How To Identify and Control Asian Citrus Psyllid

Asian citrus psyllid is a dangerous pest for anyone who's growing a citrus tree. Sustainability specialist Huan Song discusses this invasive pest and how to handle it.

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If you’ve ever traveled internationally, you may have filled out a form declaring whether you are carrying any agricultural products or have been on any foreign farms during your trip. This precaution is because many invasive plants and pests can hitch a ride.

The Asian citrus psyllid (Diaphorina citri) is an exotic pest that has rapidly spread across North America. It has become pervasive in just a few short decades since its introduction in the late 1990s

Psyllids are a group of insects that eat plant sap and specialize in a single host plant or a closely related family. As the name implies, the Asian citrus psyllid attacks citrus plants.

They are also a vector of the bacterial citrus disease, Huanglongbing (HLB). HLB is also known as citrus greening disease. Infected trees develop yellowing leaves, stunted fruit, and eventually die after a few years. Unfortunately, there are no cures.

Together, the Asian citrus psyllid and HLB are some of the most economically devastating problems for commercial citrus growers worldwide.

Identifying Asian Citrus Psyllid

An orange fruit on a tree infected with HLB, transmitted by Asian citrus psyllid.
An orange tree infected with HLB, transmitted by Asian citrus psyllid.

Asian citrus psyllid and HLB disease come from tropical and subtropical regions of southern Asia, where citrus originates.

Asian citrus psyllid was first detected in Florida in the late 1990s. Now, these pests can be found in southern parts of US, the Virgin Islands, Hawaii, Guam, and any warm climates where citrus are grown.

Many plants in the family Rutaceae and genus Citrus are susceptible including the curry leaf, grapefruit, key lime, lemon, lime, orange, pomelo, and tangerine, to name a few. 

Psyllids can be misidentified as aphids but they are from different taxonomic families. While psyllids are very small (three to four millimeters long), they look more like miniature cicadas. They use jumping as a primary way of getting around but can also fly short distances.

Adults have brown mottled bodies and wings. They can appear dusty as they are covered in waxy, whitish secretions and leave waxy droppings on affected plants. The nymphs are yellow or orange in color with red eyes. Nymphs get progressively larger with every instar or developmental stage.

Eggs are around 0.3 millimeters long and almond-shaped. They progress from pale yellow to orange as they prepare to hatch.

Life Cycle

Asian citrus psyllid nymphs on green leaf.
The lifecycle of these pests is incredibly rapid.

Each female of the Asian citrus psyllid species can lay 500-800 eggs in her lifetime. She will lay her eggs on the growing shoots of citrus plants, typically in the folds of new growth. Nymphs have five instars and mature in 15-47 days depending on environmental factors.

Because of their rapid lifecycle, these pests can have 9-10 generations per year. This will slow down during winter or dry months, if these conditions are applicable. 

Common Habitats

Asian citrus psyllid bugs on citrus tree.
Nymphs can only survive on new growth.

Adult Asian citrus psyllids are typically found in large numbers on the lower side of the leaves of their host plants. They are most active during the growth period of citrus plants.

Adults lay eggs on the growing tips of citrus plants and near unfurling leaves. Nymphs can only survive on the new growth where they have recently hatched. 

What Do Psyllids Eat?

Asian citrus psyllid bugs feeding on citrus stems.
While the damage they cause is a problem, the disease Asian citrus psyllid transmits is more concerning.

Adult Asian citrus psyllids feed on the newly developed leaves of citrus plants. They directly affect their host plants by feeding on plant tissue. But more damagingly, they are a vector for the fatal bacterial disease Huanglongbing (HLB).

As Asian citrus psyllids feed on an infected citrus plant, they also ingest the bacteria spread it to other plants. While there are multiple species of psyllids on citrus plants, Asian citrus psyllid is the only species that can transmit HLB. A few psyllids can take down a whole tree. 

Nymphs feed on the sap of plant tissues from the growing tips of plants, immature leaves, soft stems, and flowers. As they feed, they also inject a salivary toxin into the plants. This causes the new flush tips of their host plants to become deformed or die. The damage to the new leaves will stunt growth.

A telltale sign of these nymphs is a waxy, curly tube with a bulb coming out of the backend of their bodies which they produce to get rid of waste.

How to Control Asian Citrus Psyllid

Asian citrus psyllids on citrus leaf.
This is one pest problem you cannot ignore.

Because of the significant threat that Asian citrus psyllids pose to the citrus industry, there are many national and state-level efforts to quarantine and monitor these pests. Check your local agricultural commissioner’s website for specific hotlines to call if you suspect your trees may be infected.

Throughout the state of California, for example, HLB has been recorded in residential areas. There are multiple PSAs produced by the state to help home gardeners identify and report the issue. There is no cure for HLB, so the only way to manage the disease is by reducing the population and spread of psyllids.

Inspect the growing tips of your citrus trees carefully and frequently. Check the new leaves and twigs. Psyllids and nymphs are very small so you may need to inspect your plants using a magnifying glass. Be on the lookout for the waxy tubules produced by Asian citrus psyllid nymphs. 

Organic or Chemical Control

Hand spraying orange tree with insecticidal soap.
Apply controls regularly to cover several lifecycles.

Home gardeners can use horticultural oils, insecticidal soaps, and pyrethrins for control. However, the spray must make direct contact with psyllids to be effective. And you should spray outside hours when pollinators and beneficial insects are active to avoid harming them.

Because of the rapid life cycle of Asian citrus psyllids, spray every 7-10 days while new leaves are growing. These methods are typically not as effective as other chemical controls. 

Foliar spray or soil drenching with imidacloprid can combat Asian citrus psyllids. However, these are not organic insecticides. The most effective spray treatment against Asian citrus psyllids is a combination of soil drenching and foliar sprays applied by professionals. 

Kaolin clay and diatomaceous earth spread around and on citrus trees is an effective deterrent and control for psyllids. However, gardeners in humid and rainy areas may opt for something else. Both treatments have to be reapplied after rain and in humidity.

Environmental Control

lacewing larvae eating aphid pests on green leaf.
Encourage beneficial insects like lacewing larvae to tackle the problem.

Asian citrus psyllids have natural enemies including lacewing larvae, syrphid larvae, spiders, birds, and lady beetles. Creating an environment in your home garden that supports these beneficial natural enemies is a good way to help reduce psyllid populations. 

On a larger scale, one of the most promising biological controls is Tamarixia radiata, a small parasitic wasp. The female wasps lay their eggs under or inside Asian citrus psyllid nymphs and the growing wasp larvae feed on the nymphs from the inside out, leaving behind a hollow “mummy” shell.

In California, researchers from the University of California Riverside have been working with the California Department of Food and Agriculture to rear and release these wasps into residential parts of Southern California. However, planting their host plants is necessary to bring them in and get them to stay.

Be aware that ants feed on the honeydew and tubules produced by Asian citrus psyllid nymphs and will defend them to protect this food source. If you know that parasitic wasps have been released in your area by your local agricultural service, control the population of ants in your garden to maintain the effectiveness of these wasps. 

Preventing Asian Citrus Psyllid

Citrus tree infected with HLB disease.
Look out for signs of HLB in your citrus trees throughout the season.

If you think your citrus tree may be showing symptoms of HLB, call your local hotline as soon as possible to get a leaf sample tested. There are also maps available through the agricultural commissioner’s office which document where infections have already occurred.

If there has been a documented case of HBL within two miles of your trees, it is likely your plants are already infected. Trees may not show symptoms of HLB immediately. Get your trees tested and removed if they are already infected to prevent the spread of HLB to neighboring trees.

The most effective way to prevent this invasive pest is to properly fertilize and prune your citrus trees at the appropriate times.

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