Alliance for Community Trees News

Fungus Threatens Southern California Street Trees

By Conni Kunzler | June 24, 2017

Source: Steve Scauzillo, “Love them or hate them, ficus trees lining city streets are dying from a new fungal disease,” San Gabriel Valley Tribune

Los Angeles, CA (June 17, 2017) – Tens of thousands of mature street trees in Southern California are susceptible to a new, deadly fungal strain that kills at alarming speeds and threatens to destroy the urban forest in older cities known for their tree-lined streets.

Branch die back 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 advisor for the University of California Cooperative Extension in Los Angeles.

Because of the disease’s rapid spread, all 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 Commissioner 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 die back, 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.

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.

Read the full article.

 

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