FRESNO, Calif. — A citrus disease that has killed millions of citrus trees and cost growers billions of dollars across Florida and Brazil has been detected in California, despite the industry’s best efforts to keep it at bay.

After a week of testing the U.S. Department of Agriculture confirmed at noon Friday that citrus greening was detected in a lemon-grapefruit hybrid tree in a residential neighborhood of Los Angeles County.

The disease stands to threaten not only California’s nearly $2 billion citrus industry, but treasured backyard trees scattered throughout the state.

“Huanlongbing is called the world’s worst disease of citrus,” said Dr. Robert Leavitt of the California Department of Food and Agriculture. “It had been present until now in all of the world’s major citrus producing areas – except California.”

The bacterial disease, also known as huanglongbing, is carried by the Asian citrus psyllid and attacks a tree’s vascular system, producing bitter fruit and eventually killing the tree. Sap-sucking pysllids that feed on an infected tree become carriers of the disease.

It is not a threat to humans.