From: Scott Sincoff, ENN
Published May 9, 2012 09:52 PM

Invasive Fungus Damages Californian Avocado

A newly found fungal disease has been linked to a steady decline of landscape and avocado trees in suburban Southern California neighborhoods, says a newly released University of California-Riverside study. Besides a decline of avocado trees in the Los Angeles area, researchers from the Plant Pathology department at University of California-Riverside also have linked this new fungus to the branch dieback of trees.


A team led by Akif Eskalen, an extension plant pathologist at UC-Riverside, believes the new fungus is a new species of the genus Fusarium and has not yet been identified with a specific classification. The team states that the fungus is passed on by the Tea Shot Hole Borer, which is an exotic ambrosia beetle that is tinier than a sesame seed. According to the research team the Tea Shot Hole Borer, also known by its scientific name of Euwallacea fornicates, passes a disease known as "Fusarium dieback" to the local landscapes on the southern part of California.

The research team stated that the fungal disease was found on 18 different plant species internationally, including citrus varieties, persimmon, tea and guava. Eskalen also stated that the invasive species was also found transmitting the disease in 2009. "The beetle-fungus combination has caused severe damage to avocado trees there," said Eskalen.

Eskalen also states that the beetle and fungus have a reciprocal relationship, also known as symbiosis. "When the beetle burrows into the tree, it inoculates the host plant with the fungus it carries in its mouth parts," said Eskalen. "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."

Eskalen has confirmed that both the California Food and Drug Administration and the Agricultural Commissioner of Los Angeles County have verified the species classification of the beetle.

The fungus was first detected in Los Angeles County in 2003, but it was not until February 2012, however, when it negatively impacted the avocado industry. Eskalen also stated that this is the same beetle that caused an avocado shortage in Israel in 2009 and could cause economic concern among avocado growers in California. "The California Avocado Commission is concerned about the economic damage this fungus can do to the industry here in California," said Eskalen.

Eskalen and his research team want avocado farmers and gardeners to look after their trees and to report any sign of the fungus. "Symptoms in avocado include the appearance of white powdery exudates 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."

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