Last week, California’s orange growers expanded a quarantine zone to cover over 1,000 square miles of infected land in Riverside, San Bernardino, Los Angeles and Orange counties. 

California’s multibillion-dollar citrus industry is at risk of losing its harvest to a disease formally called Huanglongbing, named from Asian citrus psyllid, a small insect that came to the U.S. through the port of Miami and has been devastating citrus crops nationwide for almost a decade.

Since last year, University of Arizona citrus researchers have been working in partnership with other universities as part of federal grant to slow the spread of the disease and help to find a solution.

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“We reduce substantially transmission to new trees from already infected trees. And hopefully overall we reduce the disease and reduce the inoculum in the environment,” said Judith Brown, professor in the School of Plant Sciences at the University of Arizona and lead researcher in a federal grant. She’s lead professor of a multi-university grant with a goal of stopping the spread of greening.

Brown's four-year grant is designed to deliver a kind of therapy to tree leaves that become infected by the Asian citrus psyllid, the insect that carries the disease bacterium

“It’s a way to target specific genes and silence them or stop them from being expressed or stop them from making proteins,” she said.

Just since 2009, the USDA has spent over $400 million to cure citrus greening disease.The disease has cost nearly half of its $1.5 billion fruit value in just 10 years. 

EDITOR'S NOTE: This story has been updated to clarify the disease has been found in residential trees in California.