WASHINGTON — California must improve its oversight of the state's organic farmers or face Agriculture Department sanctions, federal investigators say.

In a new report, investigators recount both "significant improvements" and lingering shortcomings in how more than 2,000 certified organic farmers are monitored. In particular, investigators cite a longstanding lack of compliance and enforcement procedures designed to keep the fast-growing organic industry honest.

California's organic growers post sales of more than $1.8 billion a year. Nationwide, organic sales are increasing annually at a double-digit rate. With food labeled organic commanding premium prices, compliance and enforcement efforts are supposed to ensure standards are met.