'Yellow Dragon Disease' threatens fruit crop A citrus disease that has killed millions of 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. The US Department of Agriculture has confirmed that citrus greening was detected in a lemon-grapefruit hybrid tree in Los Angeles County. The disease stands to threaten not only California's nearly $2bn (£1.24bn) citrus industry, but treasured garden trees scattered throughout the state. The bacterial disease, also known as huanglongbing, or Yellow Dragon Disease, 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, lice that feed on an infected tree, become carriers of the disease. It is not a threat to humans.