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The Plant Doctor

A Serious Threat for Citrus: Asian Citrus Psyllid & Huanglongbing Disease

Steve Tjosvold
Environmental Horticulture Farm Advisor
UC Cooperative Extension

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With the official finding of Asian citrus psyllid in Santa Clara County in February 2015 and in San Benito County (Hollister) on April 11, 2015, the insect that transmits the destructive pathogen that causes Huanglongbing disease (HLB) is now on the doorsteps of the Monterey Bay Area if not already here.

It is imperative that gardeners understand the seriousness of this pest and its associated disease. HLB is one of the most devastating diseases of citrus in the world. Diseased trees produce green, bitter, inedible, and misshapen fruit. Once a citrus tree is infected it will eventually die. All citrus in California-- the $2 billion commercial citrus industry and the millions of citrus trees estimated to be in backyards and landscapes-- are all at risk. The progression of the problem around the world and in the United States (e.g. Florida and Texas) has been consistent. Once the psyllid has established itself in these areas, the bacterium that causes the disease has followed. That’s why it is important now to be on the alert for the psyllid in our own backyards.

Asian citrus psyllid feeds mainly on Citrus species, at least two species of Murraya and several other genera all in the family of Rutaceae. They are small brownish insects (1/16 to 1/8 inch long) and progress through 5 juvenile stages to the adult stage. They extract large quantities of sap from the plant and produce copious amounts of honeydew.

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The honeydew coats the leaves of the tree, encouraging sooty mold to grow. Flushing citrus leaves often are severely damaged and leaves drop.

What can you do to protect California citrus trees from this threat? Do not move citrus plants, plant material or fruit into or out of your area. Only plant trees from reputable, licensed nurseries in your area. Inspect trees for the Asian citrus psyllid and HLB monthly, and whenever watering, spraying, pruning or tending trees. Dry or double bag plant clippings prior to disposal. When grafting trees, only use registered budwood that comes with source documentation. If you see evidence of the psyllid or HLB, contact your local agricultural commissioner’s office or call the California Department of Food and Agriculture’s hotline to report the insect or disease: 1-800-491-1899. For more information, see the excellent website available at http://californiacitrusthreat.org