Q: Why do I have a yellow sticky card on my lemon tree? — Jack, Los Osos
A: Periodically, insects from other countries end up in California and can create serious problems for farmers and homeowners.
Since these insects are new to the area, they have no natural predators here. As a result, it takes a lot of time and money to figure out how to control them or eradicate them, if necessary.
New insects find their way to California more often than we might realize. The Center for Invasive Species at UC Riverside reports that an average of six new species is established in the state every year, causing a loss of an estimated $3 billion.
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The Asian citrus psyllid (ACP) was found in Southern California in 2008 and has since made its way up the coast and to the San Joaquin Valley. ACP is mottled brown in color and about the size of an aphid, approximately an eighth of an inch long. It feeds on all varieties of citrus, including some closely related ornamentals such as mock orange and orange jasmine. It prefers new tender growth and injects a salivary toxin while feeding that causes the new leaf tips to twist or burn back.
The bacterium that it injects causes the disease Huanglongbing (HLB). HLB causes shoots to yellow and results in asymmetrically shaped fruit. The disease, for which there is no known cure, can kill a tree within five to eight years.
A biological control program began in 2012 with the release of a tiny wasp, Tamarixia radiata. This wasp parasitizes ACP and is completely harmless to pets and humans. Researchers continue to monitor and evaluate Tamarixia and its ability to manage ACP.
County agriculture officials are working closely with the California Department of Agriculture to monitor for ACP by placing yellow sticky cards in commercial orchards and residential trees.
The public can help stop the spread of ACP by not moving citrus plants between counties. If you have citrus in your yard, examine the new tender growth for any signs of the pest. If you suspect ACP, contact the CDFA Exotic Pest Hotline at 1-800-491-1899.
For more information, download these free UC ANR publications on ACP and HLB:
Save the date!! The UCCE Master Gardener’s Tomato Extravaganza will be held from 10 a.m. to 2 p.m. Aug. 29 at the Garden of the Seven Sisters, 2156 Sierra Way, San Luis Obispo. It will feature tomato and basil tastings, a plant sale, presentations, and more. Watch for the full article on Aug. 26!