Saving the Giant Sequoia Forest

Posted on June 13, 2023 by landscapeexpert

For several years, climate change and drought created conditions for uncontrolled California wildfires. These wildfires burned with such intensity, several Giant Sequoia, (Sequoiadendron giganteum), forests were heavily damaged. We have lost approximately 20% of the entire species, over 10,000 Giant Sequoias have been destroyed the past three years alone.

Although these magnificent trees are fire adapted, with an incredibly thick outer bark protecting the cambium within, the recent fires burned with such incredible intensity scores of trees were incinerated. Another fire adaptation are the Sequoia cones that normally open after a fire, distributing thousands of seeds that germinate and replenish the burned groves. Yet the fires were so hot, even the cones were destroyed, so the trees produced no new seedlings.

All of the groves are located in a relatively small band on the western slope of the southern Sierra range. Due to climate change, the southern Sierra range has become a dryer environment, very different than 2,000 years ago when these magnificent trees first germinated. As the forest regenerates, shrubs, fir, and cedar have replaced the Sequoias.

Sequoia seedlings require a lot of water to germinate and grow into juvenile trees. The hotter, drier climate and competition with other less favorable species, reduces Sequoia germination and ultimately, the survival of the species. Imagine Sequoia National Park without any Sequoia trees. Your kids and grandchildren might end up never being able to visit and enjoy these incredible trees. My father took me to the park when I was a child. My love for this species influenced my decision to study horticulture, eventually making my profession, first as a landscape contractor, later as a consultant and expert witness as certified and registered consulting arborist.

Fortunately, the Save the Redwoods League has teamed with the US Forest Service and National Park Service undertaking replanting thousands of redwood seedlings throughout several burned forest areas. The goal is to reestablish groves that can be managed to become fire resistant again. It is a massive undertaking, that has never been tried before. While the odds of any seedling becoming a massive, thousand year old monarch are depressingly low, (one in 10 billion), it is the morally right undertaking for mankind. Without restoration, the redwood groves will convert to shrub lands, a sad ending for the official state tree of California.

Read about the restoration efforts in this article from the Los Angeles Times.https://landscapeexpertwitness.com/wp-content/uploads/2023/06/Los-Angeles-Times-eNewspaper.pdf

Bromeliads in the Landscape

Posted on January 14, 2023 by landscapeexpert

With spring time on the horizon, it was time to start sprucing up my landscape garden. I try to make the garden interesting using a variety of plant materials with differing form, texture and foliage color. My latest planting incorporates bromeliads into the landscape. There are countless species to select from, their form, leaf color, texture and flowering are extremely unique and incredibly beautiful. Fortunately, there is a fantastic nursery in north San Diego County specializing in bromeliads and tillandsia, www.birdrocktropicals.com

Visits are by reservation only, but well worth it. Although I’m a horticulturist, bromeliads are a specialty species I had little actual knowledge on species planting and maintenance requirements. I have a very difficult planter area that is full shade in the winter, full sun in the summer. Another planter changes varies from shade to part shade seasonally.

I received a great education while guided through the nursery, learned a great deal about bromeliad breeding, potting and maintenance. Another great tip they provided was leaving the plant in the container while planting in the landscape. Bromeliads, similar to orchids, are tropical understory plants. They are adapted to very poor, thin tropical soils and do not like heavy, clay poorly drained soils. Unlike typical ornamentals. they also prefer contained environments, smaller plants do not like being potted into large containers. They should remain in smaller containers until they grow multiple pups, filling the container to the point where watering becomes difficult.

Another advantage of planting them in their containers is being able to remove them if the environment becomes to shady or sunny for the individual plant. I’m excited about these beautiful plants, hoping they grow and multiply!

Why Attorneys Hire an Arborist Expert Witness

Posted on February 3, 2022 by landscapeexpert

Whether an attorney represents a plaintiff or defendant, they hire an expert who will provide compelling testimony to support their client. Sometimes, multiple experts from a variety of disciplines may be required. When should an attorney consider hiring a certified or registered consulting arborist as an expert witness?

Living with trees implies accepting a certain amount of risk in exchange for the wonderful benefits trees provide. While the risk of a tree limb or whole tree failure resulting in a fatal injury is low, hazards caused by trees that result in personal injury or property damage lawsuits are not uncommon.

Tree species and proximity to infrastructure may be a factor in accidents with personal injury or property damage. Tree roots seek out moisture regardless of their location. Structural roots emanate from the trunk to the edge of the crown, also known as the drip line, then small moisture absorbing root grow far beyond. Tree root systems may grow 1.5 times the tree crown diameter.

Trip, Slip and Fall Accidents

In the urban environment, tree proximity to hardscape may result in roots growing beneath concrete sidewalks and paved streets while seeking moisture. Roots will grow into adjacent water meters and sewer laterals, especially older leaking, permeable infrastructure. Once established beneath a paved surface, a root continues growing, over time enlarging in diameter.

Over time, these surfaces may begin to lift along the crack or expansion joint. Adjacent sidewalk panels may lift several inches, resulting in a hazardous condition for pedestrians and bicyclists.

Uplifted sidewalk panels resulted in bicyclist personal injury lawsuit

After sidewalk was removed, large structural roots were observed beneath the sidewalk.

Multiple roots damaged the sidewalk, created the hazardous condition and resultant accident.

Eventually root enlargement lifts concrete infrastructure, including water meter boxes and sidewalks. Cracks may develop across a sidewalk panel, in my experience, most concrete sidewalk uplifts occur along an expansion joint.

In their pursuit of moisture, roots from neighboring trees ignore property lines. They can grow beneath garage slabs and foundations, especially in situations where there has been a water or sewer leak beneath the slab. Moisture discharged beneath slabs, footing and foundations create an attractive environment for root development.

Neighbor’s Ficus tree root grew beneath their garage slab, resulting in property damage lawsuit.

Roots suspected of lifting sidewalk panels and water meter box that resulted in personal injury lawsuit.

After sidewalk was removed, large roots observed growing around the water leaking water meter.

Installing street trees within small concrete confined planters is an invitation for root damaging infra-structure. Leaking water meters, fittings and sewer connections increase soil moisture, an invitation for root growth.

A root penetrating a leaking sewer lateral or potable water meter pipe or fitting will quickly establish a mass of roots within and surrounding the pipe. Root growth may continue from the sewer lateral into the public sewer main. Over time, the root growth may block or cause a sewer back up to neighboring properties.

Roots deform a sewer lateral beneath garage slab.

Section of removed sewer lateral filled with roots.

Improperly designed, installed or maintained sprinkler systems may result in over-spraying paved pedestrian sidewalks. Regardless of cause, their is no reason to allow sprinklers to over-spray onto paved surfaces, it wastes a vital resource while creating an obvious slip and fall hazard.

Park sprinklers over-spraying a public sidewalk, resulted in a personal injury lawsuit.

Tree failures and forensic tree risk assessment

Tree limb and whole tree failures may result in personal injury and property damage lawsuits. Whole tree failures may occur due to loss of load bearing structural roots, whether due to root rot disease, construction impacts, mechanical root damage, or soil failure. Limb drops may occur for a variety of known reasons, typically the failure occurs during a weather event. Sometimes, a tree will drop a limb for unknown reasons, referred to as sudden or summer limb drop. Stems may contain defects such as cankers, decay, and cracks that may be predisposed to failure when enough force exceeds the wood carrying capacity. Forensic tree risk assessment may determine why the tree failed and whether the defects were open and obvious.

Stem failure resulted in personal injury and property damage lawsuit.

Tree and landscape appraisal for fire damage, trespass and vandalism

California has suffered countless wildfires the past two decades, resulting in substantial property damage. Tree appraisal for loss due to fire may be an important aspect in legal cases, especially when several major utilities are under scrutiny for causing wildfires.

The same holds true for tree loss or diminution in value due to trespass and vandalism. You may love your tree, but your neighbor may not. Neighbors frequently engage in tree disputes, sometimes resulting in trespass and vandalized trees. You may love your tree, but your neighbor may not.

Avocado groove scorched from wildfire in Fallbrook. Appraisal performed for insurance and tax purposes.

Oak tree property damage claim due to Thomas fire.

Tree and landscape appraisal for property damage lawsuit caused by Thomas fire mudslide.

Palm tree nursery burned due to vandalism, appraised palm value for property damage lawsuit.

Bamboo hedge poisoned by neighbor, property damage lawsuit.

Tree loss due to neighbors pruning, resulting in property loss lawsuit.

Arboriculture standard of care

Tree service contractors may become involved in a lawsuit for failing to satisfy the industry standard of care. When a tree failure occurs, the landscape maintenance or tree care contractor may find themselves as defendants in a lawsuit. A plaintiff may contend the landscaper or tree care company should have known the tree had defects but was the contractor responsible for risk assessment?

A C-27 landscape contractor may not be a certified arborist or provide arboricultural tree care, certified arborist may not be a trained or knowledgeable of Tree Risk Assessor Qualified, (TRAQ).

To determine a contractor’s standard of care, I examine their membership in industry associations such as the California Landscape Contractor Association, (CLCA), the International Society of Arboriculture, (ISA), the American Society of Consulting Arborists, (ASCA), and Professional Tree Care Association. I determine whether the certified arborist and tree care professionals adhere to the American National Standards Institute, (ANSI) A300 arboriculture standard practices and Z133 safety requirements. I check their standing on the California State Licensing Board.

In summary, personal experience, education and training are essential qualifications an attorney looks when selecting an arborist expert witness. Having expertise in multiple disciplines is an added benefit. My qualifications as a professional horticulturist, a C-27 landscape contractor, a certified arborist, registered consulting arborist and tree risk assessor qualified and land development manager enable me to opine on a broad array of landscape, tree, plant and land development issues.

Tree Roots Lifting up Sidewalk?

Posted on August 11, 2020 by landscapeexpert

Who is Better Qualified to Opine on Root Damage, Civil Engineer or Certified Arborist?

I was retained by a defendant attorney to determine whether her client’s tree was responsible for lifting the adjacent civil sidewalk that resulted in a plaintiff trip and fall lawsuit. Based on the photographs and tree species, White mulberry (Morus alba), I was fairly certain her client’s tree was responsible for the sidewalk damage.

The attorney retained me and requested a site inspection and tree root assessment. I trenched adjacent to the sidewalk and within a short time, encountered a three-inch diameter root growing under the sidewalk. Further excavation revealed a network of two to four-inch diameter roots that had grown under the sidewalk, resulting in the tree roots lifting up the sidewalk panel, creating a hazardous condition resulting in a trip and fall accident.

I informed the attorney that tree roots lifting up the sidewalk, or root encroachment from her client’s tree resulted in the sidewalk damage, she said her civil engineer expert claimed it impossible for a tree root to lift a concrete sidewalk. I questioned the engineers knowledge and experience with trees, was the civil engineer a certified arborist or horticulturist?

Although the answer was no, she felt his qualification as a civil engineer was superior to my qualifications as a certified arborist, tree risk assessor qualified, registered consulting arborist and a college educated horticulturist. Her dilemma was having two experts who disagreed and she requested I alter my opinion.

I told the attorney altering my opinion to suit her needs was unethical, and I removed myself from the case.

What Causes Tree Roots To Lift up a Sidewalk?

The common myth is trees have tap roots that grow straight down into the soil. While this may occur in very deep, loam soils, the reality is most containerized nursery grown trees lose their tap root in the container. Once planted in our poor Southern California soils, when the tap root encounters physical soil obstructions, such as rock, clay or hardpan, the tap root divides and grows multiple roots around the obstacle, forming a fibrous root system. Tap root grows into fibrous root system.

Trees require a spreading root system to maintain structural stability. Trees dissipate energy generated during a storm or wind event by transmitting leaf, limb and trunk movement down to the roots. A spreading root system anchors the tree movement and dissipates the energy far more effectively than a single tap root system.

Most tree roots grow within the top 24-inches of the soil horizon. Roots in top 24″ of soil. Over time, structural tree roots (2-inch diameter and greater) growing within a shallow soil adjacent to sidewalks, footings, foundations, walls or othersub-surface infrastructure may cause damage.

Just as a twig grows into a branch, and then a limb, roots increase in length and circumference. Irrigation water, sewer or water service leaks increase subsoil moisture beneath sidewalks or garage slabs, creating a perfect environment for root growth.

Cracked garage slab

As the root circumference increased, it exerts pressure on the concrete slab or footing above the root. Depending on the species, root diameter might increase 1/8-1/4” annually.

Within five to eight years, a small feeder root may grow to one-inch in diameter or greater.

Ficus root cracked the garage slab

The root growth may be compared to the action of a hydraulic jack, as the circumference increases, the upward pressure on the sidewalk or slab may crack and or eventually cause tree roots to lift the sidewalk. Concrete lifting may often occur at an expansion joint between concrete panels

Sidewalk lifted at expansion joint

Root network beneath sidewalk.

Roots seek out soil moisture, they can and will grow under walls, footings and garage slabs. Roots are opportunistic, leaky plumbing, old cast iron sewer lateral or water services contribute to the soil moisture needed for roots to flourish.

Sewer lateral root damage

Roots may infiltrate pvc, abs and cast-iron pipe through even the smallest of cracks or holes.

Once inside, the roots expand in size and quantity, eventually completely clogging the utility.

If the tree crown has grown over a sidewalk or adjacent structure, it is a reasonable assumption structural roots (two-inch diameter and greater) have grown under the sidewalk, slab or footing.

Root growing under house footing

Planter areas confined by concrete pose one of the greatest risks for root damage. City sidewalks often incorporate small, square planters within the sidewalk easement.

Roots lifting water meter and sidewalks

Confined planters quickly fill with structural roots, as well as damaging girdling root. As the tree crown grows, so to do water absorbing feeder roots. Over time, root mass and size increases, structural roots may begin to grow beneath concrete improvement while seeking out moisture.

Leaking water meter, high soil moisture, confined growing space.

The tree pictured above and to the right had a leaky water meter adjacent to the small sidewalk planter. The leaky service provided idea soil moisture conditions for the roots to lift the water meter box, adjacent sidewalks and crack the curb and gutter.

Preventative measures to minimize root encroachment include a variety of root barrier methods. All root barrier systems work best when the tree is installed. Once roots have enlarged and matured, barrier mitigation is not successful.

In summary, our Southern California poor, shallow soils do not support deep tree tap root systems. Most trees grow fibrous spreading root systems. Structural roots emanating from the root collar extend to the edge of the tree crown, (drip line). Most structural roots growing beneath sidewalks range from two to four inches in diameter, lifting sidewalk panels on average one-two inches. Trees growing in confined planters or adjacent to concrete, utilities or foundations may develop structural roots capable of lifting, cracking or damaging adjacent improvements.

Dealing with legal issues due to tree roots lifting up a sidewalk?

Attorneys should select an expert based on the case criteria, not simply a title, license or certificate. Choose an expert most appropriate to address the cause of the problem and develop opinions based on sound, industry practices.

Finally, A Turf Block Driveway With Thriving Turf!

Posted on June 23, 2020 by landscapeexpert

Rarely have I seen a successful turf block driveway. Turf block, turf stone, turf pavers are systems installed as living turf driveway alternatives. The material provides structural support via plastic or concrete cells that are filled with a soil media for turf installation. The block is designed to support vehicular traffic on driveways while providing a green alternative to concrete or asphalt driveways.

Turf blocks have been used for decades, but rarely have I seen thriving turf grass within the block. Not because of the product, but usually due to turf establishment and failure issues. Due to reduced soil root area, soil compaction, irrigation infiltration and damaged soil structure result in poor turf establishment. Soil preparation, drainage and proper irrigation coverage and operation are required to grow turf inside of a turf block system.

Lastly, using vigorous, warm season turf grasses that spread by horizontal solons, rhizomes, and rooting improves the successful establishment of turf grass, such as the Tiff hybrid Bermuda grasses developed for sports fields. Cool season turfs including rye, bluegrass and turf type fescues are clumping turfs that do not spread horizontally, thereby limiting establishment and healthy growth. Cool season grasses are more susceptible to leaf and soil borne diseases, are easily stressed during hot summer months, nor are they tolerant of vehicular and pedestrian traffic and compaction conditions.

Tiff hybrid Bermuda is well established within the turf block

Trip, Slip and Fall Hazard: Hidden Depressions in Grade

Posted on May 19, 2020 by landscapeexpert

Successful landscapes require:

Proper grading, drainage and amended soil.
An automatic irrigation system achieving 100% head to head coverage.
Properly installed, high quality plant material.

Each of these functions may require a specific type component, installed at a specific height or location to reduce the potential of creating a site hazard that may result in an accident. In commercial applications, landscape plans usually include details and specifications dictating type of product and how it should be installed.

Many common landscape products may be improperly installed including:

Pop up heads may be incorrectly set to grade against a sidewalk.
Valve or drainage boxes set too high or low relative to finish grade.
Shrub head installed on a riser adjacent to concrete improvement.
Hidden, obscured depressions in grade due to substandard compaction, settlement and subsidence.
Drainage box set too low.

Improper product selection or substandard installation practices may appear obvious. A pop up sprinkler head set above the top of adjacent concrete sidewalk creates a trip hazard. A drainage structure set well below the turf grade creates a trip slip and fall hazard. Selecting and installing a spray head on a rigid riser next to a pedestrian sidewalk is a sub-standard industry practice that creates a trip and fall hazard.

Spray head on a riser next to a sidewalk creates a trip hazard.

Not all landscape hazards are visible. Turf areas may have grade depressions or holes that are hidden by overgrown turf grass. Depending on the cause and time period, turf grass may completely hide the depth, location and size of the depression or hole, creating a hidden hazard.

A depression, rut or hole may result from several factors. Repeated mowing on saturated turf may create ruts. Overwatering may cause irrigation or utility trench settlement. A dead tree removed from a turf area may result in a future depression if the grade is not properly backfilled and compacted.

A seven inch deep hole hidden by turf grass.

Bermuda grass is a fast horizontal spreading turf-grass used in parks and recreation facilities throughout the country. Unless regularly aerated and de-thatched, Bermuda grass in known to grow a thick layer of thatch. Over time, the thatch layer can increase the turf grade several inches above adjacent sidewalk and curbs.

The backfill in utility trenches installed across pre-existing turf may settle, creating a depression in the sub-grade. The photo depicts the edge of a trench cut across an asphalt driveway, across a turf area. The trench backfill eventually settled, creating a trench sub-grade depression hidden by the Bermuda grass.

Thatch, hidden depression and sanded turf.

The depression resulted in a trip and fall accident. After the accident, several hidden turf depressions were “sanded” to fill depressions to proper grade.

Not all landscape hazards are open and obvious. Even a perfectly installed landscape may develop hazardous conditions if not regularly inspected and maintained.

Irrigation systems should be monitored, inspected, tested and adjusted monthly. Turf should be trimmed around utility boxes and vaults regularly, aerated and de-thatched annually to maintain optimum performance and minimize grade changes. Drainage structures should be grade adjusted, repaired or replaced when damaged. Valve, electrical and junction boxes should be monitored for grade changes and adjusted as required. Bark mulch thickness should be monitored and supplemented annually to maintain proper coverage and grade.

In summary, a properly installed landscape is composed of several systems and components that require regular ongoing maintenance for optimum performance, efficiency and safety. Pro-active landscape maintenance may reduce potential hazards, resultant accidents and lawsuits. These actions demonstrates an Owner’s recognition of protecting the health and safety of the public, pedestrians, friends and family who may visit and use the site and may prove useful in a legal action.

A Horticulturists Local Neighborhood Walk

Posted on May 13, 2020 by landscapeexpert

I took my usual walk through local neighborhoods surrounding Balboa Park in San Diego. A glorious spring day, I couldn’t help but marvel at the beautiful ornamental landscape trees, shrubs and vines in bloom everywhere! Very uplifting, glad plants are not affected by the virus!

Arborist Online Learning Opportunities in the Covid Era

Posted on May 12, 2020 by landscapeexpert

In a recent blog, I discussed using online media for a site online site inspection involving a Torrey pine tree root conflict with adjacent asphalt paving. That marked the first time I used an online media tool rather than being physically present at the site. My client and I used Facetime to conduct the real time inspection.

As the restrictions ease, I believe the use of online media such as Zoom, Hangouts, Facetime etc will increase. I have already presented this concept to a legal client in Northern California concerning an irrigation inspection. Do I really need to fly from San Diego to San Francisco, rent a car, drive to the site, observe irrigation defects, then reverse the process returning home or, can I watch the inspection over the web? The level of scrutiny required depends on the individual case.

A slide from Dr. Smiley’s presentation

Like so many other industries, the tree industry is rapidly adapting to the new Covid – 19 reality. Today, I attended an online Zoom seminar titled Sidewalks, Urban Plazas and Tree Roots. This seminar was presented through the ISA Southern Extension. I believe it was originally going to be part of a “normal” ISA Southern Association Annual meeting that was cancelled due to Covid.

The online presentation occurred through Zoom with over 1000 arborists throughout the U.S. and other countries attending. The topic concerned tree roots damaging sidewalks, presented by Dr. Thomas Smiley. Once a few technical glitches were adjusted, the presentation was almost identical to what I had experienced attending many seminars.

The slides presented alongside the audio streaming from Dr. Smiley was easy to view. I became immersed in the content and found myself taking pics of some of the slides. The topic provided test data results using different techniques designed to reduce root intrusion beneath sidewalks.

Incorporating root growth inhibitor practices

The presentation lasted an hour, same amount of time I’m accustomed to when attending a seminar. Although I already knew a great deal about the topic, I still came away with new information for use in my practice, including a great specification detail incorporating multiple root growth inhibitor practices that may reduce sidewalk damage due to roots.

In the past month, I’ve been able to continue my consulting practice from my home office. I’ll continue to utilize more online media tools, whether for learning, conducting site inspection work, and client meetings. I believe these new opportunities are one of the (few) beneficial results from the Covid-19 virus.

I recently provided a client with a proposal to develop landscape maintenance specifications for commercial properties located in several different climatic regions. The proposal did not include any site visits. All data collection would occur online through various means. Using online data collection versus conducting multiple site visits saved the client thousands of dollars.

I’m looking forward to these new opportunities utilizing online media sources as potential replacement for physical presence. Hopefully it will prove an efficient, effective, cost saving technique without sacrificing product accuracy.

Joshua Tree Extinction by End of Century?

Posted on April 14, 2020 by landscapeexpert

I just read an article in the Los Angeles Times about a potential listing of the Joshua tree as an endangered species. The western Joshua tree, Yucca brevifolia, is one of two genetically distinct species that occur in California. It range extends from Joshua Tree national park westward along the northern slope of the San Bernardino and San Gabriel mountains, northward along the eastern flank of the Sierra Nevada and eastward to Death Valley.

Approximately 40% of the western tree range is on private land, the eastern range is centered in the Mojave National Preserve and eastward into Nevada.

After decades of climate change, development, drought and wildfires, the species is facing a rapidly increased the risk of extinction. State Department of Fish and Wildlife Commission will decide in June whether to accept the department’s recommendation to declare the tree an endangered.

As usual, there are two sides to the issue. Conservationists see this as a triumph of state environmental law while critics claim it as a misguided overreach because Joshua trees are already protected under many city and county ordinances and within the 800,000 acre national park.

Environmentalists argue existing state and local ordinances are largely inadequate at protecting species habitat loss, the endangered species listing will finally provide a statewide protection for the species, including requiring wildlife managers devise a recovery plant for the species, which could limit development in SoCal real estate.

The Joshua tree exists in high desert communities such as Yucca Valley or Hesperia, communities with lower average median household incomes. They are concerned the listing would impose additional burdens to real estate development, making it tougher to improve their property or curtail new development in their communities.

However, researchers warn time is running out. The tree’s range is contracting at lower elevations, its reproduction has come to a halt. Trees are failing to reproduce at lower, hotter elevations. They could become extinct in California by the end of the century!

This would be a terrible outcome for a truly incredible species. This remarkable species deserves protection. I believe this tree, in its own way is as majestic in its high desert setting as the coast redwood. These are species distinct to our California heritage. The Joshua tree deserves protection for our future generations to enjoy, marvel and be uplifted by this unique species.

Download a pdf of the article here: Los Angeles Times – eNewspaper

California Olive Trees Dying from Exotic Pest Infestation

Posted on April 10, 2020 by landscapeexpert

Olive tree displaying decline symptoms

With so many trees dying in natural and landscape settings, I’ve observed a disturbing trend throughout San Diego, and I assume most of the state. Property owners allowing dead and declining trees, palms and shrubs to remain in place. The problem with this practice, aside from aesthetics, is the dead plant may serve as a vector, whereby flying insects such as beetles, leaf hoppers, spittle bugs etc. may spread the disease to other uninfected trees.

Over the past decade, drought and climate change has taken a toll on millions of trees throughout California. Drought weakened trees succumb to secondary invaders such as wood boring bark beetles. There appears to be a continuous proliferation of new exotic pests resulting in diseases that are killing millions of trees in nature and within our urban forests and residential landscape settings.

Gold spotted oak borer

First collected and identified in 2004 was the gold spotted oak borer, (GSOB). This flathead borer is responsible for killing over 100,000 live and black oaks in San Diego County alone. There is no effective prevention or cure.

Reports of the disease known as citrus greening, previously confined to China, appeared in Florida, threatening the entire U.S. industry. The disease is a vector-transmitted pathogen by the

Citrus damaged by Asian citrus psyllid

Asian citrus psyllid. This disease ravaged Florida citrus growers. Once infected, there is no cure.

Another exotic pest first detected in Southern California in 2003 has been infesting hundreds of different species and is now established throughout the southland.

The Polyphagous shot hole borer is a small ambrosia beetle responsible for transmitting Fusarium disease to many tree species including avocado,

Sycamore bleeding from shot hole borer

box elder, coast live oak, maple, liquidambar, coral, sycamore and many other species. Fusarium is a vascular clogging disease for which there is no cure.

The list goes on and on. Climate change and an ever more connected world will continue the trend toward future invasive erotic pests.

In early 2000, olive trees, (Olea europea) became very popular as a landscape tree, heavily planted throughout southland landscapes. For the past decade, olive trees have been declining from a number of diseases. Two of the diseases are fatal, both display similar symptoms, making diagnosis difficult.

Foliage display tip and marginal burn symptoms

Symptoms appears as leaf marginal burning, tip dieback, leaf scorch, and loss of foliage color. Defoliation proceeds from the top down and outside in toward the trunk. Small twigs die back, eventually larger branches and entire limbs die. Depending on location and season, the decline may be rapid or slowly over the years.

Xylella or Verticillium?

Disease Infection

Diseases known as quick decline, leaf scorch, or variegated chlorosis are caused by Xylella fastidiosa, the bacteria best known for causing Pierce’s disease on grapes, but also attacks citrus, peach, almonds, oleander, olives and many other species.
Verticillium wilt affects olive trees in commercial and landscape plantings and many other species. The disease is caused by soil-borne fungi, Verticillium albo-atrim and dahliae.

Both are vascular clogging diseases, where the fungus or bacteria spreads throughout the vascular system, restricting water movement within the xylem tissue. However, they have separate means of transmission. Unfortunately, neither disease has a cure, infected trees and shrubs decline over time, usually resulting in death.

Description and Spread

Xylella is transmitted by the glassy-winged sharpshooter, (Homalodisca vitripennis), leaf hoppers and spittle bugs. These vectors are xylem feeding insects.
The pathogen multiplies and spreads throughout the host tissue, restricting water movement through the xylem tissue.
Insect vectors feeding on infected trees (such as olive and oleander) may acquire the bacterium and carry it to new hosts.

Verticillium is a soil-borne fungus, it invades the root system of olives when the soil temperature is cool.

After penetrating through roots, the fungus multiplies within the xylem tissue, interrupting and reducing water movement from the roots to the leaves.
Each disease clogs the vascular system, interrupting water movement from the roots to the leaves.
Both diseases have similar symptoms making identification difficult.

Common Symptoms: (not all symptoms may be present)

Xylella:

Tip burn
Leaf scorch beginning at the tip toward the stem (petiole).
Marginal browning, scorch and yellowing.
Twigs and branches dieback beginning in the upper crown.
Desiccated leaf and fruit drop.
Production of suckers.
Crown dieback

Oleander infected with Xylella

Verticillium:

Symptoms appear in spring.
Newer leaves curl inward.
Dead fruit clusters remain attached.
Loss of leaf color and luster.
Leaf and fruit drop follow.
Inward leaf curl

Progressive decline

Dead fruit retained

Individual branches and or large portions of the tree may die within one season.
The tree may not die, growth may develop on unaffected portions of the tree and suckering from the crown.
The new growth continues until re-infected; the cycle repeats the following year.
Vascular staining
Vascular staining may be present.

Control

There is no cure for Xylella or Verticillium. Recommendations for both diseases include:

Remove suspected plants immediately to prevent vectoring disease to other susceptible host plants, i.e.: olive, oleander, sweetgum, grapes, etc.
Integrated pest management to control insect vectors may help slow disease spread but spraying to control leafhoppers is expensive and futile.
Control of nearby weeds and grasses to help limit insect vectors.
Pruning out infected limbs may improve the appearance, but it is impossible to prune “below” the infected wood, so pruning does not get rid of the disease.
Fungicide applications are not effective.
Remove declining and dead trees immediately.
Replant with disease resistant species.

Avoiding the disease is most effective but not always possible. Soils are easily contaminated with Verticillium from former planting and the pathogen may survive in the soil for several years, ready to infect newly planted susceptible species.

While greenhouse soils may be heat pasteurized to kill the fungus, that is impossible in the landscape. Solarizing landscape soils has some effect at reducing verticillium infected soils. Prior to planting, rototill and irrigate the soil as deeply as possible. Cover the area with six mil plastic, seal the edges with soils to secure for six to eight weeks.

Effective cultural practices such as fertilizer application, irrigation management, weed and insect control may assist in preventing infection and possibly reduce the effects of the disease. Most of these practices focus on improving plant vigor that help mask the disease, however these treatments are not curative.

It is important to note, many of the foliar symptoms described above may also be due to drought or poor irrigation practices. There are also foliar diseases that may produce similar symptoms but are only minor and may not pose a serious threat.

Diagnostic laboratory testing is the definitive method for a positive identification of the disease.

The important take away is this: Don’t ignore decline symptoms in olive and other susceptible species, as the plant may be infected with a fatal vascular disease. Declining and dead trees left in place may serve as a source for the disease to be vectored by beetles, sharpshooters and other pests to healthy nearby trees. Remove dead or dying trees to prevent disease spread.