Los Angeles, California – A fungal disease once thought confined to the humid groves of the southeastern United States has now firmly taken root in California. The California Department of Food and Agriculture (CDFA) announced this week that the quarantine zone for sweet orange scab—caused by the fungus Elsinoë australis—has been expanded to include Los Angeles and Ventura counties following the discovery of multiple infected citrus trees.
Sweet orange scab is not new to citrus growers in wetter climates like Florida. Still, its spread into arid and semi-arid regions, such as Southern California, suggests the disease is adapting—and rapidly. The implications could be far-reaching. While the fungus does not render citrus fruit inedible, it leaves unsightly scabs and blemishes on the surface, compromising the appearance and marketability of fresh fruit. Infected trees can experience premature fruit drop and slowed growth, particularly in vulnerable varieties such as tangerines and sweet oranges.
The fungus spreads through microscopic spores, easily carried on pruning tools, green waste, and plant containers. Even residential gardeners can unknowingly contribute to its spread by moving infected material between properties or failing to properly disinfect equipment. Though the United States Department of Agriculture (USDA) notes that there is currently no treatment available, property owners are not required to remove infected trees. Instead, the USDA is advising farmers to remove any affected fruit and thoroughly clean tools that have come into contact with diseased plant material.
The expanding quarantine imposes strict limits on the movement of citrus fruit and nursery stock from affected areas, a precaution aimed at slowing the disease’s progression toward California’s Central Valley—home to the state’s vast commercial citrus industry. The possibility that sweet orange scab could establish itself in the Central Valley has raised concerns among growers, regulators, and agricultural scientists alike. California produces over 80% of the nation’s fresh citrus, and any disruption in that supply chain—whether cosmetic or structural—poses an economic risk both locally and nationally.
What makes the presence of Elsinoë australis in California particularly troubling is not just its ability to deform fruit, but the broader pattern it signals. A growing number of pathogens and pests—previously associated with other regions or climates—are appearing in new places. This includes invasive insects, such as the Asian citrus psyllid, and destructive fungi, including citrus greening disease. The arrival of sweet orange scab in a dry region like Ventura suggests that climate variability, increased plant transport, and evolving ecological conditions are redrawing the boundaries of where and how agricultural diseases thrive.
For now, containment is the priority. Agricultural officials continue to conduct inspections, issue guidelines, and work with growers and residents alike to slow the spread.
