The disease is known as huanglongbing, or HLB, and it was found in an 8-year-old lemon/pummelo hybrid in someone's yard in Hacienda Heights. From that one tree officials worry it could spread all over the state.
"There is no cure for this disease," said Kurt Floren, the Los Angeles County Agricultural Commissioner. "It could be disastrous to the citrus industry within the state of California."
It happened in Florida. The disease first appeared in 2005 and has cost the citrus industry 6,600 jobs and billions of dollars in damage.
In an infected tree the leaves might have spots and the fruit could go from ripe back to green. A pest known as the Asian citrus psyllid acts as a carrier spreading HLB from tree to tree.
"They will ingest the bacterium that causes this disease if it's present in that tree, then flying off to another tree to feed on another leaf. They pierce, they feed and inadvertently inject that bacterium," Floren said.
Tuesday inspectors from the California Department of Food and Agriculture went door to door, mapping and testing trees in the area. They've set up a perimeter, about half-a-mile near the 60 Freeway and Hacienda Boulevard. They will remove any infected tree.
Sharing fruit is something officials say they need to stop to prevent the disease from spreading. There will be a quarantine on all citrus products in the area.
"This will restrict the movement of any citrus and citrus plant material," Floren said.
Anyone who thinks they have spotted a diseased tree is urged to call the California Department of Food and Agriculture at (800) 491-1899.