Pests That Threaten Citrus Trees of Southern California

Few places in the world are more hospitable to citrus trees than Southern California. But unfortunately, even in a place with a nearly ideal climate for these fruit-bearing trees, the trees must still survive amid a variety of insects and other pests. In fact, while these pests and parasites threaten the citrus trees growing in residential yards, they pose an even greater threat to our state’s important commercial citrus industry. 

Accordingly, residents, commercial growers, and property managers must familiarize themselves with some of the most notable citrus pests and the symptoms they cause. This will allow for prompt treatment, or, when necessary, removal of the afflicted trees. 

We’ll discuss four of the most dangerous and common citrus pests below. 

Asian Citrus Psyllid (Diaphorina citri)

The Asian citrus psyllid is undoubtedly the gravest threat that faces California citrus trees. These tiny six-legged critters are originally native to southeast Asia, but they eventually reached U.S. shores and have established populations throughout southern California. 

The feeding activities of these insects cause moderate damage to the trees, usually manifesting as contorted leaves at the ends of young shoots. But they actually present an even greater threat: Asian citrus psyllids are one of the only vectors for citrus greening disease – a devastating bacterial pathogen of citrus trees. 

Citrus Leaf Miner (Phyllocnistis citrella)

The citrus leaf miner is another invasive species, originally native to southeast Asia. It also has another trait in common with the Asian citrus psyllid: It can cause distorted, contorted leaves to appear on afflicted trees. Fortunately, while citrus leaf miners may reduce a given tree’s vigor, they rarely cause afflicted trees to die outright. This highlights the importance of having citrus pests positively identified at the first sign of their presence. 

Citrus leaf miner larvae tunnel under the surface of citrus tree leaves. This damages the leaves, which means they can’t photosynthesize effectively, thereby causing the tree considerable stress. Leaf miners can be identified by noting the winding “mines” they create inside leaves, which generally have a dark center. This dark coloration is caused by the larvae’s droppings (frass). 

California Red Scale (Aonidiella aurantii)

California red scale is another exotic pest, but this one has been around for a lot longer than the Asian citrus psyllid or the citrus leaf miner. Unlike the psyllid, which was first found in the U.S. in 1998, and the leaf miner, which first appeared in California in the early 2000s, California red scale has been in the country since the civil war. 

These tiny red insects can cause fairly significant damage to citrus trees, including leaf drop, the production of misshapen leaves, and bark splitting. In severe cases, this pest can cause the death of infected citrus trees.  

Citrus Thrips (Scirtothrips citri)

Citrus thrips can cause quite a bit of damage to citrus trees, but they rarely cause the death of those that are afflicted. However, they can severely damage a growing crop, so they’re of extreme importance to commercial growers (as well as homeowners who simply want healthy fruit crops). 

Citrus thrips are very small insects, who are relatively easily identified by noting their yellow-orange coloration and fringed wings. Their feeding activities cause damage to the citrus fruits themselves, as they can leave silver-colored scars on the surface of the fruit. It is the second-instar life stage that causes the bulk of the damage, as these insects typically feed beneath the calyx of the growing citrus fruits.  


Remember that it is important to take citrus pests seriously and spring into immediate action whenever they’re suspected of being present. This will help limit the damage caused and give your trees the best chance of recovery. 

If you observe citrus pests or symptoms that hint at their presence, give your friends at Evergreen Arborist Consultants a call. One of our certified arborists will visit your property, inspect your trees and recommend a mitigation strategy.   

Asian Citrus Psyllids Threaten Southern California Trees

Thanks to the area’s warm climate and thriving agricultural industry, southern California is especially vulnerable to invasive pests and exotic plant diseases. And while there are several species that local homeowners, property managers and farmers must be aware of, few are quite as troubling as the Asian citrus psyllid and the associated disease that the insect causes.

We’ll explain everything you need to know about these non-native pests below, including their appearance and the method by which they harm trees.

Asian Citrus Psyllids and Citrus Greening Disease

Asian citrus psyllids (Diaphorina citri) are small, sap-sucking insects native to South Asia. These six-legged invaders began showing up in Florida about 20 years ago, but they soon colonized an entire swath of the southeast, stretching from South Carolina to Texas. About 10 years later, the insects made their way to California, where they began plaguing citrus trees in suburban and urban areas, as well as some of the state’s citrus farms.

Citrus psyllids harm trees via their feeding habits, which typically affect new leaf growth. However, the insects themselves aren’t the true threat – it is the bacterial disease that they spread which is most concerning.

Called citrus greening disease or Huanglongbing, the ailment is caused by a bacterium known as Candidatus Liberibacter spp. Once introduced to the bite wounds caused by the insect, the bacteria multiply inside the plant, triggering a host of physiological problems.

Unfortunately, citrus greening disease may take two years or more to begin triggering visible symptoms. But during this lengthy incubation period, the trees remain a viable source of the bacteria, which can spread to other psyllids feeding on it.

Identifying Asian Citrus Psyllids

Asian citrus psyllids are somewhat hard to identify, given their very small size; most are only about 1/8 inch long. They have dark, mottled brown bodies, with lighter colored heads, and black-tipped antennae. Their wings have dark edges with pale centers, and they’re typically widest at the back.

Asian citrus psyllids often adopt a stereotypical “head down” feeding posture, which can also be helpful when trying to identify them. These insects are occasionally mistaken for aphids, but psyllids are much more active pests, who frequently jump around on their host plants.

Symptoms of Asian Citrus Psyllids and Citrus Greening Disease

Some homeowners may notice live Asian citrus psyllids crawling around on their citrus trees (most common citrus varieties appear vulnerable to the insects and the disease they spread). However, because the insects are quite small, you’re more likely to notice the results of the insects’ feeding activities.

Most of the damage caused by Asian citrus psyllids will afflict the new shoots and leaves growing on the tree. These new tissues will often become twisted, curled, gnarled and deformed, thanks to the salivary toxin the pests inject when feeding. The insects may also leave honeydew in their wake, which can coat leaf surfaces and encourage the growth of sooty mold.

If the psyllids on your tree have managed to infect it with citrus greening disease, you’ll likely see additional symptoms. The first thing most people will notice is that the tree’s leaves will begin to develop asymmetrical yellow blotches. But as the disease progresses, the symptoms will begin afflicting the tree’s fruit too.

For example, instead of reaching a typical size, most of the fruits on afflicted trees will remain relatively small. Additionally, the juice contained in the fruit will start to taste bitter with time, and many of the fruit will remain green, rather than turning yellow or orange (hence the name, citrus greening disease).


Because the Asian citrus psyllid and citrus greening disease are such formidable threats to southern California’s trees and agricultural industry, vigilant monitoring and prompt action are imperative. So, be sure to observe your citrus trees regularly for any signs of trouble.

If you suspect that one of your trees is infested with psyllids or already infected with citrus greening disease, give your friends at Evergreen Arborist Consultants a call. We’ll have one of our certified arborists visit your property, inspect your trees, and recommend a prudent course of action.

Know Your Enemy: Six Insects That Attack Avocado Trees

The avocado tree has become one of the most popular tree species grown by residents of southern California.

Some grow these trees for their delicious fruit, while others simply appreciate the way they look or the shade they provide. But regardless of your motivation from growing these fruit-bearing trees, you’ll need to familiarize yourself with some of the insects that often damage them.

We’ll try to help you do so below, by explaining six pests that attack avocado trees. By learning the habits and basic biology of the following insects, you’ll have a better chance of recognizing infestations at the early stages.

1. Avocado Thrips

Avocado thrips – known to biologists as Scirtothrips perseae – were first documented in California back in 1996, and they’re currently found throughout the state.

Adult avocado thrips are yellow-brown in color and have three red dots between their eyes, which makes them pretty easy to distinguish from other thrip species. Larval avocado thrips are usually white to bright yellow in color, and they’re also found on the trees in many cases.

Avocado thrip adults and larvae are typically spotted feeding on the undersides of immature leaves and fruit. Infestations can also be detected by noting the scarring their feeding behaviors cause to the tree’s fruit (the skin of avocados on infected trees is often likened to “alligator skin”).

2. Western Avocado Leafroller

Western avocado leafrollers are important pests of avocado trees, and they also feed on citrus trees in some cases. As adults, these leafrollers have orange to brown wings with scattered dark markings, but it is the larval (caterpillar) stage that causes problems for avocado trees.

The caterpillars, which reach about ¾ to 1 inch in length, are typically bright yellow-green during their first few instars, but they become darker green with time. To verify their identity, look for a single dark mark on each side of the caterpillar’s thorax – no other avocado-feeding caterpillar bears such markings.

These caterpillars feed on the leaves of avocado trees, and they occasionally cause significant defoliation. You may also notice these insects by observing the rolled-up leaves they use while pupating.

3. Long-Tailed Mealybugs

Several mealybug species can attack avocado trees, but the long-tailed mealybug is the most likely one to infest avocado trees. Nevertheless, positive identification of the mealybug species infesting your trees is crucial to implementing a proper management plan.

Mealybugs cause damage to avocados in a few different ways. They feed on phloem sap, which can cause trees to suffer from a loss of vigor if the insects occur in high numbers. Sick or stressed trees may also struggle to endure the feeding activities of these insects.

Additionally, mealybugs can spread sticky honeydew over the plant’s surfaces. This often leads to the growth of black sooty molds, which may damage any fruit present.

4. Omnivorous Looper

The omnivorous looper is a generalist predator that feeds on a variety of different plant and tree species. It is often found in low numbers in the habitat, but disruptions to local food webs can allow its numbers to explode.

The adults are generally 2-inch-wide, orange moths, with a black band through the center of their wings. The larvae are usually yellow to dark green with gold heads. As they approach maturity, most caterpillars develop longitudinal stripes that extend down their bodies.

Some of the most important signs of looper infestations include damaged leaves and scarred fruit. Most avocado trees will tolerate low-level outbreaks, but when the insects occur in high numbers, the damage caused can be significant.

5. Orange Tortrix

The orange tortrix typically prefers feeding on grape vines, but they’ll also attack avocado trees when presented with the opportunity. Because the damage they cause is often quite similar to that caused by leafrollers, it is important to properly identify these insects before beginning a treatment regimen.

Adult life stages are generally about ½ inch long, orange to brown in color, and they often bear a diffuse V-shaped marking on their wings. Meanwhile, the larvae are typically straw-colored with tan heads. Multiple life stages are usually observed on the same tree at the same time.

The orange tortrix caterpillar primarily feeds on the leaves of avocado trees, but they’ll also damage fruit stems in some cases. You may also observe rolled-up leaves, which the insects use during their pupal stage.

6. Avocado Lace Bug

The avocado lace bug is a tiny pest of avocado trees that generally measures about 2 millimeters in length. The adults bear small, lacey wings that extend rearward, while the younger nymphs lack wings entirely.

These insects often go unnoticed by those who don’t carefully examine their trees. They’re usually easiest to spot by looking at the underside of your tree’s leaves, where they’ll appear like tiny black spots.

Avocado lace bugs cause harm to avocado trees via their piercing-sucking mouthparts, which they use to access the sugar-rich fluids contained inside the trees’ leaves. Light infestations are unlikely to seriously stress avocado trees, but heavy infestations can cause large-scale damage to the foliage, and thereby expose the tree to opportunistic pathogens.


If you suspect that your avocado trees are suffering from insect infestations, give your friends at Evergreen Arborist Consultants a call. We’ll have one of our experienced arborists inspect your trees, confirm the identity of the pests and recommend a prudent management strategy.

Bark Beetles

Bark Beetles

The world is home to about 6,000 bark beetle species – known to biologists as the subfamily Scolytinae. One of the most famous examples is the elm bark beetle (Scolytus schevyrewi), which transmits the fungi responsible for causing Dutch elm disease. However, the most important bark beetles for North American trees (particularly conifers) are undoubtedly the bark beetles of the genus Dendroctonus.

Basic Bark Beetle Life Cycle

Most – if not all – pine beetles form large aggregations, consisting of thousands of adult beetles. Mating usually follows the mass arrival at a single tree, and the females begin tunneling through the tree’s tough outer bark soon thereafter. Once under the outer bark, the females usually begin constructing egg galleries – small tunnels cut into the living inner bark (phloem) or the tree. The eggs are laid along the sides of these galleries, where they will remain until they hatch shortly later.

Upon hatching, the larvae begin feeding voraciously on the nutrient-rich phloem. These feeding tunnels are often visible under the bark of afflicted trees. Like many other insects, pine beetles spend most of their lives in the larval, rather than adult, life stage. Nevertheless, they eventually complete their larval life stage and pupate under the bark of the tree.

A short while later, the adult beetles emerge from their pupal state, and seek out other beetles, thus starting the process anew.

Native Pine Beetle Species

The bulk of the economically important bark beetles are members of the genus Dendroctonus. Most bark beetles are small, black to brown insects that are about one-quarter-inch long. But despite their small size, these miniscule bark munchers can cause a lot of trouble for the trees they infest. Biologists clearly understood this when originally describing these pests – their generic name, Dendroctonus, literally means “tree killer.”

As currently construed, the genus Dendroctonus contains nearly 20 species of bark-eating beetles. Most of these species range from the far northern reaches of North America down as far south as Nicaragua; however, two species inhabit northern Europe and Asia. Though they all exhibit the same basic life history, the various species differ with regard to their preferred host species, gallery-creating behaviors and morphology.

Southern California is home to four native bark beetle species.

  • Western pine beetle (Dendroctonusbrevicomis) – The western pine beetle is an aggressive bark beetle, capable of killing even otherwise healthy trees. Its primary hosts include the ponderosa and Coulter pines.


  • Mountain pine beetle (Dendroctonus ponderosae) – As its name suggests, the mountain pine beetle ranges throughout most of the Rocky Mountain region, but it also spills into the Sierra Nevada range as well. The mountain pine beetle primarily attacks four different pines, including ponderosa, sugar, lodgepole and white.


  • Jeffrey pine beetle (Dendroctonus jeffreyi) – Jeffrey pine beetles are so-named for their habit of feeding solely on Jeffrey pines. Often, Jeffrey pines cause a widening circle of dead trees, which may grow in circumference from one year to the next.


  • Red turpentine beetle (Dendroctonusvalens) – The red turpentine beetle has the largest range of any of the North American bark beetles. However, this beetle is not usually responsible for widespread die offs. This species has been documented inhabiting more than 40 different conifer species, although it usually feeds on the phloem of pines.

Exotic Beetles

In addition to the native bark beetles that have been co-evolving alongside their hosts for thousands of years, several invasive bark beetle species have been introduced to California and other locations. Currently, three species – the banded elm bark beetle (Scolytus schevyrewi), the Mediterranean pine engraver (Orthotomicus erosus) and the redhaired pine bark beetle (Hylurgus ligniperda) — have been documented to occur within the state’s borders. Note that while these insects are still considered bark beetles, they are not categorized in the same genus as the North American natives are.

In addition to threatening pines and other conifers as native bark beetles do, these exotic invaders may also introduce pathogens, fungi and other harmful organisms to North American ecosystems.

The Defenses of Trees

Conifers do not simply stand by and allow pine beetles to destroy their tissues, they actively defend themselves from beetle attacks. Their primary weapon against the beetles is their thick, sticky sap, which begins flowing from the holes the beetles create in the inner bark. However, pine beetles often attack trees en masse, which often overwhelms the host tree’s ability to repel the beetles.

You can often see the evidence of bark beetle attacks, via “pitch tubes.” Pitch tubes are holes made by the beetles, which have hardened sap that has flowed out of the hole. Sometimes, it is possible to see dead beetles trapped inside the sap.

Environmental Impact

Like most other native insects and pests, pine beetles rarely cause widespread problems for the ecosystem as a whole. Single trees may often die, but the forests continue, largely unaffected. In fact, the beetles play important roles in ensuring biodiversity and forest succession. However, this historical trend has been disturbed by habitat alteration, increasingly frequent and prolonged droughts and commercial forestry operations.

Accordingly, vast swaths of trees are dying off in portions of the country. This is most pronounced in areas that have suffered through prolonged droughts, as the lack of water reduces the amount of sap available to the trees to use in defense.

aphids on a green leaf. macro

Aphids that Infested Her Birch Trees

Evergreen Arborist Consultants recently received a call from a homeowner regarding aphids that infested her birch trees.  She was very concerned about treating the aphids without harming her pets.  The aphids were damaging the birch tree leaves and staining her concrete from the honeydew.  Honeydew is a sticky black liquid, secreted by aphids as they feed on plant sap.  Ants were also attracted to the sugar-rich substance and were as much of a nuisance as the aphids.  Aphids are among the most destructive insect pests on ornamental plants.  Aphids are small, soft-bodied insects with long slender mouthparts that they use to pierce stems, leaves, and other tender plant parts and suck out fluids. The damage they cause to plants has made them enemies of farmers and gardeners.  Large populations can turn leaves yellow and stunt shoots.  Aphids may transmit viruses from plant to plant on certain vegetable and ornamental plants.

When considering whether to apply insecticides for aphid control, remember that many larger plants can tolerate light to moderate levels of aphid infestations.  Larger aphid populations typically decline due to hot weather.  One method of controlling aphids is spraying a high volume of water to the underside and tops of leaves.  If that’s not effective, apply water-soap solution insecticidal soap.  The insecticidal soap uses potassium salts of fatty acids.  The potassium salts weaken the insect’s waxy protective outer shell.  Be sure to follow the label’s directions.  Insecticidal soap is highly preferable to chemical pesticides because it possess toxins that can kill beneficial insects which don’t cause long-term detrimental effects on the environment.  Repeated application may be necessary as these pesky bugs tend to return if left untreated.

Pasadena Beetle Infested Tree



The City of Pasadena decided to take down a massive tree on North Hill Avenue after it was confirmed that the tree was dying due to a beetle infestation. The tree had withstood the windstorm in the area that occurred a year ago and felled many trees in the city, but the tree recently started to look unhealthy. Ed Carney, who lives on North Hill Avenue, said he had someone stop by the house a couple months before the tree was to be taken down, and mentioned the unhealthy tree. Carney had already notified an arborist when he became concerned for the tree, and the arborist inspected the tree several times and identified the beetle infestation. An independent specialist confirmed the results.

The tree was one of the largest trees in the city and was possibly hundreds of years old. The city said it needed to remove the tree due to safety concerns. The removal required a crane and the tree cut down from the top first. During removal, traffic was redirected around the area.

Evergreen Arborists Consultants, Inc. has experience in examining thousands of trees. We evaluate a tree’s signs and symptoms ranging from decay, poor branch structure, poor pruning, and maintenance practices and roots. Evaluation may help reduce possible personal injury and property damage from falling trees or branches. Please call us today for a consultation.

Oak Tree Damage

Cal Fire officials recently spotted a California black oak tree in Idyllwild, CA, that was infested with the gold spotted oak borer. This beetle has already destroyed 80,000 oak trees in San Diego County, but officials hadn’t expected to see it so far outside of the estimated zone of infestation. “Our concern is that it’s been found 40 miles outside the zone of infestation. That’s a long way. How did it get here?” asks Julie Hutchinson, Battalion Chief and Cal fire spokeswoman. Hutchinson thinks it was carried into the Idyllwild area in a load of firewood and cautions people to use firewood where they’ve bought it.

The adult gold spotted oak borer is about a half-inch long and forest green, with six golden spots on its wings. The larvae feed on the soft tissues of oak trees directly under the bark. This soft tissue is the supply route for water and nutrients, and the damage caused by the beetle stresses the tree until the tree dies.

The infected tree was discovered when a Cal Fire employee noticed that the tree had much smaller leaves and the leaves were starting to turn brown. When the tree was checked a few weeks later, the tree was dying and the leaves were brown. About a dozen larvae were extracted from the tree and DNA-analyzed to confirm the species. The tree was subsequently taken down and shipped to San Diego County, within the area the beetle has already infected. The extent of the infestation in Idyllwild won’t be determined until spring, when adults emerge.

Evergreen Arborists Consultants, Inc. has examined thousands of trees. We are Los Angeles certified arborists, tree experts, and tree specialists who provide arboriculture and tree expert advice to Beverly Hills, Brentwood,  West Hollywood, Santa Monica, Malibu, Palos Verdes, Encino, Pasadena, and Sherman Oaks. We specialize in Los Angeles trees, and conducting detailed investigations and providing independent analysis. Please call us today for a consultation.

Whitefly: Attacking Plants and Leaving a Sticky Mess

Fort Lauderdale residents are noticing an increasingly pervasive nuisance pest in the rugose spiraling whitefly. These pests have invaded South Florida, originally spotted in 2009 in Miami-Dade. The pest lays eggs in a spiral pattern on leaves. When the eggs hatch, the flies feed off leaves and then secrete a sticky goo that covers leaves and anything below where the insects are. If the goo isn’t cleaned up, sooty mold forms.

The whitefly infestations have been observed to spread very quickly. One tree nursery and mulch manufacturer noticed that the 30-acre farm was totally infested. “I’ve never seen anything infect anything so quickly. You blink and all of a sudden your entire palm tree farm is infested,” said Dave Tomlinson, vice president of Amerigrow Recycling.

Michael Orfanedes, with the University of Florida and Broward County Extension Education commented, “It’s a nuisance of historical proportions. The whiteflies may disfigure [trees] and even potentially weaken them, but people need to be careful not to overact. The most significant problem to date is the nuisance factor, which is considerable and extensive.”

Whitefly infestations can be controlled using natural predators like Lady Beetles and by using natural soaps and spraying with a strong stream of water, or with various pesticides. There are three types of whitefly currently found in Florida: The ficus whitefly, the rugose spiraling whitefly, and the Bondar’s nesting whitefly.

Asian Longhorn Beetle Eradication

Clermont County, Ohio discovered they had an Asian longhorn beetle infestation last summer. The beetle tunnels into trees in the larval stage and kills by cutting off the water and nutrient supply to the trees. The beetles are especially attracted to maple trees, but also attack 12 other types of trees, including willows, elms, and poplars, which means they are a serious threat to the Ohio forests and timber industry. The beetles are believed to have arrived in cargo shipments from Asia containing wooden materials.

To reduce the spread of the beetle, agriculture officials are requiring trucks be covered with tarp while hauling infested trees. The infested trees are being chipped down to a size where the beetles won’t survive. Because thousands of infested trees were removed last year, when the beetles emerge this spring the hope is that the population will be drastically reduced.

The federal Animal and Plant Health Inspection Service released a plan earlier this month that would cut down every beetle-infested tree as well as every other healthy tree they could attack within a half-mile radius of the infected tree. They say this is the most effective eradication method. Two other options in the plan would treat healthy trees with a protective pesticide.

The beetles are difficult to detect – from the ground, well-trained individuals only spot about 30% of lightly infested trees, while trained climbers detect about 70%. State and federal funding is available to eradicate the beetle and for reforestation programs.