The California Department of Food and Agriculture has placed the southern part of San Luis Obispo County under quarantine after one Asian citrus psyllid was trapped in Arroyo Grande.
The quarantine involves 84 square miles, according to a news release.
The regulations prohibit the movement of citrus and curry tree nursery stock out of the quarantine area. In addition, they require that all citrus fruit be cleaned of leaves and stems before leaving the quarantine.
Exceptions are made for nursery stock and budwood grown in U.S. Department of Agriculture-approved structures.
The rules apply to both commercial and residential citrus.
Asian citrus psyllids are a concern because they not only weaken trees by sucking plant juices but they also can transmit citrus greening.
Greening, also known as huanglongbing or HLB, is caused by a bacteria that's harmless to humans and other animals but deadly to citrus trees.
In Florida where the disease is endemic, it had caused $3.63 billion in lost revenues as of 2012, according to University of Florida figures.