Asian Citrus Psyllid and HLB Disease

By Kim Wilson and Linda Robertson, UC Master Gardeners

Asian Citrus psyllid (ACP) and the devastating citrus disease Huanglongbing (HLB) are a serious concern for all California residents who enjoy citrus, whether from their yards or the market.  Understanding this threat and participating in the eradication of the pest from our county is crucial to the maintenance of our backyard and commercial citrus.

Asian Citrus Psyllid: The Pest

• Asian Citrus psyllid (ACP) is a tiny, winged insect that can carry the deadly citrus tree disease Huanglongbing (HLB). The disease can be transmitted to citrus and certain other plants, including orange jasmine, and curry leaf plants.
• Not all ACP carry the disease. They must feed on an infected tree to acquire the bacteria. Once the insect has the bacterium in its system, it will transmit to all trees it feeds on for the rest of its life.
• ACP prefers new growth on citrus, therefore, its most likely to be found on newly flushed leaves.
• ACP has been found occasionally in SLO County, but it is not considered to be established.

Huanglongbing (HLB): The Disease

• HLB is transmitted by feeding by an infected ACP or by grafting with infected scion wood. It is one of the most devastating diseases of citrus and there is currently no cure.
• Newly infected trees do not show symptoms for 2-3 years after the initial infection, thus, serve as a stealth source of the disease.
• ACP can feed on an infected tree and transmit the disease to every tree it feeds on for the remainder of its life.
• Infected trees will die in 5-10 years.
• HLB has not yet been found in SLO County.

Current Status

• HLB has been found in Los Angeles, Orange, Riverside, San Bernardino, and San Diego Counties. So far it has not been found in SLO County or any adjacent counties.
• Currently, ACP is not widespread or established in San Luis Obispo County. The last finding of an ACP in this county was in 2021.
• Tamarixia wasps, a natural enemy of the ACP, have been released periodically in the county by the CDFA.

Monitoring

Department of Food and Agriculture (CDFA), in conjunction with county agriculture offices, has an intensive monitoring program to track the pest and disease. Monitoring involves placement of yellow sticky traps in residential and commercial citrus trees and inspection of trees sold in local nurseries or shipped from elsewhere. Results guide quarantine zones, residential chemical, and biological control measures.

Course of Action When ACP Found in a Residential Trap in SLO County

• If a psyllid is found, the county will determine how to treat for it.
• Treatment programs are tailored depending on the number on insects found. Treatment may involve chemical treatment of the target tree and neighboring properties.
• If foliar treatments are applied, they are not applied when citrus is in bloom, to protect the flowers and pollinating insects. Only citrus tree foliage is sprayed. Tarps are used to protect surrounding vegetation. There is no preharvest interval for the spray.
• The treatment program is optional, but it is strongly recommended to help prevent the establishment of the pest and, therefore, the devastating HLB disease into this county.

How Can We Help Save Our Citrus?

• Call (805) 781-5910 and volunteer to have a trap placed in your citrus trees. More traps mean we have a better chance to detect and eradicate the pest.
• DO NOT MOVE CITRUS: within or out of SLO County. Do not remove or share citrus trees, clippings, or scion wood.
• You can move fruit, but make sure there are no attached leaves or stem.
• Prunings can be disposed of in green waste because the county is not considered to be infested with the ACP. But to be safe, you may want to leave them to dry out for a week or two.
• If you have a potted citrus you want to move within SLO County, call the SLO Ag office and they will send an inspector to evaluate if it is safe to move - (805) 781-5910.
• BUY LOCAL: buy citrus trees from reputable commercial nurseries selling trees inspected by County Agriculture Officials.
• If you graft citrus, use only registered budwood with source documentation. Information on registered budwood is available online from the Citrus Clonal Protection Program, https://ccpp.ucr.edu/
• Check your citrus trees monthly. Look for evidence of curling or other damage on newly flushed leaves. Examine new feather flush growth with a hand lens for ACP or orange nymphs and waxy white tubules, which are unique to the ACP. 
• If you suspect ACP is present or have questions concerning ACP or HLB, contact the CDFA pest hotline at 1-800-491-1899 for verification and advice. Do not take suspicious samples to a nursery, Master Gardener Helpline or Ag office.
• Control ants on citrus trees with Tanglefoot. Ants protect insects like ACP from beneficial insects because the ants feed on honeydew produced by the feeding nymphs

References

Asian Citrus Psyllid/Huanglongbing. Notice of Treatment. CDFA

https://www.cdfa.ca.gov/plant/acp/treatment_maps.html

Asian Citrus Psyllid Update, SLO County Farm Bureau. http://www.slofarmbureau.org/news/article/asian-citrus-psyllid-update

Grafton-Cardwell, Elizabeth and Matthew Daugherty. Asian Citrus Psyllid and Huanglongbing Disease. Pest Notes, Publication 74155. UCIPM. http://ipm.ucanr.edu/PDF/PESTNOTES/pnasiancitruspsyllid.pdf

Asian Citrus Psyllid and Huanglongbing Disease Management Guidelines--UC IPM. http://ipm.ucanr.edu/PMG/PESTNOTES/pn74155.html

California Citrus Threat. Protect Your Citrus - California Citrus Threat. https://californiacitrusthreat.org/protect-your-citrus

Residential ACP Management. UCANR. http://ucanr.edu/sites/ACP/Homeowner_Options/Homeowner_Management/