When criticized for the amount of chemicals they use, growers often point to the benefit those chemicals provide in the form of increased yield, which means more food can be produced cheaply. There are many ways to measure productivity, but by at least one yardstick, the claim seems to have merit. Economic data show a correlation between the high rate of chemical use in Ventura County and the value of farm production.

Ventura County growers apply about 7 million pounds of chemicals to their crops each year. That works out to an average of about 70 pounds per acre of harvested cropland. That's more than twice the per-acre volume of chemicals used by farmers in Fresno County, the state's biggest agricultural county in both acreage and crop value. But at $9.87 in annual crop value per acre of harvested land, Ventura County growers are four times as economically productive as their counterparts in Fresno County, where growers manage to generate only $2.56 for each of the 1.1 million acres of cropland.

Ventura County farmers are facing new restrictions on runoff from their fields and orchards adopted to protect local waterways. Stretches of Calleguas Creek, the Santa Clara River and the Ventura River have been identified by state water-quality regulators as impaired by a variety of contaminants, many of them linked to agriculture.

Some of those substances -- the pesticides DDT, toxaphene, chlordane, dieldrin, -- have been banned or discontinued and are a legacy of long-ago farming practices. Others, however, are still used today. These include nitrogen from fertilizer (which also runs off suburban lawns and flower beds), and such pesticides as endosulfan and chlorpyrifos. The latter is a member of one of the most dangerous classes of pesticides, the organophosphates, which are chemically related to military nerve gas.

State and federal regulators are also moving slowly, prodded in some cases by litigation and court orders, to ban or force the reformulation of a broad array of pesticides because they worsen air pollution, emitting volatile organic compounds that contribute to formation of ground-level ozone.

The California Department of Pesticide Regulation has launched a broad effort to crack down on polluting emissions from pesticide use, facing a federal court ruling in April that found the department in violation of the Clean Air Act for failing to do so. The judge ordered DPR to adopt regulations that will reduce pesticide-related VOC emissions by 20 percent from 1990 levels in five air basins -- the San Joaquin Valley, Ventura County, the Sacramento and Los Angeles areas, and the Southeast Desert -- by 2008.

The ruling came in response to a suit filed by a coalition of environmental groups and anti-pesticide activists, among them several in Ventura County -- Wishtoyo Foundation, Ventura Coastkeeper and Community and Children's Advocates Against Pesticide Poisoning.

The immediate effect will likely be further reduction in availability of soil fumigants, which account for four of the five most heavily used agricultural chemicals in Ventura county. And that will increase pressure on local growers to seek alternatives.