinas River Valley, valuable farmland and sensitive wildlife have coexisted for centuries. The lush valley, described in John Steinbeck's East of Eden and nicknamed "America's Salad Bowl," grows 60 percent of the nation's lettuce.

The nonprofit Resource Conservation District of Monterey County, which works with landowners to sustain wildlife habitat, surveyed 181 leafy greens growers who manage more than 140,000 acres.

The survey showed that more than 30,000 acres had been affected by trapping, poisoning, fencing or removal of natural habitat.

Tracie Cone,

The Associated Press