Invasive Asian Citrus Psyllid is established in southern California, but not established here … yet

The Asian Citrus Psyllid (ACP), a tiny mottled-brown insect, was first detected in California in 2008, and threatens citrus in California's home gardens and agriculture.  We still have the opportunity to control the psyllid and protect our citrus from the fatal disease.

Why worry about the Asian Citrus Psyllid (ACP)?

Californians love their citrus. Over 60% of Californians have citrus plants. ACP is a serious threat to California citrus. The Asian Citrus Psyllid (Diaphorina citri) is already established in southern California, but ACP is not widespread in northern California or in the central valley, although the psyllid has been detected.

ACP can spread an incurable disease to citrus.

ACP concerns both the home gardener and the commercial citrus grower since the psyllid can spread the deadly huanglongbing (HLB) disease. The psyllid can carry the bacterium that causes HLB and, if infected, it transmits the disease HLB from tree to tree as it feeds.

In Florida, ACP was not controlled and quickly spread on nursery shipments of citrus and orange jasmine. The Asian citrus psyllid spread an incurable disease, huanglongbing (HLB), also known as citrus greening.  According to the USDA Agricultural Research Service, HLB reduced citrus production in Florida by 75%, more than doubling production costs.

It is critical to control the psyllid to protect our citrus, especially since HLB the disease is already in parts of southern California.

What plants can provide food and shelter for ACP?

 

Citrus and related plants in the Rutaceae family have the potential to be a host plant, providing food and shelter for the psyllid.  The psyllid feeds and reproduces on all kinds of citrus plants as well as Indian curry leaf. ACP can also thrive on plants we don't think of as citrus, such as the ornamental orange jasmine.  For a list of possible hosts, go here.

Here are some common hosts of the Asian citrus psyllid:

• Citrus (limes, lemons, oranges, grapefruit, mandarins…)
• Fortunella (kumquats)
• Citropsis (cherry orange)
• Murraya paniculata (orange jasmine)
• Bergera koenigii, formerly Murraya koenigii  (Indian curry leaf)
• Severinia buxifolia (Chinese box orange)
• Triphasia trifolia (limeberry)
• Clausena indica (wampei)
• Microcitrus papuana (desert-lime)

What is the dread, incurable disease, huanglongbing (HLB)?

Huanglongbing, also known as citrus greening or yellow dragon disease, is one of the most destructive diseases of citrus worldwide.  Citrus is the primary host of HLB, but other citrus relatives, like the Indian curry leaf tree, can get the disease.  The disease-causing bacteria of HLB only infect a network of cells called the phloem, which distributes nutrients throughout a tree. Starved of nutrients, infected trees bear low-quality fruits, and the trees decline and die within a few years.Once infected, there is no cure. 

HLB is spread most often by citrus psyllids, but it can be spread through plant grafting and movement of infected plant material. Indeed, it might be the case that HLB arrived in southern California in 2012 through the sharing of a graft of infected pomelo budwood that was illegally imported.

Detection of HLB-infected trees is made difficult by the fact that the symptoms of HLB may not show for months or even several years. Asian citrus psyllids can pick up the HLB pathogen as young immature nymphs only weeks after a tree is infected, and then the insects mature and fly away, spreading the fatal disease HBL to other trees as they feed.

Healthy-looking citrus plants and citrus cuttings are no guarantee that they are disease-free.

Why are there multi-county quarantines on citrus fruits, leaves, and trees, including non-citrus plants like the Indian curry plant?

This map shows the total number of Asian citrus psyllid detections since 2008 per square mile.  You will notice that not only are there many detections in the San Jose area, but we have detected the psyllid in the Fremont, San Leandro, Walnut Creek, San Francisco areas also.

The Asian citrus psyllid is here, but HLB the disease is not here in northern California. The psyllid has been found in Alameda County as well as in other counties in northern California. Fortunately, there have been no instances of the HLB disease being found locally at this point in 2024. 

Critical efforts to protect our citrus involve slowing the spread of the psyllid; so we are under California Department of Food and Agriculture (CDFA) quarantine for the ACP insect, specifically the regional Nursery Stock Quarantine Zone 2 and Bulk Citrus Quarantine Zone 7. These quarantines include the counties where ACP has been detected but not routinely so, and where HLB has not been detected.  Maps and quarantine information can be found here. Through regulation of movement of citrus by nurseries and commercial citrus growers, we hope to give scientists time to develop effective management or a cure for HLB before our citrus crops are infected.

Quarantines control the spread of ACP, which limits the spread of the fatal disease HLB

The quarantine includes citrus and the Indian curry leaf plant because they are common hosts for the Asian citrus psyllid, the insect that can transmit the incurable disease to all types of citrus. Infected plants take time to show symptoms; so just because a plant looks healthy does not mean that it is free of disease.

So the first line of defense is to prevent proliferation of the ACP since if we don't have the psyllid, then the disease HLB cannot spread to citrus in the home garden or commercial orchards. The quarantine for Zone 2 is aimed at limiting the movement of citrus and other plants that may be contaminated with eggs, immature nymphs and adult ACP. 

Home gardeners as well as commercial nurseries and growers need to comply with regulations on movement of citrus. We all need to work together to save our citrus.

What does the Asian citrus psyllid quarantine mean for the home gardener?

This blog from the UC Master Gardeners of Santa Clara has a really nice summary of do's and don'ts of the Asian citrus psyllid quarantine for the homeowner:

What the Asian citrus psyllid quarantine means

Clean fruits can be moved out of the quarantine zone

Homegrown citrus fruit totaling less than 25 pounds and that is clean of all stem and leaf material can be moved out of the quarantine area. Washing the fruit is a good extra precaution to take.

Plants and fruit can be moved within the quarantine zone

Plant material (whole plants, leaves) from backyard citrus or curry leaf plants may be transported within the quarantine area.

Plants can NOT be moved out of the quarantine zone

Plant material other than fruit (whole plants, leaves) from backyard citrus or curry leaf plants can NOT be transported out of the area. However, it CAN be put into local green waste collection.

How to Look for the Asian Citrus Psyllid

 

ACP is a tiny sap-sucking insect, the size of an aphid.

The wings are  brown along the edge, with a clear gap along the back edge.

 

The psyllid feeds with its rear end tilted up at a 45^o angle.

 

The tilted body and wing pattern are key characteristics.

 

Look at new leaves for adult and juveniles (nymphal) psyllids and the curly, waxy tubules they produce.  The waxy tubules are another key characteristic of ACP.

Look for ant activity in the tree, often an indication that pests are there, though it might not be ACP. You can ask UC master gardeners for help with ant management. We can help with identification of the pest.

Informative YouTube video - UCANR 2016 video: Check your citrus trees for Asian citrus psyllid
More ACP photos and monitoring information can be found here.

 How to Look for the disease HLB

 

    
It can take several months to a year for infected trees to show symptoms of huanglongbing (HLB).

Look for blotchy yellowed leaves where the mottling is not the same on both sides. However, identification is tricky because citrus trees often have yellow leaves because of nutritional deficiencies.  If you think your tree might have HLB, call Call California's Pest Hotline (800) 491-1899 or contact your local Agricultural commissioner. (510) 670-5232, and they will help with identification.

Later symptoms include small oddly shaped fruit, bitter juice and excessive fruit drop. Eventually the tree stops producing fruit and dies.

More HLB information and photos can be found here. Click through a photoslide show here for great information and photos.

Thoughtful movement and sourcing of citrus plants, leaves and grafts can keep our citrus safer

Know where your home is in relation to the pest and disease. Check here.

Much of the bay area counties, including Alameda county, is inside a psyllid-infested quarantine area, so don't move host plants to or through uninfested areas of the state. (See the tag below.)

Keep citrus plants local! Innocent sharing or movement of infected plants or other materials can have long-term effects costly to all Californians. 

Citrus trees in nurseries in the quarantine areas will have a tag on them. (See the photo below.) The tag explains that the tree should not be moved out of the quarantine area. Alameda county is part of the Asian Citrus Psyllid Nursery Quarantine Zone 2 that includes Marin, Sonoma, Napa, Solano, Yolo, Sacramento, San Joaquin, Contra Costa, Santa Clara and more. Here are quarantines and maps of affected counties.

Be sure to buy citrus trees only from a reputable nursery. Remember trees may take many months to show the effect of infection by HLB.

Source budwood from a reliable, reputable source such as the Citrus Clonal Protection Program. Here is more information on sourcing of citrus budwood, rootstocks and seedlings from Givaudan Citrus Variety Collection at UC Riverside. If you don't know where the plants, budwood, plant leaves came from, then don't buy them! They may harbor pests or disease, including ACP and HLB, with the potential to cause great harm to our citrus crops.

The psyllids can't live on citrus fruit. So as long as you brush or wash the fruit and make sure it
is free of leaves and twigs before transporting it, it is ok to move it.

What can the home gardener do to slow the spread of ACP and HLB?

• Buy trees locally.
• Check for Asian citrus psyllids and report them.
• Control for ants; they farm and protect psyllids and other pests.
• Be supportive of the inspections, quarantines, bans on sales or imports and other actions of the CDFA.
• Be supportive of the pest detection efforts of the Alameda County Department of Agriculture (Agriculture Commissioner's office) by allowing insect survey traps on your property.
• Keep a Lookout. Learn the symptoms of HLB
• Report Sightings. Be a “citizen scientist”.  Call California's Pest Hotline (800) 491-1899 or contact your local Agricultural commissioner. (510) 670-5232

Resources:

Asian Citrus Psyllid Distribution and Management - very informative to both growers and home gardeners

https://ucanr.edu/sites/ACP/

 

CDFA Huanglongbing (HLB)

https://www.cdfa.ca.gov/citrus/pests_diseases/hlb/regulation.html 

 

CDFA Citrus Pest and Disease Prevention Division

https://www.cdfa.ca.gov/citrus/ 

 

UCANR site for resources 

https://ucanr.edu/sites/ucanr/News/Asian_citrus_psyllid_and_huanglongbing_disease/

 

UCCE news tagged HLB

https://ucanr.edu/sites/UCANR/index.cfm/Richard%20Minnich?blogtag=HLB&blogasset=96361

 

Very informative 2016 PPT from Beth Grafton-Cardwell, Dept of Entomology, UC Riverside

https://awm.sbcounty.gov/wp-content/uploads/sites/84/2022/04/ACP-and-HLB-Beth-Grafton-Cardwell-UCR.pdf 

 

UC IPM Pest note for Homeowners

https://ipm.ucanr.edu/PMG/PESTNOTES/pn74155.html 

 

 

UC IPM Quick tip for homeowners

https://ipm.ucanr.edu/QT/asiancitruscard.html 

 

 

Huanglongbing (HLB)/Citrus Greening Disease Information

https://www.fdacs.gov/Agriculture-Industry/Pests-and-Diseases/Plant-Pests-and-Diseases/Citrus-Health-Response-Program/Citrus-Pests-and-Diseases/HLB-Citrus-Greening

 

California Department of Food and Agriculture 

https://www.cdfa.ca.gov/citrus/ 

 

UC Riverside Center for Invasive Species Research

https://cisr.ucr.edu/invasive-species/asian-citrus-psyllid 

 

Invasive Spotight: Asian Citrus Psyllid and HLB  2023

https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=57064

 

USDA Agricultural Research Service - Citrus Greening Portal

https://aglab.ars.usda.gov/learn-and-explore/citrus-greening-portal

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