Cooperative Extension San Joaquin County
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Posts Tagged: Asian citrus psyllid

Huanglongbing is a growing threat to California’s citrus industry

A symptom of HLB in citrus is the yellowing of leaves on an individual limb or in one sector of a tree's canopy. (Photo: Citrus Pest and Disease Prevention Program)
Huanglongbing (HLB) is a devastating bacterial disease of citrus that is starting to spread rapidly in urban areas of Southern California. The disease is spread by the invasive insect Asian citrus psyllid.

Asian citrus psyllid was first identified in California in 2008, and has been found from San Diego and Imperial counties in the south, all the way to Sacramento County in the north. See a map of Asian citrus psyllid and huanglongbing distribution in California.

UC Agriculture and Natural Resources specialists and advisors are working with the citrus industry, USDA and CDFA to control ACP populations and keep HLB contained while researchers search for a cure for the disease.

In order to find and remove infected trees before ACP can spread the disease to other trees, UC scientists are focusing research on early HLB detection technologies (EDTs). When infections first start, the bacteria are in just a few leaves. If the sampler doesn't collect those leaves, the disease can be missed. It can take one to two years for the bacteria to distribute itself throughout the tree so this sampling error doesn't occur. 

Early detection technologies use whole tree responses to early infections. For example, Carolyn Slupsky, food science and technology professor at UC Davis, measures changes in tree metabolism (its day-to-day chemical function) when it becomes infected. Every leaf on the tree is connected to the tree's metabolism, so it doesn't matter which leaf is collected. This type of test can detect an infected tree within weeks or months after infection instead of years. 

Scientists are also studying ways to modify ACP so the insects are unable to spread HLB, and studying the use of conventional breeding, genome editing or genetic engineering to develop disease-resistant citrus. Read summaries of the research here.

Young Asian citrus psyllids, called nymphs, produce a white, waxy substance.
Keeping Asian citrus psyllid and huanglongbing disease at bay depends in large part on the active involvement of commercial citrus growers and California residents who have citrus trees in their home landscapes. The UC ANR Asian Citrus Psyllid Distribution and Management website provides detailed guidelines for growers and residents to monitor for Asian citrus psyllid and huanglongbing, and learn about options for reducing psyllid populations and responding to the disease if it's in your area.

View a four-minute video that shows how to monitor for ACP presence in residential citrus:

Posted on Friday, May 31, 2019 at 2:21 PM
Focus Area Tags: Pest Management

UC has boots on the ground in an unrelenting search for Asian citrus psyllid

With two magnifying loops around her neck and a truck stocked with vials and tools for insect collection, Joanne O'Sullivan scouts Ventura County citrus orchards every day. She walks the perimeter, examining newly emerging leaves and tapping branches with a PVC wand to bat pests onto her clipboard.

O'Sullivan is one of four scouts hired and trained by UC Agriculture and Natural Resources scientists to carefully and continuously monitor citrus orchards for Asian citrus psyllid, an invasive pest in California that can spread the devastating huanglongbing disease.

Joanne O'Sullivan is one of the scouts hired by UC to search for and collect Asian citrus psyllids.

In Florida, where the pest was left unchecked when it first invaded citrus growing regions, the disease swept through the state. Citrus production in the Sunshine State plummeted 60 percent in 15 years.

“We don't want to let that happen here,” said Beth Grafton-Cardwell, UC Cooperative Extension entomology specialist. Grafton-Cardwell hired O'Sullivan and her colleagues who monitor citrus in San Diego, Imperial, Riverside and San Bernardino counties to scour dozens of orchards to document how treatments to control ACP are working. Next year scouts will be added in Tulare and Kern counties.

When ACP are found, they are carefully bottled and sent to the lab to determine whether they carry the bacterium that causes huanglongbing disease.

O'Sullivan taps branches with a PVC wand to knock off insects.

The expansive ACP monitoring effort is funded by a $1.45 million multi-agency coordination grant from the USDA. The project funds promising tools and long-term solutions to reduce the spread of huanglongbing. Led by Neil McRoberts, a professor of plant pathology at UC Davis, the grant also provides funds for two other activities. 

One is a collaboration with California Citrus Mutual to offer free citrus tree removal to homeowners in areas where HLB is known to occur. The second is modeling data from the CDFA HLB survey program, in which psyllids and symptomatic plant tissue are tested for the bacteria. Trees may have the disease but not show symptoms, so testing the psyllids is a more effective way to find infected trees. The modeling work will improve the ability to predict the locations of infected trees.

However, the main thrust is monitoring citrus treatments and their impacts on the ACP population with a team of scouts. A mix of conventional and organic farmers and growers who use biological integrated pest management programs to manage their orchards were recruited for the project. The farmers make ACP treatment decisions informed by research results that show the best treatments and timing.

“Most growers are coordinating their treatments to get a bigger bang for their buck,” Grafton-Cardwell said.

If she finds ACP, O'Sullivan places them in vials to be sent to a lab for testing to determine whether they are carrying the bacterium that causes huanglongbing disease.

With just six months of data, the monitoring program has already yielded important information about Asian citrus psyllid.

“We're seeing more psyllids on the borders than the centers of groves,” Grafton-Cardwell said. “And so eventually, we will make recommendations that at certain times of year or when populations are low, the grower will only need to spray the borders of the grove."

This will reduce costs and the impact of pesticides on natural enemies.

"The early data have also revealed which chemicals are the most effective for psyllid control. We've found that organic growers need to be more aggressive in the frequency of treatments, because the organic insecticides are not as effective as conventional insecticides," she said.

At 8 of the 49 Ventura County ranches in the project, yellow sticky traps were placed in trees to monitor for ACP's natural enemies, including lady bugs, green lacewings, and Tamorixia radiata, tiny wasps from Pakistan that were released in California to battle ACP.

O'Sullivan spends her days looking for ACP and rooting for natural enemies that can help control them.

When O'Sullivan sees one of the natural enemies at work in the field, she pauses to observe the process.

“Sometimes I'll see a lacewing munching on an ACP and I'll say, ‘Go man, go!'” O'Sullivan said.

Posted on Friday, July 28, 2017 at 8:19 AM

UC puts high science online in easy-to-read citrus research updates

California citrus farmers have their ears perked for all news related to Asian citrus psyllid (ACP) and huanglongbing (HLB) disease, but the very latest advances have been available only in highly technical research journals, often by subscription only.

UC Cooperative Extension scientists are now translating the high science into readable summaries and posting them on a new website called Science for Citrus Health to inform farmers, the media and interested members of the public.

“The future of the California citrus depends on scientists finding a solution to this pest and disease before they destroy the industry,” said Beth Grafton-Cardwell, UC Cooperative Extension citrus entomology specialist. “Our farmers want to stay on top of all the efforts to stop this threat.”

The new 'Science for Citrus Health' website can be found at

Grafton-Cardwell and UC Cooperative Extension biotechnology specialist Peggy Lemaux are the two scientists behind the new website. When scientists make progress toward their goals, Grafton-Cardwell and Lemaux craft one-page summaries with graphics and pictures to provide readers with the basics.

For example, the website outlines scientific endeavors aimed at stopping the spread of huanglongbing disease by eliminating the psyllid's ability to transfer the bacterial infection. This section is titled NuPsyllid, and contains summaries of three research papers including one by UC Davis plant pathologist Bryce Falk.

Falk is collecting viruses found in Asian citrus psyllid; so far he has identified five. He is looking into the potential to utilize one of the viruses as is or modify one of the viruses to block the psyllid's ability to transmit the bacterium.  For example, the virus might out compete the bacterium in the psyllid's body.   

Another focus of the website is HLB early detection techniques (EDTs). If HLB-infected trees are found and destroyed before they show symptoms, ACP is less likely to spread the disease to other trees. EDT research described on the website includes efforts to detect subtle changes in the tree that take place soon after infection, such as alterations in the scents that waft from the tree (studied by UC Davis engineer Cristina Davis), changes in the proteins in the tree (studied by UC Davis food scientist Carolyn Slupsky) and starch accumulation in the leaves (studied by UC farm advisor Ali Pourreza).

Other research areas on the Science for Citrus Health website are solutions for established orchards and replants.

As more research is published, more one-page descriptions will be added to the website. The website contains a feedback form to comment on the science and the summaries.

UC Cooperative Extension specialist Beth Grafton-Cardwell is one of two UC ANR scientists who have developed the Science for Citrus Health website.
Posted on Tuesday, July 18, 2017 at 8:54 AM

Top 10 pests in gardens and landscapes and how to control them

Download the free booklet at the bottom of the page!

1. Ants

Most people deal with ants around their home at some point. Because most ants live outdoors, focus efforts on keeping ants from entering buildings by caulking entryways. Follow good sanitation practices to make your home less attractive to ants. Spraying ants inside the home will not prevent more ants from entering. Use baits to control the ant colony. Pesticide baits work by attracting worker ants who then take the poison back to the nest where the entire colony, including queens, can be killed. In the landscape, ants protect honeydew-producing pest insects from predators, so use sticky barriers or insecticide baits to keep ants out of trees and shrubs.


2. Aphids

Aphids can curl leaves and produce sticky honeydew, but they rarely kill plants and you usually can wash them off with water. When aphid numbers get high, natural enemies such as lady beetles (lady bugs), lacewings, syrphid fly larvae, soldier beetles and others frequently feed on them, eliminating the need for pesticides. Protect these good bugs by avoiding the use of insecticides that can be toxic to a broad variety of insects. Ants protect aphids from these natural enemies, so keep ants away from your garden as well. When pesticides are necessary, use less toxic products such as insecticidal soaps and oils.


3. Asian citrus psyllid and Huanglongbing disease

The Asian citrus psyllid (ACP) and the deadly bacterial disease it spreads, Huanglongbing (HLB), threaten citrus trees in backyards and on farms. There is no cure or effective control method for HLB disease.  All types of citrus—including oranges, grapefruit, lemons, and mandarins—are affected as well as a few closely related ornamentals. ACP and HLB have already devastated the Florida citrus industry, and now that it is in the Western U.S. it is threatening the California citrus industry as well.


4. Gophers

Gophers are small burrowing rodents that feed on roots of many types of plants. A single gopher can ruin a garden in a short time, and gopher gnawing can damage irrigation lines and sprinkler systems. In lawns, their mounds are unsightly and interfere with mowing. Early detection is critical to prevent damage. Use both traps and underground fencing to manage gopher problems. Toxic baits are available but can pose threats to wildlife, pets, and children, especially in backyard situations.


5. Leaf-feeding caterpillars

Caterpillars, which are the larvae of butterflies and moths, damage plants by chewing on leaves, flowers, shoots, and fruit. Caterpillars in fruit or wood can be difficult to manage because they are hidden most of their life and can cause serious damage even when numbers are low. However, many plants, especially perennials, can tolerate substantial leaf damage, so a few leaf-feeding caterpillars often aren't a concern. Handpicking and beneficial predators and parasites often provide sufficient control. Look for feeding holes, excrement, webbed or rolled leaves, caterpillars, eggs, and good bugs.


6. Peach leaf curl

Peach leaf curl is a fungal disease that affects only peach and nectarine trees. Distorted, reddened foliage in the spring is a distinctive symptom. New leaves and shoots thicken and pucker and later may die and fall off. An infection that continues untreated for several years can lead to a tree's decline. To prevent peach leaf curl, treat peach and nectarine trees with a copper fungicide every year after leaves fall. After symptoms appear in the spring, any treatment will not be effective. When planting new trees, consider buying peach tree varieties that are resistant to the disease.


7. Rats

Rats eat and contaminate food, garden produce, and fruit, and transmit diseases to humans and pets. Manage rats by removing food and shelter, eliminating entryways into buildings, and trapping. Snap traps are the safest, most effective, and most economical way to trap rats. For Norway rats, place traps close to walls, behind objects, in dark corners, and in places where you have found rat droppings. For roof rats, place traps in off-the-ground locations such as ledges, shelves, branches, fences, pipes, or overhead beams. Ensure traps are out of reach of children and pets.


8. Scales

Scale insects suck plant juices and are pests of many trees and shrubs. Infestations can cause yellowing or premature dropping of leaves, sticky honeydew, and blackish sooty mold. Plant parts can distort or die back, depending on the species and abundance of scales. Most plants tolerate low to moderate numbers of scales. Provide plants with proper cultural care, especially irrigation. Encourage scale predators such as lady beetles or lacewings and look for parasite emergence holes in scale covers. Use sticky barriers or insecticide baits to selectively control scale-tending ants. Consider replacing problem-prone plants because most scales are highly specific to certain plants.


9. Snails and slugs

These slimy mollusks emerge from hiding at night and chew holes in leaves and flowers of many succulent garden plants and fruit. Management requires a vigilant and integrated approach that includes eliminating moisture and hiding spots, trapping, setting up barriers, and handpicking. Regularly remove snails from shelters you can't eliminate such as low ledges on fences, undersides of decks, and meter boxes. Place traps in your garden and dispose of trapped snails and slugs daily. Reduce moist surfaces by switching to drip irrigation or watering in the morning rather than later in the day. Consider snail-proof plants such as impatiens, geraniums, begonias, lantana, nasturtiums, and many plants with stiff leaves and highly scented foliage such as sage, rosemary, and lavender.


10. Weeds in landscapes

Prevent weed invasions in new beds with good site preparation. Keep weeds out with an integrated program that includes competitive plants, mulches, and hand removal. Be particularly vigilant about removing aggressive perennial weeds. You rarely should need herbicides in established landscape plantings. Mulches prevent weed seed germination by blocking sunlight. Remove small weeds by hand before they flower and set seed. Use shallow cultivation or hoeing to remove annual weeds from ornamental plantings. Only use herbicides for special-problem situations before establishing new plantings or for difficult-to-control perennial weeds.


To see all of the University of California's Statewide Integrated Pest Management Program's information on home, garden, and landscape pests, visit

For other short pest “Quick Tips” like the ten above, see

 To read even more in-depth, peer-reviewed information on many other common home and landscape pests in California, see the Pest Notes series at

Download your free UC IPM Quick Tips Booklet of the Top Ten Pests in Gardens and Landscapes and How to Control Them with the link below! 

Posted on Friday, June 10, 2016 at 12:30 PM
  • Author: Tyler Ash

A second natural enemy of Asian citrus psyllid joins the battle

An adult male (left) and female diaphorencyrtus aligarhensis on a citrus leaf. (Photo: Mike Lewis)
The battle against Asian citrus psyllid (ACP) is continuing in California on many fronts, motivated by the insect's ability to spread huanglongbing (HLB), the worst citrus disease in the world. HLB has been found in only one isolated tree in California, and everybody who enjoys California citrus wants it to stay that way.

Farmers are diligently treating orchards where the pest has been found, county ag commissioners are monitoring traps to keep tabs on ACP movement, and UC researchers are looking into a wide variety of novel techniques to disarm ACP and the disease. In December, UC Cooperative Extension biological control specialist Mark Hoddle began releasing a newly imported natural enemy of ACP, Diaphorencyrtus aligarhensis (DA).  

“We've released about 2,000 now at select urban sites,” Hoddle said. “It's too early to tell if we are getting attacks, but we are monitoring carefully for this type of activity.”

Hoddle said it isn't the ideal time for DA to become established in California citrus. Cool weather and short days have hindered ACP population growth, so DA likely are struggling to find enough ACP to attack.

“But we keep pumping them out there as the alternative is letting them to die in quarantine,” Hoddle said. “At least if they are outside they may find some ACP to kill.”

DA is about the size of Abraham Lincoln's nose on a penny. (Photo: Mike Lewis)
Hoddle has searched the world for natural enemies of exotic pests since he joined the UC Division of Agriculture and Natural Resources in 1997. He collected DA in Pakistan three years ago, then raised and studied colonies of the sesame-seed-sized insect in quarantine at UC Riverside. The wasp joins a cousin, Tamarixia radiata, also imported from Pakistan by Hoddle, to search out and destroy Asian citrus psyllid. He began releasing Tamarixia in 2011.

Since then, CDFA has raised a million Tamarixia and released them in Southern California for ACP management.  It appears Tamarixia has become established, is moving around on its own and killing Asian citrus psyllids. State and federal agencies are now beginning to work with DA as well.

“We've given starter colonies of the new insect to CDFA. They have a mass rearing facility at Mt. Rubidoux in Riverside, where they currently mass produce Tamarixia,” Hoddle said.

USDA plans to set up field cages around citrus trees in late spring or early summer and prune them severely to encourage new growth. ACP will be placed in the cages to enjoy the fresh, aromatic stems and leaves on the trees, and DA will be released in large numbers to attack the ACP.

“Infested branches will be trimmed off trees, taken to the lab where parasitoids are then harvested,” Hoddle said. “The adult ACP will be trapped inside the cages and killed.”

For more details, photos and a video about the new enemy of Asian citrus psyllid, see the Center for Invasive Species Research website.

An initiative to manage endemic and invasive pests and diseases is part of UC Agriculture and Natural Resources Strategic Vision 2025.



Posted on Tuesday, February 10, 2015 at 6:10 AM

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