The nation's largest agribusiness and biotech companies are pouring millions of dollars into California to stop the first-ever initiative to require special labels on foods made with genetically modified ingredients, a sign of their determination to keep the measure from sparking a nationwide movement. So far, farming giants such as Monsanto, Dupont Pioneer and Cargill have contributed nearly $25 million to defeat the proposal, with much of that cash coming in the past few days. Monsanto, the largest contributor, gave $4.2 million this week. It's nearly 10 times the amount raised by backers of the ballot measure who say California's health-conscious shoppers want more information about the food they eat. With nearly three months to go before the November election, the measure's opponents appear to be following the previous blueprint developed by major industries to defeat ballot initiatives in the nation's largest consumer market: Raise large sums of money to swamp the airwaves with negative advertising. The food initiative, known as Proposition 37, ... would require most processed foods to bear a label by 2014 letting shoppers know if the items contain ingredients derived from plants with DNA altered with genes from other plants, animals, viruses or bacteria. It's an epic food fight between the pesticide companies and consumers who want to know what's in their food," said Stacy Malkan, media director for the California Right to Know campaign.