Asian Citrus Psyllid Damage: Tips On Treatment For Asian Citrus Psyllids

Asian Citrus Psyllid Damage: Tips On Treatment For Asian Citrus Psyllids

By: Darcy Larum, Landscape Designer

If you’re noticing problems with your citrus trees, it could be pests – more specifically, Asian citrus psyllid damage. Learn more about the Asian citrus psyllid life cycle and the damage these pests cause, including treatment, in this article.

What is an Asian Citrus Psyllid?

The Asian citrus psyllium is an insect pest threatening the future of our citrus trees. Asian citrus psyllid feeds on citrus tree leaves during its adult and nymph stages. While feeding, the adult Asian citrus psyllid injects a toxin into the leaves. This toxin causes the leaf tips to break off or grow curled and twisted.

While this curling of the leaves does not kill the tree, the insect can also spread the disease Huanglongbing (HLB). HLB is a bacterial disease that causes citrus trees to turn yellow and causes the fruit to not fully ripen and grow deformed. Citrus fruits from HLB will also grow no seeds and will taste bitter. Eventually, HLB infected trees will stop producing any fruit and die.

Asian Citrus Psyllid Damage

There are seven stages of the Asian citrus psyllid life cycle: egg, five stages of the nymph phase and then the winged adult.

  • Eggs are yellow-orange, small enough to be overlooked without a magnifying glass and laid in the curled tips of new leaves.
  • The Asian citrus psyllid nymphs are tan-brown with white stringy tubules hanging from their bodies, to run honey away from their bodies.
  • The adult Asian citrus psyllid is a winged insect about 1/6” long with tan and brown mottled body and wings, brown heads and red eyes.

When the adult Asian citrus psyllid feeds on leaves, it holds its bottom up in a very distinctive 45-degree angle. It is often identified just because of this unique feeding position. The nymphs can only feed on young tender leaves, but they are easily identified by the white waxy tubules hanging from their bodies.

When psyllids feed on leaves, they inject toxins that distort the shape of the leaves, causing them to grow twist, curled and misshaped. They can also inject the leaves with HLB, so it is important to regularly check your citrus trees for any signs of Asian citrus psyllid eggs, nymphs, adults or feeding damage. If you find signs of Asian citrus psyllids, contact your local county extension office immediately.

Treatment for Asian Citrus Psyllids

The Asian citrus psyllid primarily feeds on citrus trees such as:

  • Lemon
  • Lime
  • Orange
  • Grapefruit
  • Mandarin

It can also feed upon plants like:

  • Kumquat
  • Orange jasmine
  • Indian curry leaf
  • Chinese box orange
  • Lime berry
  • Wampei plants

Asian citrus psyllids and HLB have been found in Florida, Texas, Louisiana, Alabama, Georgia, South Carolina, Arizona, Mississippi and Hawaii.

Companies, like Bayer and Bonide, have recently put insecticides on the market for Asian citrus psyllid control. If this insect is found, all plants in the yard should be treated. Professional pest control may be the best option though. Professionals trained and certified in handling Asian citrus psyllids and HLB will usually use a foliage spray containing TEMPO and a systemic insecticide like MERIT.

You can also prevent the spread of Asian citrus psyllids and HLB buy buying only from reputable local nurseries and not moving citrus plants from state to state, or even county to county.

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How to Manage Pests

Asian Citrus Psyllid and Huanglongbing Disease

Asian citrus psyllid adult and nymphs.

Adults feed on and deposit eggs on the newly developing citrus flush.

ACP nymphs are yellowish with red eyes. They produce white waxy tubules.

Young citrus leaves twist as the ACP nymphs feed and grow.

Asian citrus psyllid "mummies" caused by Tamarixia radiata parasitism.

Ants tend psyllid nymphs, protecting them from natural enemies in order to harvest their honeydew.

The Asian citrus psyllid, Diaphorina citri, is a tiny, mottled brown insect about the size of an aphid. This insect poses a serious threat to California's citrus trees because it vectors the pathogen that causes huanglongbing disease (HLB). This disease is the most serious threat to citrus trees worldwide—including those grown in home gardens and on farms. The psyllid feeds on all varieties of citrus (e.g., oranges, grapefruit, lemons, and mandarins) and several closely related ornamental plants in the family Rutaceae (e.g., calamondin, box orange, Indian curry leaf, and orange jessamine/orange jasmine).

The Asian citrus psyllid (or ACP), damages citrus directly by feeding on newly developed leaves (flush). However, more seriously, the insect is a vector of the bacterium Candidatus Liberibacter asiaticus, associated with the fatal citrus disease HLB, also called citrus greening disease. The psyllid takes the bacteria into its body when it feeds on bacteria-infected plants. The disease spreads when a bacteria-carrying psyllid flies to a healthy plant and injects bacteria into it as it feeds.

HLB can kill a citrus tree in as little as 5 years, and there is no known cure or remedy. All commonly grown citrus varieties are susceptible to the pathogen. The only way to protect trees is to prevent the spread of the HLB pathogen by controlling psyllid populations and destroying any infected trees.

The Asian citrus psyllid is widely distributed throughout Southern California and is becoming more widespread in the Central Valley and further north. The first tree with HLB was found in March 2012 in a home garden in Los Angeles County and a few years later was found in residences in Orange and Riverside Counties. Spread of the disease began to rapidly accelerate in these areas in 2017. Removal of infected trees by the California Department of Food and Agriculture (CDFA) has occurred wherever they have been found.

The presence of HLB in pockets of Southern California emphasizes that it is critical to control psyllid populations so that disease spread is limited.

BACKGROUND

The Asian citrus psyllid and the HLB disease originated in eastern Asia or the Indian subcontinent and then spread to other areas of the world where citrus is grown. The psyllid was first found in the United States in 1998 in Palm Beach County, Florida on backyard plantings of orange jessamine, Murraya paniculata, and spread rapidly over a 3-year period. HLB spread equally rapidly in Florida.

In 2008, the Asian citrus psyllid was first detected in California. The psyllid spread throughout Southern California, particularly in urban and suburban environments, but also in commercial groves. The psyllid has since expanded its range to the Central Valley and the Central Coast, and has been found as far north as the San Francisco Bay Area and sites near Sacramento.

The first infected tree found in California is believed to have been the result of illegal grafting of an infected bud (taking plant tissue from one tree and inserting it into another to form a new branch). The infected tree was destroyed to prevent further spread of the bacterium. Since that time, additional infected trees have been found in southern California’s residential areas these may have resulted from illegally imported diseased trees, illegal grafting of infected budwood, and, more recently, the natural spread of the bacterium by the psyllid. CDFA is continuing to detect and eliminate infected trees.

To protect the state's commercial and residential citrus from HLB, it is important to control the psyllid, prevent the accidental introduction of any infected host plant, and detect and remove any infected plants found in California as quickly as possible. The job of detecting infected trees is made difficult by the fact that it takes one to several years for symptoms of HLB to begin to show in the trees. Meanwhile, psyllids can pick up the HLB pathogen as nymphs and spread it only a few weeks after the tree is infected when they fly away as adults. Therefore, it is important to monitor and control psyllids in citrus trees and immediately report any suspected plant symptoms to the county agricultural commissioner.

IDENTIFICATION

Psyllid Life Stages

The adult Asian citrus psyllid is a small brownish-winged insect about the size of an aphid. Its body is 1/6 to 1/8 inch long with a pointed front end, red eyes, and short antennae. The wings are mottled brown around the outer edge except where a clear stripe breaks up the pattern at the back. The adult psyllid feeds with its head down, almost touching the leaf, and the rest of its body is raised from the surface at an almost 45-degree angle with its back end in the air . No other insect pest of citrus positions its body this way while feeding.

Adults typically live 1 to 2 months. Females lay tiny yellow-orange almond-shaped eggs in the folds of the newly developed leaves of citrus. Each female can lay several hundred eggs during her lifespan.

The eggs hatch into nymphs that are wingless, flattened, yellow or orange to brownish, and 1/100 to 1/14 inch long. Nymphs molt 4 times, increasing in size with each nymphal stage (instar), before maturing into adult psyllids. Late instar nymphs have distinctive red eyes. The nymphs can only feed on soft, young plant tissue and are found on immature leaves, stems and flowers of citrus.

The nymphs remove sap from plant tissue when they feed and excrete a large quantity of sugary liquid (honeydew). Each nymph also produces a waxy tubule from its back end to help clear the sugary waste product away from its body. The tubule's shape—a curly tube with a bulb at the end—is unique to the Asian citrus psyllid and can be used to identify the insect.

There are other psyllids such as Eucalyptus psyllids, tomato psyllids, and Eugenia psyllid that can be found in home gardens. The Asian citrus psyllid is easily distinguished from these in its adult stage by the brown band along the edge of its wing interrupted by a clear area, its characteristic body tilt, and, in the nymph stage, the shape of the waxy tubules it produces.

DAMAGE

The Asian citrus psyllid damages citrus when its nymphs feed on new shoots and leaves. They remove sap from the plant tissue and inject a salivary toxin as they feed. This toxin can inhibit or kill new shoots, deforming new leaves by twisting and curling them. If the leaves mature after sustaining this damage then they will have a characteristic notch.

There are many other insect pests that can cause twisting of leaves, such as aphids, citrus leafminer, and citrus thrips. The twisting of leaves doesn't harm trees and can be tolerated, but the death of new growth will retard the growth of young trees that are less than 5 years old.

Excess sap (honeydew) that the psyllid nymphs excrete accumulates on leaf surfaces. This promotes the growth of sooty mold, which is unsightly but not harmful. Other insect pests of citrus also excrete honeydew, including aphids, whiteflies, and soft scales.

Most importantly, the Asian citrus psyllid, through its feeding activity, can inoculates the tree with the bacterium that causes HLB, ultimately killing the tree. It only takes a few psyllids to spread the disease.

HLB Disease

An early symptom of HLB in citrus is the yellowing of leaves on an individual limb or in one sector of a tree's canopy. Leaves that turn yellow from HLB will show an asymmetrical pattern of blotchy yellowing or mottling of the leaf, with patches of green on one side of the leaf and yellow on the other side.

Citrus leaves can turn yellow for many other reasons and often discolor from deficiencies of zinc or other nutrients. However, the pattern of yellowing caused by nutrient deficiencies typically occurs symmetrically (equally on both sides of the midvein), between or along leaf veins.

As the disease progresses, the fruit size becomes smaller, and the juice turns bitter. The fruit may remain partially green, which is why the disease is also called citrus greening. The fruit becomes lopsided, has dark aborted seeds, and tends to drop prematurely.

Chronically infected trees are sparsely foliated with small leaves that point upward, and the trees have extensive twig and limb dieback. Eventually, the tree stops bearing fruit and dies. Fruit and tree health symptoms may not begin to appear for 2 or more years after the bacteria infect a tree.

MONITORING AND MANAGEMENT

In response to the establishment of ACP in California, CDFA began an extensive monitoring program to track the distribution of the insect and disease. This program involves CDFA and other personnel regularly checking thousands of yellow sticky traps for the psyllid, in both residential areas and commercial citrus groves throughout the state. The program also includes frequent testing of psyllids and leaf samples for the presence of the pathogen.

Monitoring results are being used to delimit quarantine zones, guide releases of biological control agents, intensify testing for HLB, and prioritize areas for chemical control programs. In areas where HLB has been found, home gardeners need to take an active role in controlling the psyllid throughout the year, by watching for disease symptoms and supporting disease testing and tree removal activities.

ACP and HLB Quarantines

ACP quarantine zones have been established throughout the state that restrict movement of citrus trees and fruit in order to prevent psyllids from being moved to new, uninfested areas of California. Additional, more restrictive HLB quarantine zones have been established to help keep HLB from spreading. Citrus trees and close relatives that could be hosts of the psyllid can't be taken out of quarantine areas. Fruit can be moved, but only if it is washed and free of stems and leaves that could harbor psyllids.

Whether you are inside or outside a quarantine area, it is very important to assist with the effort to reduce Asian citrus psyllids and report suspected HLB symptoms in your trees. Your efforts will slow the spread of HLB and provide time for scientists to work on finding a cure for the disease. For maps and information about the quarantine areas, see the UC ANR ACP Distribution and Management website.

How You Can Help

UC citrus entomologist Beth Grafton-Cardwell, Ph.D., explains how to monitor citrus trees for Asian citrus psyllid. (1:00)

Residents and landscapers can help combat the psyllid by inspecting their citrus trees and reporting infestations of the Asian citrus psyllid in areas where they are not known to occur or suspected cases of the disease. For more photos of the Asian citrus psyllid and HLB symptoms, visit the California Citrus Threat website.

The best way to detect psyllids is by looking at tiny newly-developing leaves on citrus trees whenever flush (clusters of new leaves) is forming. Mature citrus trees typically produce most of their new growth in the spring and fall, but young trees and lemons tend to flush periodically year round during warm weather.

Slowly walk around each tree and inspect the flush. Look for signs of psyllid feeding and damage, including twisted or notched leaves, nymphs producing waxy deposits, honeydew, sooty mold, or adult psyllids. If you think psyllids are present, use a hand lens to look for small yellow eggs, psyllid nymphs with their waxy tubules, and adults. Immature stages (eggs and nymphs) are found on tender new leaves and they don't fly, so monitoring efforts are most effective when directed toward these stages on citrus flush.

If you think you have found the insect, immediately contact the CDFA Exotic Pest Hotline at 1-800-491-1899. CDFA staff will tell you if you are in an area that is new to the psyllid or if it is common in your area.

If you are in an area that is new to the psyllid, CDFA may come to your residence and take a sample. If the insect is identified as an Asian citrus psyllid, then the quarantine may expand to include that location, and citrus and other ACP host plants will be treated with insecticides by CDFA personnel to control the psyllid.

In areas known to be widely infested with the psyllid, you will need to treat for the psyllid yourself. This can be confirmed by calling the CDFA hotline. This publication provides information on how you can treat your infested trees. If you need further assistance, contact your local UC Master Gardener program or a landscaping and pest control professional for more information about the steps you can take to control the psyllid.

Monitoring citrus trees for symptoms of HLB disease is critical for early detection and management. Immediately report suspected cases of the disease to your county agricultural commissioner's office or call the CDFA hotline at 1-800-491-1899. If the tree is found to be infected with the HLB pathogen, it will be removed immediately to prevent further spread of the disease. It is critical that residents cooperate with tree removal.

Symptoms of HLB take a long time to develop after a tree is first infected, perhaps upwards of 2 years or more for mature trees. However, infected trees can be a source of the bacterium for the psyllid much sooner. This means that in areas where HLB is known to be present, just because a tree looks to be free of HLB symptoms does not mean that it hasn’t been infected. Therefore, for residential areas where HLB is becoming widespread it is worth considering proactive removal of your citrus trees, even if they have not yet tested positive for the disease, to help contain HLB spread. At the very least, in these high HLB risk areas, home gardeners should be discouraged from planting new citrus trees given the high potential for them to become infected in the near future.

Biological Control

A number of predators and parasites feed on ACP. The nymphs are killed by tiny parasitic wasps and various predators, including lady beetle adults and larvae, syrphid fly larvae, lacewing larvae, and minute pirate bugs. Some spiders, birds, and other general predators feed on adult psyllids.

Several species of tiny parasitoid wasps, collected by University of California researchers, have been brought to California for host-testing, mass-rearing, and release. The most promising of these, Tamarixia radiata, strongly prefers ACP nymphs, and under ideal conditions can significantly reduce psyllid populations.

Females of this tiny wasp, which poses no threat to people, lay their eggs underneath ACP nymphs, and after hatching, the parasitoid larvae feed on and kill the psyllid. To find evidence of this wasp at work, keep an eye out for ACP “mummies”, which look like hollowed-out nymphal shells. This wasp has been released at thousands of sites throughout Southern California since early 2012. More recently, T. radiata releases have been made in Central California and a second wasp (Diaphorencyrtus aligarhensis) that attacks the younger ACP nymphs was released in Southern California.

Tamarixia and other natural enemies have reduced ACP populations in Southern California, but they have not eradicated the pest and have not halted the spread of HLB. In the absence of ants, these beneficial insects will at least help to reduce psyllids, especially in areas where it is not possible or practical to institute chemical psyllid control measures. Visit the ACP Distribution and Management website to see a map of where these parasites have been released in California.

Ant Control to Protect Natural Enemies

Ants directly interfere with biological control of ACP, so it is very important for residents to control ants around their citrus trees. Ants “farm” the psyllid honeydew, feed it to their young and vigorously protect psyllids from predators and parasites (also called natural enemies). Ants do this to preserve this food source for their colony.

Ant control is especially important in areas of California where the very aggressive Argentine ant is found. Argentine ants can significantly reduce Tamarixia and Diaphorencyrtis attack rates on ACP. For information on ant identification and management in the landscape, see the UC IPM Pest Notes: Ants.

Chemical Control

In areas where ACP has newly arrived, or where residential citrus trees are close to commercial citrus operations, CDFA conducts residential insecticide treatments to control psyllids. When a psyllid is found in these areas, all citrus and other ACP host plants on a property and nearby properties receive an application of two insecticides: a foliar pyrethroid insecticide to quickly kill adults and immature psyllids by direct contact and a soil-applied systemic insecticide to provide sustained control of nymphs tucked inside young leaves. This combination of treatments may protect trees against psyllids for many months. Home gardeners are encouraged to be vigilant and consider supplementary applications of their own when they see psyllids on their trees.

Because of the threat ACP poses to both backyard and commercial citrus and the urgency of containing this pest, home gardeners outside the areas that are part of the CDFA residential treatment program are encouraged to consider implementing their own psyllid control measures if psyllids are found in their area.

Home gardeners can hire a landscape pest control professional to apply insecticides, or make treatments themselves. Landscape professionals have access to the same pesticides applied by CDFA, which include the systemic imidacloprid and foliar applications of the pyrethroid beta-cyfluthrin.

Home gardeners can apply broad-spectrum foliar sprays (carbaryl, malathion) to rapidly control adults and protect plants for many weeks. The systemic insecticide imidacloprid (Bayer Advanced Fruit, Citrus & Vegetable and other products) is available for use as a soil drench, which moves through the roots to the growing tissues of the plant. This systemic insecticide provides good control of the nymphs for 1 to 2 months. Nymphs are hard to reach with foliar sprays because they are tucked inside the small, developing flush.

Apply the soil drench during summer or fall when roots are actively growing. Broad-spectrum foliar sprays and systemic insecticides are toxic to honey bees, so don't apply them when the citrus trees are blooming.

There are also a number of organic and "soft" foliar insecticides such as oils and soaps (horticultural spray oil, neem oil, insecticidal soap) that can help to reduce psyllids. These insecticides are generally lower in risk to beneficial insects (natural enemies and pollinators) however, they are also less persistent so applications need to be made frequently when psyllids are observed (every 7 to 14 days). Oil and soap insecticides must make direct contact with the psyllid so should be applied carefully to achieve full coverage of the tree. See the "Active Ingredients Compare Risks" button in this publication online for more information about potential hazards posed by these materials.

Treatment Considerations
  • Always follow label instructions for the safe and effective use of the product.
  • Only apply insecticides if psyllids have been observed in your area.
  • Only apply insecticides to host plants of psyllids (citrus and closely related hosts).
  • Avoid using insecticides during bloom to limit impacts on bees.
  • Thoroughly wet the foliage when spraying, including undersides of leaves.

REFERENCES

Citrus Pest and Disease Prevention Program. California Citrus Threat page. Online at CaliforniaCitrusThreat.com/ and in Spanish at PeligranCitricosEnCalifornia.com. (Accessed on September 25, 2018.)

Grafton-Cardwell EE, Godfrey KE, Rogers ME, Childers CC, Stansly PA. 2006. Asian Citrus Psyllid. UC ANR Publication. 8205. Oakland, CA.

Polek M, Vidalakis G, Godfrey KE. 2007. Citrus Bacterial Canker Disease and Huanglongbing (Citrus Greening). UC ANR Publication. 8218. Oakland, CA.

Rust MK, Choe D-H. 2012. Pest Notes: Ants. UC ANR Publication 7411. Oakland, CA.

UC Agriculture and Natural Resources. California Master Gardeners website. (Accessed on September 25, 2018.)

United States Department of Agriculture. Citrus Greening Disease home page. (Accessed on September 25, 2018.)

PUBLICATION INFORMATION

Pest Notes: Asian Citrus Psyllid and Huanglongbing Disease (formerly titled Asian Citrus Psyllid)

AUTHORS: Elizabeth E. Grafton-Cardwell, Entomology, UC Riverside and Lindcove Research and Extension Center, and Matthew P. Daugherty, Entomology, UC Riverside.

TECHNICAL EDITOR: K Windbiel-Rojas
ANR ASSOCIATE EDITOR: AM Sutherland
EDITOR: B Messenger-Sikes

Produced by University of California Statewide IPM Program

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Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2018 The Regents of the University of California. All rights reserved.

For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See our Home page, or in the U.S., contact your local Cooperative Extension office for assistance.

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Accessibility /PMG/PESTNOTES/pn74155.html revised: October 23, 2018. Contact webmaster.


Damage

Asian citrus psyllid attacks all varieties of citrus and very closely related ornamental plants in the family Rutaceae (mock orange, Indian curry leaf, orange jasmine and other Murraya species). This pest attacks new citrus leaf growth and, because of the salivary toxin that it injects, causes the new leaf tips to twist or burn back.

However, the more serious damage that it causes is due to the psyllid vectoring the bacterium (Candidatus Liberibacter asiaticus) that causes Huanglongbing (HLB or citrus greening) disease. Huanglongbing causes shoots to yellow, asymmetrically (blotchy mottle), and results in asymmetrically shaped fruit with aborted seeds and bitter juice. The disease can kill a citrus tree within 5 to 8 years, and there is no known cure for the disease.

Asian citrus psyllid arrived in Southern California from Mexico in 2008 and is now well established in Southern California and spreading northward. Huanglongbing was found in residential trees in Los Angeles County in 2012, likely due to illegal importation of infected plant material it is spreading from that area and spreading northward from Mexico.

In Florida, the psyllid and disease were rapidly spread throughout the state on nursery plants such as Murraya. It is thought that Huanglongbing was present in a small number of Florida backyard citrus trees for a number of years, and it took the arrival of Asian citrus psyllid to move the disease into commercial citrus orchards. Florida citrus growers are now applying broad-spectrum pesticides more than eight times per year to reduce Asian citrus psyllid and slow the spread of the disease. Pesticides can reduce the number of psyllids, but an adult psyllid carries the bacteria for most of its life and can sometimes transmit the disease faster than pesticides will kill it.

Currently, pesticide applications to California citrus orchards are designed to limit and slow the spread of Asian citrus psyllid and Huanglongbing throughout California. Keeping the psyllid numbers low will help prevent the psyllids from finding and spreading the bacterium that causes the disease.

Adult psyllids can be detected through visual surveys of new flush (new leaf growth), net sampling, tap sampling and use of yellow sticky cards. Immature stages (eggs and nymphs) are limited to new growth, so direct visual monitoring efforts on "feather flush" are needed to detect these stages.

For more information, read UC ANR Publication 8205, Asian Citrus Psyllid, and 8218, Citrus Bacterial Canker Disease and Huanglongbing (Citrus Greening). For more information about the location of Asian citrus psyllid and Huanglongbing, and to view management strategies for various citrus growing regions, see the UC ANR website Asian Citrus Psyllid Distribution and Management.

If you see the Asian citrus psyllid in areas of California where it is not yet known to occur, please contact the California Department of Agriculture (CDFA) Exotic Pest Hotline at 1-800-491-1899. Personnel from CDFA will inspect plants for the presence of this psyllid and send specimens to diagnostic laboratories for identification and determination of the presence of the Huanglongbing bacterium in psyllids and plant tissue.


Spotlights

Agricultural Research Service (ARS) researchers in Florida have developed “attract-and-kill” traps to control Asian citrus psyllids in the suburbs where citrus trees are popular landscape plantings.

The Asian citrus psyllid (Diaphorina citri), also called the Asiatic citrus psyllid or ACP, is a notorious pest that prefers citrus and closely related plants for hosts, particularly species within the genera Citrus, Citropsis, and Murraya. Although the spread of this vector is a concern, with vigilant scouting for obvious symptoms, and close inspections to detect the pests themselves, we can work together to be proactive in protecting our citrus. Here IDTools presents a set of IDaids that support the detection and identification of the Asian citrus psyllid. Visit Search IDaids to find identification resources for many more plant pests.


How to Prevent Psyllids

The best preventive measure is to make sure that your plants remain in the best state of health. When it is healthy, it will be more resistant to infestation. This is true not only in the case of psyllids, but with other pests as well. You also need to keep the surroundings clean and always check your plant for damage. To add, avoid overfertilizing and overwatering the plants as it will make it more attractive for psyllids. Act as soon as possible before the problem escalates.


UC Riverside discovers first effective treatment for citrus-destroying disease

New license agreement commercializes innovative, safe technology

UC Riverside scientists have found the first substance capable of controlling Citrus Greening Disease, which has devastated citrus farms in Florida and also threatens California.

The new treatment effectively kills the bacterium causing the disease with a naturally occurring molecule found in wild citrus relatives. This molecule, an antimicrobial peptide, offers numerous advantages over the antibiotics currently used to treat the disease.

UCR geneticist Hailing Jin, who discovered the cure after a five-year search, explained that unlike antibiotic sprays, the peptide is stable even when used outdoors in high heat, easy to manufacture, and safe for humans.

“This peptide is found in the fruit of greening-tolerant Australian finger limes, which has been consumed for hundreds of years,” Jin said. “It is much safer to use this natural plant product on agricultural crops than other synthetic chemicals.”

Currently, some growers in Florida are spraying antibiotics and pesticides in an attempt to save trees from the CLas bacterium that causes citrus greening, also known as Huanglongbing or HLB.

“Most antibiotics are temperature sensitive, so their effects are largely reduced when applied in the hot weather,” Jin said. “By contrast, this peptide is stable even when used in 130-degree heat.”

Jin found the peptide by examining plants such as the Australian finger lime known to possess natural tolerance for the bacteria that causes Citrus Greening Disease, and she isolated the genes that contribute to this innate immunity. One of these genes produces the peptide, which she then tested over the course of two years. Improvement was soon visible.

“You can see the bacteria drastically reduced, and the leaves appear healthy again only a few months after treatment,” Jin said.

Because the peptide only needs to be reapplied a few times per year, it is highly cost effective for growers. This peptide can also be developed into a vaccine-like solution to protect young healthy plants from infection, as it is able to induce the plant’s innate immunity to the bacteria.

Jin’s peptide can be applied by injection or foliage spray, and it moves systemically through plants and remains stable, which makes the effect of the treatment stronger.

The treatment will be further enhanced with proprietary injection technology made by Invaio Sciences. UC Riverside has entered into an exclusive, worldwide license agreement with Invaio, ensuring this new treatment goes exactly where it’s needed in plants.

“Invaio is enthusiastic to partner with UC Riverside and advance this innovative technology for combating the disease known as Citrus Greening or Huanglongbing,” said Invaio Chief Science Officer Gerardo Ramos. “The prospect of addressing this previously incurable and devastating crop disease, helping agricultural communities and improving the environmental impact of production is exciting and rewarding,” he said. “This is crop protection in harmony with nature.”

The need for an HLB cure is a global problem, but hits especially close to home as California produces 80 percent of all the fresh citrus in the United States, said Brian Suh, director of technology commercialization in UCR’s Office of Technology Partnerships, which helps bring university technology to market for the benefit of society through licenses, partnerships, and startup companies.

“This license to Invaio opens up the opportunity for a product to get to market faster,” Suh said. “Cutting edge research from UCR, like the peptide identified by Dr. Jin, has a tremendous amount of commercial potential and can transform the trajectory of real-world problems with these innovative solutions.”


Asian Citrus Psyllid (ACP)

The Asian citrus psyllid (ACP) is a pest that acts as a carrier or vector spreading "huanglongbing" (HLB), a devastating disease of citrus trees. This bacterial disease is transmitted to healthy trees by the psyllid after it feeds on infected plant tissue.

Quarantine Information

Regional Quarantine Zone Overview

  • Active Regional Quarantines Web Application - 3/9/21
  • Maps: See Regional Quarantine Zones in sections below:
    • Bulk Citrus
    • Host Nursery Stock
  • Bulk Citrus Regional Quarantine Zones (Google Earth file)
  • Nursery Regional Quarantine Zones (Google Earth file)
  • Quarantine Update Notification Log
  •  Note: All maps are PDF documents.

Bulk Citrus Regional Quarantine Zones

Zones and Counties

Zone 1: comprises uninfested counties where HLB has not been detected, there are no contiguous citrus growing regions, and it is not proximate to the border with Mexico.

  • Zone 1 Counties: Alpine, Amador, Butte, Calaveras, Colusa, Del Norte, El Dorado, Glenn, Humboldt, Inyo, Lake, Lassen, Mariposa, Mendocino, Modoc, Mono, Napa, Nevada, Plumas, Santa Cruz, Shasta, Sierra, Siskiyou, Sonoma, Sutter, Tehama, Trinity, Tuolumne, and Yuba.

ZONE 2: comprises counties that are partially infested with ACP, HLB has not been detected, a geographical barrier exists between it and adjacent contiguous citrus growing regions (i.e., Zones 4, 5, and 6), a contiguous citrus growing region exists within the zone, sufficient citrus commodity cleaning and packing capacity exists within the zone, and geographical barriers separate it from zones that are heavily infested with ACP and where HLB has been detected (i.e., Zone 6).

  • Zone 2 Counties: Fresno, Kern, Kings, Madera, Merced, San Joaquin, Stanislaus, and Tulare

ZONE 3: comprises counties that are partially infested with ACP, HLB has not been detected, a geographical barrier exists between it and adjacent contiguous citrus growing regions (i.e., Zone 2, 3, and 4), a contiguous citrus growing region exists within the zone, sufficient citrus commodity cleaning and packing capacity exists within the zone, and geographical barriers separate it from zones that are heavily infested with ACP (i.e., Zone 4) or where HLB has been detected (i.e., Zone 6).

  • Zone 3 Counties: Monterey, San Benito, and San Luis Obispo

ZONE 4: comprises counties that are generally infested with ACP, HLB has not been detected, a geographical barrier exists between it and adjacent contiguous citrus growing regions (i.e., Zones 2, 3, and 4), a contiguous citrus growing region exists within the zone, sufficient citrus commodity cleaning and packing capacity exists within 8 the zone, geographical barriers separate it from Zone 6 where HLB has been detected, and it is not proximate to the border with Mexico.

  • Zone 4 Counties: Santa Barbara and Ventura

ZONE 5: comprises counties that are generally infested with ACP, HLB has not been detected, a geographical barrier exists between it and adjacent contiguous citrus growing regions (i.e., Zones 4 and 6), a contiguous citrus growing region exists within the zone, sufficient citrus commodity cleaning and packing capacity exists within the zone, a geographical barrier separates it from Zone 6 where HLB has been detected, and it is proximate to the border with Mexico.

  • Zone 5 Counties: Imperial and San Diego Counties, and a Portion of Riverside and San Bernardino Counties

ZONE 6: comprises counties, or portions of counties, that are generally infested with ACP, HLB has been detected in some areas, a geographical barrier exists between it and adjacent contiguous citrus growing regions (i.e., Zones 2, 4, and 5), a contiguous citrus growing region exists within the zone, sufficient citrus commodity cleaning and packing capacity exists within the zone, and it is not proximate to the border with Mexico.

    Zone 6 Counties: Los Angeles and Orange Counties, and a Portion of Riverside and San Bernardino Counties as described below.

In the Crestmore Heights and Riverside areas: Beginning at the intersection of the Union Pacific railroad tracks and the Jurupa Hills Country Club boundary at 33.972709 latitude and -117.444986 longitude then, starting northerly along the Jurupa Hills Country Club boundary to its intersection with the intersection of Linares Avenue and Moraga Avenue then, northerly along Moraga Avenue to its intersection with Avenue Juan Diaz then, northerly along said avenue to its intersection with Peralta Place then, northerly along said place to its intersection with Limonite Avenue then, westerly along said avenue to its intersection with Camino Real then, northerly along said real to its intersection with Granite Hill Drive then, easterly along said drive to its intersection with the Sunnyslope City Boundary at 34.013533 latitude and -117.441269 longitude then, easterly along said boundary to its intersection with Granite Hill Drive then, northerly along said drive to its intersection with the Oak Quarry Golf Club boundary at 34.019669 latitude and -117.437699 longitude then, northeasterly along said boundary to its intersection with the Riverside and San Bernardino county boundaries at 34.034006 latitude and -117.433997 longitude then, easterly along said boundary to its intersection with Sierra Avenue then, northerly along said avenue to its intersection with Sierra Avenue and Jurupa Avenue then, easterly along Jurupa Avenue to its intersection with Alder Avenue then, northerly along said avenue to its intersection with Santa Ana Avenue then, easterly along said avenue to its intersection with Maple Avenue then, northerly along said avenue to its intersection with Slover Avenue then, easterly along said avenue to its intersection with Cedar Avenue then, northerly along said avenue to its intersection with Valley Boulevard then, westerly along said boulevard to its intersection with W Valley Boulevard then, easterly along said boulevard to its intersection with S Riverside Avenue then, northerly along said avenue to its intersection with E San Bernardino Avenue then, easterly along said avenue to its intersection with San Bernardino Avenue then, easterly along said avenue to its intersection with W Olive Street then, easterly along said street to its intersection with Cypress Avenue then, southerly along said avenue to its intersection with W C Street then, easterly along said street to its intersection with N Rancho Avenue then, southerly along said avenue to its intersection with W F Street then, easterly along said street to its intersection with Pennsylvania Avenue then, southerly along said avenue to its intersection with W H Street then, easterly along said street to its intersection with E H Street then, easterly along said street to its intersection with N Mount Vernon Avenue then, southerly along said avenue to its intersection with I-10 E then, easterly along said highway to its intersection with Hunts Lane then, southerly along said lane to its intersection with S Hunts Lane then, southerly along said lane to its intersection with E Washington Street then, easterly along said street to its intersection with Sierra Vista Drive then, southerly along said drive to its end then, southerly along an imaginary line to its intersection with Prado Lane at 34.038381 latitude and -117.267737 longitude then, southerly along said lane to its intersection with Utility Access Road then, southerly along an imaginary line to its intersection with Scotch Lane at 34.023560 latitude and -117.263430 longitude then, southwesterly along said lane to its intersection with Scotch Lane and at 34.021848 latitude and -117.263959 longitude then, southeasterly along an Imaginary Line to its intersection with the Riverside/San Bernardino County line at 34.018800 latitude and -117.257880 longitude then, southerly along an Imaginary Line to its intersection with Rattlesnake Ridge at 34.013657 latitude and -117.256658 longitude then, southerly along an Imaginary Line to its intersection with an Unnamed Road at 34.007724 latitude and -117.257830 longitude then, southerly along an Imaginary Line to 33.994941 latitude and -117.256701 longitude then, southwesterly along an Imaginary Line to its intersection with Hidden View Lane at 33.986770 latitude and -117.263300 longitude then, southerly along said lane to its intersection with Pigeon Pass Road then, southerly along said road to its intersection with Climbing Rose Drive then, westerly along said drive to its intersection with Barclay Drive then, southerly along said drive to its intersection with Ironwood Avenue then, westerly along said avenue to its intersection with Day Street then, southerly along said street to its intersection with Gateway Drive then, westerly along said drive to its intersection with Valley Springs Parkway then, southerly along said parkway to its intersection with Eucalyptus Avenue then, westerly along said avenue to its intersection with Eastridge Avenue then, westerly along said avenue to its intersection with River Run then, southerly along said run to its intersection with an Imaginary Line at the end of said run then, southwesterly along said line to its intersection with Sycamore Canyon River at 33.9253452 latitude and -117.307673 longitude then, westerly along said river to its intersection with an Imaginary Line then, westerly along said line to its intersection with Barton Street at 33.925540 latitude and -117.313980 longitude then, westerly along said street to its intersection with Cottonwood Avenue then, westerly along said avenue to its intersection with Cottonwood Avenue and an Imaginary Line then, westerly along said line to its intersection with Wood Road then, southerly along said road to its intersection with Cannon Road then, westerly along said road to its intersection with Alessandro Boulevard then, southerly along said boulevard to its intersection with Berry Road then, westerly along said road to its intersection with Crystal View Terrace then, northwesterly along said terrace to its intersection with Overlook Parkway then, westerly along said parkway to its intersection with Washington Street then, northerly along said street to its intersection with Victoria Avenue then, southwesterly along said avenue to its intersection with Madison Street then, northwesterly along said street to its intersection with Arlington Avenue then, westerly along said avenue to its intersection with Streeter Avenue then, northerly along said avenue to its intersection with Rochester Street then, westerly along said street to its intersection with Rexford Drive then, northerly along said drive to its intersection with Central Avenue then, westerly along said avenue to its intersection with Hillside Avenue then, northerly along said avenue to its intersection with Mountain View Avenue then, westerly along said avenue to its intersection with Sheppard Street then, northerly along said street to its intersection with Jurupa Avenue then, northerly along said avenue to its intersection with the United Pacific railroad tracks then, northwesterly along said tracks to the point of beginning.

ZONE 7: comprises counties that are partially infested with ACP, HLB has not been detected, there are no contiguous citrus growing regions, and it is not proximate to the border with Mexico.

  • Zone 7 Counties: Sacramento, Santa Clara, San Mateo, Alameda, Contra Costa, Marin, San Francisco, Solano, Placer and Yolo Counties


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