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).

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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.

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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.

Turkey Tail Fungus: Everything You Need to Know

In many ways, fungi represent some of the most important and omnipresent threats to trees.

Many fungi subsist almost entirely on the tissues of trees, and thanks to their reproductive strategy, their spores can be found nearly everywhere. And unfortunately, scientists estimate that there are millions of fungal species in the world.

Below, we’ll explain the basics of one such species and discuss how it may affect your trees. The species is known to biologists and arborists as Trametes versicolor, but most people simply call it what it looks like: the turkey tail fungus.

Turkey Tail Identification

Turkey tail fungus is named for its resemblance to a turkey’s tail – that’s plain to see when you look at it. In general appearance, it looks like a vaguely semicircular fan, with rings of varying colors (in fact, “versicolor” means “of several colors”). The fan-shaped fungus is only a millimeter or two thick, but it occasionally reaches 4-inches in diameter.

Note that when we describe the turkey tail fungus, we are really only discussing the fruiting body or mushroom – a structure that biologists call a sporocarp. The bulk of the organism grows as thin fibers called mycelia, which are found inside the tree or soil.

Turkey tail fungus does look somewhat similar to a few other species. The best way to distinguish it from its lookalikes relies on subtle characteristics, such as pore size. This is generally outside of the capabilities of amateurs, so while you can often arrive at a tentative identification of the fungus, you’ll likely need professional help to arrive at a positive identification.

Trees Vulnerable to Turkey Tail Fungus

It’s hard to know for sure, but many biologists believe that turkey tail may be the most common decomposer of hardwood trees in the United States. The species is, in fact, absurdly common, and you can probably find it during a brief walk through any hardwood forest.

Nevertheless, while it does occasionally attack conifers, turkey tail fungus is primarily a threat to hardwoods. A few of its most common targets include the following:

  • Crape myrtles
  • Apples
  • Plane trees
  • Maples
  • Walnuts
  • Willows
  • Tuliptrees
  • Oaks
  • Sweet gums
  • Eucalyptus
  • Elms

However, it is important to remember that turkey tail fungus can affect an incredibly broad subsection of trees, so you don’t want to rely on its host species to confirm or disconfirm its identity.

Turkey tail fungus is likely most commonly seen on dead trees, shed branches and old firewood, but it also attacks living individuals. It most commonly attacks wounded trees (or those that have been improperly pruned), but it is also a problem for trees that have become stressed by improper care, water stress or disease.

Sequalae: What Happens When Turkey Tail Fungus Infects a Tree

Turkey tail fungus – like many other fungi – digests and decomposes the structural elements of a tree’s cells. Turkey tail primarily attacks a component of the tree’s cell walls, called lignin.

Lignin is typically dark brown in color, which means that when the fungus destroys it, the infected wood often becomes very pale or white in color. This is part of the reason turkey tail is said to cause white rot (as opposed to brown rot, which is caused by other fungi).

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If you suspect that some of your trees have become infected with turkey tail virus, give your friends at Evergreen Arborist Consultants a call and we’ll have one of our certified and experienced arborists visit your property.

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.

Mushrooms: Potential Harbingers of Doom

Many homeowners and property managers are surprised when the arborist or tree-care professional they enlisted to prune a tree, spends the bulk of his time explaining the dangers of a tiny little mushroom, growing out of their 100-foot-tall tree.

Surely such a tiny, insignificant little outgrowth poses no threat to the mighty oak growing above it – or does it?

People tend to view mushrooms as rather benign components of the natural world, whether they are growing in the forest or on the trees beside their homes. But in actuality, mushrooms provide important clues about often-unseen world. And while they don’t always foreshadow future tree problems, their presence should never be ignored.

The Anatomy of a Fungus

Mushrooms are the fruiting bodies of fungi. Functionally similar to seed pods, most mushrooms contain millions of tiny spores inside their gills. When the time is right, the mushroom releases its spores, and they float in the wind, until reaching a suitable growing site. There they will start a new fungal colony and begin the process anew.

But while mushrooms are visually obvious, most of a fungal colony lives out of sight. The exact location in which they grow depends upon the species in question and its preferred food source, but many live in the soil or the wood of trees. Taking the form of numerous threadlike filaments called hyphae, the fungus lives in these places, digesting various tissues with which they are in contact. The hyphae will produce mushrooms that break through the surface of the soil or tree once the environmental conditions are right.

You can see these hyphae for yourself by venturing out to the local forest and scooping back a bit of soil. Often, you will see many white or gray threads heading in many directions – these are fungal hyphae.

Decay, Destruction and the Circle of Life

The feeding activity of some fungal hyphae can break down the cellular structure of a tree’s wood. As this happens, the tree’s structural integrity is compromised, and if allow to progress for a length of time, large branches may drop or the entire trunk may fail.

And this is why your arborist spent more time worrying about the mushroom than he did pruning your tree. Not only does the presence of this mushroom indicate that the tree may require removal, it serves as a warning that the branches and trunk may have already become instable. He may not even be able to climb the tree safely.

But it is important to remember that while fungi may be deadly for your growing trees, these same organisms are necessary for life on earth. Were it not for these wood-eating fungi, the world would be overrun with dead trees, and the nutrients inside the dead wood would be forever removed from the food chain.

Additionally, fungal decay provides opportunities for many animals. For example, red-cockaded woodpeckers of the southeastern United States are unable to penetrate the healthy hardwood of the longleaf pines growing in their native lands. However, the birds easily excavate nests in pines that have advanced heartwood rot (which results from fungal decay), as the rot softens the wood considerably.

Not All Mushrooms Are Alike

It is important to recognize that the world is home to thousandsmillionsof different mushroom-producing fungi, and not all of them are destructive to trees. Some, for example, feed on organic material in the soil more than the roots or the tree’s tissues. Accordingly, mushrooms do not always indicate a problem.

The best strategy for dealing with a mushroom growing from your tree’s trunk or roots is to contact a qualified arborist, who can identify the mushroom (often by sending it to a diagnostic laboratory for analysis) and then recommend a prudent plan of attack. The tree may require removal to ensure continued safety, but the arborist may also be able to simply remove an infested branch; if you are really lucky, he’ll tell you that the mushroom is from a non-pathogenic fungal colony, and you don’t have to worry about it at all.

But in all cases, prompt assessment is crucial so contact your favorite arborist without delay.

The Asian Citrus Psyllid: An Exotic Pest Threatens California’s Citrus Industry

Invasive pests and fungi are some of the deadliest threats to many trees. Because the trees under attack have not evolved mechanisms to combat the alien attackers, significant losses can occur very quickly.

Unfortunately, California’s citrus trees are currently under threat from just such a pest, known as the Asian citrus psyllid (Diaphorina citri). First documented in Florida in 1998, psyllids have significantly damaged the state’s citrus production. Recently, the state destroyed 250,000 acres of trees in a desperate attempt to regain control. (Valentine, 2014) Time will tell if their efforts were in vain.

Plenty of Precedent

Unfortunately, history amply demonstrates the damage exotic species can cause.

Around 1900, a pathogenic fungus of Japanese origin arrived on American shores. The fungus, known as chestnut blight (Cryphonectria parasitica), soon began killing American chestnut trees (Castanea dentata) at an alarming rate. In as little as 40 years, the trees essentially disappeared. While a few scattered individuals cling to life, scientists are still trying to solve the problem and save the species that formerly dominated eastern forests.

A more recent example comes in the form of an Asian beetle, called the emerald ash borer (Agrilus planipennis). During the larval stage, these beetles feed on the inner bark of the trees. This destroys the tree’s ability to transport water and nutrients up and down the trunk, ultimately killing the tree. First documented near Detroit, Michigan in 2002, the beetle has spread throughout most of the eastern United States, killing tens of millions of ash trees along the way.

The Bad News Bug

Psyllids damage citrus trees through their feeding behavior. Like the other members of the family Hemiptera, these eighth-of-an-inch-long insects are “true bugs,” who feed via piercing-sucking mouthparts. When feeding, they pierce the surfaces of leaves and then suck out the sap on which they feed. In addition to the trauma caused by their mouthparts, psyllids inject toxic saliva into the plant, which causes further harm.

These insects have hitchhiked around the world, colonizing the Middle East, Central America, South America, Mexico and several Caribbean Islands, along its way. Since colonizing Florida, Asian citrus psyllids have spread to Louisiana, Georgia and South Carolina as well.

While California’s psyllid problem is not yet as dire as Florida’s is, the destructive bugs have been documented in nine counties within the state. So far, psyllids have not yet colonized many of the most important commercial citrus groves, but without an aggressive response, the problem is sure to grow over time.

Even Worse News Bacteria

The invasive insects are only half of the problem. Psyllids in many parts of the world harbor bacteria that cause “Citrus Greening Disease,” also known as Huanglongbing (a Chinese term, which translates to “Yellow Dragon Disease”). The bacteria– known as Candidatus Liberibacter asiaticus* – infects the phloem of citrus trees. Among other problems, the bacteria cause twigs to die, trees to bloom off-season and a general decline in health and vigor. Additionally, the bacteria cause trees to produce green fruit, thus giving the disease its common name.

After years of nervously watching cases appear in Baja, Mexico, California researchers found what they feared. In March of 2012, samples from a single tree in a residential yard in Hacienda Heights tested positive for the problematic bacteria. Fortunately, this is the only documented case in the state, but it is unlikely to be the last.

Hope on the Horizon

A cure for Huanglongbing still eludes scientists, but they continue to attack the problem. Some trees have responded to treatments for a brief time, but they all succumb eventually. To help prevent the spread of the disease, the United States Department of Agriculture has imposed a quarantine, banning interstate commerce of citrus trees from the nine infected counties.

Nevertheless, it is ultimately preferable to control the insects that spread the disease. The insect itself causes damage, but it is also the vector for the debilitating bacteria.

Biological control efforts may offer some relief in the future, as several animals parasitize (and ultimately kill) psyllids in their native lands. Scientists have released two different ectoparasites of the psyllids in Florida: Tamarixia radiata and Diaphorencyrtus aligarhensis. Both insects have proven effective in reducing local psyllid populations, but further research is required to determine the viability of the solution in other locations. Over the past few years, scientists in California have released 75,000 Tamarixia radiata. (Lopez, 2013)

*Interesting note: The tern “Candidatus” refers to the fact that these bacteria have not yet been cultured in a laboratory.

References

Lopez, R. (2013, August 4). Citrus growers use predator wasp to fight disease threat. L.A. Times.

Valentine, K. (2014, November 6). ASIAN CITRUS PSYLLIDS FOUND IN GROVE NEAR EXETER. ABC Action News.