Beetle-fungus disease threatens crops and landscape trees in Southern California

May 8, 2012 By Iqbal Pittalwala
Close-up of the Tea Shot Hole Borer, which spreads a fungus that threatens avocado and other trees. Credit: Gevork Arakelian.

(Phys.org) -- A plant pathologist at the University of California, Riverside has identified a fungus that has been linked to the branch dieback and general decline of several backyard avocado and landscape trees in residential neighborhoods of Los Angeles County.

The fungus is a new species of Fusarium.  Scientists are working on characterizing its specific identification.  It is transmitted by the Tea Shot Hole Borer (Euwallacea fornicatus), an exotic ambrosia beetle that is smaller than a sesame seed. The disease it spreads is referred to as “Fusarium dieback.”

“This beetle has also been found in Israel and since 2009, the beetle-fungus combination has caused severe damage to avocado there,” said Akif Eskalen, an extension plant pathologist UC Riverside, whose lab identified the fungus.

To date, the Tea Shot Hole Borer has been reported on 18 different plant species worldwide, including avocado, tea, citrus, guava, lychee, mango, persimmon, pomegranate, macadamia and silk oak.

The finger points to a beetle exit hole on an avocado trunk. Credit: Eskalen Lab, UC Riverside.

Eskalen explained that the beetle and fungus have a symbiotic relationship.

“When the beetle burrows into the tree, it inoculates the host plant with the fungus it carries in its mouth parts,” he said. “The fungus then attacks the vascular tissue of the tree, disturbing water and nutrient flow, and eventually causing branch dieback. The beetle larvae live in galleries within the tree and feed on the fungus.”

Although the beetle was first detected in Los Angeles County in 2003, reports of its negative impact on tree health were paid no attention until February 2012, when Eskalen found both the beetle and fungus on a backyard avocado tree showing dieback symptoms in South Gate, Los Angeles County. The Agricultural Commissioner of Los Angeles County and the California Food and Drug Administration have confirmed the identity of the beetle.

Photo shows an example of wood discoloration due to Fusarium dieback. Credit: Eskalen Lab, UC Riverside.

“This is the very same fungus that caused avocado dieback in Israel,” Eskalen said. “The California Avocado Commission is concerned about the economic damage this fungus can do to the industry here in California.

“For now, we are asking gardeners to keep an eye on their trees and report to us any sign of the fungus or beetle,” he added. “Symptoms in avocado include the appearance of white powdery exudate in association with a single beetle exit hole on the bark of the trunk and main branches of the tree.  This exudate could be dry or it can appear as a wet discoloration.”

A team of UCR scientists has been formed to study Fusarium dieback in Southern California.  Eskalen and Alex Gonzalez, a field specialist, are already conducting a survey to determine the extent of the beetle infestation and the likely extent of the infection in trees and other host plants.  Richard Stouthamer, a professor of entomology, and Paul Rugman-Jones, an associate specialist in entomology, are studying the biology and genetics of the beetle.

Explore further: Beetle suspect in deaths of red bay trees

Related Stories

Invasive beetle attacks redbay trees

January 13, 2008

A beetle imported from Asia is spreading around the southeast United States, leaving dead and dying redbay trees in its wake.

Laurel wilt of redbay and sassafras: Will avocados be next?

April 2, 2008

Scientists with the USDA Forest Service Southern Research Station (SRS), Iowa State University, and the Florida Division of Forestry have provided the first description of a fungus responsible for the wilt of redbay trees ...

Tree-killing fungus officially named by scientists

June 30, 2008

The USDA Forest Service Southern Research Station (SRS) today announced that an SRS scientist and other researchers have officially named the fungus responsible for killing redbay and other trees in the coastal plains of ...

Spread of fungus-farming beetles is bad news for trees

July 13, 2011

(PhysOrg.com) -- North Carolina State University researchers have found that a subset of fungus-farming ambrosia beetles may be in the early stages of a global epidemic threatening a number of economically important trees, ...

Recommended for you

How the finch changes its tune

August 3, 2015

Like top musicians, songbirds train from a young age to weed out errors and trim variability from their songs, ultimately becoming consistent and reliable performers. But as with human musicians, even the best are not machines. ...

4 million years at Africa's salad bar

August 3, 2015

As grasses grew more common in Africa, most major mammal groups tried grazing on them at times during the past 4 million years, but some of the animals went extinct or switched back to browsing on trees and shrubs, according ...

A look at living cells down to individual molecules

August 3, 2015

EPFL scientists have been able to produce footage of the evolution of living cells at a nanoscale resolution by combining atomic force microscopy and an a super resolution optical imaging system that follows molecules that ...

New lizard named after Sir David Attenborough

August 3, 2015

A research team led by Dr Martin Whiting from the Department of Biological Sciences recently discovered a beautifully coloured new species of flat lizard, which they have named Platysaurus attenboroughi, after Sir David Attenborough.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.