Mainstream food producers are diving into the organic market, which accounts for less than 2 percent of U.S. food sales but has been expanding by more than 20 percent per year. Salivating at this impressive growth rate, many large companies are gobbling up smaller organic producers. In just the latest example, Dean Foods Co., the largest milk producer in the U.S., earlier this month bought up Horizon Organic, one the biggest organic food producers in the nation. Horizon has met with impressive success by targeting its products toward parents with young kids, who tend to be particularly concerned about health. This fall, the company will introduce the first organic baby formula. Horizon is also in the midst of a major deal that would put its products into Costco stores across the nation. As more retail outlets stock organic products, industry experts predict that organic prices will start dropping.