More than 1,600 mature street trees in Long Beach and tens of thousands throughout Southern California are susceptible to a new, deadly fungal strain that kills at alarming speed and threatens to destroy the urban forest in older cities known for their tree-lined streets, scientists say.

Branch dieback disease caused by botryosphaeria fungus has already infected more than 25 percent of the region’s ficus trees, also know as Indian laurel-leaf fig, said Donald Hodel, researcher and horticultural adviser for the University of California Cooperative Extension in Los Angeles.

Because of the disease’s rapid spread, all of the region’s ficus trees could die in 10-30 years, leaving cities with the incredibly expensive task of removing them and planting new trees. More importantly, the wiping out of ficus microcarpa would end a 70-year legacy of mature shade trees enjoyed by 10 million Los Angeles County residents at a time when scientists say global warming is sending temperatures to record highs.

“It is unfortunate we are losing so many trees within the urban forest so rapidly,” said Jerry Turney, plant pathologist and senior biologist for the Los Angeles County Agricultural Commission said. “It will be a fast changeover.”

Fungus discovered

The infection of ficus microcarpa trees, the most popular shade trees planted in the 1950s and 1960s, was first discovered in 2008 by Hodel and others studying similar plant diseases attacking agricultural crops.

Plant biologists and university researchers say the infestation of urban ficus trees is a recent development, one that can kill the 60- to 70-foot shade trees in two to three years and has no known cure.

“It is new to us,” said Turney. “We grew these trees for decades and decades with no problems at all.”

In 2009, a journal article documented a fungal disease known for infecting agricultural crops that began infecting the popular city trees for the first time. At that time, scientists called it sooty canker but had misidentified the fungal strain, said Akif Eskalen, a professor at the UC Riverside Department of Plant Pathology and Microbiology. The plant pathologist fingerprinted the fungus’ DNA and reported the news in a 2012 journal article. The breakthrough could lead to a cure or at least more study, he said.

Urban forest at risk

However, over the next five years, a lack of response from cities and counties discouraged him. Nobody was interested in saving the shade trees infamous for their sprawling roots that tear up sidewalks and cause cities legal nightmares from slip-and-fall cases, he said.

“But the point is, if you are living in that neighborhood and the ficus tree is making good shade, you don’t want to lose it. It is important for the value of the house,” Eskalen said.

Yet, many cities and counties are losing the battle with ficus tree dieback, potentially exposing thousands of homes and downtown business districts to direct sunlight and higher electric bills, he said.

Hodel’s earlier journal article reported the disease was “causing severe damage and death” in Santa Monica, Long Beach, Lakewood, Beverly Hills and Whittier. Hodel wrote the disease’s advancement “is often spectacular” killing seemingly healthy ficus trees among a row planted on a street median or parkway in only a few years.

Of Long Beach’s approximately 92,000 street trees, there are 3,147 ficus trees, about half of which are the Indian laurel-leaf fig species, said Art Cox, the city’s street maintenance supervisor. He did not know how many of those are infected with the fungus, but, he said, over the past decade, Long Beach has lost approximately 30 street trees to the disease.

Public Works Director Craig Beck said the city in recent years has been removing ficus trees from parkways and street medians to alleviate the strain on infrastructure.

“They are fine in parks or areas where their roots have room to grow, but they are such an aggressive tree and their roots get so large that they cause a significant amount of damage to infrastructure when in a small parkway,” he said.

Ficus trees targeted for removal include those lining the Second Street medians in Belmont Shore.

City parks, such as Bixby and Willow Springs, are dotted with a handful of ficus trees, said Kelly Parkins, parks maintenance supervisor. However, she explained, those include two different species: ficus macrophylla and ficus benjamina, which are not prone to botryosphaeria infection.

Among Los Angeles County’s 154,000 street trees, 2,452 are ficus species, said Steven Frasher, spokesman for the Department of Public Works. He did not know how many of those are infected with botryosphaeria, or what Eskalen calls Bot Canker for short.

He said the department is removing some of the ficus trees presently, some because they are dying and others because of damage to sidewalks.

The policy set by the Board of Supervisors requires every tree to be replaced on a 1-to-1 ratio. “We believe it is a big thing for the county to maintain its urban forest,” he said.

Disease spreads rapidly

Three years ago, Turney was driving from his South Pasadena home to his laboratory in South Gate when he saw a couple of ficus trees on Alhambra’s Main street whose deep green canopy had turned brown and thin. He stopped and took pictures.

During a scouting trip last month, Turney examined the same tree located on a parkway strip on Main Street, east of Fremont Avenue. He found more dead ficus trees.

“I was shocked how fast it went on Main Street,” Turney said. “Three years ago, I saw two trees showing the symptoms. Now, it is killing 10 trees. These all went quickly in a three-year period.”

As he walked beneath the dying and dead trees, he pointed to the small bungalows once shaded from the sun. “These homes will all be in the full sun come August,” he predicted.

Alhambra’s Public Works Department is aware of the disease infecting its ficus trees, said Chris Paulson, director of administrative services.

“They are aware of it. They are trying to determine the best course of action to see how bad they are,” he said. “They may say let’s remove these and put some new ones in.”

On Pasadena’s Green Street, a canopy of bright green leaves from branches of ficus trees planted on both sides of the commercial street stretching from Orange Grove Boulevard to Hill Street make it the most shade-filled in the Crown City. Yet, many of the specimens in Pasadena are already infected with the fungal disease, Turney said.

On the eastern edge of Green Street, Turney walked up to a sickly parkway tree on the south side of Green Street near Pasadena City College in Pasadena.

Usually, Turney talks excitedly about trees. This time, his cadence slowed. He became like a physician delivering bad news to a terminally ill patient.

“This is all dead wood,” he began, sloughing off pieces of bark clearly infected with charcoal-colored spores from the fungus fruit. “This particular ficus microcarpa is in severe decline. There is nothing anyone can do to save it,” Turney said, adding: “You can see the fate of all these trees down here.”

Turney first heard of the disease killing ficus trees in Whittier eight or 10 years ago. “When I saw it, I didn’t know what it was,” he said.

Though many of these trees are removed by cities because of roots upending sidewalks, the 13 trees removed in Whittier on Painter Avenue between Hadley and Philadelphia streets were due to what was then known as sooty canker, now most likely due to botryosphaeria fungus, Eskalen said.

Burbank removed 400 ficus trees in the Magnolia Park district during the past year.

Botryosphaeria has infected ficus trees on Wilshire Boulevard on the west side of Los Angeles, said William McKinley, a certified arborist who works for Glendale and other cities.

McKinley said it is so new it has not come across his radar that often. In fact, a recent examination of ficus trees in Glendale at Mountain Street and Verdugo Road found them in good health. “They are very full and thick,” McKinley said.

Spores spread by pruning

The fungus attacks the woody portion of the plant, leaving large rivets inside the tree’s bark and branches called cankers. The cankers cut off the flow of water and nutrients to the plant, causing the leaves to fall off and the branches to turn charcoal black and eventually die.

The cankers are filled with black spores the size of pencil points that are transported by raindrops, wind or human means. “The primary means of transmission is through pruning tools,” McKinley said.

One way to prevent botryosphaeria spores from spreading from tree to tree is to soak the pruning tools in bleach between uses or throw away the blades like a doctor would a tongue depressor. Using chain saws also spreads the disease because they cannot be disinfected, he said.

The best way to stop the spread is to keep trees watered, healthy, and practice safe pruning methods, experts say. In other words, prevention is the best cure.

“There is no way to treat it or stop it,” Turney said.

Stress lowers trees immunity

Ficus trees are poor choices for parkways, McKinley said. They need more room for their roots. Because they are grouped close together, they fight over nutrients, leaving them weakened.

Some city or construction crews cut their roots to prevent more sidewalk damage, creating more stress. “This is the tree everyone hates. They are notorious for breaking sidewalks,” Turney said.

Five years of drought also stressed these parkway trees, Turney said. But some that have not been watered are doing fine, while others are dying, a conundrum Turney and other scientists cannot understand.

Other diseases — as well as some pests — are killing other varieties of parkway trees throughout Southern California. The liquid amber trees are dying in Alhambra and elsewhere, Turney said, as are crepe myrtle trees. Oleander bushes along freeway shoulders are dying from oleander leaf scorch.

At The Paseo shopping center in Pasadena, some ficus trees are showing signs of the disease, while others look healthy, Turney reported. The ficus on Green Street near Orange Grove Avenue look OK, as compared with the tree canopy near Pasadena City College, which is nearly gone.

New trees take much care

McKinley suggests once the ficus die out, cities should plant a variety of trees, not just one kind. So if one gets a disease, all the trees on the block will not die. “You don’t want to lose the urban forest. That’s why you need to diversify,” he said.

Eskalen urges chemical companies to work on a fungicide that is specific to the particular botryosphaeria strain. “A fungicide study needs to be done in order to find a specified fungicide that you can then recommend to arborists to apply,” he said. Unfortunately, studies funded by agriculture are aimed at diseases that kill crops. No one is stepping up to fight the death of urban trees, he said.

Without more research, the fast-moving pathogen will continue to infect more and more trees, since ficus are often planted close together on skinny parkways, Eskalen said. New trees need to be watered regularly to survive in Southern California’s increasingly harsh Mediterranean climate.

Despite evidence of the cankers eating away at urban ficus trees, Turney remained optimistic.

“When I see a dead tree it is an opportunity for a new tree. All is not lost. We will find a way,” he said.